Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools

Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools

Version 2.93 (26-Jul-23)

Copyright © 1996-2023
Samuel M. Goldwasser
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Table of Contents

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    Author and Copyright

    Author: Samuel M. Goldwasser

    For contact info, please see the Sci.Electronics.Repair FAQ Email Links Page.

    Copyright © 1994-2024
    All Rights Reserved

    Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

    1.This notice is included in its entirety at the beginning.
    2.There is no charge except to cover the costs of copying.


    Although working on small appliances is generally less risky than dealing with equipment like microwave ovens, TVs, and computer monitors, those that plug into the wall can still produce a very lethal electric shock as well cause a fire from incorrect or careless repairs both during servicing or later on. It is essential that you read, understand, and follow all safety guidelines contained in this document and in the document: Safety Guidelines for High Voltage and/or Line Powered Equipment.

    Improper repair of battery operated devices can also result in bad consequences for you, the device, and any equipment attached to it.

    We will not be responsible for damage to equipment, your ego, county wide power outages, spontaneously generated mini (or larger) black holes, planetary disruptions, or personal injury or worse that may result from the use of this material.

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    Note: The chapters: "AC Adapters" and "Batteries" have been relocated to the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    Where do you keep your dead appliances?

    If you have ever tried to get a small household appliance or portable power tool repaired, you understand why all that stuff is likely to be gathering dust in your attic or basement closet or junk box. It does not pay! This may be partially by design. However, to be fair, it may take just as much time to diagnose and repair a problem with a $20 toaster as a $300 VCR and time is money for a repair shop. It is often not even economical to repair the more expensive equipment let alone a $40 electric heater. The cost of the estimate alone would probably buy at least one new unit and possibly many more.

    However, if you can do the repair yourself, the equation changes dramatically as your parts costs will be 1/2 to 1/4 of what a professional will charge and of course your time is free. The educational aspects may also be appealing. You will learn a lot in the process. Many problems can be solved quickly and inexpensively. Fixing an old vacuum cleaner to keep in the rec room may just make sense after all.

    This document provides maintenance and repair information for a large number of small household appliances and portable power tools. The repair of consumer electronic equipment is dealt with by other documents in the "Notes on the Troubleshooting and Repair of..." series. Suggestions for additions (and, of course, correction) are always welcome.

    You will be able to diagnose problems and in most cases, correct them as well. Most problems with household appliances are either mechanical (e.g., dirt, lack of or gummed up lubrication, deteriorated rubber parts, broken doohickies) or obvious electrical (e.g., broken or corroded connections, short circuits, faulty heating elements) in nature. With minor exceptions, specific manufacturers and models will not be covered as there are so many variations that such a treatment would require a huge and very detailed text. Rather, the most common problems will be addressed and enough basic principles of operation will be provided to enable you to narrow the problem down and likely determine a course of action for repair. In many cases, you will be able to do what is required for a fraction of the cost that would be charged by a repair center - or - be able to revive something that would otherwise have gone into the dumpster - or remained in that closet until you moved out of your house (or longer)!

    Since so many appliances are variations on a theme - heating, blowing, sucking, rotating, etc. - it is likely that even if your exact device does not have a section here, a very similar one does. Furthermore, with your understanding of the basic principles of operation, you should be able to identify what is common and utilize info in other sections to complete a repair.

    Should you still not be able to find a solution, you will have learned a great deal and be able to ask appropriate questions and supply relevant information if you decide to post to (recommended),, or It will also be easier to do further research using a repair textbook. In any case, you will have the satisfaction of knowing you did as much as you could before finally giving up or (if it is worthwhile cost-wise) taking it in for professional repair. With your newly gathered knowledge, you will have the upper hand and will not easily be snowed by a dishonest or incompetent technician.

    Some Tidbits

    You may not realize the following:

    I will be happy to revise these comments if someone can provide the results of evaluations of any of these devices conducted by a recognized independent testing laboratory. However, I won't hold my breath waiting.

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    Basic Appliance Theory

    What is inside an appliance?

    There isn't much rocket science in the typical small appliance (though that is changing to some extent with the use of microcomputer and fuzzy logic control). Everything represents variations on a relatively small number of basic themes:

    Basic electrical principles

    Relax! This is not going to be a tutorial on computer design. Appliances are simple devices. It is possible to repair many appliance faults without any knowledge beyond 'a broken wire is probably a problem' or 'this part is probably bad because it is charred and broken in half'. However, a very basic understanding of electrical principles will enable you to more fully understand what you are doing. Don't worry, there will be no heavy math. The most complicated equations will be variations on Ohm's law: V=I*R and P=V*V/R.

    Voltage, current, and resistance

    If you have any sort of background in electricity or electronics, then you can probably skip the following introductory description - or have some laughs at my expense.

    The easiest way to explain basic electrical theory without serious math is with a hydraulic analogy. This is of the plumbing system in your house:

    Water is supplied by a pipe in the street from the municipal water company or by a ground water pump. The water has a certain pressure trying to push it through your pipes. With electric circuits, voltage is the analog to pressure. Current is analogous to flow rate. Resistance is analogous the difficulty in overcoming narrow or obstructed pipes or partially open valves.

    Intuitively, then, the higher the voltage (pressure), the higher the current (flow rate). Increase the resistance (partially close a valve or use a narrower pipe) and for a fixed voltage (constant pressure), the current (flow rate) will decrease.

    With electricity, this relationship is what is known as linear: double the voltage and all other factors remaining unchanged, the current will double as well. Increase it by a factor of 3 and the current will triple. Halve the resistance and for a constant voltage source, the current will double. (For you who are hydraulic engineers, this is not quite true with plumbing as turbulent flow sets in, but this is just an analogy, so bear with me.)

    Note: for the following 4 items whether the source is Direct Current (DC) such as a battery or Alternating Current (AC) from a wall outlet does not matter. The differences between DC and AC will be explained later.

    The simplest electrical circuit will consist of several electrical components in series - the current must flow through all of them to flow through any of them. Think of a string of Christmas lights - if one burns out, they all go out because the electricity cannot pass through the broken filament in the burned out bulb.

    Note the term 'circuit'. A circuit is a complete loop. In order for electricity to flow, a complete circuit is needed.

                              Switch (3)
                   _____________/ ______________
                  |                             |
                  | (1)                         | (4)
          +-------+--------+                +---+----+
          |  Power Source  |                |  Load  |
          +-------+--------+                +---+----+
                  |            Wiring (2)       |

    1. Power source - a battery, generator, or wall outlet. The hydraulic equivalent is a pump or dam (which is like a storage battery). The water supply pipe in the street is actually only 'wiring' (analogous to the electric company's distribution system) from the water company's reservoir and pumps.

    2. Conductors - the wiring. Similar to pipes and aqueducts. Electricity flows easily in good conductors like copper and aluminum. These are like the insides of pipes. To prevent electricity from escaping, an insulator like plastic or rubber is used to cover the wires. Air is a pretty good insulator and is used with high power wiring such as the power company's high voltage lines but plastic and rubber are much more convenient as they allow wires to be bundled closely together.

    3. Switch - turns current on or off. These are similar to valves which do not have intermediate positions, just on and off. A switch is not actually required in a basic circuit but will almost always be present.

    4. Load - a light bulb, resistance heater, motor, solenoid, etc. In true hydraulic systems such as used to control the flight surfaces of an aircraft, there are hydraulic motors and actuators, for example.

      With household water we usually don't think of the load. However, things like lawn sprinklers, dishwasher rotating arms, pool sweepers, and the like do convert water flow to mechanical work in the home (some homes, at least!). Hydraulic motors are used to aircraft and spacecraft, large industrial robots, and all sorts of other applications.

    Here are 3 of the simplest appliances:

    Now we can add one type of simple control device:

    1. Thermostat - a switch that is sensitive to temperature. This is like an automatic water valve which shuts off if a set temperature is exceeded. Most thermostats are designed to open the circuit when a fixed or variable temperature is exceeded. However, air conditioners, refrigerators, and freezers do the opposite - the thermostat switches on when the temperature goes too high. Some are there only to protect against a failure elsewhere due to a bad part or improper use that would allow the temperature to go too high and start a fire. Others are adjustable by the user and provide the ability to control the temperature of the appliance.

    With the addition of a thermostat, many more appliances can be constructed including (this is a small subset):

    Electric heaters and cooking appliances usually have adjustable thermostats.

    Hair dryers may simply have several settings which adjust heater power and fan speed (we will get into how later). The thermostat may be fixed and to protect against excessive temperatures only.

    That's it! You now understand the basic operating principle of nearly all small appliances. Most are simply variations (though some may be quite complex) on these basic themes. Everything else is just details.

    For example, a blender with 38 speeds just has a set of buttons (switches) to select various combinations of motor windings and other parts to give you complete control (as if you need 38 speeds!). Toasters have a timer or thermostat activate a solenoid (electromagnet) to pop your bread at (hopefully) the right time.

    1. Resistances - both unavoidable and functional. Except for superconductors, all materials have resistance. Metals like copper, aluminum, silver, and gold have low resistance - they are good conductors. Many other metals like iron or steel are fair but not quite as good as these four. One, NiChrome - an alloy of nickel and chromium - is used for heating elements because it does not deteriorate (oxidize) in air even at relatively high temperatures.

      A significant amount of the power the electric company produces is lost to heating of the transmission lines due to resistance and heating.

      However, in an electric heater, this is put to good use. In a flashlight or table lamp, the resistance inside the light bulb gets so hot that it provides a useful amount of light.

      A bad connection or overloaded extension cord, on the other hand, may become excessively hot and start a fire.

    The following is more advanced - save for later if you like.

    1. Capacitors - energy storage devices. These are like water storage tanks (and similar is some ways to rechargeable batteries). Or, a system consisting of a a rubber diaphragm separating the water from a volume of trapped air. As water is pumped in, energy is stored as the air is compressed as in the captive air or expansion tanks found in home heating systems or well water storage tanks.

      Capacitors are not that common in small appliances but may be used with some types of motors and in RFI - Radio Frequency Interference - filters as capacitors can buffer - bypass - interference to ground. The energy to power an electronic flash unit is stored in a capacitor, for example. Because they act like reservoirs - buffers - capacitors are found in the power supplies of most electronic equipment to smooth out the various DC voltages required for each device.

    2. Inductors - their actual behavior is like the mass of water as it flows. Turn off a water faucet suddenly and you are likely to hear the pipes banging or vibrating. This is due to the inertia of the water - it tends to want to keep moving. Electricity doesn't have inertia but when wires are wound into tight coils, the magnetic field generated by electric current is concentrated and tends to result in a similar effect. Current tends to want to continue to flow where inductance is present. (For the more technical reader, the air chamber used to prevent/minimize the water hammer effect is the equivalent of an RC snubber!)

      The windings of motors and transformers have significant inductance but the use of additional inductance devices is rare in home appliances except for RFI - since inductance tends to prevent current from changing, it can also be used to prevent interference from getting in or out.

    3. Controls - rheostats and potentiometers allow variable control of current or voltage. A water faucet is like a variable resistor which can be varied from near 0 ohms (when on fully) to infinite ohms (when off).

    Ohm's Law

    The relationships that govern the flow of current in basic circuits (without capacitance or inductance - which is the case with many appliances) are contained in a very simple set of equations known an Ohm's Law.

    The simplest of these are:

                        V = I * R (1)
                        I = V / R (2) 
                        R = V / I (3)
    Where: Power in watts (W) is equal to voltage times current in a resistive circuit (no capacitance or inductance). Therefore, rearranging the equations above, we also obtain:
                        P = V * I      (4)
                        P = V * V / R  (5)
                        P = I * I * R  (6)
    For example: As noted above: (Note that the common use of the term 'water pressure' is actually not correct. The most likely cause of what is normally described as low water pressure is actually high resistance in the piping between your residence and the street. There is a pressure drop in this piping just as there would be a voltage drop across a high value resistor.)

    DC and AC

    While electricity can vary in any way imaginable, the most common forms for providing power are direct current and alternating current:

    A direct current source is at a constant voltage. Displaying the voltage versus time plot for such a source would show a flat line at a constant level. Some examples:

    An Alternating Current (AC) source provides a voltage that is varying periodically usually at 60 Hz (U.S.) or 50 Hz (many other countries). Note that 1 Hz = 1 cycle per second. Therefore, a 60 Hz AC voltage goes through 60 complete cycles in each second. For power, the shape of the voltage is a sinusoid which is the smoothest way that anything can vary periodically between two levels.

    The nominal voltage from an AC outlet in the U.S. is around 115 VAC. This is the RMS (Root Mean Square) value, not the peak (0 to maximum). In simple terms, the RMS value of an AC voltage and the same value of a DC voltage will result in identical heating (power) to a resistive load. For example, 115 VAC RMS will result in the same heat output of a broiler as 115 VDC.

    Direct current is used for many small motor driven appliances particularly when battery power is an option since changing DC into AC requires some additional circuitry. All electronic equipment require various DC voltages for their operation. Even when plugged into an AC outlet, the first thing that is done internally (or in the AC adapter in many cases) is to convert the AC to various DC voltages.

    The beauty of AC is that a very simple device - a transformer - can convert one voltage into another. This is essential to long distance power distribution where a high voltage and low current is desirable to minimize power loss (since it depends on the current). You can see transformers atop the power poles in your neighborhood reducing the 2,000 VAC or so from a local distribution transformer to your 115 VAC (actually, 115-0-115 were the total will be used by large appliances like electric ranges and clothes dryers). That 2,000 VAC was stepped down by a larger transformer from around 12,000 VAC provided by the local substation. This, in turn, was stepped down from the 230,000 VAC or more used for long distance electricity transmission. Some long distance lines are over 1,000,000 volts (MV).

    When converting between one voltage and another with a transformer, the amount of current (amps) changes in the inverse ratio. So, using 230 kV for long distance power transmission results in far fewer heating losses as the current flow is reduced by a factor of 2,000 over what it would be if the voltage was only 115 V, for example. Recall that power loss from P=I*I*R is proportional to the square of the current and thus in this example is reduced by a factor of 4,000,000!

    Many small appliances include power transformers to reduce the 115 VAC to various lower voltages used by motors or or electrical components. Common AC adapters - often simply called transformers or wall warts - include a small transformer as well. Where their output is AC, this is the only internal component other than a fuse or thermal fuse for protection. Where their output is DC, additional components convert the low voltage AC from the transformer to DC and a capacitor smoothes it out.

    Series and parallel circuits

    Up until now, we have been dealing with the series circuit - all parts are in a single line from power source, wiring, switches, load, and anything else. In a series circuit, the current must be the same through all components. The light bulb and switch in a flashlight pass exactly the same value of amperes. If there were two light bulbs instead of one and they were connected in series - as in a Christmas tree light set - then the current must be equal in all the bulbs but the voltages across each one would be reduced.

    The loads, say resistance heating elements, are now drawn with the schematic symbol (as best as can be done using ASCII) for a resistor.

                   _____________/ __________________
                  |                 I -->           |
                  |                        ^    ^   |
                  |                        |    |   / R1
                  |                        |   V1   \ Load 1
          +-------+--------+               |    |   /
          |  Power Source  |                    v__ |
          +-------+--------+              V(S)  ^   |
                  |                             |   / R2
                  |                        |   V2   \ Load 2
                  |                        |    |   /
                  |                        v    v   |
    The total resistance, R(T), of the resistors in this series circuit is:
                        R(T) = R1 + R2                (7)
    The voltage across each of the resistors would be given by:
                        V1 = V(S) * R1 / (R1 + R2)    (8)
                        V2 = V(S) * R2 / (R1 + R2)    (9)
    The current is given by:
                        I = V(S)  / (R1 + R2)        (10)
    However, another basic configuration, is also possible. With a parallel circuit, components are connected not one after the other but next to one another as shown below:
                   _____________/ ___________________________
                  |                      I -->  |            |
                  |                 ^           |            |
          +-------+--------+        |           / R1         / R2
          |  Power Source  |       V(S)         \ Load 1     \ Load 2
          +-------+--------+        |           /            /
                  |                 v           |v I(1)      |v I(2)
    Now, the voltages across each of the loads is necessarily equal but the individual currents divide according to the relative resistances of each load.

    The total resistance, R(T), of the parallel resistors in this circuit is:

                        R(T) = (R1 * R2) / (R1 + R2)  (11)
    The currents through each of the loads would be given by:
                        I1 = V(S)/R1                  (12)
                        I2 = V(S)/R2                  (13)
    The total current is given by:
                        I = I1 + I2                   (14)
    Many variations on these basic arrangements are possible but nearly all can be reduced systematically to a combination of series or parallel circuits.

    On-line educational resources

    > The How Stuff Works Web site has some really nice introductory material (with graphics) on a variety of topics relating to technology in the modern world. Of relevance to this document are articles on motors, power adapters, relays, batteries, etc.

    Check out Sam's Neat, Nifty, and Handy Bookmarks in the "Education and Tutorials" area for links to introductory material on electronics and other related fields.

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    Appliance Troubleshooting


    Appliances run on either AC line power or batteries. In the latter case, there is little danger to you except possibly from burns due to short circuits and heating effect or irritation from the caustic chemicals from old leaky batteries.

    However, AC line power can be lethal. Proper safety procedures must be followed whenever working on live equipment (as well as devices which may have high energy storage capacitors like TVs, monitors, and microwave ovens). AC line power due to its potentially very high current is actually considerably more dangerous than the 30 kV found in a large screen color TV!

    These guidelines are to protect you from potentially deadly electrical shock hazards as well as the equipment from accidental damage.

    Note that the danger to you is not only in your body providing a conducting path, particularly through your heart. Any involuntary muscle contractions caused by a shock, while perhaps harmless in themselves, may cause collateral damage - there are many sharp edges inside this type of equipment as well as other electrically live parts you may contact accidentally.

    Safety myths

    For nearly all the appliances we will be covering, there is absolutely no danger of electrical shock once the unit is unplugged from the wall socket (not, however, just turned off - the plug should be removed from the wall socket).

    You may have heard warnings about dangers from unplugged appliances. Perhaps, these were passed down from your great great grandparents or from local bar room conversation.

    Except for devices with large high voltage capacitors connected to the line or elsewhere, there is nothing inside an appliance to store a painful or dangerous charge. Even these situations are only present in microwave ovens, fluorescent lamps and fixtures with electronic ballasts, universal power packs for camcorders or portable computers, or appliances with large motors. Other than these, once an appliance is unplugged all parts are safe to touch - electrically that is. There may still be elements or metal brackets that are burning hot as metal will tend to retain heat for quite a while in appliances like toasters or waffle irons. Just give them time to cool. There are often many sharp edges on sheetmetal as well. Take your time and look before you leap or grab anything.

    Note that this list of dangerous appliances doesn't include CRT-type TVs, computer monitors, and other similar electronic equipment - which most certainly can store a dangerous charge on the CRT long after being unplugged - only because they aren't normally considered appliances. :)

    Safety guidelines

    The purpose of this set of guidelines is not to frighten you but rather to make you aware of the appropriate precautions. Appliance repair can be both rewarding and economical. Just be sure that it is also safe!

    Should I unplug appliances when not in use?

    There is no hard and fast rule. Personally, I do unplug heating appliances when I am done with them. The quality of internal construction is not always that great and this is a minor annoyance to avoid a possible fire hazard should something fail or should such an appliance accidentally be left on.

    BTW, electronic equipment should always be unplugged during lightning storms since it may be very susceptible to power surge and lightning damage. Don't forget the telephones and computer modems as well. This is not as much of a problem with small appliances that do not include electronic controllers as except for direct lightning strikes, the power switch will provide protection.

    Troubleshooting tips

    Many problems have simple solutions. Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a dead appliance, the most likely cause might just be a bad line cord or plug! Try to remember that the problems with the most catastrophic impact on operation (an appliance that blows fuses) usually have the simplest causes (a wire shorting due to frayed insulation).

    If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive - especially with AC line powered appliances).

    Whenever working on precision equipment, make copious notes and diagrams. Yes, I know, a toaster may not exactly be precision equipment, but trust me. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc.

    Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly.

    Select a work area which is well lighted and where dropped parts can be located - not on a deep pile shag rug. Something like a large plastic tray with a slight lip may come in handy as it prevents small parts from rolling off of the work table. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box to eat dinner.

    Basic hand tools

    A basic set of precision hand tools will be all you need to work on most appliances. These do not need to be really expensive but poor quality tools are worse than useless and can cause damage. Stanley and Craftsman tools are fine. Needed tools include a selection of Philips and straight blade screwdrivers, socket drivers, open end or adjustable wrenches of various sizes, needlenose pliers, wire cutters, tweezers, and dental picks.

    An electric drill or drill press with a set of small (1/16" to 1/4") high quality high speed drill bits is handy for some types of restoration where new holes need to be provided. A set of machine screw taps is also useful at times.

    A medium power soldering iron and rosin core solder (never never use acid core solder or the stuff for sweating copper pipes on electrical or electronic repairs!) will be required if you need to make or replace any soldered connections. A soldering gun is desirable for any really beefy soldering. See the section: Soldering techniques.

    A crimping tool and an assortment of solderless connectors often called 'lugs' will be needed to replace damaged or melted terminals in small appliances. See the section: Solderless connectors.

    Old dead appliances can often be valuable sources of hardware and sometimes even components like switches and heating elements. While not advocating being a pack rat, this does have its advantages at times.

    Soldering techniques

    Soldering is a skill that is handy to know for many types of construction and repair. For modern small appliances, it is less important than it once was as solderless connectors have virtually replaced solder for internal wiring. However, there are times where soldering is more convenient - for example, when performing repairs at 1 AM and a replacement crimp lug is not available.

    Use of the proper technique is critical to reliability and safety. A good solder connection is not just a bunch of wires and terminals with solder dribbled over them. When done correctly, the solder actually bonds to the surface of the metal (usually copper) parts.

    CAUTION: You can easily turn a simple repair (e.g., bad solder connections) into an expensive mess if you use inappropriate soldering equipment and/or lack the soldering skills to go along with it. If in doubt, find someone else to do the soldering or at least practice, practice, practice, soldering and desoldering on a junk unit first!

    Effective soldering is by no means difficult but some practice may be needed to perfect your technique.

    The following guidelines will assure reliable solder joints:

    Practice on some scrap wire and electronic parts. It should take you about 3 minutes to master the technique!

    Desoldering techniques

    Occasionally, it will be necessary to remove solder - either excess or to replace wires or components. A variety of tools are available for this purpose. The one I recommend is a vacuum solder pump called 'SoldaPullet' (about $20). Cock the pump, heat the joint to be cleared, and press the trigger. Molten solder is sucked up into the barrel of the device leaving the terminal nearly free of solder. Then use a pair of needlenose pliers and a dental pick to gently free the wires or component. Other approaches that may be used in place of or in addition to this: Solder Wick which is a copper braid that absorbs solder via capillary action; rubber bulb type solder pumps, and motor driven vacuum solder rework stations (pricey).

    See the document: Troubleshooting and Repair of Consumer Electronic Equipment for additional info on desoldering of electronic components.

    Soldering pins in plastic connectors

    The thermoplastic used to mold many common cheap connectors softens or melts at relatively low temperatures. This can result in the pins popping out or shifting position (even shorting) as you attempt to solder to them to replace a bad connection, for example.

    One approach that works in some cases is to use the mating socket to stabilize the pins so they remain in position as you solder. The plastic will still melt - not as much if you use an adequately sized iron since the socket will act as a heat sink - but will not move.

    An important consideration is using the proper soldering iron. In some cases, a larger iron is better - you get in and out more quickly without heating up everything in the neighborhood.

    Solderless connectors

    Most internal connections in small appliances are made using solderless connectors. These include twist on WireNuts(tm) and crimped terminal lugs of various sizes and configurations.

    WireNuts allow multiple wires to be joined by stripping the ends and then 'screwing' an insulated thimble shaped plastic nut onto the grouped ends of the wires. A coiled spring (usually) inside tightly grips the bare wires and results in a mechanically and electrically secure joint. For appliance repair, the required WireNuts will almost always already be present since they can usually be reused. If you need to purchase any, they come in various sizes depending on the number and size of the wires that can be handled. It is best to twist the individual conductor strands of each wire together and then twist the wires together slightly before applying the WireNut.

    Crimped connectors, called lugs, are very common in small appliances. One reason is that it is easier, faster, and more reliable, to make connections using these lugs with the proper crimping equipment than with solder.

    A lug consists of a metal sleeve which gets crimped over one or more wires, an insulating sleeve (usually, not all lugs have these), and a terminal connection: ring, spade, or push-on are typical.

    Lugs connect one or more wires to the fixed terminals found on switches, motors, thermostats, and so forth.

    There are several varieties:

    The push-on variety are most common in small appliances.

    In the factory, the lugs are installed on the wires with fancy expensive equipment. For replacements, an inexpensive crimping tool and an assortment of lugs will suffice. The crimping tool looks like a pair of long pliers and usually combines a wire stripper and bolt cutter with the crimping function. It should cost about $6-10.

    The crimping tool 'squashes' the metal sleeve around the stripped ends of the wires to be joined. A proper crimp will not come apart if an attempt is made to pull the wires free - the wires will break somewhere else first. It is gas-tight - corrosion (within reason) will not affect the connection.

    Crimping guidelines:

    Wire stripping

    In order to make most connections, the plastic or other insulating covering must be removed to expose the bare copper conductors inside. The best way to do this is with a proper wire stripper which is either adjustable or has dedicated positions for each wire size. It is extremely important that the internal conductor (single wire or multiple strands) are undamaged. Nicks or loss of some strands reduces the mechanical and electrical integrity of the connection. In particular, a seriously nicked wire may break off at a later time - requiring an additional repair or resulting in a safety hazard or additional damage. The use of a proper wire stripper will greatly minimize such potential problems.

    A pen knife or Xacto knife can be used in a pinch but a wire stripper is really much much easier.

    Attaching wires to screw terminals

    Screw terminals are often seen in appliances. In most cases, lugs are used to attach one or more wires to each terminal and when properly done, this usually is the best solution. However, in most cases, you can attach the wire(s) directly if a lug is not available:
    1. The best mechanical arrangement is to put the wire under a machine screw or nut, lock washer, and flat washer. However, you will often see just the screw or nut (as in a lamp switch or wall socket). For most applications, this is satisfactory.

    2. Avoid the temptation to put multiple wires around a single terminal unless you separate each one with a flat washer.

    3. Strip enough of the wire to allow the bare wire to be wrapped once around the terminal. To much and some will poke out and might short to something; too little and a firm mechanical joint and electrical connection may be impossible.

    4. For multistranded wire, tightly twist the strands of stripped wire together in a clockwise direction as viewed from the wire end.

    5. Wrap the stripped end of the wire **clockwise** around the terminal post (screw or stud) so that it will be fully covered by the screw head, nut, or flat washer. This will insure that the wire is grabbed as the screw or nut is tightened. A pair of small needlenose pliers may help.

    6. Hold onto the wire to keep it from being sucked in as the screw or nut is tightened. Don't overdo it - you don't need to sheer off the head of the screw to make a secure reliable connection.

    7. Inspect the terminal connection: the bare wire should be fully covered by the head of the screw, nut, or flat washer. Gently tug on the wire to confirm that it is securely fastened.

    Test equipment

    Very little test equipment is needed for most household appliance repair.

    First, start with some analytical thinking. Many problems associated with household appliances do not require a schematic. Since the internal wiring of many appliances is so simple, you will be able to create your own by tracing the circuits in any case. However, for more complex appliances, a schematic may be useful as wires may run behind and under other parts and the operation of some custom switches may not obvious. The causes for the majority of problems will be self evident once you gain access to the interior - loose connections or broken wires, bad switches, open heating element, worn motor brushes, dry bearings. All you will need are some basic hand tools, a circuit and continuity tester, light oil and grease, and your powers of observation (and a little experience). Your built in senses and that stuff between your ears represents the most important test equipment you have.

    The following will be highly desirable for all but the most obvious problems:

    1. Circuit tester (neon light) - This is used to test for AC power or confirm that it is off. For safety, nothing can beat the simplicity of a neon tester. Its use is foolproof as there are no mode settings or range selections to contend with. Touch its two probes to a circuit and if it lights, there is power. (This can also take the place of an Outlet tester but it is not as convenient (see below). Cost: $2-$3.

    2. Outlet tester (grounds and miswiring) - This will confirm that a 3 prong outlet is correctly wired with respect to Hot, Neutral, and Ground. While not 100% assured of correct wiring if the test passes, the screwup would need to be quite spectacular. This simple device instantly finds missing Grounds and interchanged Hot and Neutral - the most common wiring mistakes. Just plug it into an outlet and if the proper two neon light are lit at full brightness, the outlet is most likely wired correctly. Cost: about $6.

      These are just a set of 3 neon bulbs+resistors across each pair of wires. If the correct bulbs light at full brightness - H-N, H-G - then the circuit is likely wired correctly. If the H-G light is dim or out or if both the H-G and G-N are dim, then you have no ground. If the N-G light is on and the H-G light is off, you have reversed H and N, etc.

      What it won't catch: Reversed N and G (unlikely unless someone really screwed up) and marginal connections since the neon bulbs doesn't use much current. For this (particularly important for the G since it won't do any good if its resistance back to the service panel is too high) you need a real load like a 100 W light bulb. Or, build a tester consisting of 100 W light bulbs (instead of neon lamps) wired between each of the prongs.

      It also won't distinguish between 110 VAC and 220 VAC circuits except that the neon bulbs will glow much brighter on 220 VAC but without a direct comparison, this could be missed.

      For something that appears to test for everything but next week's weather:

      (From: Bill Harnell (

      Get an ECOS 7105 tester! (ECOS Electronics Corporation, Oak Park, Illinois, 708-383-2505). Not cheap, however. It sold for $59.95 in 1985 when I purchased somewhere around 600 of them for use by our Customer Engineers for safety purposes!

      It tests for:

      Correct wiring, reversed polarity, open Ground, open Neutral, open Hot, Hot & Ground reversed, Hot on neutral, Hot unwired, other errors, over voltage (130 VAC+), under voltage (105 VAC-), Neutral to Ground short, Neutral to Ground reversal, Ground impedance test (2 Ohms or less ground impedance - in the equipment ground conductor).

      Their less expensive 7106 tester performs almost all of the above tests.

      FWIW, I have no interest in the ECOS Corporation of any kind. Am just a very happy customer.

    3. Continuity tester (buzzer or light) - Since most problems with appliances boil down to broken connections, open heating elements, defective switches, shorted wires, and bad motor windings, a continuity tester is all that is needed for most troubleshooting. A simple battery operated buzzer or light bulb quickly identifies problems. If a connection is complete, the buzzer will sound or the light will come on. Note that a dedicated continuity tester is preferred over a similar mode on a multimeter because it will operate only at very low resistance. The buzzer on a multimeter sounds whenever the resistance is less than about 200 ohms - a virtual open circuit for much appliance wiring.

      A continuity tester can be constructed very easily from an Alkaline battery, light bulb or buzzer, some wire, and a set of test leads with probes. All of these parts are available at Radio Shack.

                           AA, C, or D cell    1.5 V flashlight bulb or buzzer
                                  +|  -             +------------------+
         Test probe 1  o-----------| |--------------|  Bulb or buzzer  |-------+ 
                                   |                +------------------+       |
         Test probe 2  o-------------------------------------------------------+

      CAUTION: Do not use this simple continuity tester on electronic equipment as there is a slight possibility that the current provided by the battery will be too high and cause damage. It is fine for most appliances.

    4. GFCI tester - outlets installed in potentially wet or outdoor areas should be protected by a Ground Fault Circuit Interrupter (GFCI). A GFCI is now required by the NEC (Code) in most such areas. This tester will confirm that any outlets protected by a GFCI actually will trip the device if there is a fault. It is useful for checking the GFCI (though the test button should do an adequate job of this on its own) as well as identifying or testing any outlets downstream of the GFCI for protection.

      Wire a 3 prong plug with a 15 K ohm 1 W resistor between H and G. Insulate and label it! This should trip a GFCI protected outlet as soon as it is plugged in since it will produce a fault current of about 7 mA.

      Note that this device will only work if there is an actual Safety Ground connection to the outlet being tested. A GFCI retrofitted into a 2 wire installation without a Ground cannot be tested in this way since a GFCI does not create a Ground. However, jumpering this rig between the H and and a suitable earth ground (e.g., a cold water in an all copper plumbing system) should trip the GFCI. Therefore, first use an Outlet Tester (above) to confirm that there is a Safety Ground present.

      The test button works because it passes an additional current through the sense coil between Hot and Neutral tapped off the wiring at the line side of the GFCI and therefore doesn't depend on having a Ground.

      If you want to be fancier, you can build a combination outlet and GFCI tester. Wire up a neon indicator with current limiting resistor) across each pair of wires. Add a 15K ohm 1 W resistor in series with a pushbutton switch between H and G. If the H-G neon is lit (indicating a proper Ground connection), pressing the button should trip the GFCI.

    5. Multimeter (VOM or DMM) - This is necessary for actually measuring voltages and resistances. Almost any type will do - even the $14.95 special from Sears. Accuracy is not critical for household appliance repair but reliability is important - for your safety if no other reason. It doesn't really matter whether it is a Digital MultiMeter (DMM) or analog Volt Ohm Meter (VOM). A DMM may be a little more robust should you accidentally put it on an incorrect scale. However, they both serve the same purpose. A cheap DMM is also not necessarily more accurate than a VOM just because it has digits instead of a meter needle. A good quality well insulated set of test leads and probes is essential. What comes with inexpensive multimeters may be too thin or flimsy. Replacements are available. Cost: $15-$50 for a multimeter that is perfectly adequate for home appliance repair.

      Note: For testing of household electrical wiring, a VOM or DMM can indicate voltage between wires which is actually of no consequence. This is due to the very high input resistance/impedance of the instrument. The voltage would read zero with any sort of load. See the section: Phantom voltage measurements of electrical wiring.

    Once you get into electronic troubleshooting, an oscilloscope, signal generator, and other advanced (and expensive) test equipment will be useful. For basic appliance repair, such equipment would just gather dust.

    Getting inside consumer electronic equipment

    Yes, you will void the warranty, but you knew this already.

    Appliance manufacturers seem to take great pride in being very mysterious as to how to open their equipment. Not always, but this is too common to just be a coincidence.

    A variety of techniques are used to secure the covers on consumer electronic equipment:

    1. Screws: Yes, many still use this somewhat antiquated technique. Sometimes, there are even embossed arrows on the case indicating which screws need to be removed to get at the guts. In addition to obvious screw holes, there may be some that are only accessible when a battery compartment is opened or a trim panel is popped off.

      These are almost always of the Philips variety though more and more appliances are using Torx or security Torx type screws. Many of these are hybrid types - a slotted screwdriver may also work but the Philips or Torx is a whole lot more convenient.

      A precision jeweler's screwdriver set including miniature Philips head drivers is a must for repair of miniature portable devices.

    2. Hidden screws: These will require prying up a plug or peeling off a decorative decal. It will be obvious that you were tinkering - it is virtually impossible to put a decal back in an undetectable way. Sometimes the rubber feet can be pryed out revealing screw holes. For a stick-on label, rubbing your finger over it may permit you to locate a hidden screw hole. Just puncture the label to access the screw as this may be less messy then attempting to peel it off.

    3. Snaps: Look around the seam between the two halves. You may (if you are lucky) see points at which gently (or forcibly) pressing with a screwdriver will unlock the covers. Sometimes, just going around the seam with a butter knife will pop the cover at one location which will then reveal the locations of the other snaps.

    4. Glue: Or more likely, the plastic is fused together. This is particularly common with AC adapters (wall warts). In this case, I usually carefully go around the seam with a hacksaw blade taking extreme care not to go through and damage internal components. Reassemble with plastic electrical tape.

    5. It isn't designed for repair. Don't laugh. I feel we will see more and more of this in our disposable society. Some devices are totally potted in Epoxy and are 'throwaways'. With others, the only way to open them non-destructively is from the inside.
    Don't force anything unless you are sure there is no alternative - most of the time, once you determine the method of fastening, covers will come apart easily. If they get hung up, there may be an undetected screw or snap still in place. However, sometimes it is just impossible (by design) to disassemble an appliance without doing some damage. That's life (and aids the manufacturer's bottom line!).

    When reinstalling the screws, first turn them in a counter-clockwise direction with very slight pressure. You will feel them "click" as they fall into the already formed threads. Gently turn clockwise and see if they turn easily. If they do not, you haven't hit the previously formed threads - try again. Then just run them in as you normally would. You can always tell when you have them into the formed threads because they turn very easily for nearly the entire depth. Otherwise, you will create new threads which will quickly chew up the soft plastic. Note: these are often high pitch screws - one turn is more than one thread - and the threads are not all equal.

    The most annoying (to be polite) situation is when after removing the 18 screws holding the case together (losing 3 of them entirely and mangling the heads on 2 others), removing three subassemblies, and two other circuit boards, you find that the adjustment you wanted was accessible through a hole in the case just by partially peeling back a rubber hand grip! (It has happened to me).

    When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced and that they will not get caught in moving parts. This is particularly critical for AC line operated appliances and those with motors to minimize fire and shock hazard and future damage to the device itself. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well. As long as it does not get in the way, additional layers of tape will not hurt and can provide some added insurance against future problems. I often put a layer of electrical tape around connections joined with WireNuts(tm) as well just to be sure that they will not come off or that any exposed wire will not short to anything.

    Getting built up dust and dirt out of a equipment

    This should be the first step in any inspection and cleaning procedure.

    Appliances containing fans or blowers seem to be dust magnets - an incredible amount of disgusting fluffy stuff can build up in a short time - even with built-in filters.

    Use a soft brush (like a new cheap paint brush) to remove as much dirt, dust, and crud, as possible without disturbing anything excessively. Some gentle blowing (but no high pressure air) may be helpful in dislodged hard to get at dirt - but wear a dust mask.

    Don't use compressed air on intricate mechanisms, however, as it might dislodge dirt and dust which may then settle on lubricated parts and contaminating them. High pressure air could move oil or grease from where it is to where it should not be. If you are talking about a shop air line, the pressure may be much much too high and there may be contaminants as well.

    A Q-tip (cotton swab) moistened with politically correct alcohol can be used to remove dust and dirt from various hard to get at surfaces.

    Lubrication of appliances and electronic equipment

    The short recommendation is: Don't add any oil or grease unless you are positively sure it is needed. Most parts are lubricated at the factory and do not need any further lubrication over their lifetime. Too much lubrication is worse then too little. It is easy to add a drop of oil but difficult and time consuming to restore a tape deck that has taken a swim.

    NEVER, ever, use WD40! WD40 is not a good lubricant despite the claims on the label. Legend has it that the WD stands for Water Displacer - which is one of the functions of WD40 when used to coat tools for rust prevention. WD40 is much too thin to do any good as a general lubricant and will quickly collect dirt and dry up. It is also quite flammable and a pretty good solvent - there is no telling what will be affected by this.

    A light machine oil like electric motor or sewing machine oil should be used for gear or wheel shafts. A plastic safe grease like silicone grease or Molylube is suitable for gears, cams, or mechanical (piano key) type mode selectors. Never use oil or grease on electrical contacts.

    One should also NOT use a detergent oil. This includes most automotive engine oils which also have multiple additives which are not needed and are undesirable for non-internal combustion engine applications.

    3-In-One(tm) isn't too bad if that is all you have on hand and the future of the universe depends on your fan running smoothly. However, for things that don't get a lot of use, it may gum up over time. I don't know whether it actually decomposes or just the lighter fractions (of the 3) evaporate.

    Unless the unit was not properly lubricated at the factory (which is quite possible), don't add any unless your inspection reveals the specific need. Sometimes you will find a dry bearing, motor, lever, or gear shaft. If possible, disassemble and clean out the old lubricant before adding fresh oil or grease.

    Note that in most cases, oil is for plain bearings (not ball or roller) and pivots while grease is used on sliding parts and gear teeth.

    In general, do not lubricate anything unless you know there is a need. Never 'shotgun' a problem by lubricating everything in sight! You might as well literally use a shotgun on the equipment!

    Common appliance problems

    Despite the wide variety of appliances and uses to which they are put, the vast majority of problems are going to be covered in the following short list:
    1. Broken wiring inside cordset - internal breaks in the conductors of cordsets or other connecting cords caused by flexing, pulling, or other long term abuse. This is one of the most common problem with vacuum cleaners which tend to be dragged around by their tails.

      Testing: If the problem is intermittent, (or even if it is not), plug the appliance in and turn it on. Then try bending or pushing the wire toward the plug or appliance connector end to see if you can make the internal conductors touch at least momentarily. Ii the cordset is removable, test between ends with a continuity checker or multimeter on the low ohms scale. If it is not detachable, open the appliance to perform this test.

    2. Bad internal connections - broken wires, corroded or loosened terminals. Wires may break from vibration, corrosion, poor manufacturing, as well as thermal fatigue. The break may be in a heating element or other subassembly. In many cases, failure will be total as in when one of the AC line connections falls off. At other times, operation will be intermittent or erratic - or parts of the appliance will not function. For example, with a blow dryer, the heating element could open up but the fan may continue to run properly.

      Testing: In many cases, a visual inspection with some careful flexing and prodding will reveal the location of the bad connection. If it is an intermittent, this may need to be done with a well insulated stick while the appliance is on and running (or attempting to run). When all else fails, the use of a continuity checker or multimeter on the low ohms scale can identify broken connections which are not obviously wires visibly broken in two. For testing heating elements, use the multimeter as a continuity checker may not be sensitive enough since the element normally has some resistance.

    3. Short circuits. While much less frequent than broken or intermittent connections, two wires touching or contacting the metal case of an appliance happens all too often. Partially, this is due to the shoddy manufacturing quality of many small appliances like toaster ovens. These also have metal (mostly) cabinets and many metal interior parts with sharp edges which can readily eat through wire insulation due to repeated vibrations, heating and cooling cycles, and the like. Many appliances are apparently designed by engineers (this is being generous) who do not have any idea of how to build or repair them. Thus, final assembly, for example, must sometimes be done blind - the wires get stuffed in and covers fastened - which may end up nicking or pinching wires between sharp metal parts. The appliance passes the final inspection and tests but fails down the road.

      A short circuit may develop with no operational problems - but the case of the appliance will be electrically 'hot'. This is a dangerous situation. Large appliances with 3 wire plugs - plugged into a properly grounded 3 wire circuit - would then blow a fuse or trip a circuit breaker. However, small appliances like toaster, broilers, irons, etc., have two wire plugs and will just set there with a live cabinet.

      Testing: Visually inspect for bare wires or wires with frayed or worn insulation touching metal parts, terminals they should not be connected to, or other wires. Use a multimeter on the high ohms scale to check between both prongs of the AC plug and any exposed metal parts. Try all positions of any power or selector switches. Any resistance measurement less than 100K ohms or so is cause for concern - and further checking. Also test between internal terminals and wires that should not be connected together.

      Too many people like to blame everything from blown light bulbs to strange noises on short circuits. A 'slight', slow, or marginal short circuit is extremely rare. Most short circuits in electrical wiring between live and neutral or ground (as opposed to inside appliances where other paths are possible) will blow a fuse or trip a breaker. Bad connections (grounds, neutral, live), on the other hand, are much much more common.

    4. Worn, dirty, or broken switches or thermostat contacts. These will result in erratic or no action when the switch is flipped or thermostat knob is turned. In many cases, the part will feel bad - it won't have that 'click' it had when new or may be hard to turn or flip. Often, however, operation will just be erratic - jiggling the switch or knob will make the motor or light go on or off, for example.

      Testing: Where there is a changed feel to the switch or thermostat with an associated operational problem, there is little doubt that the part is bad and must be replaced. Where this is not the case, label the connections to the switch or thermostat and then remove the wires. Use the continuity checker or ohmmeter across each set of contacts. They should be 0 ohms or open depending on the position of the switch or knob and nothing in between. In most cases, you should be able to obtain both readings. The exception is with respect to thermostats where room temperature is off one end of their range. Inability to make the contacts open or close (except as noted above) or erratic intermediate resistances which are affected by tapping or jiggling are a sure sign of a bad set of contacts.

    5. Gummed up lubrication, or worn or dry bearings. Most modern appliances with motors are supposedly lubricated for life. Don't believe it! Often, due to environmental conditions (dust, dirt, humidity) or just poor quality control during manufacture (they forgot the oil), a motor or fan bearing will gum up or become dry resulting in sluggish and/or noisy operation and overheating. In extreme cases, the bearing may seize resulting in a totally stopped motor. If not detected, this may result in a blown fuse (at the least) and possibly a burnt out motor from the overheating.

      Testing: If the appliance does not run but there is a hum (AC line operated appliances) or runs sluggishly or with less power than you recall when new, lubrication problems are likely. With the appliance unplugged, check for free rotation of the motor(s). In general, the shaft sticking out of the motor itself should turn freely with very little resistance. If it is difficult to turn, the motor bearings themselves may need attention or the mechanism attached to the motor may be filled with crud. In most cases, a thorough cleaning to remove all the old dried up and contaminated oil or grease followed by relubing with similar oil or grease as appropriate will return the appliance to good health. Don't skimp on the disassembly - total cleaning will be best. Even the motor should be carefully removed and broken down to its component parts - end plates, rotor, stator, brushes (if any) in order to properly clean and lubricate its bearings. See the appropriate section of the chapter: Motors 101 for the motor type in your appliance.

    6. Broken or worn drive belts or gears - rotating parts do not rotate or turn slowly or with little power even through the motor is revving its little head off. When the brush drive belt in an upright vacuum cleaner breaks, the results are obvious and the broken belt often falls to the ground (to be eaten by the dog or mistaken for a mouse tail - Eeek!) However, there are often other belts inside appliances which will result in less obvious consequences when they loosen with age or fail completely.

      Testing: Except for the case of a vacuum cleaner where the belt is readily accessible, open the appliance (unplugged!). A good rubber belt will be perfectly elastic and will return to its relaxed length instantly when stretched by 25 percent and let go. It will not be cracked, shiny, hard, or brittle. A V-type belt should be dry (no oil coating), undamaged (not cracked, brittle, or frayed), and tight (it should deflect 1/4" to 1/2" when pressed firmly halfway between the pulleys).

      Sometimes all that is needed is a thorough cleaning with soap and water to remove accumulated oil or grease. However, replacement will be required for most of these symptoms. Belts are readily available and an exact match is rarely essential.

    7. Broken parts - plastic or metal castings, linkages, washers, and other 'doodads' are often not constructed quite the way they used to be. When any of these fail, they can bring a complicated appliance to its knees. Failure may be caused by normal wear and tear, improper use (you tried to vacuum nuts and bolts just like on TV), accidents (why was your 3 year old using the toaster oven as a step stool?), or shoddy manufacturing.

      Testing: In many cases, the problem will be obvious. Where it is not, some careful detective work - putting the various mechanisms through their paces - should reveal what is not functioning. Although replacement parts may be available, you can be sure that their cost will be excessive and improvisation may ultimately be the best approach to repair. See the section: Fil's tips on improvised parts repair.

    8. Insect damage. Many appliance make inviting homes for all sort of multi- legged creatures. Evidence of their visits or extended stays will be obvious including frayed insulation, short circuits caused by bodily fluids or entire bodies, remains of food and droppings. Even the smallest ventilation hole can be a front door.

      The result may be any of the items listed in (1) to (7) above. Once the actual contamination has been removed and the area cleaned thoroughly, inspect for damage and repair as needed. If the appliance failed while powered, you may also have damage to wiring or electronic components due to any short circuits that were created by the intruders' activities.

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Types of Parts Found in Small Appliances

    So many, so few

    While there are an almost unlimited variety of small appliances and power tools, they are nearly all constructed from under two dozen basic types of parts. And, even with these, there is a lot of overlap.

    The following types of parts are found in line powered appliances:

    Battery and AC adapter powered appliance use most of the same types of parts but they tend to be smaller and lower power than their line powered counterparts. For example, motors in line powered devices tend to be larger, more powerful, and of different design (universal or induction compared to permanent magnet DC type). So, we add the following: The only major category of devices that these parts do not cover are gas discharge lamps and lighting fixtures (fluorescent, neon, mercury, and sodium), which we will discuss in a separate chapters.

    Cordsets - wire and plug

    A 'cordset' is a combination of the cord consisting of 2 or 3 insulated wires and a plug with 2 or 3 prongs. Cord length varies from 12 inches (or less) for some appliances like toasters to 25 feet or more for vacuum cleaners. Most common length is 6-8 feet. The size of the wire and type of insulation also are important in matching a replacement cordset to an appliance.

    CAUTION: Some cordsets are more than what meets the eye. See the section: When a cordset is more than a cord and plug.

    Most plug-in appliances in the U.S. will have one of 3 types of line cord/plug combinations:

    1. Non-polarized 2 prong: The 2 prongs are of equal width so the plug may be inserted in either direction. These are almost universal on older appliances but may be found on modern appliances as well which are double insulated or where polarity does not matter. (Note: it **must** not matter for user safety in any case. The only time it can matter otherwise is with respect to (1) possible RFI (Radio Frequency Interference) generation or (2) service safety (this would put the center contact of a light bulb socket or internal switch and fuse on the Hot wire).

    2. Polarized 2 prong: The prong that is supposed to be plugged into the Neutral slot of the outlet is wider. All outlets since sometime around the 1950s (???) have been constructed to accept polarized plugs only one way. While no appliance should ever be designed where the way it is plugged in can result in a user safety hazard, a lamp socket where the shell - the screw thread part - is plugged into Neutral is less hazardous when changing a light bulb. In addition, when servicing a small appliance with the cover removed, the Hot wire with a polarized plug should go to the switch and fuse and thus most of the circuitry will be disconnected with the switch off or fuse pulled.

      Thus, if you are replacing a plug and don't know (or didn't label) how the old one was hooked up, the narrow prong should go to the fuse, switch, thermostat or other control, center of the socket, etc. Since you may have trouble finding non-polarized plugs these days, this applies to older appliances as well and there is really no problem in replacing a non-polarized plug with a polarized one on an appliance.

    3. Grounded 3 prong: In addition to Hot and Neutral, a third grounding prong is provided to connect the case of the equipment to safety Ground. This provides added protection should internal wiring accidentally short to a user accessible metal cabinet or control. In this situation, the short circuit will (or is supposed to) blow a fuse or trip a circuit breaker or GFCI rather than present a shock hazard. DO NOT just cut off the third prong if your outlet does not have a hole for it. Have the outlet replaced with a properly grounded one (which may require pulling a new wire from the service panel). As a short term solution, the use of a '3 to 2' prong adapter is acceptable IF AND ONLY IF the outlet box is securely connected to safety Ground already (BX or Romex cable with ground). Grounding also is essential for surge suppressors to operate properly (to the extent that they ever do) and may reduce RFI susceptibility and emissions if line filters are included (as with computer equipment and consumer electronics). Power conditioners require the Ground connection for line filtering as well.
    Each of these may be light duty (less than 5 Amps or 600 Watts), medium duty (8 A or 1000 W) or heavy duty (up to 15 A or 1800 W). The rating is usually required to be stamped on the cord itself or on a label attached to the cord. Thickness of the cord is not a reliable indication of its power rating! (Note: U.S. 115 VAC 15 amp circuits are assumed throughout this document unless otherwise noted.)

    Light duty cordsets are acceptable for most appliances without high power heating elements or heavy duty electric motors. These include table lamps, TVs, VCRs, stereo components, computers, dot matrix and inkjet printers, thermal fax machines, monitors, fans, can openers, etc. Electric blankets, heating pads, electric brooms, and food mixers are also low power and light duty cordsets are acceptable. The internal wires used is #18 AWG which is the minimum acceptable wire size (highest AWG number) for any AC line powered device.

    Medium or heavy duty cordsets are REQUIRED for heating appliances like electric heaters (both radiant and convection), toasters, broilers, steam and dry irons, coffee makers and electric kettles, microwave and convection ovens, laser printers, photocopiers, Xerographic based fax machines, canister and upright vacuum cleaners and shop vacs, floor polishers, many portable and most stationary power tools. The internal wires used will be #16 AWG (medium duty) or #14 AWG (heavy duty).

    For replacement, always check the nameplate amps or wattage rating and use a cordset which has a capacity at least equal to this. The use of an inadequate cordset represents a serious fire hazard.

    Three prong grounded cordsets are required for most computer equipment, heavy appliances, and anything which is not double insulated and has metal parts that may be touched in normal operation (i.e., without disassembly).

    The individual wires in all cordsets except for unpolarized types (e.g., older lamp cord) will be identified in some way. For sheathed cables, color coding is used. Generally, in keeping with the NEC (Code), black will be Hot, white will be Neutral, and green will be Safety Ground. You may also find brown for Hot, blue for Neutral, and green with a yellow stripe for Safety Ground. This is used internationally and is quite common for the cordsets of appliances and electronic equipment.

    For zip cord with a polarized plug, one of the wires will be tagged with with a colored thread or a ridge on the outer insulation to indicate that it is the Neutral wire. For unpolarized types, no identification is needed (though there still may be some) as the wires and prongs of the plug are identical. However, fewer and fewer devices use non-polarized cords/plugs now so you are more likely to see this with older ones.

    In general, when replacement is needed, use the same configuration and length and a heavy duty type if the original was heavy duty.

    Before disconnecting the old cord, label connections or make a diagram and then match the color code or other wire identifying information. In all cases, it is best to confirm your final wiring with a continuity tester or multimeter on the low ohms scale. Mistakes on your part or the manufacturer of the new cord are not unheard of!

    Common problems: internal wiring conductors broken at flex points (appliance or plug). With yard tools, cutting the entire cord is common. The connections at the plug may corrode as well resulting in heating or a broken connection.

    Testing: Appliance cordsets can always be tested with a continuity checker or multimeter on a the low ohms scale.

    Squeeze, press, spindle, fold, mutilate the cord particularly at both ends as while testing to locate intermittent problems.

    If you are too lazy to open the appliance (or this requires the removal of 29 screws), an induction type of tester such as used to locate breaks in Christmas tree light strings can be used to confirm continuity by plugging the cord in both ways and checked along its length to see if a point of discontinuity can be located. A permanent bench setup with a pair of outlets (one wired with reverse polarity and clearly marked: FOR TESTING ONLY) can be provided to facilitate connecting to either of the wires of the cordset when using an induction type tester.

    Note: broken wires inside the cordset at either the plug or appliance end are among the most common causes of a dead vacuum cleaner due to abuse it gets - being tugged from the outlet, vacuum being dragged around by the cord, etc. Many other types of appliances suffer the same fate. Therefore, checking the cord and plug should be the first step in troubleshooting any dead appliance.

    If the cord is broken at the plug end, the easiest thing to do is to replace just the plug. A wide variety of replacement plugs are available of three basic types: clamp-on/insulation piercing, screw terminals, and wire compression.

    Where damage is present at the appliance end of the cord, it may be possible to just cut off the bad portion and reinstall what remains inside of the appliance. As long as this is long enough and a means can be provided for adequate strain relief, this is an acceptable alternative to replacement of the entire cordset.

    When a cordset is more than a cord and plug

    While most appliances use normal cordsets, some, especially an increasing number of newer ones include various circuitry in the plug itself:

    Appliance cord gets hot

    This applies to all high current appliances, not just space heaters though these are most likely to be afflicted since they are likely to be run for extended periods of time.

    Of course, if the problem is with an *extension* cord, then either it is overloaded or defective. In either case, the solution should be obvious.

    Some cords will run warm just by design (or cheapness in design using undersized conductors).

    However, if it is gets hot during use, this is a potential fire hazard.

    If it is hot mainly at the plug end - get a heavy duty replacement plug - one designed for high current appliances using screw terminals - at a hardware store, home center, or electrical supply house. Cut the cord back a couple of inches.

    If the entire cord gets warm, this is not unusual with a heater. If it gets really hot, the entire cord should be replaced. Sometimes with really old appliance, the copper wires in the cord oxidize even through the rubber insulation reducing their cross section and increasing resistance. This leads to excessive power dissipation in the cord. Replacement *heavy duty* cordsets are readily available.

    Note that just because the cord itself gets warm does NOT mean that the wiring in the walls is heating significantly. The smallest allowable wiring size inside the walls is #14 which has a resistance of about 2.5 ohms per thousand feet. An appliance drawing 10 A through 50 feet of cable (100 total feet of wire going both ways) would result in a 2.5 V drop and 25 W dissipation. But since this is distributed over 50 feet of cable, heating in any location is minimal.

    Extension cords

    We treat extension cords too casually - abusing them and using underrated extension cords with heavy duty appliances. Both of these are serious fire and shock hazards. In addition, the use of a long inadequate extension will result in reduced voltage due to resistive losses at the far end. The appliance may not work at full capacity and in some cases may even be damaged by this reduced voltage.

    Extension cord rules of use:

    Extension cords of any type, capacity, and length can be easily constructed from components and wire sold at most hardware stores and home centers. This is rarely economical for light duty polarized types as these are readily available and very inexpensive. However, for heavy duty 3 prong extensions, a custom constructed one is likely to save money especially if an unusual length is required. Making up a heavy duty extension with a 'quad' electrical box with a pair of 15 amp duplex outlets is a very rugged convenient alternative to a simple 3 prong socket.

    Common problems: internal wiring conductors broken at flex points (socket or plug). With yard tools, cutting the entire cord is common. The connections at the plug may corrode as well resulting in heating or a bad or intermittent connection.

    Testing: Extension cords can always be tested with a continuity checker or multimeter on a the low ohms scale.

    Extension cord repair

    Determining the location of a break in an extension cord

    This isn't worth the time it would take to describe for a $.99 6 foot K-Mart special but it might make sense for a 100 foot heavy duty outdoor type. If the problem is near one end, a couple of feet can be cut off and a new plug or socket installed. If more towards the middle, the wires can be cut and spliced or two smaller cords could be made from the pieces.

    But, how do you locate the break?

    Internal wiring - cables and connectors

    Wiring isn't super glamorous but represents the essential network of roads that interconnect all of the appliance's internal parts and links it to the outside world.

    Inside the appliance, individual wires (often multicolored to help identify function) or cables (groups of wires combined together in a single sheath or bundle) route power and control signals to the various components. Most are insulated with plastic or rubber coverings but occasionally you will find bare, tinned (solder coated), or plated copper wires. In high temperature appliances like space heaters and toasters, the insulation (if present) will be asbestos (older) or fiberglass. (Rigid uninsulated wires are also commonly found in such applications.) Particles flaking off from either of these materials are a health hazard if you come in contact, inhale, or ingest them. They are also quite fragile and susceptible to damage which may compromise their insulating properties so take care to avoid excessive flexing or repositioning of wires with this type of insulation. Fiberglass insulation is generally loose fitting and looks like woven fabric. Asbestos is light colored, soft, and powdery.

    Note that it is unlikely there would be asbestos in any common consumer electronics like TVs, computer monitors, or microwave ovens since under normal conditions, nothing inside should get really hot. However, it might be found in very old large appliances including stoves, water heaters, and air conditioners. Nowadays, Fiberglas and rock wool (also known as mineral wool or slag wool) insulation are used. Older houses are another story and asbestos covered pipes are common.

    Color coding will often be used to make keeping track of the wires easier and to indicate function. However, there is no standard except for the input AC line. Generally, black will be used for Hot, white will be used for Neutral, and green or uninsulated wire will be used for Safety Ground. While this is part of the NEC (Code) for electrical wiring (in the U.S.), it is not always followed inside appliances. You may also find brown for Hot, blue for Neutral, and green with a yellow stripe for Safety Ground. This is used internationally and is quite common for the cordsets of appliances and electronic equipment.

    Where a non-polarized plug (cordset) is used, either AC wire can be Hot and both wires will typically (but not always) be the same color.

    Other colors may be used for switched Hot (e.g., red), thermostat control, motor start, solenoid 1, etc. Various combinations of colored stripes may be used as well. Unfortunately, in some cases, you will find that all the wiring is the same color and tracing the circuit becomes a pain in the you-know-what.

    Where multiple wires need to go from point A to point B along the same path, they will often be combined into a single cable which is bundled using nylon or cloth tie-wraps or run inside a single large flexible plastic sheath. For electronic interconnects and low voltage control and signal wiring, molded flat cables are common (like those for the cables to the diskette and hard drives of your PC). These are quite reliable and can be manufactured at low cost by fully automatic machines.

    The thickness of the insulation of a wire or cable is not a reliable indication of its capacity or voltage rating. A fat wire may actually have a very skinny central conductor and vice-versa. In some cases, the wire conductor size and voltage rating will be printed on the insulation but this not that common. If replacement is needed, this information will be essential. However, the ampacity (maximum current) can be determined from the size of the metal conductor and for any of the line powered appliances discussed in this document, wire with a 600 V rating should be more than adequate.

    The type of insulation is critical in appliances that generate heat - including table lamps and other lighting fixtures. There is special high temperature insulated wire (fixture wire) which should be used when replacement is needed. For heating appliances like toasters, hair dryers, and deep friers, fiberglass or high temperature silicone based rubber insulated wire or insulating sleeves must be used should the original wiring need replacement. An appliance repair motor rebuilding shop would be the most likely source - common electronics distributors may not carry this stuff (especially if you only need a couple feet)!

    Connections between individual wires and between individual wires and other components are most often made by crimp or screw terminals, welding, or press-in contacts. For cables, actual multipin and socket connectors may be used.

    Common problems: internal wiring conductors broken, corroded, or deteriorated due to heat or moisture. Dirty, corroded, weakened, or damaged connector contacts are common requiring cleaning and reseating or replacement. Damage to insulation from vibration, heat, movement, or even improper manufacture or design is also possible. Careless reassembly during a previous repair could result in pinched broken wires or insulation as well as short circuits between wires, or wiring and sharp sheet metal parts.

    Testing: Inspect for obvious breaks or wires that have pulled out of their terminations. Integrity of wiring can be determined with a continuity checker or multimeter on a the low ohms scale. Flexing and wiggling wires especially at connections while observing the meter will identify intermittents.

    Switches - power, mode, or speed selection

    Most appliances have at least one switch to turn the appliance on and off. In some cases, this may be combined with a thermostat or other control. However, switches serve a variety of functions as well. In all cases, the function of a switch is the same - to physically make (on) or break (off) the circuit or connect one signal to another. Common problems with switches include: dirt, worn, or melted contacts, broken plastic or fiber parts, bad connections to terminals.

    Testing: Switches can always be tested with a continuity checker or a multimeter on a low ohms scale.

    WARNING: Mercury is a heavy metal and is poisonous. I know it is fun to play with beads and globs of the stuff (and I have done it) but do not recommend it, at least not on a daily basis. Dispose of any from broken mercury switches or thermometers safely. If you insist on keeping it, use a piece of paper as a scoop and put the mercury in a bottle with a tightly sealed cap. See the section: Comments on mercury poisoning.

    About mercury wall switches

    The types of mercury switches used for wall switches are quite clever and provide in effect a snap action (called hysteresis) due to their construction and the surface tension of the liquid mercury itself. This despite the fact that the motion of the toggle lever is totally smooth and silent. It is not possible to put the lever in such a position that there could be marginal contact and random on-off cycles. The mercury capsule inside such a switch consists of a metallic shell with an insulating (glass or ceramic) spacer in between the two halves. Connection to the switch's wiring is made via sliding contacts to the metal portion of the capsule. There is a small hole toward one side in the spacer. Rotating the capsule results in the mercury flowing through the hole to make contact:

    Problems are rare with these mercury switches. In fact, GE mercury switches used to carry a *50* year warranty! I don't know if they still do.

    In principle, these are also the safest type of switch since any sparking or arcing takes place inside the sealed mercury capsule. However, the contact between the screw terminals and the capsule are via sliding contacts (the capsule is press fit between the metal strips to which the screws are attached) and with time, these can become dirty, worn, or loose. For this reason, some electricians do not like mercury switches, particularly for high current loads.

    Comments on mercury poisoning

    While I recognize the dangers of mercury poisoning, I was one of those who used to play with mercury quite extensively from broken thermometers, mercury switches, and any other sources I could find. In high school, I used to go through the back storage rooms in search of mercury. This was before the era of regulations protecting everyone from everything. I still have a couple pounds of the stuff, safely stored.

    The danger isn't so much from occasional contact with metallic mercury as from mercury vapor which may build up in an enclosed spaces and from soluble mercury compounds. You get significant contact with metallic mercury from amalgam ("silver") tooth fillings and while there is controversy about their safety and some people have had their old fillings ripped out at great expense (and disconfort!), there is as far as I know, no conclusive scientific evidence linking mercury poisoning to amalgam fillings.

    Having said that, I agree that it's probably a bad idea to be playing with mercury on a daily basis but pushing a few drops of it around or losing one drop to the floorboards isn't going to make everyone sick. If this were the case, half the houses in the World would be HAZMAT zones from broken fluorescent lamps - which have significant metallic mercury in them.

    If anyone has evidence to the contrary, please cite refereed scientific publications and I will read them, not hyped popular press reports.

    Relays - electrically activated switches for power or control

    Relays are switches that are activated by an electrical signal rather than a button or toggle. They are used to switch power (as in an central air conditioning system) or control signals (as in a telephone or modem). For more information on relays, see the document: Notes on the Troubleshooting and Repair of Audio Equipment and other Miscellaneous Stuff.

    Contact configurations

    The arrangement of contacts on a switch is often abbreviated mPnT where: In addition, you may see: This also applies to relays except that the contact switching is activated by an electrical signal rather than a finger.

    The most common types are:

    Electrical overload protection devices - fuses and circuit breakers

    The purpose of fuses and circuit breakers is to protect both the wiring from heating and possible fire due to a short circuit or severe overload and to prevent damage to the equipment due to excess current resulting from a failed component or improper use (using a normal carpet vacuum to clear a flooded basement).

    Fuses use a fine wire or strip (called the element) made from a metal which has enough resistance (more than for copper usually) to be heated by current flow and which melts at a relatively low well defined temperature. When the rated current is exceeded, this element heats up enough to melt (or vaporize). How quickly this happens depends on the extent of the overload and the type of fuse.

    Fuses found in consumer electronic equipment are usually cartridge type - 1-1/4" mm x 1/4" or 20 mm x 5 mm, pico(tm) fuses that look like green 1/4 W resistors, or other miniature varieties. Typical circuit board markings are F or PR.

    More than you could ever want to know about fuses can be found at the Littlefuse Web site. Go to Resouces->Reference Materials->Fusology to start.

    Circuit breakers may be thermal, magnetic, or a combination of the two. Small (push button) circuit breakers for appliances are nearly always thermal - metal heats up due to current flow and breaks the circuit when its temperature exceeds a set value. The mechanism is often the bending action of a bimetal strip or disc - similar to the operation of a thermostat. Flip type circuit breakers are normally magnetic. An electromagnet pulls on a lever held from tripping by a calibrated spring. These are not usually common in consumer equipment (but are used at the electrical service panel).

    At just over the rated current, it may take minutes to break the circuit. At 10 times rated current, the fuse may blow or circuit breaker may open in milliseconds.

    The response time of a 'normal' or 'rapid action' fuse or circuit breaker depends on the instantaneous value of the overcurrent.

    A 'slow blow' or 'delayed action' fuse or circuit breaker allows instantaneous overload (such as normal motor starting) but will interrupt the circuit quickly for significant extended overloads or short circuits. A large thermal mass delays the temperature rise so that momentary overloads are ignored. The magnetic type breaker adds a viscous damping fluid to slow down the movement of the tripping mechanism.

    Common problems: fuses and circuit breakers occasionally fail for no reason or simply blow or trip due to a temporary condition such as a power surge. However, most of the time, there is some other fault with the appliance which will require attention like a bad motor or shorted wire. Dirty, corroded, or weak contacts (holding the fuse or circuit breaker) may get hot and contribute to nuisance tripping. Circuit breakers can also go bad just due to age (this particularly applies to those in the electrical service panel - one that buzzes and/or trips occasionally for no apparent reason may need replacement).

    Testing: Fuses and circuit breakers can be tested for failure with a continuity checker or multimeter on the low ohms scale. A fuse that tests open is blown and must be replaced (generally, once the circuit problem is found and repaired.) Of course, if the fuse element is visible, a blown fuse is usually easy to identify without any test equipment. A circuit breaker that tests open or erratic after the reset button is pressed, will need replacement as well.

    Note that in general, circuit breakers should NOT be used for repeated switching nor should they be reset on a circuit with any substantial load (or overload or short circuit). Their contacts are not designed for this type of operation. Here are some additional comments:

    (From: Tom Hardy (

    Many people use circuit breakers as switches (including my father-in-law!). The problem is that the contacts become burned, creating resistance and thus abnormal heating causing the breaker to be unable to carry its rated load. The other thing this does (especially with Square-D QO style breakers) through heating is causes the buss bar contact to loose it's spring tension (in reference to circuit breakers installed in an electrical service panel). This will (as happened to my father-in-law) burn up part of the buss bar and ruin the electric panel. Most people will just reset a breaker if it trips, without first removing the load. This also causes burned contacts as mentioned above. I have found many defective breakers before they go bad, usually feeding higher current appliances. Just turn on the appliance for 15 to 20 minutes and then feel the front of the breaker with your hand. If its warm or hot, there is usually reason to suspect future trouble if it's not replaced.

    Fuse postmortem

    Quite a bit can be inferred from the appearance of a blown fuse if the inside is visible as is the case with a glass cartridge type. One advantage to the use of fuses is that this diagnostic information is often available!

    This information can be of use in directly further troubleshooting.

    Fuse or circuit breaker replacement

    As noted, sometimes a fuse will blow for no good reason. Replace fuse, end of story. In this situation, or after the problem is found, what are the rules of safe fuse replacement? It is inconvenient, to say the least, to have to wait a week until the proper fuse arrives or to tromp out to Radio Shack in the middle of the night.

    Even with circuit breakers, a short circuit may so damage the contacts or totally melt the device that replacement will be needed.

    Five major parameters characterizes a fuse or circuit breaker:

    1. Current rating: This should not be exceeded (you have heard about not putting pennies in fuse boxes, right?) (The one exception to this rule is if all other testing fails to reveal which component caused the fuse to blow in the first place. Then, and only then, putting a larger fuse in or jumpering across the fuse **just for testing** will allow the faulty component to identify itself by smoking or blowing its top!) A smaller current rating can safely be used but depending on how close the original rating was to the actual current (or how much surge current there is on power-on), an underrated fuse may blow immediately.

      Some equipment may use fuses with strange current ratings like 1.65 A instead of 1.5 A. In such cases, it won't hurt to try a common lower current value like 1.5 A. The worst that will happen is that it will blow, probably not immediately but some time in the future even if there is no problem. Using the next higher common value like 1.75 A isn't recommended except for testing. The irony is that these strange values are often used in the primaries of switchmode power supplies where their function is to blow due to catastrophic failure, not a slight overload, and it really doesn't matter if they are slightly larger (but only slightly larger!). However, for reasons of liability, this is still not recommended. Don't do it!

    2. Voltage rating: This is the maximum safe working voltage of the circuit (including any inductive spikes) which the device will safety interrupt. Thus, you may see fuses where the elements look like [|------|] versus [|==--==|]. Aside from the shape and size, the type of material used for the fuse element as well as what's surrounding it (e.g., air or sand) will affect voltage rating. It is safe to use a replacement with an equal or high voltage rating.

      And, it's quite likely that there will be no difference between 125 V and 250 V fuses except the labeling. It really doesn't cost more to make higher voltage fuses in the same package size of the type found in consumer electronic equipment so any labeling like this would be more of a regulatory issue.

      For high voltage, current limited equipment (up to 500 V or more, up to 10 times the fuse current rating), it may still be acceptable to use a 250 V fuse.

    3. AC versus DC: Fuses rated for AC and DC may not be the same. For a given voltage, a shorter gap can be used to reliably interrupt an AC circuit since the voltage passes through zero 120 (100) times a second. For example, a fuse rated 32 VDC may look similar to one rated for 125 VAC.

    4. Type: Normal, fast blow, slow blow, etc. It is safe to substitute a fuse or circuit breaker with a faster response characteristic but there may be consistent or occasional failure mostly during power-on. The opposite should be avoided as it risks damage to the equipment as semiconductors tend to die quite quickly.

    5. Mounting: It is usually quite easy to obtain an identical replacement. However, as long as the other specifications are met, soldering a normal 1-1/4" (3AG) fuse across a 20 mm fuse is perfectly fine, for example. Sometimes, fuses are soldered directly into an appliance.

      However, any soldering of wires directly to a fuse should be done with care and it may weaken the fuse element or its connection if the fuse doesn't just fall apart. Thus, where soldered-in fuses are used, obtain replacements with wire leads that preattached or solder in a fuse holder.

    Thermal protection devices - thermal fuses and thermal switches

    These devices protect against excessive temperature due to either a fault in the appliance (locked motor overheating) or improper use (blow dryer air blocked). They are at least as important as normal fuses or circuit breakers for prevention of fire and damage due to overheating. Also see the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    There are three typical types:

    1. Thermal fuses: This is similar to an electrical fuse but is designed to break the circuit at a specific temperature. These are often found in heating appliances like slow cookers or coffee percolators or buried under the outer covering of motor windings or transformers. Most also have an electrical fuse rating as well. Like electrical fuses, these are one-time only parts. A replacement that meets both the thermal and electrical rating is required.

      CAUTION: When replacing a thermal fuse, DO NOT SOLDER it if at all possible. If the device gets too hot, it may fail immediately or be weakened. Crimp or screw connections are preferred. It is normally possible to obtain "crimp rings" when you order - they may be included. Then, just cut off the old fuse but leave some wire, slip the old and new wires into a crimp ring (twist them for added mechanical stability) and compress the ring tightly with a pair of pliers. Note the direction: If the appliance uses a polarized plug, it is recommended that the isolated lead of the thermal fuse be attached to the Hot AC wiring and the bare metal body of the thermal fuse which is connected to one lead be attached to the wiring of the appliance. This is a minor point but it doesn't cost anything!

                             *                     *
            To AC Hot -------||--     ______     --||-------- To appliance wiring
                                 New Thermal Fuse
        * Twisted and crimped connection for maximum mechanical strength.
      If you must solder, use a good heat sink (e.g., wet paper towels, little C-clamps) on the leads between the thermal fuse and the soldering iron, and work quickly!

    2. Thermal switches or thermal protectors (strip type): These use a strip of bimetal similar to that used in a thermostat. Changes in temperature cause the strip to bend and control a set of contacts - usually to to break a circuit if the set temperature is exceeded. Commonly found in blow dryers and other heating appliances with a fixed selection of heat settings. They may also be found as backup protection in addition to adjustable thermostats.

    3. Thermal switches or thermal protectors (disk type): These use a disk of bimetal rather than a strip as in most thermostats. The disk is formed slightly concave and pops to the opposite shape when a set temperature is exceeded. This activates a set of contacts to break (usually) a circuit if the rated temperature is exceeded. They may also be found as backup protection in addition to adjustable thermostats. A typical thermal switch is a small cylindrical device (i.e., 3/4" diameter) with a pair of terminals and a flange that is screwed to the surface whose temperature is to be monitored.

    In some applications, device types (2) and (3) may be used as the primary temperature regulating controls where adjustment is not needed with (1) as the protection of last resort. For example, a hair dryer may depend on air-flow to maintain the desired temperature. But it will have a bimetal strip-type thermostat to shut off power if the air-flow is blocked for some reason and a thermal fuse to permanently disable the device should the thermostat fail to open.

    Comments on importance of thermal fuses and protectors

    Like a normal fuse or circuit breaker, a thermal fuse or thermal protector provides a critical safety function. Therefore, it is extremely ill advised to just short it out if it fails. Some designs even make this option extra tempting by providing an easy way to bypass even one buried inside a power transformer - using an additional, normally unused terminal.

    For testing, it is perfectly acceptable to temporarily short out the device to see if the equipment then operates normally without overheating. This will confirm that a one-time thermal fuse has blown, or that a resettable type is malfunctioning. However, while these devices do sometimes just fail on their own, most likely, there was another cause. If you know what it was - you were trying to charge a shorted battery pack, using your window fan to mix cement, or something was shorted externally, then the fuse served its protective function and the equipment is fine. IT SHOULD BE REPLACED WITH THE SAME TYPE or the entire transformer, motor, or whatever it was in should be replaced! This is especially critical for unattended devices. Otherwise, especially with unattended devices, you have a situation where if the overload occurred again or something else failed, the equipment could overheat to the point of causing a fire - and your insurance company may refuse to cover the claim if they find that a change was made to the circuit. And even for portable devices like blow dryers and portable power tools, aside from personal safety should the device malfunction, the thermal protector is there to prevent damage to the equipment itself - don't leave it out!

    More on thermal fuses

    (From: Paul Grohe (

    The following is From Microtemps' literature (`95 EEM Vol.B p1388):

    "The active trigger mechanism of the thermal cutoff (TCO) is an electrically non-conductive pellet. Under normal operating temperatures, the solid pellet holds spring loaded contacts closed. When a pre-determined temperature is reached, the pellet melts, allowing the barrel spring to relax. The trip spring then slides the contact away from the lead and the circuit is opened. Once TCO opens a circuit, the circuit will remain open until the TCO is replaced....."

    Be very careful in soldering these. If the leads are allowed to get too hot, it may "weaken" the TCO, causing it to fail prematurely. Use a pair of needle-nose pliers as heat sinks as you solder it.

    I have replaced a few of these in halogen desk lamp transformers. The transformers showed no signs of overheat or overload. But once I got it apart, the TCO's leads had large solder blobs on them, which indicated that the ladies that assembled the transformers must have overheated the cutouts leads when they soldered them.

    The NTE replacement package also comes with little crimp-rings, for high-temp environments where solder could melt or weaken (or to avoid the possibility of soldering causing damage as described above --- sam).

    Controls 1 - adjustable thermostats and humidistats

    Thermostats are use to regulate the temperature in heating or cooling type appliances. Common uses include heaters, air conditioners, refrigerators, freezers, hair dryers and blow dryers, toaster ovens and broilers, waffle irons, etc. These are distinguished from the thermal switches discussed above in that they usually allow a variable temperature setting.

    Four types are typically found in appliances. The first three of these are totally mechanically controlled:

    1. Bimetal strip: When two metals with different coefficients of thermal expansion are sandwiched together (possibly by explosive welding), the strip will tend to bend as the temperature changes. For example, if the temperature rises, it will curve towards the side with the metal of lower coefficient of expansion.

      In a thermostat, the bimetal strip operates a set of contacts which make or break a circuit depending on temperature. In some cases the strip's shape or an additional mechanism adds 'hysteresis' to the thermostat's characteristics (see the section: What is hysteresis?).

    2. Bimetal disk: This is similar to (1) but the bimetal element is in the shape of a concave disk. These are not common in adjustable thermostats but are the usual element in an overtemperature switch (see the section: Thermal protection devices - thermal fuses and thermal switches).

    3. Fluid operated bellows: These are not that common in small appliances but often found in refrigerators, air conditioners, baseboard heaters, and so forth. An expanding fluid (alcohol is common) operates a bellows which is coupled to a set of movable contacts. As with (1) and (2) above, hysteresis may be provided by a spring mechanism.
    Other variations on these basic themes are possible but (1)-(3) cover the vast majority of common designs.

    Testing of mechanical thermostats: Examine for visible damage to the contacts. Use a continuity checker or ohmmeter to confirm reliable operation as the knob or slider is moved from end to end if it will switch at room temperature. Gently press on the mechanism to get the contacts to switch if this is not possible. Use an oven on low or a refrigerator or freezer if needed to confirm proper switching based on temperature.

    1. Electronic thermostats: These typically use a temperature variable resistance (thermistor) driving some kind of amplifier or logic circuit which then controls a conventional or solid state relay or thyristor.
    Testing of electronic thermostats: This would require a schematic to understand exactly what they are intended to do. If a relay is used, then the output contacts could perhaps be identified and tested. However, substitution is probably the best approach is one of these is suspected of being defective.

    Humidistats, as their name implies, are used to sense relative humidity in humidifiers and dehumidifiers. Their sensing material is something that looks kind of like cellophane or the stuff that is used for sausage casings. It contracts and expands based on the moisture content of the air around it. These are somewhat fragile so if rotating the control knob on a humidifier or dehumidifier does not result in the normal 'click', this material may have been damaged or broken.

    Testing of mechanical humidistats: examine for visible damage to the contacts. Use a continuity checker or ohmmeter to confirm reliable operation as the knob or slider is moved from end to end. Gently press on the mechanism to get the contacts to switch if this is not possible. Gently exhale across the sensing strip to confirm that the switching point changes.

    What is hysteresis?

    An intuitive explanation of hysteresis is that it is a property of a system where the system wants to remain in the state that it is in - it has memory.

    Examples of systems with hysteresis:

    Examples of systems which ideally have little or no hysteresis: Hysteresis is usually added thermostats by the use of a spring mechanism which causes the mechanism to want to be in either the open or closed position but not in between. Depending on the appliance, there may be anywhere from 0 hysteresis (waffle iron) to 5-10 degrees F (space heater). Sometimes, the thermal mass of the heated device or room provides the hysteresis since any change to the temperature will not take place instantaneously since the heating element is separated from the thermostat by a mass of metal. Therefore, some overshoot - which in effect performs the same function as a hysteresis mechanism - will take place.

    Controls 2 - rheostats and potentiometers

    These controls are usually operated by a knob or a slide adjustment and consist of a stationary resistance element and a wiper that can be moved to determine where on the fixed element it contacts. In some cases, they are not actually user controls but are for internal adjustments. In other cases, they are operated by the mechanism automatically and provide a means of sensing position or controlling some aspect of the operation. Rheostats and potentiometers come in all sizes from miniature circuit board mounted 'trimpots' to huge devices capable of handling high power loads. The resistance element may be made of fine wire ('wirewound') or a carbon composition material which is silkscreened or painted on.

    Interlocks - prevent operation with case or door open

    Most of these are simple switches mechanically activated by the case or door. Sometimes, optical or magnetic interlocks are used (rare on small appliances but common on things like printers). Line cords that are firmly attached to the case and disconnect automatically when the case is removed are another example of an interlock. Interlocks may be designed to prevent injury during normal operation (e.g.. food processor blades will not start when cover is removed) or during servicing (remove AC power to internal circuits with case removed).
    1. Interlock switches: Various kinds of small switches may be positioned in such a way that they disconnect power when a door is opened or cover is removed. These may fail due to electrical problems like worn or dirty contacts or mechanical problems like a broken part used to activate the interlock.

      Testing: Use an ohmmeter or continuity checker on the switches. The reading should either be 0 ohms or infinite ohms. Anything in between or erratic behavior is indication of a bad switch or cord.

    2. Attached cordset: Should the case be opened, the cord goes with the case and therefore no power is present inside the appliance. To get around this for servicing, a 'cheater cord' is needed or in many cases the original can be easily unfastened and used directly.

      Testing: Use an ohmmeter or continuity check to confirm that both wires of the cord are connected to both AC plug and appliance connector. Wiggle the cord where it connects to the appliance and at the plug end as well to see if there might be broken wires inside.

    Light bulbs - incandescent and fluorescent

    Small incandescent light bulbs are often used in appliances for interior lighting or spot illumination. The common 'appliance bulb' is simply a 'ruggedized' 40 W incandescent light bulb in a clear glass envelope. Other types are found in vacuum cleaners, microwave overs, makeup mirrors, and so forth.

    Testing: visual inspection will often reveal a burnt out incandescent light bulb simply because the filament will be broken. If this is not obvious, use an ohmmeter - an infinite resistance means that the bulb is bad.

    See the chapter: Incandescent Light Bulbs, Lamps, and Lighting Fixtures for more info.

    Small fluorescent lamps are often found in makeup mirrors, plant lights, and battery powered lanterns.

    Testing: The best test for a bad fluorescent lamp (tube) is to substitute a known good one. Unfortunately, there is no easy go-no go test for a these as with an incandescent lamp. Other parts of the fixture (like the ballast or starter) could also be bad. Testing with a multimeter between the pair of pins at each end should show low resistance if the lamp is good. However, depending on the type of ballast, a lamp with an open filament may still work just fine even though strictly speaking, it is defective. Again, try a replacement to be sure. CAUTION: A defective ballast or starter can cause a fluorescent lamp to go bad in short order - if it still doesn't work, don't just let it continue to try to start!

    See the document: Fluorescent Lamps, Ballasts, and Fixtures for additional information.

    Indicators - incandescent or neon light bulbs or LEDs

    Whereas lighting fixtures using incandescent or fluorescent bulbs are designed to illuminate a room or small area, an indicator is simply there to let you know that an appliance is on or in a specific mode.

    There are three common types of electrical indicator lights:

    1. Incandescent bulbs: Just like their larger cousins, an incandescent indicator or pilot light has a filament that glows yellow or white hot when activated by a usually modest (1.5-28 V) source. Flashlight bulbs are very similar but usually have some mechanical method of keeping the filament positioned reasonably accurately so that the light can be focussed by a reflector or lens. Since the light spectrum of incandescent indicators is quite broad, filters can be used to obtain virtually any colored light. Incandescent indicator lamps do burn out just like 100 W bulbs if run near their rated voltage. However, driving these bulbs at reduced voltage can prolong their life almost indefinitely.

      Incandescent indicator lamps are often removable using a miniature screw, bayonet, or sliding type base. Some are soldered in via wire leads. Others look like cartridge fuses.

      Testing: Visual inspection will often reveal a burnt out incandescent light bulb simply because the filament will be broken. If this is not obvious, use an ohmmeter - an infinite resistance is means that the bulb is bad.

    2. Neon lamps: These are very common as AC line power indicators because they are easy to operate directly from a high voltage requiring only a high value series resistor.

      They are nearly all the characteristic orange neon color although other colors are possible and there is a nice bright green variety with an internal phosphor coating that can actually provide some illumination as well. While neon bulbs do not often burn out in the same sense as incandescent lamps, they do darken with age and may eventually cease to light reliably so flickering of old Neon bulbs is quite common. This is almost always just due to the natural aging process of the indicator and does not mean the outlet or appliance itself is bad.

      Some Neon bulbs come in a miniature bayonet base. Most are soldered directly into the circuit via wire leads.

      Testing: Inspect for a blackened glass envelope. Connect to AC line (careful - dangerous voltage) through a series 100K resistor. If glow is weak or absent, Neon bulb is bad.

    3. Light Emitting Diodes (LEDs): LEDs come in a variety of colors - red, yellow, and green are very common; blue is now available as are virtually all other colors including white. These run on low voltage (1.7-3 V) and relatively low currents (1-20 mA). Thus, they run cool and are easily controlled by low voltage logic circuits. LEDs have displaced incandescent lamps in virtually all electronic equipment indicators and many appliances. Their lifetime easily exceeds that of any appliance so replacement is rarely needed.

      LEDs are almost always soldered directly into the circuit board since they rarely need replacement.

      As an item of interest which has nothing to do with appliance repair, many automotive tail lights are now red LEDs, particularly the middle brake light. In fact, the red (stop) lights in many traffic signals are now LED clusters that screw directly into a normal 115 VAC socket. This is done because one of these will outlast 50 normal incandescent lamps and the cost of replacement far exceeds the cost of the lamp itself. How can you tell which type is used? Easy, move your eyes (or head) from side-to-side while looking at the red light; since the LED actually pulses 120 times per second (for 60 Hz power), you will see a series of spots - an incandescent lamp will appear continuous. Yellow and green will probably follow shortly but all I've seen so far are the red ones using LEDs.

      Testing: Use a multimeter on the diode test scale. An LED will have a forward voltage drop of between 1.7 and 3 V. If 0 or open, the LED is bad. However, note: some DMMs may not produce enough voltage on the diode test scale so the following is recommended: Alternative: Use a 6 to 9 V DC supply in series with a 470 ohm resistor. LED should light if the supply's positive output is on the LED's anode. If in doubt, try both ways, If the LED does not light in either direction, it is bad.

    4. Electroluminescent (EL) panels (sometimes used in night lights): These produce a cool soft light (usually bluish-greenish) consuming very little power (well they don't produce all that much light, either!). A thin layer of non-conducting light emitting material is sandwiched between a pair of electrodes, one of which is transparent or translucent. They can be virtually any size though a typical night light might be 2 x 2-1/2 inches or so. The device is basically a capacitor that emits light when an AC voltage (typically 115 VAC) is applied to its plates. There may be some additional components like a current limiting resistor in series and an MOV or other surge suppressor across the actual EL device (particularly on units designed to operate on 220/240 VAC.

      Testing: Check for bad connections and bad components with a multimeter. An open series resistor, shorted EL device, or faulty (partially shorted) MOV is possible. However, sometimes these failures won't show up except when normal voltage is applied. Measure on the AC volts range across the EL device - there should be a high AC reading, probably over 100 VAC.

    Heating elements - NiChrome coils or ribbon, Calrod, Quartz

    All heating elements perform the same function: convert electricity into heat. In this they have one other characteristic in common: they are all nearly 100% efficient. The only electrical energy which does not result in heat is the slight amount of light (usually red-orange) that is produced by a hot element.

    There are 3 basic types of heating elements. Nearly every appliance on the face of the planet will use one of these:

    1. NiChrome coil or ribbon: NiChrome is an alloy of Nickel and Chromium which has several nice properties for use in heating appliances - First, it has a modest resistance and is thus perfect for use in resistance heating elements. It is easily worked, is ductile, and is easily formed into coils of any shape and size. NiChrome has a relatively high melting point and will pretty much retain its original shape and most importantly, it does not oxidize or deteriorate in air at temperatures up through the orange-yellow heat range.

      NiChrome coils are used in many appliances including toasters, convection heaters, blow-dryers, waffle irons and clothes dryers.

      The main disadvantage for our purposes is that it is usually not possible to solder this material due to the heating nature of its application. Therefore, mechanical - crimp or screw must be used to join NiChrome wire or ribbon to another wire or terminal. The technique used in the original construction is may be spot welding which is quick and reliable but generally beyond our capabilities.

      Testing: Visual inspection should reveal any broken coil or ribbon. If inspection is difficult, use a multimeter on the low ohms scale. Check for both shorts to the metal chassis as well as an open element (infinite ohms).

    2. Calrod(tm) sealed element: This encloses a fine coiled NiChrome wires in a ceramic filler-binder inside a tough metal overcoat in the form of a shaped rod with thick wire leads or screw or plug-in terminals.

      These are found in toaster oven/broilers, hot plates, coffee makers, crock pots and slow cookers, electric range surface elements, conventional and convection ovens and broilers.

      Testing: When these fail, it is often spectacular as there is a good chance that the internal NiChrome element will short to the outer casing, short out, and melt. If there is no visible damage but the element does not work, a quick check with an ohmmeter should reveal an open element or one that is shorted to the outer casing.

    3. Quartz incandescent tube: These are essentially tubular high power incandescent lamps, usually made with a quartz envelope and thus their name.

      These are found in various kinds of radiant heaters. By running a less than maximum power - more orange heat - the peak radiation is in the infra-red rather than visible range.

      Testing: Look for a broken filament. Test with an ohmmeter just like an incandescent light bulb.

    Repair of broken heating elements

    In appliances like waffle irons and toaster ovens, these are usually welded. This is necessary to withstand the high temperatures and it is cheap and reliable as well. Welding is not normally an option for the doit yourselfer. However, if you are somewhat suicidal, see the section: Improving sensitivity of garage door openers receivers for a more drastic approach.

    I have used nuts and bolts, say 6-32, bolt, wire, washer, wire, washer, lockwasher, nut. Depending on how close to the actual really hot element it is, this may work. If you are connecting to the coiled element, leave a straight section near the joint - it won't get as hot.

    The use of high temperature solder or brazing might also work.

    The best approach is probably to use high temperature crimp connectors:

    (The following from: (Stephen Dunbar))

    You can connect heating element wires with high-temperature solderless connectors that are crimped onto the wires. Be sure to get the special high-temp connectors; the ordinary kind will rapidly oxidize and fall apart at high temperatures. If you want to join two wires to each other, you'll need either a butt splice connector (joins the wires end-to-end) or a parallel splice connector (the wires go into the connector side-by-side). To fasten a wire to a screw terminal you can use a ring or spade connector (though as noted above, a screw, nut, and washer(s) should work fine --- sam). If your waffle iron has quick disconnect terminals you'll need the opposite gender disconnect (AkA Faston). These come in both .187" and .250" widths.

    Your best bet for getting these connectors in small quantity is probably a local appliance parts outlet that caters to do-it-yourselfers. If you can't find what you need there, try Newark Electronics (branches all over the place). I have an old copy of their catalog which lists SPC Technology Voltrex Brand High Temperature Barrel Terminals in several styles: ring, spade, disconnect, and butt splice. The prices were around $10 to $12 per 100 (this catalog is a couple of years old) for wires in the 22-18 or 16 to 14AWG size ranges, almost twice that for the heftier wire gauges. (Be sure to determine the wire gauge of your heating elements so you can get the right size terminal.)

    You can spend a *lot* of money on crimp tools, but for occasional light use you can probably get by with one of those $10 gadgets that crimp, strip & cut wires, and cut bolts--the sort of thing you'd find in your local home center or Radio Shack.

    (From: Nigel Cook (

    The thin stainless steel strip found spot welded to multicell NiCd batteries make good crimps for joining breaks in heater resistance wire. Form a small length of this strip around a needle or something similar to make a tight spiral with enough clearance to go over doubled-up heater wire. Abraid or file the cut ends of the broken wire. Crimp into place with a double lever action crimper. If there is an area of brittle heating element around the break then cut out and splice in a replacement section with two such crimps. Such a repair to my hot-air paint stripper (indispensable tool in my electronics tool-kit) has survived at least 50 hours.

    (From: Dan Sternberg (

    Another old trick for nichrome repair is to make a paste of Borax, twist the two broken end together, and energize the circuit. A form of bond welding takes place. I've have used this on electric clothes dryer heater elements with good luck.

    (From: DaveC.)

    Here's a "quick fix" that sometimes works for a long time and sometimes fails quickly (depending, I think, on just how old and brittle the nichrome wire is).

    Mix some ordinary "Boraxo" powdered hand soap with a little water to make a thick paste -- and you don't need much.

    Take the broken ends of wire, bend a small loop into each, and interlock the loops so the wires stay together.

    Pack the Boraxo paste around the joint, and turn on the heater.

    Keep your eyes on that joint. As the coil heats up, the hook joint will be the worst connection, so it'll naturally get the hottest.

    When it gets hot enough, the nichrome wires will melt, and, being fluxed by the borate, will fuse together into a blob. The blob, now being *larger* than the rest of the wires, will immediately cool down, and will never again get as "red hot" as the rest of the heater.

    Allow the coils to cool down and, using pliers, carefully crush any glassy flux deposit that remains on the joint.

    If the joint doesn't behave as I describe, or if the wires are too brittle to be formed into hooks, the wires are likely too old to produce a long-lasting joint. If the joint behaves as I described, it may last for a good long time.

    Solenoids - small and large

    Solenoids are actuators operated by electromagnets that are used to operate valves, slide or engage various parts, eject or prevent opening of a door, and other functions. While shapes and sizes may vary, all electrically operated solenoids use an electromagnet - AC or DC - to pull on a movable piece called an armature which generally moves back and forth but rotary motion is also possible.

    Solenoids are usually two position devices - they are not used to provide intermediate amounts of force or travel like motors.

    Sizes ranges from small 1/2" long units providing a fraction of an ounce of force and 1/8" travel to large 3" long units providing many pounds of force with travels of 2" or more.

    Testing: Inspect for free movement. Use an ohmmeter to confirm that the coil is intact. There could be other problems like shorted turns in the coil but these would be less common than lack of lubrication or an open coil. Check voltage on operating solenoid to determine whether drive power is present.

    Small electronic components - resistors, capacitors, diodes

    A variety of small electronic components may be found in appliances though unlike true electronic equipment, these do not usually run the show. For more information on these types of components, see any good introductory electronics text.

    Transformers - low voltage, high voltage

    A transformer consists of a laminated iron or ferrite core and 2 or more insulated windings that are most often not connected to each other directly. If one set of windings is used as the input for AC power or an audio signal (the 'primary' winding), the voltage appearing on each of the other windings (the 'secondary' winding(s)) will be related by the ratio of the number of turns on each of the windings. However, you don't get something for nothing: The current is related by the inverse of this ratio so the power doesn't change (except due to unavoidable losses).

    Transformers are used in nearly every type of electronic equipment both for power and signals, and throughout the electrical distribution network to optimize the voltage/current used on each leg of the journey from the power plant to the user.

    The types we are interested in with respect to household appliances and power tools are most often use to convert the AC line voltage to some other value, lower or higher:

    1. Low voltage power transformers are found in AC wall adapters and electronic equipment as part of their power supplies to generate 1 or more DC voltages to run the device, recharge its batteries, etc. Their outputs are typically between 2 and 48 VAC but almost any other value is possible.

    2. High voltage power transformers are found in microwave ovens, old TVs and audio equipment based on vacuum tubes, oil burner ignitions, and some neon signs. Their output can go as high as 15,000 V or more.

    3. Flyback (or LOPT), inverter, and other more specialized transformers are driven by a high frequency oscillator or chopper in various equipment like TVs and monitors (HV, LV, and other power supplies), PCs and some of their peripherals, electronic flash units. Note that these will NOT operate from the AC line directly and are therefore useless unless driven by a proper electronic circuit.
    There are also a couple of other common types of AC line operated transformers used in servicing:
    1. Isolation transformers are wound 1:1 so that the output voltage is the same as the input voltage. However, with no direct connection between windings, equipment can be tested with less risk of shock.

    2. Variable transformers (or "Variacs", which is one brand name) allow the output voltage to be adjusted between 0 and full (or slightly above) line voltage which is useful for testing purposes where the behavior of a piece of equipment is being determined. Some very old light dimmers may use this technology as well (newer ones use solid state phase control. See the sections starting with: Dimmer switches and light dimmers.)
    See the document: Troubleshooting and Repair of Consumer Electronic Equipment for more information on these types of transformers.

    Motors - universal, induction, DC, timing

    A large part of the functionality of modern appliances is based on the use of motors of one form or another. We devote an entire chapter to motors. The following is just an introduction.

    Motors come in all shapes and sizes but most found in small appliances can be classified into 5 groups:

    1. Universal motors.
    2. Single-phase induction motors.
    3. Shaded pole induction motors.
    4. Small permanent magnet DC motors. Synchronous timing motors.
    See the chapter: Motors 101 for more detailed information on the common types of motors found in small appliances.

    Fans and Blowers - bladed or centrifugal

    The entire purpose of a particular appliance may be to move air or this may simply be needed for cooling. Obviously, portable and window fans are an example of the former. However, many appliances have built in fans you may not even be aware of as part of the motor(s) or other rotating components.

    There are two primary types of configurations:

    1. Bladed fans: We are all familiar with the common desk or window fan. This uses a set of rotating blades - typically 3-5 to gather and direct air. In the specific case of an oscillating desk fan, a gear drive linked to the motor also permits the general direction of air movement to be controlled in a back-and-forth motion. I recently saw one where in addition to moving back and forth, the front grille can be set to rotate at an adjustable rate providing more variation in air flow.

      The direction of the air movement with respect to blade rotation is determined by the pitch - the tilt - of the blades. Although reversing air direction is possible by reversing the motor, one direction is usually more effective than the other due to the curve of the blades.

    2. Centrifugal blowers: These use a structure that looks similar to a squirrel cage to suck air from the center and direct it out a plenum formed around the blower. While these may be found in all sizes, the most common household application is in the vacuum cleaner. Large versions of these blowers are used in central heating and airconditioning systems, window air conditioners, and oil burners.

      Direction of rotation of the blower motor does not change the direction of airflow. However, one direction will be more effective than the other (where the blower is rotating in the same direction as the way exit port on the air plenum points. Because of this, it is not possible for a vacuum cleaner to blow out the suction hose due to a reversed motor (which in itself is for all intents and purposes, impossible as well). This is usually caused by back flow due to a blockage.

    Bearings and bushings

    The shafts of rotating parts normally are mounted in such a way that friction is minimized - to the extent needed for the application. A bearing is any such joint with more specific terms used to describe the typical types found in small appliances - or lawnmower, automobile engines, or 100 MW turbines.

    Mechanical controllers - timing motors and cam switches

    While these are not that common on small appliances, they may be present in washing machines, dryers, dishwashers. and refrigerator defrost timers. They in themselves may be considered small appliances - and often can be repaired or replaced easily.

    Most of these are just small timing motors (synchronous motors running off of the AC line) which rotate one or more cams (disks with bumps) which activated one or more switches at appropriate times during the rotation cycle. Typical cycle times range from a minute or less to several hours (refrigerator defrost timer). Most like washing machine timers are in the 1 hour range. Sometimes, the motor is stopped during certain portions of the cycle awaiting completion of some other operation (i.e., fill).

    These controllers therefore consist of several parts:

    Testing: If the controller is not working at all, check for power to the motor. Listen for the sound of the motor parts rotating. Check for gummed up lubrication or broken parts.

    If some of the circuits do not work, check the switches for dirty or worn contacts or broken parts.

    Electronic controllers - simple delay or microprocessor based

    These can range from a simple R-C (resistance-capacitance) circuit to provide the time delay in a toaster to sophisticated microprocessor based systems for programming of a coffee maker or microwave oven.

    While generally quite reliable, bad solder connections are always a possibility as well as failed parts due to operation in an environment prone to temperature extremes.

    Testing: Check for bad solder connections and connectors that need to be cleaned and reseated. Inspect for obviously broken or burned parts. Test components for proper value.

    For digital clock/programmers or microprocessor based controllers, not much else can be done without a schematic - which not likely to be easily available.

    Batteries - Alkaline, Lithium, Nickel-Cadmium, Lead-Acid

    More and more small appliances and power tools are cutting their cords and going to battery power. Although there are a large number of battery types, the most common for power applications (as opposed to hearing aids, for example) are: See the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs, and Other Related Information for more details.

    AC adapters and chargers - wall 'warts' with AC or DC outputs

    These wall adapters are used to power many small electronic devices and appliances directly and/or to recharge their batteries. They usually plug directly into the wall socket and convert the 115 VAC (U.S.) to a lower voltage - 3 V to 24 V AC or DC typical. More sophisticated units may actually be a switching power supply with smart electronic control of battery charging and power management. The following are typical types: In some cases, a single adapter will put out multiple voltages. See the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs, and Other Related Information for more details.

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    AC Line and Battery Powered Household Appliances

    Table lamps

    This is the most popular type of lighting for reading or general illumination. The type described in this section takes normal 115 VAC light bulbs.

    The common table lamp is just a light duty cordset, switch, and sockets for one or more incandescent light bulbs. In many cases, the switch and socket are combined into one assembly. In other designs, particularly where more than one bulb can be lit independently (for example, a large bulb up top and a night light in the base), a separate switch (rotary or push-push) selects the light bulb(s) to be turned on.

    For the most common combined switch and socket, there are several varieties and these are all generally interchangeable. Therefore, if you want to take advantage of the added convenience of a 3-way bulb allowing low, medium, and high illumination, it is a simple matter to replace the simple on-off switch in your lamp with a 3-way switch (not to be confused with the 3-way switches used in house wiring to control a single light fixture from 2 places).

    Virtually the same switch/socket combo is used where there is a bulb in the top and the base. But instead of switching the extra contact inside a 3-way socket, that terminal goes to the bottom lamp holder.

    Push-push, pull chain, and rotary switches are common for simple on-off control. The 3-way switches are usually of the rotary variety with off-low-medium-high selected as the knob is rotated. The 3-way bulb has two filaments which can be switched on individually or in combination to provide the 3 levels of illumination.

    Dimmer sockets can often be substituted for the normal kind as long as conventional incandescent bulbs (and not compact fluorescents) are to be used.

    Touch and even sound activated switch-sockets are also available though my personal recommendation is to stay away from them.

    Most common problems: burned out bulb, worn switch, bad plug or cord. Where the light flickers, particularly if jiggling or tapping on the switch has an effect, a bad switch is almost always the problem. Switch failure is more common when using high wattage bulbs but can occur just due to normal wear and tear.

    Replacements for most common switches and sockets are readily available at large hardware stores, home centers, and electrical supply houses. It is best to take along the old switch so that an exact match (if desired) can be obtained. While the thread sizes for the screw on socket shells are quite standard, some older lamps may have an unusual size. For more complicated switches with multiple sockets, label or otherwise record the wiring. If color coded, cut the wires so that the colors are retained at both the lamp and switch ends.

    Rebuilding a basic table lamp

    As noted in the Introduction, virtually any table lamp can be restored to like-new electrical condition for a few dollars at most. The following is the detailed procedure for the majority of common table lamps found in the U.S.

    This is assumed to be the type of lamp which has a combination socket and switch with a metal (brass-colored usually) outer shell. It is your decision as to whether a simple on-off switch or a 3-way type is to be used - they are usually interchangeable and a normal light bulb can be put into a 3-way socket (two clicks of the knob will be needed to switch a normal light bulb on or off, however). You can also put a 3-way bulb into a normal socket but you will, of course, only get one level of illumination (medium). For lamps with lighted bases, also see the section: Lamps with night-light bulbs in their base.

    You will need: (1) a new socket/switch of the appropriate type and (2) a new cordset (if you want to replace this as well). A polarized type plug is desirable to minimize the possibility of shock when changing bulbs. A medium size straight blade screwdriver and wire strippers are the only required tools.

    Lamps with night-light bulbs in their base

    These are the types of lamps where either the normal bulb on top or a smaller one in the base (or both) can be turned on using a turn-key or pull-chain.

    This is a standard, if somewhat unusual socket. It is basically the same as a 3-way type but with the extra connection going to the bulb in the base of the lamp. In the old days when sockets were assembled with screws instead of rivets, it might have been possible to modify a new 3-way socket to provide the extra connection.

    An electrical supply parts distributor or lamp store should have what you need or be able to order it for you.

    Take note of the connections as you remove the old socket to avoid mistakes. When routing the wires to the bulb in the base, avoid allowing the hot bulb from contacting the insulation - the plastic stuff might melt (for a 7 W or less wattage bulb and high temperature insulation is probably not an issue, however).

    What causes a lamp to flicker?

    Many things can cause the light bulb in a table lamp to flicker:

    High intensity lamps

    These include several types but they all use a transformer to reduce the 115 VAC to something lower like 12-24 V.

    Tensor(tm) (and their clones) high intensity lamps have been around for over 30 years and are essentially unchanged today. They use a low voltage transformer producing 12-24 VAC along with a special high output light bulb that looks similar to an automotive tail light. However, it uses substantially more current for the same voltage and puts out a much more intense, whiter light. These are not halogen lamps though their spectral characteristics are similar since the filaments run hotter than normal incandescents - and have shorter lives.

    Some will have multiple levels of illumination based on selecting taps on the transformer. Normal dimmers may not work (and should not be used) with these due to their transformer design - damage to the dimmer or lamp may result and this may be a fire hazard.

    Problems with Tensor lamps tend to center around the socket and switch. These may fail due to overheating as a result of the high temperature and high current operation. Replacements are available but they may take some effort to locate. A replacement lamp may be cheaper. (I often find complete Tensor lamps in perfect operating condition at garage sales for around $2.

    Halogen lamps and fixtures

    Halogen lamps share many of the design characteristics of high intensity lamps in that they are designed for local high intensity lighting and use a transformer usually (though some may use solid state voltage conversion instead). While some halogen lamps come with dimmers, some of the advantages of the halogen cycle are lost if the bulbs are not run at full power. The worst case is where they are operated just below full power - too cool for the halogen cycle to take place but hot enough for substantial filament evaporation to occur.

    Should the dimmer portion of such a fixture fail or become unreliable, it may a blessing in disguise since the lamp will either run at full intensity or can be easily rewired to do so by bypassing the electronics and just using the on/off switch!

    WARNING: halogen bulbs run extremely hot and are a serious fire hazard and burn hazard if not properly enclosed. When changing a halogen bulb, wait ample time for the old one to cool or use an insulated non-flammable glove or pad to remove it. When installing the new bulb, make sure power is off, and do not touch it with your fingers - use a clean cloth or fresh paper towel. If you do accidentally touch it, clean with alcohol. Otherwise, finger oils may etch the quartz and result in early - possibly explosive failure - due to weakening of the quartz envelope.

    Safety guidelines for use of halogen lamps

    These guidelines were prompted by a number of fires including some fatalities that have been linked to improper use of halogen lamps - in particular the high power torchiere variety of floor lamps. However, the guidelines apply to many other types of halogen lamps including work-lights, desk lamps, slide and overhead projectors, and other lamps or fixtures where the bulb is not entirely enclosed and thermally insulated from the exterior.

    (Source: The Associate Press except as noted).

    Safety groups recommend the following precautions for owners of halogen torchere lamps with tubular bulbs:

    Bad connections in halogen lamps

    (From: Norbert Koot ( I have used the same technique to fix both these problems: with a medium power soldering iron, simply tin the contact. Then before it cools, hold a center punch in the molten solder to make a cup shape of sorts. This keeps the bulb secure in the spring-loaded lamp contacts.

    Touch lamp problems

    These are susceptible to damage from voltage surges or just plain old random failures. In addition, the current surge that often results at the instant an incandescent bulb burns out (the bright flash) may blow the thyristor in the electronics module.

    If the lamp is stuck on, the thyristor is probably shorted. The specific part can be replaced but to be sure it is bad, some testing will be needed and it is probably soldered in place. However, if you have repaired an ordinary lamp, you will be able to replace the entire module fairly easily.

    If the lamp is stuck off, there could be a bad connection or bad bulb, or the electronics module is defective. Again, replacement is straightforward.

    Erratic problems could be due to bad connections, dried up electrolytic capacitors (especially if the electronics module is near the hot bulb), E/M interference (e.g., a dimmer or vacuum cleaner on the same circuit), or power spikes (thunderstorms or EMP from nuclear detonations). An inexpensive surge suppressor/AC line filter may reduce or eliminate the random switching from external causes.

    Some problems are of the following type:

    "I have 2 touch lamps in the bed room and they are both plugged in to the same receptacle. Every once in a while the lamps come on by themselves for no apparent reason. Even more strange is that every so often just one lamp turns on by itself."

    (From: Tim Moore (

    These use a MOSFET type circuit to switch the lamps on and off. The circuit is attached to the metal in the lamp base. When you touch it the impedance changes ever so minutely but enough to change the MOSFET from off to on and visa versa. My wife could never get our lamps to switch, she often had to blow on her hand first to get it moist so it would make better contact. Here is part of the problem. It takes a certain amount of signal from the lamp base to switch the circuit. Electronic parts all have acceptable ranges of operation and when put into identical circuits they sometimes perform differently. One circuit might need a good hard touch while the other might need only a slight touch. Power surges would often switch one of my lamps, although it didn't happen often. A strong radio signal could do it too. The bottom line is that these lamps are not rocket science and can't be counted on as 100% reliable. Sorry, that's the truth. You give up a little to get the convenience of just having to touch them. I ended up removing mine - an electrical storm wiped one out and wiped the other out a few years later.

    Touch lamps and RF interference

    While many people swear by touch lamps, nearly as many swear at them since in addition to frequent failures (bulb burn-outs killing the triac, for example), they can also be tempermental, cycling through their brightness settings and/or turning on or off due to static electricity, power line transients causing RFI, and stray pickup from the local ham rig.

    (Portions from: John Evans - N0HJ (

    Here is a fix my buddy, Ed, a fellow ham radio operator, has come up with to solve this problem.

    As usual it took 8 months and 10 minutes to fix.

    Two parts: 1/4 watt, 1k Ohm resistor and 2.5 mH 1/2 watt size molded coil. Connect in-line with the touch wire.

    I send 2 or more watts from my rig. My son works the CB.

    You'll find it on when you get home.

    So the darn thing is an oscillator which changes frequency when you touch it. The circuit does the rest. By adding the resistor/inductor pair, its sensitivity is reduced and the problem disappears.

    One more thing: (Most important!), you won't hear interference FROM the oscillator in the lamp anymore on your radio.

    And don't open up the module inside the lamp base, you are wasting your time there, and adding more work to glue the module back together.

    Just Choke off the sense wire with the resistor and 2.5 mH choke. You'll be fine.

    Incandescent fixtures

    A fixture is normally permanently mounted to a wall or ceiling. However, aside from not usually having a plug - being directly wired - they are similar to table lamps in what is inside.

    There will be one or more sockets for light bulbs - often all wired in parallel so that all the bulbs come on at the same time. For wall fixtures, there may be a switch on the fixture though most often the switch is mounted on the wall elsewhere.

    Unlike table lamps where most of the heat rises from the bulb away from the socket, mounting the sockets horizontally or inverted (base up) can result in substantial heating and eventual deterioration of the socket and wiring. Common problems relate to this type of problem - bad connections or brittle wire insulation. Replacement parts are generally available at home centers and electrical supply houses. Just make sure to kill power before working on any fixture wired into your house's electrical system!

    Removing the base of a broken light bulb

    Turn off power and double check! Wear safety goggles to protect against flying bits of glass.

    Then use a pair of needlenose pliers or any other tool that will grip what is left of the base to twist it free. A piece of a raw potato may even work!

    Locating burnt out bulbs in series circuits

    Christmas and other decorative lights are constructed as series strings of low voltage light bulbs as shown below:

        Male o------O----O----O----O----O----O----O----O---+
        Plug                                               |

    Or the following which permits several strings to be connected end-to-end:

                |             Bulbs                           |
        Male o--+---O----O----O----O----O----O----O----O---+  +--o Female
        Plug                                               |       Socket

    Many variations on these are possible including multiple interleaved series strings. One of the bulbs in each circuit may be a flasher. All newer light sets must include a fuse as well.

    In a series connected circuit, if one bulb burns out, all lights go out. The newer types include a device in each bulb which is supposed to mechanically short out that bulb if it burns out. However, these don't always work or you may have a set that doesn't have this feature.

    The following assumes a single series circuit - large light sets (e.g., perhaps 50 or more) will have multiple series strings so you will have to identify the particular circuit that is bad. If more than one bulb is burnt out, this may further complicate matters.

    To locate a burnt out bulb in a series string, you can use the binary search approach: pull a bulb in the middle of the string. Test the bulb and between the power cord end and the middle for low resistance. If these are ok, you know the bad bulb is in the other half. Then divide the 'bad' portion in half and test one half of it and so forth. For example, using this technique, you will need to make at most 6 sets of measurements to locate a bad bulb in a 50 light set.

    Sears, K-Mart, Radio Shack, among others sell inexpensive testers (e.g., Lite-Tester Plus, about $4). These detect the electric field generated by the (now floating) wire on the Hot side of the gap of the burnt out filament. These will also locate open wires and blown fuses in the same manner.

    I have also heard of bulb sets in which the individual bulbs are gas filled in such a way that if the filament breaks, current flows across the gap through the gas resulting in a faint glow in the burnt out bulb. I don't know if these things still exist.

    WARNING: Do not be tempted to bypass a bad bulb with a wire. This will reduce the total resistance and increase the current to the remaining lamps shortening their life. Replace a few bulbs and the entire string will pop. This is a serious safety hazard especially on older light sets that may not have internal fuses. Also, some fuses look like lamps - replace only with an identical fuse - not with a lamp!

    Comments on Christmas tree bulb/string repair

    Original type of problem: No light but fuses are good and no obvious damage.

    (From: Ken Bouchard (

    My advice, is trash them and go out and buy new ones. After all, you can get them typically around 5-10 bucks a set.

    Then you have the old set to raid bulbs from, for the ones that blow out.

    Quality control is not an issue when they build xmas lights. One slight tug of a wire, can break it, and the entire set goes dead.

    First I assume you wiggled all the bulbs, often just a loose bulb causes this. In the smaller type bulb sets the string is wired in sections, so one bulb goes out, and every 4th or 5th one is dead.

    The little bulbs were also designed, that if the filament breaks in the bulb a piece of foil inside it shorts out that bulb so that the remaining lights keep on working. This works up to a point, until more than 4-5 bulbs blow out at once, then the remaining ones get too much voltage and blow out too.

    Often the cheesy sockets get water in them and corrode, and/or the wires on the bulb get twisted or broken.

    They also use a cheap method of crimping the wiring together in these lights. Most times you can find the broken wire, by inspecting, seeing where it goes into the socket it pulls out easily.

    Well avoid doing this when the set is live (heh...) unless you like the idea of getting zapped.

    Shortening a Christmas light string

    For strings using large 115 V bulbs, this is easy as all the bulbs are in parallel like the outlets in your house. Cut off the unwanted bulbs and insulate the wire ends.

    However, for the common type of tiny bulbs that are in series, you cannot really do this easily. Removing and bypassing 1 or 2 bulbs in a 50 light string won't have much effect on the remaining bulbs but cutting it in half will double the voltage on each bulb - you will get a very bright string of lights for a very short time.

    The only way to shorten a string by more than a few percent of lights and have it survive is for the current to be limited by a bulb or resistor or to run it off of reduced voltage. A light dimmer might work except for the fact that they typically require a minimum load of 60 to 100 W - your light string is a small fraction of this.

    However, for the special case of 1/2 (give or take) the original number of bulbs, there is a simple solution: A rectifier diode (1A, 200 V PRV min.) in series with the string will cut the effective voltage approximately in half. Typical part numbers are 1N4003 though 1N4007. Even Radio Shack will carry them.

    Whatever you do, make sure your connections are secure (with wire nuts or properly soldered) and well insulated. For fire safety, the built-in fuse (usually at the plug-end) must be retained.

    Controlling a fixture or outlet from multiple locations

    Although the specific case of controlling a fixture or outlet from exactly two locations is a special case of switches at more than 2 locations, each is described separately since the former is much more common.

    Should you care, these implement the multiple input XOR (exclusive OR) logic function for controlling electrical devices.

    Note: See the section: Dimmer switches and light dimmers if you would like to have control of brightness of a lamp or fixture from multiple locations.

    The descriptions below are for using traditional mechanical switches at more than one location. There are also electronic solutions, some even are wireless, where a control module is placed between the load (e.g., lamp or fixture) and the power line and the 'switches' or user controls are mounted remotely. The X10 system is a more general way of doing this providing fully programmable timed (automatic) switching and dimming (where appropriate) from one or more locations.

    The 3-way switches (at least the basic white, ivory, or brown toggle type) can be found nearly anyplace that sells common electrical devices including hardware stores and home centers. You may have to look a little harder for 4-way switches as well as styles or colors to match your decor as these are not as widely available. However, a decent electrical supply house should have all of these.

    The wires marked A and B (sometimes called 'travelers') may be in a single (Romex) cable and should be on the screws that are both the same color.

    If you do use Romex with a black and white wire, put black tape on the insulation at the ends of the white wire (or paint the ends black) to indicate that this is a Hot wire and not a Neutral. This is required by Code but allows the use of this type of wire.

    These diagrams represent one wiring arrangement. Sometimes, there are other slight variations. For example, you might find the switches in the Neutral instead of Hot portion of the wiring - however, this is not recommended.

    UK translation for 3-way and 4-way wiring

    For 2 locations, you would think that a pair of 2-way switches rather than 3-way switches would be needed! Makes sense, huh? Actually, the number of screw terminals on the switch correlates with the 3-way or 4-way designation. (I don't know anyone who refers to 2-way switches in the US.)

    Perhaps they got it right in the UK :-).

    (From: Dion L Heap (

    I had to translate the American into the English. If anyone UK is reading this then for what we (UK) call 2 way lighting is the normal stairs light with 2 switches controlling it, (one up & one down). Both these switches are "2 way switches", to add another switch you would be creating 3 way lighting, for this you use both the existing 2 way switches and in-between the L1 & L2 you use an "intermediate switch" I asked at my supplier for a 4 way switch & they thought I was talking Japanese. A phone call to MK technical support revealed that the UK equivalent is the aforementioned intermediate switch. this has 4 points, the L1 & L2s from the 2 existing 2 way switches are taken through the intermediate.

    Identifying unmarked wiring or improperly functioning 3-way switch

    (Also see the section: Controlling a fixture or outlet from multiple locations.)

    So you forgot to label the wires before you removed the old switch, huh? :-).

    Or, you moved the wires from the old switches to the new switches but guess what? The new switches may not have the corresponding screws in the same locations and your symptoms are that one switch has to be up for the other switch to do anything - and that is if you are lucky!

    You have several options:

    Of course, kill power before touching or changing anything!

    Or a slight variation on the theme:

    (From: Greg Fretwell (

    "Pull out one of the switches (the first one you "fixed" to create this problem) mark all 3 wires. Rotate them all one terminal to the right. Try it. If no luck shift one more time. One of those should work."

    Here is one way to identify the proper wires more quickly than trial and error but requires testing the live wiring:

    1. Identify the Hot wire. With all 3 wires in each box disconnected and their ends exposed, use a tester between each one and the a earth ground (the box if metal and properly grounded). With power on, only one of the 6 wires will be live.

    Now, turn off the power and confirm that it is off by retesting the hot wire you identified above.

    1. Connect the lone screw (the different or darker colored one) on one switch to this Hot wire. Connect the same-color screws on the switch to the other two wires. This should take care of one box.

    2. With any luck, you should be able to connect the wires in the other box exactly the same way color wise.


    Check both boxes. There will be a single Hot - that goes on the common of the 3-way switch. Put the other two wires on the other two screws.

    Now, at the other switch, you will find one hot. Put that on a screw, not the common. Switch the other switch, and you'll find another hot. That is the other traveler. You've got one wire left,,, that's the other common.

    In more detail:

    Dimmer switches and light dimmers

    In the old days, a dimmer was a large high wattage rheostat put in series with the light bulb. (Some were probably also Variacs but these would have been more expensive.) Rheostats were both inefficient and producers of a lot of heat. Modern dimmers use a device called a triac (a type of thyristor) which is a solid state switch to control illumination by turning the light bulb on for only a part of each AC half-cycle (100 or 120 times a second depending on where you live) as determined by the adjustment knob or slider. This is called solid state phase control. Once switched on, it remains on for the remainder of the half-cycle:

    Dimmers are available to replace standard wall switches and even for use in place of the light bulb socket/switch in most table lamps. However, nearly all of these are designed only for normal incandescent light bulbs - not fluorescents, compact fluorescents, or high intensity or halogen lamps (or any other type of lamp with a transformer).

    (There are special dimmers for use with fluorescent lamps but these must be specifically matched to the lamp type and wattage and their dimming range is usually not very wide. See: the fluorescent lamp information at Don Klipstein's Lighting Web Site for a discussion of dimming techniques and details on several relatively simple approaches that may work for your needs.)

    Installation is generally very straightforward as there are only two wires and polarity does not matter. They simply replace the existing switch.

    To assure long life, it is best to select a dimmer with a higher power rating than your maximum load. For example, if you are using four 100 W bulbs, a 600 W dimmer should be the minimum choice and one rated at 1000 W would be better. This is particularly true if halogen bulbs are used since these may be harder on dimmers than normal types. Further derating should be applied where multiple dimmers are installed in the same outlet box resulting in greater combined heating. Higher wattage dimmer switches will have better heat sinking as well which should result in the active components - the thyristors - running cooler. Dimmers are under the most stress and generate the most heat when operating at about 50% output.

    Dimmers may fail due to power surges, excess load, momentary fault (short) at the instant of light bulb failure, or just plain old age. A failed dimmer will generally be stuck at full brightness since the thyristor will have shorted out. The mechanical on-off switch which is part of the dimmer will probably still work.

    You can't test a dimmer switch with a multimeter except to determine if it is totally shorted: With the control set mid-range, the resistance between the two terminals or wires should be high or infinite regardless of the switch position (if separate from the setting of the control). If it is under 10 ohms, the triac is shorted and at best you have a fancy on/off switch.

    To more fully test it, you can make up a simple circuit with a wall plug and cord, and the dimmer in series with a 60-100 W light bulb (less wattage may not be enough to provide enough load and the dimming range may be restricted). Make sure everything is well insulatded!

    For a 3-way type dimmer, test/connect between the common (different color wire ors crew) and each of the travelers (same color wires or screws) for all switch positions.

    It is not generally worth worrying about repair of a dimmer as they are so inexpensive. However, before replacement confirm that there is no actual problem with the wiring (like a short circuit in the fixture) and that you are not overloading the dimmer.

    Typical dimmer schematics

    These are the type of common light dimmers (e.g., replacements for standard wall switches) widely available at hardware stores and home centers.

    While designed for incandescent or heating loads only, these will generally work to some extent with universal motors as well as fluorescent lamps down to about 30 to 50 percent brightness. Long term reliability is unknown for these non-supported applications.

    CAUTION: Note that a dimmer should not be wired to control an outlet since it would be possible to plug a device into the outlet which might be incompatible with the dimmer resulting in a safety or fire hazard.

    Simplest dimmer schematic

    The first schematic is of a normal (2-way) inexpensive dimmer - in fact this contains just about the minimal number of components to work at all!

    S1 is part of the control assembly which includes R1.

    The rheostat, R1, varies the amount of resistance in the RC trigger circuit. The enables the firing angle of the triac to be adjusted throughout nearly the entire length of each half cycle of the power line AC waveform. When fired early in the cycle, the light is bright; when fired late in the cycle, the light is dimmed. Due to some unavoidable (at least for these cheap dimmers) interaction between the load and the line, there is some hysteresis with respect to the dimmest setting: It will be necessary to turn up the control a little beyond the point where it turns fully off to get the light to come back on again.

              Black o--------------------------------+--------+
                                                     |        |
                                                  |  |        |
                                               R1 \  |        |
                                            185 K /<-+        |
                                                  \  v CW     |
                                                  |         __|__ TH1
                                                  |         _\/\_ Q2008LT
                                                  +---|>|   / |   600 V
                                                  |   |<|--'  |
                                              C1 _|_  Diac    |
                                           .1 uF --- (part of |
                           S1                     |    TH1)   |
              Black o------/ ---------------------+-----------+
    The parts that fail most often are the triac, TH1, or the combination switch/control (S1/R1).

    3-way dimmer schematics

    There are at least two varieties of inexpensive 3-way style dimmer switches which differ mainly in the switch configuration, not the dimmer circuitry. You will probably have no reliable way of telling them apart without testing or disassembly.

    None of the simple 3-way dimmer controls permit totally independent dimming from multiple locations. With some, a dimmer can be installed at only one switch location. Fully electronic approaches (e.g., 'X10') using master programmers and addressable slave modules can be used to control the intensity of light fixtures or switch appliances on or off from anywhere in the house. See the section: True (electronic) 3-way (or more) dimmers.

    However, for one simple, if inelegant, approach to independent dimming, see the section: Independent dimming from two locations - kludge #3251.

    Simple 3-way dimmer schematic 1

    The schematic below is of one that is essentially a normal 3-way switch with the dimmer in series with the common wire. Only one of these should be installed in a 3-way circuit. The other switch should be a normal 3-way type. Otherwise, the setting of the dimmer at one location will always affect the behavior of the other one (only when the remote dimmer is at its highest setting - full on - will the local dimmer have a full range and vice-versa).

    Note that the primary difference between this 3-way dimmer schematic and the normal dimmer schematic shown above is the addition of an SPDT switch - which is exactly what is in a regular 3-way wall switch. However, this dimmer also includes a choke (L1) and capacitor (C2) to suppress Radio Frequency Interference (RFI). Operation is otherwise identical to that of the simpler circuit.

    This type of 3-way dimmer can be used at only one end of a multiple switch circuit. All the other switches should be conventional 3-way or 4-way types. Thus, control of brightness is possible only from one location. See the section: True (electronic) 3-way (or more) dimmers for reasons for this restriction and for more flexible approaches.

       Red 1 o--------o
                     S1   o----+------------+-----------+
                               |            |           |
       Red 2 o--------o        |         R1 \  ^ CW     |
                               |      220 K /<-+        |
                               |            \  |        |
                               |            |  |        |
                               |            +--+        |
                               |            |           |
                               |         R2 /           |
                           C2 _|_      47 K \           |
                      .047 uF ---           /         __|__ TH1
                               |            |         _\/\_ SC141B
                               |            +---|>|   / |   200 V
                               |            |   |<|--'  |
                               |        C1 _|_   D1     |
                               |   .062 uF ---  Diac    |
                               |            |           |
                               |   ::::::   |           |
       Black o-----------------+---^^^^^^---+-----------+
                             40 T #18, 2 layers
                           1/4" x 1" ferrite core 
    The parts that fail most often are the triac, TH1, or the combination switch/control (S1/R1).

    Simple 3-way dimmer schematic 2

    The schematic below is of a 3-way dimmer with a slightly more complex switching arrangement such that when the local dimmer is set to full on or full off, it is bypassed. (If you ignore the intermediate dimming range of the control, it behaves just like a normal 3-way switch.) With this scheme, it is possible to have dimmers at both locations without the dimmer circuitry ever being in series and resulting in peculiar behavior.

    Whether this is really useful or not is another story. The wiring would be as follows:

                  Location 1             Location 2
                 3-way Dimmer      A    3-way Dimmer     +---------+
                      /o----------------------o\         |  Lamp   |
        Hot o------o/    Silver 1     Silver 2   \o------|   or    |-----o Neutral
               Brass   o----------------------o   Brass  | Fixture |
                         Silver 2  B  Silver 1           +---------+
    (If dimming interacts, interchange the A and B wires to the silver screws at one dimmer).

    This one uses a toggle style potentiometer where the up and down positions operate the switches. Therefore, it has 3 states: Brass to Silver 1 (fully up), dim between Brass and Silver 1 (intermediate positions), and Brass to Silver 2 (fully down).

                            Br  /o---o            Br   o---o          Br/\/o---o
      3-way dimmer is up o---o/   S1   or down o---o\  S1    or Dim o---o  S1
                                 o---o                \o---o               o---o
                                  S2                   S2                  S2
    However, it is still not possible to have totally independent control - local behavior differs based on the setting of the remote dimmer (details left as an exercise for the reader).

    Like the previous circuit, this dimmer also includes a choke (L1) and capacitor (C3) to suppress Radio Frequency Interference (RFI). It is just a coincidence (or a matter of cost) that the 3-way dimmers have RFI filters and the 2-way type shown above does not.

      Silver 1 o---+----------------+--------------------+-----------+
                   |                |                    |           |
                   |                |                 R1 \  ^ Up     |
                   |                |              150 K /<-+        |
                   |                |                    \  |        |
                   |                |                    |  |        |
                   |                |          +---------+--+        |
                   |                |          |         |           |
                   |            C3 _|_         |      R2 /           |
                   |               ---         |    22 K \           |
                   |                |          |         /         __|__ TH1
                   |                |      C2 _|_        |         _\/\_ 
                   |                | .047 µF ---        +---|>|   / |   200 V
               Up \                 |          |         |   |<|--'  |
                   |                |          |     C1 _|_   D1     |
                   |                |          |.047 µF ---  Diac    |
                   |                |   ::::   |         |           |
                   |  Dim  o--------+---^^^^---+---------+-----------+
                   |     /               L1
         Brass o---+---o               12T #18
                               1/4" x 1/2" ferrite core
                     Down  o         
      Silver 2 o-----------+
    The parts that fail most often are the triac, TH1, or the combination switch/control (S1/S2/R1).

    True (electronic) 3-way (or more) dimmers

    The objective is to be able to control a single fixture from multiple locations with the capability of dimming as well as just power on/off.

    The simple type of 3-way dimmers are just a normal dimmer with a 3-way instead of normal switch. This allows dimming control from only one location. The other switches in the circuit must be conventional 3-way or 4-way type.

    Connecting conventional dimmers in series - which is what such a hookup would require - will not really work properly. Only if one of the dimmers is set for full brightness, will the other provide full range control. Anywhere in between will result in strange behavior. The other dimmer may have a very limited range or it may even result in oscillations - periodic or chaotic variations in brightness. The safety and reliability of such an arrangement is also questionable.

    True 3 way dimmers do exist but use a more sophisticated implementation than just a normal dimmer and 3-way switch since this will not work with electronic control of lamp brightness. One approach is to have encoder knobs (similar to those in a PC mouse) or up/down buttons at each location which send pulses and direction info back to a central controller. All actions are then relative to the current brightness. A low cost microcontroller or custom IC could easily interface to a number, say up to 8 (a nice round number) - of control positions. The manufacturing costs of such a system are quite low but due to its specialty nature, expect that your cost will be substantially higher than for an equivalent non-dimmable installation.

    If control of intensity at only one of the locations is acceptable, a regular dimmer can be put in series with the common of one of the normal 3-way switches. However, your brightness will be set by that dimmer alone. See the section: Typical dimmer schematics.

    An alternative is to use X-10 technology to implement this sort of capability. This would likely be more expensive than a dedicated multi-way switch control but is more flexible as well. X-10 transmits control information over the AC lines to select and adjust multiple addressable devices like lamps and appliances.

    However, for the adventurous, see the section: Independent dimming from two locations - kludge #3251.

    Independent dimming from two locations - kludge #3251

    Here is a scheme which will permit dimming with independent control from two locations. Each location will have a normal switch and a dimmer knob. The toggle essentially selects local or remote but like normal 3-way switches, the actual position depends on the corresponding setting of the other switch:
                     Location 1       Location 2
               +--------+  4-way SW    3-way SW
    Hot o--+---| Dimmer |----o\ /o--------o\            +---------+
           |   +--------+      /            \o----------| Fixture |------o Neutral
           |              +--o/ \o--------o      Center +---------+ Shell
           |              |                      (brass)           (silver)
           |              |            +--------+
           |              +------------| Dimmer |--+
           |                           +--------+  |
    As usual, the brass screw on the fixture or outlet should be connected to the Hot side of the wiring and the silver screw to the Neutral side.

    The dimmers can be any normal knob or slide type with an off position.

    Note that as drawn, you need 4 wires between switch/dimmer locations. 4-way switches are basically interchange devices - the connections are either an X as shown or straight across. While not as common as 3-way switches, they are available in your favorite decorator colors.

    If using Romex type cable in between the two locations, make sure to tape or paint the ends of the white wires black to indicate that they may be Hot as required by Code.

    And, yes, such a scheme will meet Code if constructed using proper wiring techniques.

    No, I will not extend this to more than 2 locations!

    Also see the section: Controlling a fixture or outlet from multiple locations.

    CAUTION: However, note that a dimmer should not be wired to control an outlet since it would be possible to plug a device into the outlet which might be incompatible with the dimmer resulting in a safety or fire hazard.

    Humming or buzzing lamps or fixtures on dimmers

    Unlike the normal AC power, the output of a cheap dimmer is a chopped waveform with sharp edges every 120th of a second for 60 Hz power (or every 100th of a second for 50 Hz power). This can result in annoying audible vibration of the filaments of the light bulbs.

    The severity of the problem is due to a variety of causes with the two most likely being related to the bulb's filament construction/supports and what, if any filtering, is provided by the dimmer itself - some are just worse than others and cost may not be a reliable indication of which-is-which.

    There is nothing really wrong with your installation - incorrect wiring would result in it not working at all, blowing a fuse or tripping a breaker, or or not working in certain positions of switches in a 3-way or 4-way (multiple switch locations) setup. If it bothers you try a different brand of bulbs or a different brand of dimmer.

    How do touch dimmers work?

    (From: Neil).

    Touch dimmers work in a couple of different ways, depending on the IC used. Simple ones, such as those in the cheap 'touch lamps' that you find for sale on market stalls, etc. normally have three or four preset brightness levels and an OFF setting, which are operated sequentially: touch once for full brightness, again to dim slightly, again to dim a bit more, etc, until the OFF setting is reached. The next touch will then bring the lamp to full brightness.

    The better (and more expensive) units, such as the touch dimmer switches that are sold as direct replacements for conventional light switches, are similar, but have many more steps. A single touch will usually bring the lamp to full brightness, while keeping your finger in contact with the touch plate will slowly dim the lamp. You just remove your finger when the lamp is at the required brightness level.

    Both kinds of touch dimmer have three basic parts;

    1. A touch sensor - this normally works by picking up mains hum from the touch plate, and rectifying it in a high-gain amplifier.

    2. A ramp generator - normally in the form of a digital counter with DAC output.

    3. A mains power control element - Generally a thyristor or triac. In some designs, this is encapsulated within the IC, while in others it is a discrete component.
    Most touch dimmers can be operated by standard push-button switches as well as a touch plate, and many can be adapted for remote control.

    There are a number of specially designed IC's available for touch dimmers, notably the HT7704B ,a four-step device for touch lamps as described above, and the SLB0586A, which is the other kind, with facilities for remote control.

    (From: Jack Schidt (

    Body detection usually follows one of three forms:

    Light dimmers and interference with radio or TV

    Due to the sharp edges on the power supplied by a cheap light dimmer, Radio Frequency Interference (RFI) may be conducted back down the wiring directly to other appliances and/or radiated through space as well. Effects will include noise bars in the picture on some TV channels and/or a buzz in the audio across portions of the AM radio band.

    (Zero crossing switching, a technique used with electrical heaters and heating appliances to minimize RFI cannot be used for lighting as it would result in way too much flicker or a very limited number of brightness levels.)

    Better light dimmers will include a bypass capacitor (e.g., .01 µF, 1kV) and a series inductor to suppress RFI but these components were often left off in basic models. The FCC has tightened up on their regulations around 1992 so replacing older dimmer switches with newer ones may be the easiest solution.

    I can't really recommend a particular model that it better in this regard. However, the package may list 'low RFI' as a feature so checking out Home Depot or wherever won't hurt.

    Installing in-line power line filters may work but other options like replacing all your house wiring with metal conduit, or only listening to FM radio are probably not realistic!

    BTW, I have used dimmers and AM radios to trace wiring inside the wall! :)

    Dimmer wall plate hot to touch

    This is probably normal if the dimmer is controlling a load which is close to (or beyond) its maximum rating. For most inexpensive dimmers, this is 600 W. Others are commonly rated up to 1,200 W. Keep in mind that the switching device (the triac) is dissipating a wattage proportional to the load. With a full 600 W load, it may be as much as 6 to 10 W (depending on the setting of the control knob), which is not a trivial amount of power - and the face plate is used as a heat sink. The larger ones have to dissipate even more power.

    My recommendation would be to get a dimmer rated for 30 to 50 percent more power than you are using. It will still get warm but will have a better (probably finned) heat sink and will be running way below it maximum rating and should be more reliable. In general, any device should be derated to boost longevity!

    Can I use a dimmer to control transformer operated low voltage lighting?

    (Portions from: Charles Sullivan (

    It is very tempting to try using a common light dimmer to control devices using power transformers. Will this work?

    It will usually work fine, but it can lead to a fire hazard and is not recommended. Most major dimmer manufacturers have special dimmers designed for this application, that prevent the hazard inherent in using a standard dimmer. It is worth your while to use one of those.

    The problem results from the inductive nature of the impedance the transformer presents to the dimmer. The load is most inductive when the transformer is lightly loaded. Even if you set up your system with a fully loaded transformer, it can become lightly loaded when bulbs burn out. If there is any small asymmetry in the firing angle of the triac on the two half cycles, there will a be small DC voltage across the transformer winding. This is no big deal - you'll get a bit of DC current, and the core will run with some DC flux, and may saturate a bit, but neither will cause significant heating or a real hazard. However, the point at which the triac turns *off* will also then be different on the two half cycles. Because ordinary dimmer circuits time the triac turn on from the turn off point, not from the line voltage zero crossing, the asymmetry in turn-off times leads to a even greater turn-on time asymmetry. If the load is sufficiently inductive, this process can "run away" until the dimmer is acting as a diode, applying nearly full line voltage across the transformer winding. Ordinarily, this would result in enough current to trip a circuit breaker or a fuse, but smaller transformers can have enough DC resistance to keep the current low enough that the breaker does not trip. When I've experimented with this, the transformer winding soon started to smoke. I didn't continue the experiments to see what would happen next, but there have been reports of fires starting this way. A suitably rated small fuse installed in series with the transformer would probably work but I wouldn't want to depend on it.

    Dimmers designed for this application can use several methods to get around the problem. Some use a DC detection circuit and shut off if DC is detected. Others use a three-wire connection scheme, such that the line- neutral voltage is available to the dimmer, and can be used for the timing reference, so that the triac is always fired at the same time relative to the line-voltage zero crossing, not relative to when the triac turns off. Thus, although there may still be a small amount of DC present due to asymmetry in the firing circuit, the system can never run away to the point of applying a much high DC voltage. (In good dimmers designed for this application, the asymmetry will also be small to begin with.)

    References for further information:

    Causes of dimmer failure

    Dimmers are such simple devices that their reliability is quite good, nearly that of a simple light switch. The pot and switch can go bad from use or just cheap/poor design, and there can always be failures from bad solder joints and other manufacturing issues.

    But there is one type of failure to which virtually all dimmers may succumb caused not by a problem in the dimmer but by a transient event when an incandescent lamp burns out. When such a lamp reaches end-of-life, the filament opens and an arc forms which can expand to essentially result in close to a short circuit across the lamp. This happens within a very short time, perhaps one cycle of the AC. At that instant, a very high current flows likely blowing the triac in the dimmer. The result is that the dimmer now is stuck at full brightness (or off, if the switch is still functional).

    Why isn't there a fuse? Actually, larger incandescent lamps do have fuses in their base, and these fuses may blow when the lamp burns out. But not fast enough to save the triac. Since dimmer switches are not designed to be repairable - they are considered disposable devices - the cost of including a fuse cannot be justified even if a fuse would work.

    The triac may also fail if the dimmer is used in an attempt to control something other than an incandescent lamp, or least, something other than a resistive load. Using a normal light dimmer to control the speed of a motor is a hit or miss affair, and may result in damage to both the dimmer and motor depending on type.

    Flashlights and lanterns

    Battery operated flashlights (torches for those on the other side of the Lake) and lanterns are among the simplest of appliances. We probably all have a box or drawer full of dead flashlights.

    The most common problem after dead batteries is very often damage due to leaky batteries. Even supposedly leak-proof batteries can leak. Batteries also tend to be prone to leaking if they are weak or dead. Therefore, it is always a good idea to remove batteries from any device if it is not to be used for a while. How to assure the batteries will be with the flashlight? Put them in separate plastic bags closed and fastened with a twist tie.

    Test the batteries with a multimeter - fresh Alkalines should measure 1.5 V. Any cell that measures less than about 1.2 V or so should be replaced as they will let you down in the end. On a battery tester, they should read well into the green region.

    Check the bulb with a multimeter on the ohms scale - a bad bulb will test open. Bulbs may fail from use just like any other incandescent lamp or from a mechanical shock - particularly when lit and hot. Replacement bulbs must be exactly matched to the number and type of batteries (cells). A type number is usually stamped on the bulb itself. There are special halogen flashlight bulbs as well - I do not really know how much benefit they provide.

    The switches on cheap flashlights are, well, cheaply made and prone to unreliable operation or total failure. Sometimes, bending the moving metal strip a bit so it makes better contact will help.

    Clean the various contacts with fine sandpaper or a nail file.

    If a flashlight has been damaged as a result of battery leakage, repair may be virtually impossible.

    High quality flashlights are another matter. Maglights(tm) and similar units with machined casings and proper switches should last a long time but the same comments apply to batteries - store them separately to avoid the possibility of damage from leakage. Keep a spare bulb with each of these - the specialty bulbs may be harder to find than those for common garbage - sorry - flashlights.

    Rechargeable flashlights include a NiCd or lead-acid battery (one or more cells in series) and the recharging circuitry either as part of the unit itself or as a plug-in wall adapter or charging stand. See the sections: "Battery chargers" and "Typical rechargeable flashlight schematics" for more information.

    Typical rechargeable flashlight schematics

    Here are circuit diagrams from several inexpensive rechargeable flashlights. These all use very 'low-tech' chargers so battery life may not be as long as possible and energy is used at all times when plugged into an AC outlet.

    First Alert Series 50 rechargeable flashlight schematic

    This one is typical of combined all-in-one units using a lead-acid battery that extends a pair of prongs to directly plug into the wall socket for charging.

    It is a really simple, basic charger. However, after first tracing out the circuit, I figured only the engineers at First Alert knew what all the diodes were for - or maybe not :-). But after some reflection and rearrangement of diodes, it all makes much more sense: C1 limits the current from the AC line to the bridge rectifier formed by D1 to D4. The diode string, D5 to D8 (in conjunction with D9) form a poor-man's zener to limit voltage across BT1 to just over 2 V.

    The Series 50 uses a sealed lead-acid battery that looks like a multi-cell pack but probably is just a funny shaped single cell since its terminal voltage is only 2 V.

    Another model from First Alert, the Series 15 uses a very similar charging circuit with a Gates Cyclon sealed lead-acid single cell battery, 2 V, 2.5 A-h, about the size of a normal Alkaline D-cell.

    WARNING: Like many of these inexpensive rechargeable devices with built-in charging circuitry, there is NO line isolation. Therefore, all current carrying parts of the circuit must be insulated from the user - don't go opening up the case while it is plugged in!

                                                 2V LB1  Light
                                               1.2A +--+ Bulb    S1
                                           +--------|/\|----------o/ o----+
                _ F1   R3         D3       |        +--+                  |
       AC o----- _----/\/\---+----|>|--+---|----------------------+       |
              Thermal  15    |    D2   |   |                 4A-h |       |
               Fuse          | +--|>|--+   |         BT1 - |+ 2V  |       |
                             | |  D4       +--------------||------|-------+
                             +----|<|--+   |               |      |       |
                               |  D1   |   |  D8   D7   D6   D5   |  D9   |
              |        |                                                  |
              |        /                                                  |
             _|_ C1    \ R1                                               |
             --- 2.2uf / 100K                                             |
              |  250V  \                                                  |
              |        |               R2          L1  LED                |
       AC o---+--------+--------------/\/\-----------|<|------------------+
                                     39K 1W       Charging

    Black & Decker Spotlighter Type 2 rechargeable flashlight

    This uses a 3 cell (3.6 V) NiCd pack (about 1 A-h). The charging circuit is about as simple as it gets!
             11.2 VRMS                                +---------------o/ o----+
      AC o-----+ T1       R1      LED1         D1     |  +| | | -             |
                )|| +----/\/\-----|>|---->>----|>|----+---||||||---+          |
                )||(      33    Charging     1N4002       | | |    |  KPR139  |
                )||(      2W                           BT1         |    LB1   |
                )||(                                   3.6V, 1 A-h |    +--+  |
                )|| +-------------------->>------------------------+----|/\|--+
      AC o-----+                                             Light Bulb +--+

    |<------- Charger ---------->|<---------- Flashlight ----------->|

    I could not open the transformer without dynamite but I made measurements of open circuit voltage and short circuit current to determine the value of R1. I assume that R1 is actually at least in part the effective series resistance of the transformer itself.

    Similar circuits are found in all sorts of inexpensive rechargeable devices. These have no brains so they trickle charge continuously. Aside from wasting energy, this may not be good for the longevity of some types of batteries (but that is another can of worms).

    Brand Unknown (Made in China) rechargeable flashlight schematic

    This is another flashlight that uses NiCd batteries. The charger is very simple - a series capacitor to limit current followed by a bridge rectifier.

    There is an added wrinkle which provides a blinking light option in addition to the usual steady beam. This will also activate automatically should there be a power failure while the unit is charging if the switch is in the 'blink' position.

    With S1 in the blink position, a simple transistor oscillator pulses the light with the blink rate of about 1 Hz determined by C2 and R5. Current through R6 keeps the light off if the unit is plugged into a live outlet. (Q1 and Q2 are equivalent to ECG159 and ECG123AP respectively.)

                R1          D1                 R3   LED1
        AC o---/\/\----+----|>|-------+---+---/\/\--|>|--+    D1-D5: 1N4002
                33    ~|    D2        |+  |   150        |
               1/2W    +----|<|----+  |   |       R4     |  D5
                            D3     |  |   +------/\/\----+--|>|--+
                  C1   +----|>|----|--+   |    33, 1/2W          |   LB1 2.4V
                1.6µF ~|    D4     |      |   | |                |   +--+ .5A
        AC o--+---||---+----|<|----+--+---|--||||--------------+-+---|/\|----+
              |  250V  |              |-  | - | |+             |     +--+    |
              +--/\/\--+              |   |   BT1      + C2 -  |      R5     |
                  R2                  |   |  2.4V    +---|(----|-----/\/\----+
                 330K                 |   |          |  22µF   |     10K     |
                                      |   |    R6    |       |/ E            |
                                      |   +---/\/\---+-+-----| Q1            |
                                      |       15K      |     |\ C  +---------+
                                      |                /  C327 |   |         |
                                      |             R7 \   PNP |   |   1702N |
                                      |           100K /       |   |   NPN |/ C
                                      |                \       +---|-------| Q2
                                      |      On        |           |       |\ E
                                      |   S1 o---------|-----------+         |
                                      +----o->o Off    |                     |
                                        Blink/Power Fail

    Solar Powered Walk Light

    This was found in a Malibu(tm) LZ1 Solar light set made by Intermatic. It uses a solar cell, approximately 4 square inches in area, to charge a pair of AA NiCd cells during the day which powers a superbright yellow LED at night. I estimate the actual light output to be 2 or 3 mW at around 595 nanometers wavelength (something like stoplight yellow). Actually, it is kind of cool in more ways than one! :) If only the cheap plastic enclosure was actually waterproof....
           |      |   D1    |            |          |
           |      | 1N4004  |            /          |
           |      |         |            \ R3     __|__
          +| SC1  |       +_|_ BT1       / 2.2K   _\_/_ LED
        +--+--+   |         _  2xAA NiCd \          |
        |Solar|   |        ___ 550mA-hr  |        |/ C
        |Cell |   |       - _            +---+----| Q2 SS8050
        +--+--+   |         |    R2      |   |    |\ E (ECG216)
          -|      |         |   20K    |/ C  /      |
           |      +---------|---/\/\---| Q1  \ R1   |
           |                |   SS9013 |\ E  / 100K |
           |                | (ECG123A)  |   |      |
    When there is enough voltage from the solar cell, Q1 is turned on and Q2 (the LED driver) is turned off. As far as I can tell, there is nothing to actually limit current to the LED except for the combination of battery, transistors, LED, and wiring resistance. Both transistors could probably be replaced with 2N3904s. So, if you were duplicating this thing, I'd recommend adding something to control the current to the LED or at least checking it first!

    Actual failure of this complex device would most likely be due to worn out NiCd cells or corrosion to due exposure to the weather.

    Operational problems like weak output or inadequate lighting time could be due to insufficient Sunlight (the thing is installed under a bush!) or extended cloudy conditions. Of course, these don't produce a huge amount of light in any case!

    Makeup mirrors

    There are a simple movable mirror with incandescent or fluorescent lighting built in.

    Replacing incandescent light bulbs can usually be done without disassembly. The bulbs may be of the specialty variety and expensive, however.

    When a unit using fluorescent bulbs will no longer come on, the most likely cause is a bad bulb. However, replacement may involve disassembly to fain access. Where two bulbs are used, either one or both might be bad. Sometimes it will be obvious which is bad - one or both ends might be blackened. If this is not the case, replacement or substitution is the only sure test. These **will** be expensive $7-10 is not uncommon for an 8 inch fluorescent bulb!

    Other possible problems: plug, cord, switch, light bulb sockets.


    A chandelier is simply an incandescent light fixture with multiple sockets. No matter how fancy and expensive, the wiring is usually very simple - all the sockets are connected in parallel to a cord which passes through the chain to a ceiling mounted electrical box.

    If none of the lights come on, check for a blown fuse or circuit breaker, bad wall switch or dimmer, a bad connection in the ceiling box or elsewhere in the house wiring, or a bad connection where the cord is joined to the individual socket wires.

    Where only one bulb does not light - and it is not a burned out bulb - a bad socket, loose wire connection at the socket, or bad connection at the point where the wires are joined (Wire Nuts(tm) or crimps) is likely.

    Overhead (and other basic slide) projectors

    (The type discussed here are overhead transparency projectors, opaque projectors, and the basic power and lighting circuits of slide projectors. Problems with the slide advance mechanism of those with automatic slide changers (e.g., Kodak Carousel) are usually mechanical in nature assuming the main motor is running. See the document: Audio Equipment and Other Miscellaneous Stufffor more information on these.)

    A basic projector consists of a really bright lamp - usually halogen but some fancy ones use a High Intensity Discharge (HID) lamp (see the document: Gas Discharge Lamps, Ballasts, and Fixtures), a cooling fan, electrical and thermal protection devices, and possibly an interlock switch to prevent operation with the cover removed. The main switch may include reduced brightness settings which adds some resistance or a diode in series with the lamp.

    (Repair of those with HID lamps unless it is a simple bad connection or failure in the protection devices is well beyond the scope of this document unless replacing the lamp is all that is needed. WARNING: The types of power supplies used for these may have capacitors that can retain a dangerous charge for a long time even after the plug is pulled.)

    A reflector and condensing lens concentrates the light more or less uniformly onto the material to be projected {transparency or whatever) and a projection lens relays and enlarges that to the screen. Note that the large Fresnel lens (which should also be cleaned) that usually serves as the transparency platform of an overhead projector is not the primary condenser but serves a similar function directing most of the light which passes through the transparency to the projection lens. There may also be one or more pieces of heat absorbing glass between the lamp and condenser. While you're in there, a careful cleaning of the optics could be useful! After making sure the unit is unplugged, use a cloth moistened with isopropyl alcohol to clean all accessible optical surfaces. Rubbing (70%) or medicinal (91%) alcohol is fine as long as it doesn't contain any additives. Be gentle - optical glass is not that hard! WARNING: Avoid contact with the glass envelope of the lamp itself. If you do touch it by accident, use a fresh cloth or paper towel and alcohol to remove all traces of skin oils since this contamination can lead to failure at the elevated temperatures at which these run.

    Like all incandescent lamps, those in projectors burn out - and since they are run at higher than normal wattage to get the most and whitest light, they usually are only rated for a small number of hours (e.g., 100). When burnout occurs, other components may be blown as well.

    Since everything runs hot, deteriorated connections, contacts, sockets, etc., are quite common. Any major damage will require repair or replacement of the offending components. The fan may be on a thermostat which can also fail. If the fan doesn't start (usually immediately or after a minute or so at most), overheating WILL occur. Check the thermostat (bypass it to test) and the fan for dry bearings, bad connections, or a bad motor.

    If replacing the bulb doesn't help, check the fuses and thermal protectors for opens. Check the outlet as the burnout may have blown the fuse or tripped the circuit breaker for that branch circuit.

    If the new bulb runs excessively bright, TURN IT OFF IMMEDIATELY! Some of these projectors use 82 V bulbs (it will say on the bulb and/or its package), and a series diode (or diodes) may be used to reduce power to the bulb to run it at an effective voltage of 82 VRMS. (The RMS value of half wave rectified 115 VAC is close to 82 V). When the old bulb blew (or even if it didn't), these diodes can fail - often shorted. The new bulb won't last long on the full line voltage. The replacement diodes need to have a PIV rating of at least 200 V (for 115 VAC power) and a current rating adequate to handle the operating current and the initial surge (which can be 10X of that). Depending on the bulb's wattage, a 25 A or higher diode may be needed. An proper replacement will be available from the projector manufacturer but will be more expensive than one purchased from an electronics distributor.

    Portable fans and blowers

    These consist of a cordset, switch, and AC motor. Oscillating fans add a gearbox to automatically swivel the fan to direct air in more than one direction. Most are of the bladed variety though some small types might use a squirrel cage type centrifugal blower.

    There are two kinds of problems: totally dead or stuck/sluggish.

    A totally dead fan can be the result of several possible causes:

    As always, your continuity checker or multimeter on the low ohms scale is your best friend and can be used to trace the wiring from the wall plug through all components of the appliance.

    Sluggish operation can be due to gummed up lubrication in the motor or any gears associated with an automatic oscillating mechanism. Disassemble, thoroughly clean, and then lubricate the motor bearings with electric motor oil. Use light grease for the gearbox but this is rarely a problem.

    A noisy fan may be due to dry motor or other bearings or loose hardware or sheetmetal. Disassemble, clean, and lubricate the motor or gearbox as above. Inspect for loose covers or other vibrating parts - tighten screws and/or wedge bits of wood or plastic into strategic locations to quiet them down.

    Damaged fan blades will result in excessive vibration and noise. These may be easily replaceable. They will be attached to the motor shaft with either a large plastic 'nut' or a setscrew. However, locating a suitable set of blades may be difficult as many cheap fans are not made by well known companies.

    Computer power supply (and other) fans

    Virtually all of these use brushless DC motors with stationary coils and a rotating multipole magnet which is part of the blade assembly. Most common problems are gummed up lubrication or worn bearings - especially for the cheap sleeve bearing variety found in most PCs. Occasionally, an electronic failure will result in a dead spot or other problem.

    Ball bearing fans rarely fail for mechanical reasons but if the bearings become hard to turn or seize up, replacement will usually be needed. (Yes, I have disassembled ball bearings to clean and relube THEM but this used only as a last resort.)

    WARNING: For power supply fans, be aware that high voltages exist inside the power supply case for some time (perhaps hours) after the unit is unplugged. Take care around the BIG capacitors. If in doubt about your abilities, leave it to a professional or replace the entire power supply!

    The only type of repair that makes sense is cleaning and lubrication. Else, just replace the fan or power supply. It isn't worth troubleshooting electronic problems in a fan!

    If you want to try to clean and lubricate the bearings, the blade assembly needs to be removed from the shaft. There should be a little clip or split washer holding it on. This is located under a sticker or plastic plug on the center of the rotating blade hub. Once this fastener has been removed, the blades will slide off (don't lose the various tiny spacers and washers!)

    Thoroughly clean the shaft and inside the bushings and then add just a couple drops of light oil. Also, add a few drops of oil to any felt washers that may be present as an oil reservoir.

    Reassemble in reverse order making sure the tiny washers and spacer go back in the proper positions.

    How long this lasts is a crap shoot. It could be minutes or years.

    Replacement fans are readily available - even Radio Shack may have one that is suitable. Nearly all run on 12 VDC but some small CPU fans may use 5 VDC. While current ratings may vary, this is rarely an issue as the power supply has excess capacity. Air flow rates may also vary depending on model but are usually adequate for use in PCs.

    Piezo fans

    These may be used for localized cooling of electronic components or some other very low air flow application. I cannot imagine a use around the house. They use a pair of piezo electric bars that vibrate thin vanes to move a few dozen air molecules per second. Drive is from the power line via a transformer or dropping resistor.

    Advantages include virtually infinite life, very low power consumption, to nearly total silence when operating. However, they aren't going to cool very much :-).

    (If you care, something that is said to be piezo electric changes shape (e.g., bends or compresses/expands) when a voltage is applied (and vice-versa). Many materials exhibit the piezo electric effect include crystals like quartz, various ceramics and plastics, and even some organic compounds. The most common example of a piezo electric device in modern technology is the beeper in a common digital watch, pocket alarm clock, or pager - in which case an electrical signal at a most annoying frequency causes the change in thickness of a ceramic disk and results in the audible tone.)

    The piezo fan I have is just a pair of thin plastic flaps or vanes, each about 1/2" x 3", separated by perhaps 1" and slightly diverging. A pair of piezo elements at one end vibrate the vanes when driven through a dropping resistor from the 60 Hz AC line. Interestingly, the resonance is actually at 50 Hz but I do not think this unit was designed for European power. A plastic housing helps to guide the air flow - what of it there is. The result is a just detectable breeze so I wouldn't recommend using one of these to cool your Pentium II!

    Except for mechanical damage, there isn't much to go wrong as long as the piezo elements themselves are getting power. However, a buildup of dirt on the vanes could change the resonant frequency to the point of greatly reducing effectiveness (to the extent that there is any to begin with!).

    Don't worry, you may never see one of these things in several lifetimes :-).

    Speed control of DC fans

    The small fans used in computers and peripherals usually run on 5, 12 (most common) or 24 VDC. Most of the time, their speed and air flow are fine for the application. However, is it possible to vary it should the need arise?

    Usually, the answer is a qualified 'yes'. Except for some that are internally regulated or thermostatically controlled, the speed is affected by input voltage. It is likely that the fan will run on anywhere from .5 to 1.25 times the nominal input voltage though starting when it is near the low end of this range may need some assistance.

    A universal DC wall adapter, adjustable voltage regulator, or (variable) series power resistor can provide this control. For example:

                         25, 2 W        + +--------+ -
        +12 VDC o-----+---/\/\---+--------| DC FAN |----o Gnd
                      |   +      |        +--------+
                      +----|(----+      12 VDC, .25 A
                        10,000 µF
                          25 V
    The 25 ohms power resistor should reduce the speed of this fan by about 25 to 30 percent. The capacitor provides full voltage for a fraction of a second to assure reliable starting.

    Speed control of small AC fans

    The following comments should also apply to many other types of appliances using shaded pole induction motors.

    These small shaded pole fans will work just fine on a Variac. Any speed you want, no overheating, etc. I had done this with all sorts of little computer cooling fans as well as larger ones (remember those old DEC PDP-11 rack fans?). My bedroom window fan is one of these on a Variac. :)

    A true rheostat (variable power resistor) will also work. However, significant power will be dissipated in the rheostat which must be sized so that the maximum power density of any portion of its element does not exceed its power handling capability - this can end up resulting in a massive device even for a small fan. For example, to vary a 120 VAC fan rated at 24 VA from between 1/2 to full power would require a 600 ohm, 25W rheostat; down to 1/4 power would require an 1,800 ohm 75 W rheostat!

    Small triac based speed controls like those used for ceiling fans may also work. Even light dimmers will *probably* work for medium size fans or banks of fans though I cannot guarantee the reliability or safety of these. The problem is that small induction motors represent a highly inductive loads for the light dimmer circuitry which is designed for a resistive load. I have achieved a full range of speeds but over only about 1/4 to 1/2 of the rotation of the control knob. There is some buzz or hum due to the chopped waveform.

    However, from my experiments, light dimmers may have problems driving a single small fan. If the load is too small, the result may be a peak in speed (but still way less than normal) at an intermediate position and the speed actually much lower when on full, or reduced speed even on full. In this case, adding a resistive load in parallel with the motor - a light bulb for example - may improve its range. It adds a sort of quaint look as well! :-)

    If you do opt for a solid state speed control, make sure you include a fuse in the circuit. A partial failure of the triac can put DC through the motor which would result in a melt-down, lots of smoke, or worse. (This isn't a problem with a light bulb load since its resistance is the same for AC and DC; a motor's DC resistance is quite low.)

    The reason these simple approaches will work for these AC motors is that they are high slip to begin with and will therefore have a high range of speed vs. input voltage. The only concern is overheating at some range of lower speeds due to reduced air flow. However, since these fans are normally protected even against stall conditions, I wouldn't expect overheating to be a problem - but confirm this before putting such fans into continuous service.

    If all you need to do is provide a fixed, reduced speed for a bank of similar AC fans, try rewiring them as two sets of parallel connected fans in series. The result will be 1/2 the normal line voltage on each fan motor which may provide exactly the speed you want! The extension to more than 2 sets of fans is left as an exercise for the student :-).

    And the shaded pole motors in fans and other appliances with multiple (fixed) speeds have several sets of windings that can be switched in or out in various combinations to vary the effective field strength.

    Ceiling fans

    While the original slow rotating ceiling mounted fan predates the widespread use of airconditioning, there is a lot to be said for the efficiency, effectiveness, and silence of this technology - not to mention the ambiance.

    A ceiling fan is just an induction motor driving a set of blades. Multiple taps on the motor windings in conjuac dansnction with a selector switch provides speed control for most inexpensive fans. Better units include a solid state motor speed control.

    The light often included with the fan unit is usually just an incandescent fixture with 1-5 bulbs and a switch. This may be a simple on-off type, a selector to turn on various combinations of bulbs, or a dimmer with continuous or discrete control of illumination.

    WARNING: Always check mechanical integrity of fan mounting when installing or servicing a ceiling fan. Original design and construction is not always as fail-safe as one might assume. Double check for loose nuts or other hardware, adequate number of threads holding fan to mounting, etc. These have fallen without warning. Only mount in ceiling boxes firmly anchored to joists - not just hanging from the ceiling drywall! Check that the fan is tight periodically. The constant vibration when running, slight as it is, can gradually loosen the mounting hardware. Furthermore, if pull chain type switches are used for the fan or light, constant tugging can also tend to loosen the entire fan.

    Failures of ceiling fans can be divided into electrical and mechanical:


    Schematics for some typical ceiling fans can be found at Gary Tait's Ceiling Fan Wiring Diagrams Page. Mechanical:

    Lubricating ceiling fans

    (From: Chris Chubb (

    I use synthetic transmission lube, 80-130 (manual gearbox, not automatic transmission fluid which is very thin --- sam). I imagine that any similar lubricant, synthetic or not, would work as well, but the synthetic flows down in better and works well.

    Do not use WD-40, 3-in-1 oil or any other lightweight oil. Motor oil is good as well, but it does not stick to the bearings as well. DO NOT use automatic transmission fluid - extremely thin.

    Grease would be perfect, white lithium, divine! But, getting the grease down into the bearings would be very difficult.

    Just about three or four drops should be all it takes. Getting it on the lower bearings of the ceiling fan will be tough. I have an oil can that I pump a drop to the tip of, then hold it against the bearings until they wick the oil inside. This is very slow. It takes about 15 minutes per fan to oil, clean the top of the blades, oil a little around the hanging ball, pull the globe off and clean the globe inside, and make sure everything is OK.

    Variable speed ceiling fan on normal circuit

    It is usually not possible to use a normal light dimmer to control the fan as this uses an AC induction motor. A dimmer can only be used on the built in light if a separate wire is available to power it.

    Doing this will likely result in a nasty hum or buzz at anything other than full brightness (speed) or off. This is both annoying and probably not good for the fan motor as well. A dimmer works by reducing the power to the light by controlling when the voltage is applied on each cycle of the AC. If it is turned on half way through the cycle half the power is provided, for example. However, with cheap lamp dimmers, this results in sharp edges on the waveform rather as peak voltage is applied suddenly rather than with the nice smooth sinusoid. It is these sharp edges causing the coils or other parts of the fan to vibrate at 120 Hz that you are hearing.

    Special speed controls designed for ceiling fans are available - check your local home center or ceiling fan supplier.

    Here is another alternative:

    (From: Rick & Andrea Lang (

    Here's a potential solution if you don't mind spending a little more for a ceiling fan (If you already have one in that location, perhaps you can put it in another room). Ceiling fans with remote control are now available. They only require power to the ceiling fan (2 wire) and a remote control. With the remote you can dim the lights, slow the fan or both. You can then use the existing new wall switch as a power ON/OFF switch also. If you choose this route, be careful of interference with garage door openers. Usually, the remotes have at least 4 frequency selections to help avoid interference with other remote systems. I put one in that three of the four frequencies opened the garage door. I lucked out on the 4th one!

    Throbbing noise from ceiling fan

    This could be due to a mechanical problem - bad bearings or blades out of balance - or an electrical problem with the speed control.

    (From: David Buxton (

    A quickie test. Get the fan turning at a speed that demonstrates the throbbing noise. Come up with a way to instantly remove power to the fan. If the noise continues for a little bit until the fan has slowed down enough, then you know the noise is in the mechanical dynamics, perhaps blades out of balance. If the noise quits instantly with power removal, then you need a better speed control better designed for fan motor control.

    Ceiling fan motor speed control and capacitor replacement

    (From: Kevin Astir (

    Ceiling fans are normally multipole, capacitor-run types. They normally run fairly close to stalled, the blades being big enough that the motor never gets anywhere near synchronous speed.

    Speed control in three speed types is by switching the value of the cap in series with the quadrature windings. The caps normally have two sections of 3 and 6 µF, with a common connection between the two sections allowing connections of 3, 6, or 9 (3 in parallel with 6) µF total.

    I have seen some caps of slightly different value, but they should be close, just translate my 3 and 6 to what you actually have in what follows.

    The higher the capacitance the higher the stall torque, so the faster the fan runs against the non-linear (square-law) torque vs. speed characteristic of the blades. (remember I said it is always pretty much stalled)

    If you miswired the cap, then you may be getting 3 or 6 and 2 (3 in *series* with 6 µF which would result in low speeds. This *is* the case if any 2 out of 3 speeds seem to be the same. The replacement caps are usually marked with what terminal is which, but originals often are not. I don't know if there is a standard color code, but manufacturers are under no obligation to adhere to it even if there was. If you are totally lost, there are only 6 possible ways to connect the capacitor. 2 of these will give you all 3 speeds (but one in wrong order). So if you keep good notes (essential here) then you could try all possibilities in 20 minutes or so...yes, you're probably working with hands over head, what you wanted easy too?

    OK, here is how to get it in 3 tries max:

    Identify the "common" capacitor lead (connects to both 3, and 6 µF sections, hopefully your replacement is marked). It is currently connected to the wrong place, so swap it with one of the other cap wires. If you now have three speeds in the correct order, then your done. If you have three speeds in the wrong order, then leave common wire alone, but swap other two. (correct order is: off-hi-med-lo usually)

    If you *didn't* have three different speeds following the first wire swap, then swap that common wire with the one wire you haven't moved yet. Now you should have three speeds, now correct the order as described, if needed.

    If you currently have three speeds, but all are too slow, then it is likely that your fan needed a higher value capacitor. another explanation might be that the old cap was getting leaky when it warmed up after start, and letting the fan have extra current, thus giving extra speed.

    In my experience, the three speed types should run from just slow enough to follow with the eye, to fast, fairly noisy, and making a fair amount of wobble on the mounting.

    Continuously variable speed types put a fixed 9 or 10 µF cap in series with the quadrature winding, and regulate voltage to both windings via lamp-dimmer style triac circuit.

    Mike's notes on ceiling fan installation

    (From: (Mike Morris).)

    Depending on what wiring you have and what new wiring needs to be installed, I would install 14/3 cables for all ceiling lights. That way, you will be able to control ceiling fan and light from two separate switches.

    Each time a new light has to be installed in our house, I make sure a 14/3 wire is installed. For three-way switches, I make it two 14/3 wires, even if I don't install a ceiling fan now. A 14/3 wire is not that much more expensive, and 10 years down the road, it might be useful.

    The local high-end lights-and-fans shops have a handout that recommends that wherever a ceiling fan is to go have the following wiring:

    1. Neutral.
    2. Ground (if local code requires it, good idea anyway).
    3. Switched hot for the lights.
    4. Switched hot for the fan.
    5. An extra wire - some brands need 2 hots for the fan, and if your brand doesn't need it, an extra conductor doesn't hurt.
    Why two switched hots? Note that this does not preclude using a fan with built-in controls - unused wire is just that. And pulling in 5 conductors during construction or remodeling costs just a little more that pulling in 2 or 3.

    The handout sheet also point out that adding a extra brace to the ceiling during any remodeling or new construction sized for a 100 pound dead weight is a good idea - it can be as simple as a couple of feet of 2x6" lumber and a couple of sheet metal fasteners. A wobbling fan can cause fatigue in a light duty metal brace rapidly. The extra cost is minimal, and it can prevent a fan from landing in the middle of the bed!

    Ceiling fan construction

    The following describes a basic capacitor run split phase induction motor, though the arrangement of pole pieces and coils is unusual compared to the typical squirrel cage variety.

    (From: George Eccles (

    I just took ceiling fan motor apart. The (center) stator has 16 coils, in 2 concentric groups of 8, arranged around the circumference of a flat disk. The groups are offset from each other by (maybe) 20 or 30 degrees. Based on resistance readings, I think one group is all wired in series. (I think) the other group is arranged in different combinations, based on the speed setting. For highest speed, I think all are in series, though I don't know what the phasing is. For the lower speeds, 1 or 2 coil pairs have their phasing reversed.

    The rotor (aka the housing) has no visible windings, and no permanent magnets. AFAIK, it's just a thin ring (maybe 1/2" thick vertically, 3/4" radially) of laminated (maybe 10 or 12) strips of ferrous metal, embedded in a slightly larger aluminum casing. The laminations are not insulated from each other. Along the innner cicumference, the laminations are interrupted with weird pattern of what might be just interlocking to the aluminum casing.

    Air cleaners

    Simple air cleaners are just a motor driven fan and a foam or other filter material. HEPA (High Efficiency Particulate Air) types use higher quality filters and/or additional filters and sealed plenums to trap particles down to a specified size (.3 micron). A clogged (neglected) filter in any air cleaner is probably the most likely problem to affect these simple devices. Failure of the fan to operate can be a result of any of the causes listed above in the section: Portable fans and blowers.

    Electronic air cleaners include a high voltage low current power supply and oppositely charged grids in the air flow. A failure of the solid state high voltage generator can result in the unit blowing air but not removing dust and particulate matter as it should. A typical unit might have 7.5 to 10 kV at 100 uA maximum (short circuit current, probably less at full voltage). Actual current used is negligible under normal conditions. This voltage is significant but the current would be just barely detectable, if at all.

    The power supplies for smaller table top devices like the AirEase(tm) Personal Space Ionization Air Cleaner from Ion Systems, Inc. would probably generate similar voltages (possibly slightly lower) but at much lower current - perhaps only, 5 to 10 uA.

    The modules are usually quite simple: a transistor or other type of switching circuit driving a step-up transformer and possibly a diode-capacitor voltage multiplier. See the sections: "Electronic air cleaner high voltage module schematic" and "Auto air purifier schematic" for an example of a typical circuit.

    Where there is no high voltage from such a device, check the following:

    On the topic of high voltage power supplies/transformers:

    (From: Marvin Moss (

    These transformers have a very large air gap in the core and are designed to be able to operate for an extended period of time when the output is short circuited. If you get a piece of dirt or aluminum foil or something conductive in the filter, it has to bear the short until you clean the filter. I found several sources of surplus high voltage power supplies in the range of 5,000 volts at 2 mA. or so for $14.95 and bought several of them. I did in fact replace one of my two supplies in my A/Cs with this unit and it has been working perfectly for about 10 years now. The voltage is not critical but too high a voltage will create excessive ozone. Too low a voltage will not filter well. I think that 3,500 to 6,000 volts is the range but I can give you more info if you want it.

    Electronic air cleaner high voltage module schematic

    At least I assume this cute little circuit board is for an electronic air cleaner or something similar (dust precipitator, positive/negative ion generator, etc.)! I received the unit (no markings) by mistake in the mail. However, I did check to make sure it wasn't a bomb before applying power. :-)

    This module produces both positive and negative outputs when connected to 115 VAC, 60 Hz line voltage. Each is about 5 kV at up to around 5 uA.

    The AC line powered driver and HV multiplier are shown in the two diagrams, below:

                       D1                                           T1  o
      H o--------------|>|----+---+--------------------+               +-----o A
                     1N4007   |   |        Sidac     __|__ SCR1     ::(
                              |   |   R3  D2 100 V   _\_/_ T106B2   ::(
      AC                  C1  |   +--/\/\---|>|      / |   200 V    ::(
     Line      Power  .15 µF _|_     1.5K   |<|--+--'  |   4 A    o ::( 350 ohms
              IL1 LED   250V ---                _|_    |  +-------+ ::(
            +--|<|---+        |              C2 ---    |  |        )::(
            |   R1   |   R2   |        .0047 µF  |     |  | .1 ohm )::(
      N o---+--/\/\--+--/\/\--+                  +-----+--+        )::(
               470      3.9K  |                                +--+    +--+--o B
               1 W      2 W   |                                |    R4    |
    The AC input is rectified by D1 and as it builds up past the threshold of the sidac (D2, 100 V), SCR1 is triggered dumping a small energy storage capacitor (C1) through the primary of the HV transformer, T1. This generates a HV pulse in the secondary. In about .5 ms, the current drops low enough such that the SCR turns off. As long as the instantaneous input voltage remains above about 100 V, this sequence of events repeats producing a burst of 5 or 6 discharges per cycle of the 60 Hz AC input separated by approximately 13 ms of dead time.

    The LED (IL1) is a power-on indicator. :-)

    The transformer was totally potted so I could not easily determine anything about its construction other than its winding resistances and turns ratio (about 1:100).

                                                A o
                                         C3       |
              R5     R6      D3   |   D4     D5   |  D6     R7       R8
      HV- o--/\/\---/\/\--+--|>|--+--|>|--+--|>|--+--|>|---/\/\--+--/\/\--o HV+
             10M    10M   |      C4       |                220K  |  10M
                          +------||-------+                      |
           D3-D6: 10 kV, 5 mA            _|_                    _|_
           C3,C4: 200 pF, 10 kV          --- C5                 --- C6
           C5,C6: 200 pF, 5 kV            |                      |
                                     B o--+----------------------+
    The secondary side consists of a voltage tripler for the negative output (HV-) and a simple rectifier for the positive output (HV+). This asymmetry is due to the nature of the unidirectional drive to the transformer primary.

    From my measurements, this circuit produces a total of around 10 kV between HV+ and HV-, at up to 5 uA. The output voltages are roughly equal plus and minus when referenced to point B.

    I assume the module would also operate on DC (say, 110 to 150 V) with the discharges repeating continuously at about 2 kHz. Output current capability would be about 5 times greater but at the same maximum (no load) voltage. (However, with DC, if the SCR ever got stuck in an 'on' state, it would be stuck there since there would be no AC zero crossings to force it off. This wouldn't be good!)

    This module is probably for a device similar to the AirEase(tm) Personal Space Ionization Air Cleaner from Ion Systems, Inc. This unit has the positive output of its HV module connected to a 3/16" diameter electrode on the side of the case. This is in contact with a piece of foam (a cylinder about 2" in diameter by 5" high) which surrounds the entire unit. While it appears that this foam should be conductive, I could not detect any evidence of this with a multimeter. The negative output is connected to a 1-1/4" conductive foam disk on the top of the unit. Unfortunately, the HV module in the AirEase was totally potted so I could not determine anything about its internal circuitry.

    Auto air purifier schematic

    Well, maybe. :-) This thing is about the size of a short hot-dog and plugs into the cigarette lighter socket. It produces a bit of ozone and who knows what else. Whether there is any effect on air quality (beneficial or otherwise) or any other effects is questionable but it does contain a nice little high voltage circuit.
                                                                       DL1 +-+ |
                                                       o  T1 +-------+-----|o|
      +12 o---+--------+----------+---------------------+ ::(        |     +-+ |
              |        |          |                D 30T )::(        | DL2 +-+
              |        |        -_|_ 4.7µF           #30 )::(        +-----|o| |
              |        |         --- 50V         +------+ ::( 3000T  |     +-+
              |       _|_ C2    + |              |        ::( #44    | DL3 +-+ |
              |       --- 470pF   +--------------|------+ ::(        +-----|o|
              |        |          |              | F 30T )::(        |     +-+ |
            +_|_ C1    |          |       D1     |   #36 )::(        | DL4 +-+
             --- 33µF  +----------|---+---|<|----|------+ ::(        +-----|o| |
            - |  16V   |          |   | 1N4002   |     o     +--+          +-+
              |        /          /   |        |/ C           o |              | 
              |     R1 \       R2 \   +--------|Q1  TIP41       +--------------+
              |     1K /     4.7K /            |\ E             |            Grid
              |        \          \              |              |
              |        |          |              |              |
      GND o---+--------+----------+--------------+--------------+
    T1 is constructed on a 1/4" diameter ferrite core. The D (Drive) and F (Feedback) windings are wound bifilar style (interleaved) directly on the core. The O (Output) winding is wound on a nylon sleeve which slips over the core and is split into 10 sections with an equal number of turns (100 each) with insulation in between them.

    DL1 to DL4 look like neon light bulbs with a single electrode. They glow like neon light bulbs when the circuit is powered and seem to capacitively couple the HV pulses to the grounded grid in such a way to generate ozone. I don't know if they are filled with special gas or are just weird neon light bulbs.

    Bug zappers

    You know the type - a purplish light with an occasional (or constant) Zap! Zap! Zap! If you listen real closely, you may be able to hear the screams of the unfortunate insects as well :-).

    The high-tech versions consist of a high voltage low current power supply and fluorescent (usually) lamp selected to attract undesirable flying creatures. (Boring low-tech devices may just use a fan to direct the insects to a tray of water from which they are too stupid to be able to excape!)

    However, these devices are not selective and will obliterate friendly and useful bugs as well as unwanted pests.

    Here is a typical circuit:

             S1        R1         C1            C2            C1-C4: .5 µF, 400 V
      H o----o/ o--+--/\/\--------||---+--------||---------+  D1-D5: 1N4007
                   |  25K        D1    |   D2        D3    |   D4
                   |         +---|>|---+---|>|---+---|>|---+---|>|---+
                  +-+        |        C3         |        C4         |
     AC Line      |o| FL1    +---+----||----+----+---+----)|----+----+--o + 
                  +-+ Lamp   |   |    R3    |        |    R4    |        500 to
                   |         |   +---/\/\---+        +---/\/\---+        600 V
                   |   R2    |       10M                 10M             to grid
      N o----------+--/\/\---+------------------------------------------o -
    This is just a line powered voltage quadrupler. R1 and R2 provide current limiting when the strike occurs (and should someone come in contact with the grid). The lamp, FL1, includes the fluorescent bulb, ballast, and starter (if required). Devices designed for jumbo size bugs (or small rodents) may use slightly larger capacitors!

    (From: Jan Panteltje (

    I have one, bought it very cheap: they are only $10 here :)

    It comes with a 25 W blue lamp inside, with wires around it. The lamp did not last long, so I replaced that with a 7 W electronic fluorescent type, that now just keeps going and going and going. The bugs do not care, they just go for the light. Then they hit the wires.

    Here, we have 230 V, in the lamp is a voltage doubler, with 2, 220 nF capacitors, 2 silicon diodes, and a 10 K Ohm series resistor in the mains. The whole thing cannot be touched by humans from outside. The voltage between the wires is something like 620 V. If an insect shorts the wires, the 10K limits the current until it is destroyed (the insect that is). The insect actually explodes, the 600 V cap discharges into it.

    (From: (Abe Shultx)

    I grabbed a bug zapper from someone's garbage and opened it up. Instead of a voltage multiplier, there was a transformer. It had a capacitor across the output, and threw an approximately 3/4 inch loud blue arc. I don't know the cap values, because it was potted. :-(

    Electric fences

    Yes, I know, this isn't a common small appliance but....

    (From: John Harvey (

    Most DIY fence energizers use an automotive ignition coil and kits (generally minus coil) are available in Australia and probably elsewhere.

    Commercial units operate on the capacitor discharge principle and are fired at a 1.2 second interval. Voltage O/P needs to be around 5 to 8 kV (which will drop under load). The energy O/P (pulse duration) is determined by the capacitor and 10 to 20 µF is about right for a small unit (up to 2km or so). They must use a pulse grade capacitor (which has a high dV/dt) to be reliable.

    Appliance and light timers

    There are two basic types: mechanical and electronic.

    Warnings about using compact fluorescent lamps on electronic timers

    You may have seen these warnings in the instructions or on the package of electronic (not mechanical) timers and/or compact fluorescents.

    There are two issues:

    1. Providing the trickle current to operate the clock circuitry in the timer.

      Where a solid state timer is used to replace a normal switch, there is usually no connection to the Neutral so it must derive all its operating power from current through the load (though at a very low current level).

      The type of circuitry in a compact fluorescent with an electronic ballast (or other equipment with a switching power supply like a TV, some VCRs, computer, etc.) may result in this current being too low or erratic. The result will be that the timer doesn't work properly but damage isn't that likely (but no guarantees).

      If it is installed with 3 wires (Hot, Neutral, Load), then this should not be a problem.

      In addition, interference (e.g., spikes) from the CF ballast may feed back into the electronic timer and this may either confuse or actually result in failure.

    2. Damage to either or both of the devices dues to incompatibility.

      The solid state switching device - usually a triac - in the timer unit may be blown by voltage spikes or current surges when the power goes on or off into an inductive or capacitive load like an electronic ballast (or normal magnetic ballast, for that matter.

    In short, read and follow label directions! Although a given combination may actually work reliably for years even if it is not supposed to but you should be able to find a pair for which this shouldn't be a problem.

    Wall thermostats

    These can be divided into several classes depending on: It is not possible to cover all variations as that would require a complete text in itself. However, here is a summary of possible problems and solutions.

    Conventional thermostats usually use a bimetal strip or coil with a set of exposed contacts or a mercury switch. In general, these are quite reliable since the load (a relay) is small and wear due to electrical arcing is negligible. On those with exposed contacts, dirt or a sliver of something can prevent a proper connection so this is one thing to check if operation is erratic. The following description assumes a single use system - heating or cooling - using 24 VAC control which is not properly controlling the furnace or air conditioner.

    1. Locate the switched terminals on the thermostat. Jumper across them to see if the furnace or air conditioner switches on. If it does, the problem is in the thermostat. If nothing happens, there may be a problem in the load or its control circuits. Cycle the temperature dial back and forth a few times to see if the contacts ever activate. You should be able to see the contacts open and close (exposed or mercury) as well.

      (CAUTION: on an air conditioner, rapid cycling is bad and may result in tripped breakers or overload protectors so ideally, this should be done with the compressor breaker off).

    2. Check for 24 VAC (most cases) across the switched circuit. If this is not present, locate the control transformer and determine if it is working - it is powered and its output is live - you may have the main power switch off or it may be on a circuit with a blown fuse or tripped breaker. I have seen cases where the heating system was on the same circuit as a sump pump and when this seized up, the fuse blew rendering the heating system inoperative. Needless to say, this is not a recommended wiring practice. The transformer may be bad if there is no output but it is powered. Remove its output connections just to make sure there is no short circuit and measure on the transformer again.

    3. If 24 VAC is present and jumpering across the terminals does nothing, the heater valve or relay or air conditioner relay may be bad or there is a problem elsewhere in the system.

    4. Where jumpering the terminals turns on the system, the thermostat contacts may be malfunctioning due to dirt, corrosion, wear, or a bad connection. For a setback unit, the setback mechanism may be defective. Test and/or replace any batteries and double check the programming as well. On those with motor driven timers operating off of AC, this power may be missing.

    5. Where jumpering the terminals does not activate the system, check the load. For a simple heating system, this will be a relay or valve. Try to listen for the click of the relay or valve. If there is none, its coil may be open though in this case there will be no voltage across the thermostat contacts but the 24 V transformer will be live. If you can locate the relay or valve itself, check its coil with an ohmmeter.

    6. If the previous tests are ok, there may be bad connections in the wiring.
    Some additional considerations: Units that control both heating and airconditioning are more complex and will have additional switches and contacts but operate in a similar manner and are subject to similar ailments.

    Testing a thermostat

    Where a heating appliance doesn't come on or go off as it should, a bad thermostat is possible. Most thermostats in refrigerators and freezers, air conditioners, heating systems, hot plates, fryers, and the like, are simple on/off switches activated by the bending of a bimetal strip (due to the differing expansion coefficients of the two types of metal) or by the expansion of a liquid filled bulb or capillary (often in cooling appliances). Basic tests can be done with a container of hot, cold, or freezing water (depending on the application) and a multimeter (to check for the closing and opening of the contacts if it isn't visually or audibly obvious.

    Fully open mechanisms (no enclosed switches) can be totally dunked in the water as long as they are dried thoroughly afterwards. This should be avoided where the bimetal activates an enclosed 'microswitch' since it is difficult to be sure of removing all the trapped water.

    To test an air conditioner thermostat, for example, turn the knob to the highest (coldest) setting. The contacts should be closed. Then, cool the bimetal strip off with cold tap water. The contacts should open. The range can be determined with a thermometer and various combinations of hot and cold water.

    Replacing a thermostat

    The following applies to refrigerators and freezers, air conditioners, electric space heaters, as well as other small appliances.

    Removing the thermostat (unplug AC line first!) and cleaning the contacts using contact cleaner NOT sandpaper or a file (except as a laser resor) - may help temporarily. Replacement is easy if the cold control is self contained using a bimetal strip. If it uses a liquid filled bulb, the tube may snake around inside the cabinet and may be more challenging. Still no big deal. An appliance part distributor or your appliance manufacturer should have a replacement.

    Note that an exact replacement may not be needed as long as its electrical ratings (amps or HP) is at least as high, it is intended for the same application (e.g., freezer or space heater), the sensing element is similar, and it can be made to fit! This could come in handy if trying to repair a 30 year old air conditioner!

    Electric space heaters

    All types have one thing in common - they are nearly 100% efficient which means that just about every watt of power utilized is turned into heat. The remainder is used for any built in fans or the wasted light produced by glowing elements or quart lamps.

    However, this does not mean that these are the most economical heating devices. Heat pumps based on refrigeration technology can be much less costly to run since they can have coefficients of performance - the ratio of heat output to energy input - of 3 or more to 1. Thus, they are in effect, 300% or more efficient. Note that this does not violate any conservation of energy principles as these simply move heat from one place to another - the outdoors is being cooled off at the same time.

    Space heaters come in 3 common varieties:

    Problems with space heaters are nearly always related to bad heating elements, problems with the thermostat, interlock switches, or fan (if any), or bad connections. Blown fuses or tripped circuit breakers are very common with these appliances as they are heavy loads - often the maximum that can safely be plugged into a 15 A outlet - and thus overloads are practically assured if **anything** else is used on the same circuit. Since we rarely keep track of exactly what outlets are on any given circuit, accidentally using other devices at the same time are likely since the same circuit may feed outlets in more than one room - and sometimes some pretty unlikely places.

    Radiant space heaters

    These use a coiled NiChrome, Calrod(tm), or quartz lamp heating element. There is no fan. A polished reflector directs the infra red heat energy out into the room. Radiant space heaters are good for spot heating of people or things. They do not heat the air except by convection from the heated surfaces.

    Of course, first check that the outlet is live.

    As with other heating appliances, the most likely problems are with burned out heating elements; defective on/off switches, thermostats, or safety interlock or tip-over switches, bad cord or plug, or bad wiring connections. Your continuity checker or ohmmeter will quickly be able to identify which of these are the problem.

    Warning: do not be tempted to bypass any interlock or tip-over switches should they prove defective. They serve a very important fire and personal safety function. Never, ever cover the heater in any way as a serious fire hazard will result.

    Convection space heaters

    A small fan blows air over or through a heating element. This may be a NiChrome coil, Calrod(tm) element, or ceramic thermistor. This type is probably the most popular since it can quickly heat a small area. The ceramic variety are considered safer than the others (of this type) since they are supposed to operate at a lower surface temperature.

    In addition to the problems covered in the section above: "Radiant space heaters", the fan can also become sluggish or seize up due to gummed up lubrication (as well as other fan-motor problems). Since it is running in a high temperature environment, disassembly, cleaning, and lubrication may be needed periodically despite what the manufacturer may say about permanently lubricated parts.

    Oil filled electric radiators

    These are also considered convection heaters but they do not have any fan.

    The typical unit consists of a pair of heating elements providing 600, 900, or 1500 Watts depending on which are switched on. A simple bimetal adjustable thermostat is used for temperature control. The heating elements are fully submerged and sealed inside an oil filled metal finned replica of an old style radiator. The whole affair is mounted on wheels as it is quite heavy.

    Depending on design, there may be one or two thermostats (oil and air) in addition to thermal and electrical protection devices.

    Common problems with these have been the pair of power switches which tend to fail resulting in no or erratic operation. Note: if your heater is a Delongi, there has been a free (well $5 S&H) upgrade to replace the failure prone power switches and air temperature thermostat on some common models.

    The heating elements are replaceable (as a set). Since they are immersed in the oil, you MUST have the radiator on its end with the terminals straight up while changing them or else there will be a mess. Replacement will be worth the cost and effort only if you require the high settings as it is unlikely for both elements to fail. If testing reveals an open element, you will just not have the heat ranges that use it. If an element shorts to the case, it must be disconnected to prevent a shock hazard though the other one can still be safely used. Parts should be available.

    So, what about the Pelonus Disk furnace?

    (From: Kirk Kerekes (

    It is a portable electric heater, using high-power thermisters as the heating elements. This technology was originally developed by TDK a few decades ago. The premise is that the power thermisters will automatically control the heating element temperature (the thermister), so that if the air flow is blocked, the heater won't cook. The manufacturers make efficiency claims, but these seem to be bogus. (All space heaters are nearly 100% efficient. See the section: Electric space heaters --- Sam.)

    I have a bathroom version of this device, and it works.

    Electric pencil sharpeners

    AC powered pencil sharpeners consist of a small shaded pole induction motor, pencil sense switch, and some gears and cutter wheels. Aside from pencil shavings crudding up the works - which can be cleaned - the most common failure is of the cheap plastic gears. These can be easily be replaced if you can get them - the original manufacturer is likely the only source. The switch contacts may become dirty or level/bar may become misaligned or worn. Some clever repositioning or the addition of a shim may help in these cases.

    Battery operated pencil sharpeners use a small DC motor for power. These tend to be whimpier than their AC counterparts but all other comments apply. Always try a fresh set of batteries first.


    A blender really is just a high speed motor mounted inside a base. Units with 324 speeds accomplish (this more or less useless marketing gimmick) through a combination of diodes, resistors, and multiple windings on the motor. Without addressing the ultimate utility of thousands of speeds, problems with these units are more likely to be in the motor itself - open or shorted windings, or bad bearings. However, the selector switches and electrical parts can fail as well.

    The motors are typically of the series wound universal type. These have carbon brushes which are prone to wear. However, given the relatively short total usage of a blender, this is not usually a problem.

    Disconnecting (and labeling!) connections one at a time may permit the source of a problem to be localized. Diodes can be tested with a multimeter (they should read open in one and only one direction) and resistors checked as well. Shorts in a motor with multiple taps on its windings may be difficult to identify or locate. Shorted windings can result in overheating, incorrect speeds, or even a blender that runs with the power switch supposedly in the off position as the wiring is sometimes sort of strange!

    Bad bearings will result in any number of mechanical problems including excessive or spine tingling noise, vibration, a seized rotor or very sluggish rotation. Sometimes, disassembly, cleaning, and oiling will be effective but since these rotate at high speed, don't count on it. Unfortunately, cheap bronze bushings are often used instead of ball bearings. However, substituting a set from another similar unit might work since it is usually the bronze bushing and not the motor shaft that fails.

    The most sophisticated units will have a variable speed control - similar to a light dimmer. If this goes bad - the blender always runs at full speed - then the active element (triac) has probably blown. Replacement is possible and the part types should be readily available.

    Drip coffee makers

    A drip coffee maker consists of several components:
    1. A heating element: Combined or separate Calrod(tm, usually) types for operating the drip pump and then keeping the coffee warm.

    2. Thermal protector: To prevent excess temperatures.

    3. Some kind of water interlock: Prevents dripping when separate reservoir is used.

    4. Timer or controller: The simplest are mechanical while programmable units with clocks and electronic timers are also available.
    Many problems are be mechanical - clogged water passages or interlock. Extended use with hard/high mineral content water can also result in reduced heating effectiveness and/or increased heating times. It may be possible to flush the unit a couple of times with viniger.

    If there is no heating, check the element and thermal protector with an ohmmeter. If the element is open, it is probably time for a new coffee maker. The thermal protectors can be replaced but the underlying cause may be a defective, shorted overheating element so it may not be worth the trouble. Timers can develop bad contacts and bad connections are possible on electronic controller circuit board wiring.

    Drip coffee maker repair

    (From: Niels Henriksen (ap294@FreeNet.Carleton.CA).)

    I wish I had thought of this sooner rather than throwing out the first coffee maker and I had planned to throw this one out. For some reason I thought I would just look inside to see what was up.

    Where I live the water is hard (well) and there is constant scaling and buildup of calcium. We heard that all you have to do is to run a mixture of vinegar through the coffee maker to rejuvenate.

    A friend and the 2 of ours all started to leak very badly when the vinegar/water mixture when through. I though that the internal plumbing had corroded through the metal parts and the vinegar dissolved the calcium that was protecting the holes and therefore unrepairable. Who knows where these ideas come from.

    Now for the technical solution.

    The element that is used to boil the water and uses the bubbles to bring hot water to top of coffee maker is the same element that is used to keep the pot warm.

    There is a metal tube attached to the metal warming element and this unit has a heating element embedded. There are 2 rubber hoses attached. One brings cold water to heater and the other brings boiling water to top. The cold water tube has a check valve that prevents the bubbling water from going to cold water reservoir.

    When vinegar is added the calcium scales start to dissolve and in 3 of 3 so far, this blocked the metal tube. The water starts to boil and since the cold water inlet has a check valve the water pressure can only buildup to where the rubber tube is blown off the metal pipe. No damage to parts.

    To fix:

    1. Take bottom off to gain access to heater area.

    2. Remove rubber tubes which are connected with spring clamps.

    3. Run rubber tubes through your fingers to loosen scale buildup and flush out

    4. Push a thin copper wire or other bendable wire through heating tube. This is to unblock and loosen some scale.

    5. Pour straight vinegar into metal tube to dissolve calcium and use wire to loosen.

    6. Repeat several times till clean.

    7. Re-attach all parts and use.
    The solution is to start a regular process of using vinegar BEFORE the calcium has buildup to the point where when loosened it will block the tube.

    Coffee percolators

    While largely replaced by the drip coffee maker, these are still available, particularly in large sizes. The components are similar to those in a drip coffee maker - element, thermal protector, possibly a thermostat as well. The element and bottom of the water/coffee container are likely one piece to provide the best thermal conduction for the 'pump' in the middle. Even if the element is removable, it may not be worth the cost of replacement except for a large expensive unit.

    Electric kettles

    These consist of a heating element, thermal protector, and possibly a thermostat and/or timer. See comments for coffee makers.

    Electric (motor driven) clocks

    While line operated clocks have mostly been superseded by electronic (LED or LCD) clocks on nearly every kitchen appliance, many of these are still in operation on older clock radios and ranges.

    AC operated clocks depend on the AC line frequency (60 Hz or 50 Hz depending on where you live) for time keeping. The accuracy of a line operated clock is better than almost any quartz clock since the long term precision of the power line frequency is a very carefully controlled parameter and ultimately based on an atomic clock time standard.

    Therefore, most problems are related to a clock motor that does not run or will not start up following a power outage. Once running, these rarely fail.

    The most common problems are either gummed up oil or grease inside the motor and gear train, broken gears, or broken parts of the clock mechanism itself. See the sections on "Synchronous timing motors" for repair info.

    Battery operated quartz clocks usually operate on a 1.5 V Alkaline cell (do not replace with NiCds as they do not have a long absolute life between charges even if the current drain is small as it is with a clock).

    First, test the battery. Use a multimeter - usually anything greater than 1 V or so will power the clock though if it is closer to 1 V than 1.5 V, the battery is near the end of its life. The clock may run slow or fast or erratically on a low battery.

    With a good battery, failure to run properly is usually mechanical - one of the hands is hitting against the glass front or something like that. Don't forget to check any on/off switch - these are not expected but are often present presumably to permit you to start the clock at precisely the right time. I had one case where the fine wire to the solenoid that operates the once per second clock mechanism broke and had to be resoldered but this is exceedingly rare.

    If the clock consistently runs slow or fast with a known good battery, there is usually a trimmer capacitor that can be adjusted with a fine jeweler's straight blade screwdriver. Without test equipment the best you can do is trial and error - mark its original position and turn it just a hair in one direction. Wait a day or week and see if further adjustment is needed (right, like you also won the lottery!) and fine tune it.

    If the hands should fall off (what a thought!), they can usually be pressed back in place. Then, the only trick is to line up the alarm hand with the others so that the alarm will go off at the correct time. This can usually be done easily by turning the hour hand counterclockwise using the setting knob in the rear until it is not possible to turn it further. At this point, it is lined up with the alarm hand. Install all hands at the 12:00 position and you should be more or less all set.


    The mechanism consists of a shaded pole induction motor and gear train. Clean and lubricate the gears. See the section: Shaded pole induction motors for motor problems.

    Electric can openers and knife sharpeners

    There consist of a shaded pole induction motor, gear train. and power switch. Likely problems relate to broken gear teeth, dirty or worn power switch, dull cutting wheel, and broken parts. Lubrication may be needed if operation is sluggish. Parts that come in contact with the cans and lids collect a lot of food grime and should be cleaned frequently.

    Electric carving knives

    A small motor operates a pair of reciprocating mounts for the blades.

    AC powered carving knives include a momentary power switch, small motor (probably universal type), and some gearing. Congealed food goo as well as normal lubrication problems are common. The power switch is often cheaply made and prone to failure as well. The cord may be abused (hopefully not cut or damaged by careless use of the knife!) and result in an intermittent connection at one end or the other. For motor problems, see the appropriate sections on universal motors.

    For battery powered knives, bad NiCds cells are a very likely possibility due to the occasional use of this type of appliance.

    See the section: Small permanent magnet DC motors and the document: AC Adapters, Power Supplies, and Battery Packs for information on repair.

    Electric scissors

    Similar to electric carving knives except for the linkage to the blades. All other comments apply.

    Portable and stationary food mixers

    These consist of a universal motor which usually features a continuously variable speed control or a selection of 3 to 5 speeds, a gearbox to transfer power to the counter-rotating beaters, and a power switch (which may be part of the speed control).

    Sluggish operation may be due to cookie dough embedded in the gearing. Fine particles of flour often find their way into the gears - clean and lubricate. There may be a specific relationship that needs to be maintained between the two main beater gears - don't mess it up if you need to disassemble and remove these gears or else the beaters may not lock in without hitting one-another.

    The speed control may be a (1) selector switch, (2) mechanical control on the motor itself (a governor/spring/switch arrangement), or (3) totally electronic. Parts may be replaceable although, for portables at least, a new mixer may make more sense.

    For sluggish operation (non-mechanical), sparking, burnt smells, etc., see the section: Problems with universal motors.

    Food processors

    A powerful universal motor is coupled to interchangeable cutters of various types. In most respects, food processors are similar to any other universal motor driven appliance with one exception: There will be a safety interlock switch to prevent operation unless the cover is on properly and secured. This switch may go bad or its mechanical position adjustment may shift over time resulting in difficulty in engaging power - or a totally dead unit.

    As usual, cord and plug problems, bad bearings, burnt motor windings, and broken parts are all possibilities.

    Steam and dry irons

    Most modern irons (does anyone really use these anymore?) can be used dry or with steam.

    An iron consists of a sole plate with an integrated set of heating coils.

    Steam irons will have a series of holes drilled in this plate along with a steam chamber where a small amount of water is boiled to create steam. A steam iron can be used dry by simply not filling its reservoir with water. Those with a spray or 'shot of steam' feature provide a bypass to allow hot water or steam to be applied directly to the article being ironed.

    Over time, especially with hard water, mineral buildups will occur in the various passages. If these become thick enough, problems may develop. In addition, mineral particles can flake off and be deposited on the clothes.

    A thermostat with a heat adjustment usually at the top front of the handle regulates the heating element. This is usually a simple bimetal type but access to the mechanism is often difficult.

    Where an iron refuses to heat, check the cord, test the heating element for continuity with your ohmmeter, and verify that the thermostat is closed.

    An iron that heats but where the steam or spray features are missing, weak, or erratic, probably has clogged passages. There are products available to clear these.

    Newer irons have electronic timeout controllers to shut the iron off automatically if not used for certain amount of time as a safety feature. Failure of these is not likely and beyond the scope of this manual in any case.

    When reassembling an iron, take particular care to avoid pinched or shorted wires as the case is metal and there is water involved - thus a potential shock hazard.


    In addition to a fine heating element, there is a controller to determine the length of time that the bread (or whatever) is heated. A solenoid or bimetal trip mechanism is used to pop the bread up (but hopefully not totally out) of the toaster then it is 'done' and turn off the heating element at the same time.

    Since most of these are so inexpensive, anything more serious than a broken wire or plug is probably not worth repairing. The heating element may develop a broken spot - particularly if something like a fork is carelessly used to fish out an English muffin, for example. (At least unplug it if you try this stunt - the parts may be electrically live, your fork is metal, you are touching it!). They may just go bad on their own as well.

    Being a high current appliance, the switch contacts take a beating and may deteriorate or melt down. The constant heat may weaken various springs in either the switch contact or pop-up mechanism as well. Sometimes, some careful 'adjustment' will help.

    Controllers may be thermal, timer based, or totally electronic. Except for obvious problems like a bent bimetal element, repair is probably not worth it other then as a challenge.

    Automatic toaster will not drop bread

    If it really is old, then your problem is almost certainly mechanical - a spring sprung or gummed up burnt raisin bread. You will have to do a little investigative research meaning: take the thing apart! Try to determine what the bread does to cause the support to drop down. It is possible that putting the bread in is supposed to trip a microswitch which activates a solenoid, and the switch or solenoid is now defective - bad contacts or broken wires, bad coil in the solenoid, or grime.

    The following applies directly to several Sunbeam models (and no doubt to many others as well).

    (From: John Riley (

    I will assume that the toaster is either a model ATW or possibly an older model 20 or the like.

    When you drop the bread in the toaster it trips a lever that is attached to the bread rack. This lever pushes in on the contacts inside of the thermostat (color control switch) which actually turns the toaster on. In "most cases" adjusting the screw on the bottom of the toaster will do the trick. The proper adjustment is to adjust the carriage tension so that the bread rack in the side where it marked for a single slice of bread comes just to the uppermost limit of its travel. Any more is overkill.

    If you have adjusted it as mentioned above and it still won't go down, there is one more thing you can try. Take the toaster a sort of BUMP it down onto the table rather firmly. Sometimes a piece of crumb will get in between the thermostat contacts. A couple of good "bumps" on the table will usually dislodge the particle.

    If all of the above doesn't work, and you know the cord isn't bad, them you may very well have a thermostat that has gone south. They are still available for replacement on most models. Suggest you check with your local SUNBEAM AUTHORIZED SERVICE for price and availability.

    (From: B. Gordon (

    If the suggestions already given for the A20 and their successors don't work, then the problem may be corrosion of the German-silver electrical contacts. Like the rest of the 1940s-1950s Sunbeam toaster products, these contacts are much larger than they would need to be, but after 50 years or so of use, even these over-engineered switch contacts may need some light filing/cleaning. I have saved two vintage Sunbeam toasters from the appliance graveyard by this quick and simple repair technique.

    Toaster oven (broilers)

    I really liked the old original style GE toaster oven. It was very versatile and convenient for baking and toasting. The newer types seem to have lost some of these qualities. The pop open door and oven tray have apparently not been retained in any modern models that I am aware of.

    Modern toaster oven (broilers) use Calrod style elements - usually two above and two below the food rack. Depending on mode, either just the top (top brown/broil), just the bottom (oven), or both sets (toast) will be energized. Each pair may be wired in series meaning that a failure of one will result in both of the pair being dead. Very old units may use a coiled NiChrome element inside a quartz tube.

    Thermostats are usually of the bimetal strip variety with an adjustment knob. A cam or two on the shaft may also control main power and select the broil function in the extreme clockwise position.

    There may be a mode switch (bake-off-broil) which may develop bad contacts or may fuse into one position if it overheats. These are often standard types and easily replaceable. Just label where each wire goes on the switch before removing it to take to an appliance repair parts store.

    Newer models may use an electronic timer for the toast function at least. I assume it is not much more than something like an IC timer (555) operating the trip solenoid. However, I have not had to deal with a broken one as yet.

    Testing is relatively straightforward. Check the heating elements, thermostat, mode switch,, cord, and plug. While replacements for heating elements and thermostats are often available, removing the old one and wiring the new one may not be straightforward - rivets may be used for fastening and welds for the wire connections. You will have to drill the rivets with an electric drill and replace them with nuts, bolts, and lockwashers. Crimp splices or nuts and bolts can be used for the wiring. Take extra care in reassembly to avoid any bare wires touching the metal cabinet or other parts as well as insulation being cut by sharp sheetmetal parts. The high temperature fiberglas or asbestos insulation is not very robust. In the end, it may not be worth it with full featured toaster oven/broilers going for $20-30 on sale.

    Some more details and comments are provided in the section: Troubleshooting a toaster oven.

    Troubleshooting a toaster oven

    You might expect that there would be a way of obtaining a schematic. Forget it, there is no such thing. :( However, these aren't designed by rocket scientist so it should be possible to draw one out if you really need it.

    Before doing this, there are basic things to check:

    1. Toaster ovens usually operate in three modes:

      • Oven (both top and bottom should be on)
      • Toast (same)
      • Top brown (only top elements)

      The broiler option is similar to top brown.

      Thinking about which elements need to be powered for which mode, and whether the thermostat is involved (not for toasting), will help to narrow down the area of attack.

      If a heating element is found to be bad either by inspection or the ohmmeter check, it can be replaced though this may only make sense from a cost perspective if you have one that can be salvaged from another appliance. If the length and resistance are similar, it should work. Attaching the cut wires may be a challenge unless you are into welding. However, a mechanical connection with a screw and nut will work though for how long is anyone's guess. Also see below. Solder can't be used.

    2. A typical toaster oven has 2 sets of elements - either a pair of the Calrod(tm) type, top and bottom, with each pair usually wired in series or, a coil or pair of Nichrome coils, top and bottom.

      Visually inspect the heating elements. Failure of a Calrod(tm) type often results in an external wart of blemish where the internal coil shorted and melted the cladding. Nichrome (wire) elements fail by breaking somewhere along their length.

      And/or measure the resistance of each of the elements. Typical values are 10 to 12 ohms for a single Calrod type or 20 to 25 ohms for a complete Nichrome coil. (Your measurements will vary depending on the actual wattage of the oven. These values are typical in the U.S.A. for operation on 115 VAC.)

    3. If the elements are good, both top and bottom, another likely place for failure are the contacts of the mode switch(es) and thermostat. Check each of these sets of contacts and make sure they are moving appropriately and decisively - I have seen the springs lose some of their springiness over time resulting in some not working. Sometimes they can be bent back into service.

    4. Broken/deteriorated wiring is very common since everything gets very hot during use. All connections in a toaster oven are likely welded but you can replace them with either a nut and bolt or high temperature crimp. Soldering will also work if the location of the failure isn't too close to the elements.

    5. The thermostat on some of these units senses via a riveted attachment to the oven wall. If these rivets loosen with age, the oven may run hotter than normal. Drilling them out and using nuts and bolts or pop-rivets may work in this case.

    6. On newer units that have electronic controls, parts can fail but the most likely problems are probably due to cold solder joints on the little wiring board that sits in a hot area so check for these before trying to locate a datasheet for an obscure chip.

    (From: Terry (

    Get a 'wire-nut' connector. Not one of the usual ones with a wire spiral inside it; but one of the ones that has a brass insert with a screw to secure the wires. See 'Note' re set screw. Throw away the plastic outer shell. Put end of the element heating wire and the end of a short piece of heat resistant wire into the wire nut brass insert and tighten the screw; real tight cos it's going to get somewhat hot! Dress the wire and/or suspend what is now your brass connector so that it is clear of everything or use some woven 'glass' heat resistant tubing to cover the connection. Repeat at other end as necessary. Probably last for quite a while. Note: Look for one that has a set-screw that can be tightened with a hexagonal 'Allen' wrench rather than a straight edge screwdriver. With these it would seem you can get the screw and therefore contact with the wires much tighter! Another connection that might work, but have not used for this is to clip the screw terminals off the end of a duff oven element and use those as screw terminals to secure a connection to the toaster heating element wire? Those oven element terminals do get hot in normal use anyway!

    Circuit diagram of typical toaster oven/broiler

    Here is a schematic of a typical 'dumb'toaster oven/broiler - one without a P5-1000 chip if you can believe such a thing exists. :) Most of the complexity of these simple devices is actually in the sheet metal of the toast release mechanism! Like the more elaborate unit described in the section: Circuit diagram of Toastmaster toaster oven/broiler with electronic controls, there is a knob for control of the oven/broiler functions and another for toast Light/Dark. A separate lever engages the toast function which terminates when the toast is done. You will note that other than that unit having an IC for toast timing, the basic circuits are almost the same.

    Apparently, the only real difference between a "toaster oven" and a "toaster oven/broiler" is that the latter has a means of disabling the bottom heating element while in oven (non-timed) mode - and, of course, the price!

    This diagram is not based on any particular model.
                      +- - - - - - + - - - - - - - + All part of Oven Control
                      :            :               :
                     S1A      S1B _:_              :        R1          R2
      AC H o--+------/ -----------o o------+---+---:-----/\/\/\/\----/\/\/\/\---+
              |  Oven Power    Thermostat  |   |   :          Top Element       |
              |                            |   |   :                            |
              |         S2 ___ Toast On    |   |  S1C       R3          R4      |
              +------------o:o-------------+   +---/ ----/\/\/\/\----/\/\/\/\---+
                            :              |     Broil      Bottom Element      |
               +-------+    :           R5 /   Top Brown                        |
           +-->| Timer |--+ :  Toast   47K \   (Full CW)   R1-R4: 8-12 ohms     |
           |   +-------+   )|| Release     /                                    |
       Light/Dark          )|| Solenoid    |   +--+ IL1 Power                   |
       Temp. Sensor       +                +---|oo|---+ Indicator               |
                          |                NE2 +--+   |                         |
      AC N o--------------+---------------------------+-------------------------+

    Circuit diagram of Toastmaster toaster oven/broiler with electronic controls

    Well, for toast, at least! :)

    Aside from the CMOS IC based toast timer, this is a fairly basic design:

    The toast function and oven/broiler are controlled separately. A single Power/Temperature/Broil knob controls the oven/broiler. This is entirely electro-mechanical with a conventional bimetal thermostat. Toast darkness is based only on time using CD4541B timer chip to release a manually activated Toast lever. Older 'dumber' toasters often were more sophisticated in their operation using a combination of time and temperature. Not this one.

    Its conventional counterpart would be identical except using a mechanical and/or toast temperature sensor in place of the IC timer. Despite what you might think, the most likely failures are NOT in the 'high-tech' electronics but the usual burnt out heating element(s), bad cord or plug, broken wires, and tired switches.

    Convection oven noise

    Unlike a regular (non-microwave) oven, convection ovens are not totally silent. There is a small fan used to circulate the hot air (thus the name: convection oven). Depending on the oven's design and age, these fans may be anywhere from nearly silent to objectionably noisy.

    If you notice an increase in motor noise (whining or squealing, grinding, knocking) then the motor and fan should be inspected and parts replaced if necessary. Sudden failure is unlikely but if it were to happen - seized bearings, for example - an overtemperature thermal protector should shut down the heating element or entire oven. Some of these may not be self resetting (thermal fuse).

    Hot plates, waffle irons, broilers, deep friers, rice and slow cookers, woks

    These are all just a single or dual heating element, thermal protector (not all will have one), and an adjustable (usually) thermostat. As usual, check the cord and plug first, and then each of the other parts with an ohmmeter.

    Where a NiChrome coil type heating element is used, a break will be obvious. If it is very near one end, then removing the short section and connecting the remainder directly to the terminal will probably be fine. See the section: Repair of broken heating elements.

    For appliances like waffle irons, burger makers, and similar types with two hinged parts, a broken wire in or at the hinge is very common.

    Note that since these operate at high temperatures, special fiberglass (it used to be asbestos) insulated wiring is used. Replace with similar types. Take extra care in reassembly to avoid shorted wires and minimize the handling and movement of the asbestos or fiberglas insulated high temperature wiring.

    Popcorn poppers (oil type)

    An Oil popper is basically an electric frying pan with a built-in stirrer and cover. The internal parts are accessed from the bottom: Heating coil, thermostat and thermal protector, and small gear-motor similar to that used in a clock or timer. Take care to note the orientation of the motor when removing and to not damage any seals (you don't want oil seeping down under!).

    As always, check for bad connections if the popper is dead or operation is erratic.

    Problems with heating can arise in the heating element, thermostat, and thermal protector.

    If the stirrer doesn't turn, a gummed up motor or stirrer shaft (since these are only used occasionally) may be the problem. See the chapter: Motors 101.

    Popcorn poppers (air type)

    Air poppers combine a heating element and blower to heat corn kernels without the need for any unhealthy oil. Of course, you probably then drown the popcorn in butter and salt, huh? Admit it! :-).

    As always, check for bad connections if the popper is dead or operation is erratic.

    Problems with heating can arise in the heating element, thermostat, and thermal protector.

    The motor is probably a small PM DC type and there will then be a set of diodes or a bridge rectifier to turn the AC into DC. Check these and for bad bearings, gummed up lubrication, or other mechanical problems if the motor does not work or is sluggish. See the chapter: Motors 101.

    Electrical heating tape

    This is the stuff used to keep your pipes from freezing when it is -25 degrees F in the Sun. :-) They come in various lengths and plug into a normal 115 VAC outlet. There may or may not be a thermostat (you may serve that purpose!).

    Obviously, if you can disassemble the unit to the point of access to the connections to the heating element, a simple continuity check of each component (heating element, thermostat/switch, fuse if any, line cord, etc.) will identify whether there is a bad part. Similarly, if there is no switch, thermostat, or any other accessible parts - the entire thing is a sealed glob with a line cord - if there is no continuity, it is bad.

    However, for the more general case, there are two ways to test a heat tape if whether it is alive or not isn't obvious by feel and you can't get inside. If you cannot get to the connection to the actual heating element, then the tests need to be performed with any power switch or thermostat in the 'on' position. However, it may not be possible to get a thermostat to go on if you are inside a nice heated house. It may need to be bypassed or the tests run where it is cold!

    1. Check for continuity at the plug. If you have an 'on' indicator that is a neon bulb (or no indicator), it won't affect this reading. However, if it is an incandescent bulb, go to (2).

    2. Test for heating action. What a concept? :) Put the sensing end of a thermometer against the heat tape and wrap the whole thing in an insulating material like fiberglass or even bubble wrap or styrofoam peanuts. Let the temperature stabilize and record it. Then turn the heat tape on or off depending on what state it was in. If it is working you should see a perhaps small, but noticeable change in temperature.
    The actual resistance element in the heating tape really cannot be repaired safely so replacement is the only option if you find a problem there. The only possible repair would be to a cord that got cut or damaged resulting in a break in the wire or a faulty thermostat.

    Automatic bread machines

    These are actually kind of clever and according to Consumer Reports, may actually make quite decent bread. In a nutshell (whether there are nuts in your bread or not), you dump in the raw ingredients, close the lid, and the bread machine does the rest, signaling when done. Unfortunately, sometimes things go wrong and you are left with a half-baked or half-beaten mess to clean up.

    The basic components of a bread machine are:

    It should be straightforward to locate bad parts not related to the actual microprocessor - test the heating element(s) and motor for continuity and shorts. Tset the triacs (if any) for shorts as well (the resistance between any pair of pins should be more than a few ohms). However, it may be hard to be sure that something else wasn't the cause if a bad part is found. For example, a blown thermal fuse (a very common failure) may be an isolated event (these things can just grow tired of life) but could also mean that the electronic thermostat sensor isn't working or a triac or relay is stuck in the 'on' position.

    Like any other electronic device, a power surge or lightning strike can wipe out the controller rendering the bread machine dead as, well, a loaf of bread. Unless there are obviously blown parts AND you get very lucky, the only solution with any likelihood of success is a total brain transplant (controller board replacement) - which is probably more expensive than a new bread machine.

    Sewing machines

    Moth mechanical and electrical problems are possible. (Note: we are not going to deal with fancy computerized equipment as this is probably better left to a professional except for the more obvious problems like a bad cord or plug.)

    I have a 1903 Singer foot-pumped sewing machine which we have since electrified and still runs fine. A couple of drops of sewing machine or electric motor oil every so often is all that is needed. They were really built well back then.

    Although the appearance of the internal mechanism may appear intimidating at first, there really is not that much to it - a large pulley drives a shaft that (probably) runs the length of the machine. A few gears and cams operate the above (needle and thread) and below (feet and bobbin) deck mechanisms. Under normal conditions, these should be pretty robust. (Getting the adjustments right may be another story - refer to your users manual). Sometimes if neglected, the oil may seriously gum up and require the sparing use of a degreaser to loosen it up and remove before relubing.

    If the motor spins but does not turn the main large pulley, the belt is likely loose or worn. The motor will generally be mounted on a bracket which will permit adjustment of the belt tension. The belt should be tight but some deflection should still occur if you press it gently in the middle.

    If the motor hums but nothing turns, confirm that the belt is not too tight and/or that the main mechanisms isn't seized or overly stiff - if so, it will need to be cleaned and lubrication (possibly requiring partial disassembly).

    The electric motor is normally a small universal type on a variable speed foot pedal (see the section: Wiring a sewing machine speed control).

    If the motor does not work at all, bypass the foot pedal control to confirm that it is a motor problem (it is often possibly to just plug the motor directly into the AC outlet). Confirm that its shaft spins freely. All normal motor problems apply - bad wiring, worn brushes, open or shorted windings, dirty commutator. See the section: Problems with universal motors.

    Wiring a sewing machine speed control

    This assumes a basic sewing machine (nothing computer controlled) with a normal universal series wound motor (115 VAC).

    The common foot pedals are simply wirewound rheostats (variable resistors) which have an 'off' position when the pedal is released. They are simply wired in series with the universal motor of the sewing machine (but not the light) and can be left plugged in all the time (though my general recommendation as with other appliances is to unplug when not in use.

    While not as effective as a thyristor type speed controller, these simple foot pedals are perfectly adequate for a sewing machine. There are also fancier speed controls and using a standard light dimmer might work in some cases. However, there are two problems that may prevent this: the sewing machine motor is a very light load and it is a motor, which is not the same as a light bulb - it has inductance. The dimmer may not work, may get stuck at full speed, or may burn out.


    A variety of types of drive mechanisms are used in electric shavers:

    1. Vibrator (AC only): These (used by Remington among others) consist of a moving armature in proximity to the pole pieces of an AC electromagnet. The mass and spring are designed so that at the power line frequency, the armature vibrates quite strongly and is linked to a set of blades that move back and forth beneath the grille.

      If dead, check for continuity of the plug, cord, switch, and coil. IF sluggish, clean thoroughly - hair dust is not a good lubricant. Sliding parts probably do not require lubrication but a drop of light oil should be used on any rotating bearing points.

      Note that since a resonance is involved, these types of shavers may not work well or at all on foreign power - 50 Hz instead of 60 Hz or vice versa - even if the voltage is compatible.

    2. Universal motor (AC or DC): Very small versions of the common universal motors found in other appliances. A gear train and linkage convert the rotary motion to reciprocating motion for shavers with straight blades or to multiple rotary motion for rotary blade shavers. These may suffer from all of the afflictions of universal motors; bad cords, wires, and switches; and gummed up, clogged, or worn mechanical parts. Also see the sections on the appropriate type of motor. Take care when probing or disassembling these motors - the wire is very fine any may be easily damaged - I ruined an armature of a motor of this type by poking where I should not have when it was running - ripped all the fine wires from the commutator right off.

    3. DC PM motor: Often used in rechargeable shavers running of 2 or 3 NiCd cells. These may suffer from battery problems as well as motor and mechanical problems. One common type is the Norelco (and clone) rotary shaver. See the chapters on Batteries and AC Adapters as well as the sections on "Small permanent magnet DC motors".

      A shaver that runs sluggishly may have a dead NiCd cell - put it on charge for the recommended time and then test each cell - you should measure at least 1.2 V. If a NiCd cell reads 0, it is shorted and should be replaced (though the usual recommendation is to replace all cells at the same time to avoid problems in the future).

      Note that in terms of rechargeable battery life, shavers are just about optimal as the battery is used until it is nearly drained and then immediately put on charge. The theoretical 500 to 1000 cycle NiCd life is usually achieved in shaver applications.

    Sam's comments on electric shavers

    My first electric was a Remington plug-in type which served me well for several years. I called it the "lawn mower" due to the noise and vibration (it also gave a decent massage). But for the better part of 30 years, I've used the same Norelco "Rotary Triple Header with floating heads and self sharpening blades". (Actually, two of them - the other acquired in the mid-80s at a garage sale for $2). It is probably true that these shavers never produced the kind of close shave promoted by whatever national organization is in charge of hair care merchandising where each whisker is expected to be cut off 3 inches below the skin line to give a half hour more of freedom from stubble. However, unlike a blade razor, with an electric, it isn't necessary to devote one's attention 100 percent to shaving to avoid a bloody mess. This effectively results in more time in the day since other things can be done at the same time (we won't say exactly what other things).

    Over 30 years, I did have to replace the rechargeable NiCd batteries 2 or 3 times (readily available from any electronics distributor and easily installed in about 10 minutes), disassembled and cleaned the interior and lubricated the gears and motor several times (quite straightforward for anyone with even minimal mechanical skills and a Philips screwdriver), and repaired a plastic part of the on/off switch. But there was no need to buy replacement items at 6 to 24 month intervals as has been suggested is required for the current crop of electric shavers. I'm still using the original blades (they really do stay sharp, but have worn down somewhat). When the need does arise, there are still after-market replacement blade/header sets available for around $20.) Have the manufacturers of electric shavers so de-engineered mechanical designs to support the sales of expensive consumables like blades?

    The built-in charger is dirt simple consisting of a bridge rectifier and resistor, not the sophisticated microprocessor controlled affair of modern shavers that apparently don't provide any essential benefits. I really don't find the pressing need to upgrade the operating system in my shaver to MS Vista! :) Yes, it was my responsibility to plug in the charger every week or so when the batteries ran down. It did take 24 hours for a complete recharge but believe it or not, this was rarely a problem since I don't shave more than once a day (and the shaver would run plugged in even if the batteries were nearly flat if there was a pressing need). I routinely got the 500 or so charge/discharge cycles expected of NiCd batteries without the complexity that appears designed primarily to enhance the manufacturer's bottom line by making it difficult or impossible to perform simple maintenance or battery replacement with expendibles that make the overall cost of ownership higher than for blades!

    Comments on Norelco shaver maintenance and repair

    The following applies to newer models that have more computing power in their battery chargers than 5 month old PCs, not those with just a bridge rectifier for electronics. :)

    (Merged comments from: Jerry Greenberg ( and Paul Grohe (

    I used to service some of the Philips models of shavers. These are the same as the Norelco. When the batteries are dead the shaver will not run. The shaver has a sophisticated uPC (for what it does) that manages its operation. When it sees the batteries as dead, it will inhibit the shaver from being able to run. If the batteries are shorted, nothing will even light up at all.

    The little "power supply" does not have enough "juice" to run the motor. The motor runs off the cells. If the cells are *dead* (shorted), nothing will work.

    You can "test" the power supply by either listening carefully, or, holding it up to an AM (MW) radio tuned off to the end (no station) while plugging the razor in.

    If the charger is okay, but the cells are shorted or weak, you will hear a quick "ping" followed by a stretched-out, "constipated" squeal. This is the little switching power supply quitting under the "dead weight" of the cells.

    A "good" razor will have a nice, steady squeal (or "hiss" on the radio).

    Once the shaver is opened, if you are mechanically skilled, it is worth the effort to disassemble the top head assembly where the motor goes in to, and do a thorough cleaning. You can lubricate the gears and shafts with a very light silicon lubricant. The motor is held in position with two spring clips. Care must be taken to not break the plastic pieces.

    Everything snaps together. Opening the case is usually the toughest part.

    And take it apart over a paper towel. Powdered hair will fall out all over the place as you take it apart. Keep a dust-buster or vacuum near by to suck up any escaping "dust". The stuff is worse than wallboard dust!

    If you do any soldering, do it in a well ventilated place. Burning hair is not a pleasant smell! I would take the shaver completely apart (like a watch) and clean all the pieces, including the circuit board and display. Everything would be dried off, mechanical parts lubricated, new batteries installed, new blades, and then the complete re-assembly would be done. Once used to this type of work, a complete overhaul takes less than about 30 to 40 minutes. Most of the time, it only needed new batteries and blades. The shaver would be good for another few years. This especially pays for the more expensive models.

    I'm on my third set of cells after 12 years. Last month I installed new 1200 mA/H NiMh cells.

    Also: While you have the motor removed - it is a good idea to "clean" the motor brushes by connecting it to an adjustable power supply and slightly over-voltaging it to make it run faster than normal (with no load). Run it full-out for about 5 minutes (or until it runs smoothly). Run it in both directions, too. This will eliminate any "chugging", stalling or rough starts you may be experiencing with older units.

    As for original parts, Norelco will supply them if the shaver model is less than about 5 to 7 years old. Usually the replacement parts are not expensive in relation to replacing the shaver. As for replacement parts, they would only supply the complete circuit boards, batteries, and any mechanical parts if they are defective.

    Mine is as good as new now!

    Electric toothbrushes

    These are basically similar to any other small battery operated appliance or tool such as a screwdriver or drill. The permanent magnet motor runs off of rechargeable NiCd batteries and cause the bristles or whatever to oscillate, rotate, or vibrate. Interchangeable 'brush' units allow each member of the family to have their own. Coupling to the internal battery is often via a 'contactless' mechanism using a pair of coils to transfer AC inductively. Inside the hand unit, this is rectified to charge the NiCd (usually) battery. See the section: Inductively coupled charging circuit for an example of one such design.

    Problems can occur in the following areas:

    Since these must operate in a less than ideal environment (humid or actual waterlogged!), contamination and corrosion is quite possible if the case is not totally sealed. Some of the switches may be of the magnetic reed type so that there don't need to be any actual breaks in the exterior plastic housing. Even so, the motor shaft probably passes through a bushing in the housing and this will leak eventually.

    Of course, getting inside may prove quite a challenge and in general one must consider the hand unit to be a throw-away item since it is generally glued together - permanently. While it is possible to use a hacksaw to carefully cut around the case, the resulting repair once the thing is put back together will be decidedly of the 'Jerry-rigged' type and sealing will be difficult and long term reliability and safety would be questionable.

    (From: Jeff & Sandy Hutchinson (

    It's darned near impossible to replace the batteries on the Interplak toothbrush without destroying the recharging circuit. The base of the hand unit has a little pickup coil in it, and when you unscrew the cap to get at the batteries, you break the connections to the pickup coil. Best to do an exchange with the factory.

    (From: Bill Finch (

    I've done this twice. Use a tubing (or pipe) cutter at the seam. Rotate and tighten the cutter slowly until the thing falls apart. Fish out the guts and resolder a new battery in place. Slip everything back into the lower tube. Glue the top back on with PVC pipe sealant. It helps to make a simple jig to hold the top steady while the PVC cement sets. Try not to get excess cement on the external plastic or you wife will complain. A good trick here is to mask with drafting tape or whatever.

    If this fails just buy a new toothbrush.

    (From: Chip Curtis (

    I had a problem with my Braun and found that the unit's PCB was rather wet. After drying it out and coating it the unit still turned on from time to time and I noticed that during the false runs the transistor was not saturating. It didn't take long to see that the problem is caused by the transistor's base being left wide open. Any noise on the base or small current flow from PCB leakage will cause the transistor to fire and the brush noise is enough to keep it triggering and running on.

    The fix; tack a 1M or whatever (no smaller than 47K) resistor from the base of the transistor to ground. The pull-down won't hurt current consumption when the unit is off because the reed switch is open, and the small bias won't make much of a difference when the unit is running.

    Inductively coupled charging circuit

    This was found in an Interplak Model PB-12 electric toothbrush but similar designs are used in other appliances that need to be as tightly sealed as possible.

    A coil in the charging base (always plugged in and on) couples to a mating coil in the hand unit to form a step down transformer. The transistor, Q1, is used as an oscillator at about 60 kHz which results in much more efficient energy transfer via the air core coupling than if the system were run at 60 Hz. The amplitude of the oscillations varies with the full wave rectifier 120 Hz unfiltered DC power but the frequency is relatively constant.

         E1           CR2          R1                                E3
      AC o----+----+--|>|-----+---/\/\---+----+----------------+-------+  Coupling
              |   ~|  CR1     |+   1K    |    |                |        ) Coil
            +-+-+  +--|<|--+  |          |    / R2             |        ) 200T
        RU1 |MOV|     CR3  |  |      C1 _|_   \ 390K           |        ) #30
            +-+-+  +--|>|--|--+   .01µF ---   /          CR5   |     E4 ) 1-1/2"
           E2 |    |  CR4  |       250V  |    \ MPSA +---|<|---|----+--+   
      AC o----+----+--|<|--+             |    |   44 |         |    |
                  ~        |-     R3     |    | Q1 |/ C    C3 _|_  _|_ C2
                           +-----/\/\----+----+----|     .1µF ---  --- .0033µF
          CR1-CR4: 1N4005  |     15K               |\ E  250V  |    |  250V
                           |                R4       |         |    |
    The battery charger is nothing more than a diode to rectifier the signal coupled from the charging base. Thus, the battery is on constant trickle charge as long as the hand unit is set in the base. The battery pack is a pair of AA NiCd cells, probably about 500 mA-h.

    For the toothbrush, a 4 position switch selects between Off, Low, Medium, and High (S1B) and another set of contacts (S1A) also is activated by the same slide mechanism. The motor is a medium size permanent magnet type with carbon brushes.

                                  S1A  +--o->o
                     D1           _|_  |       R1,15,2W
                 +---|>|---+------o o--+   L o---/\/\---+
        Coupling |         |                   R2,10,2W |
           Coil  +        _|_ BT1          M o---/\/\---+
           120T (          _  2.4V                      |
            #30 (         ___ .5A-h        H o----------+
         13/16"  +         _                            |
                 |         |        +-------+           |
                 +---------+--------| Motor |-----------+

    Braun electric toothbrush repair

    (From: David DiGiacomo (

    This Braun electric toothbrush (original model) would turn itself on and keep running until its batteries were discharged.

    The toothbrush can be disassembled by pulling the base off with slip joint pliers (do not pull too hard because there is only about 1" of slack in the charging coil wires). With the base off, the mechanism slides out of the case.

    There is a simple charging circuit, charging LED, 2 NiCd cells, and a reed switch driving the base of an NPN transistor. The transistor collector drives the motor.

    I charged the battery, but the problem of the motor running with the reed switch open didn't recur until I held my finger on the transistor for about 10 seconds seconds. Grounding the transistor base turned it off again, and I could repeat this cycle. Since there wasn't anything else to go wrong I decided to replace the transistor. I couldn't read the marking, but it's in a SOT89 package and the motor current is 400-700 mA so it must be something like a BC868. However, I didn't have any surface mount or TO92 transistors that could handle the current, so I used a 2SD882 (small power tab package), which I was able to squeeze into some extra space in the center of the charging coil.

    Hand massagers

    These are simply motors with an off-axis (eccentric) weight or electromagnetic vibrators. If the unit appears dead, check the plug, cord, on/off switch, internal wiring, and motor for continuity. Confirm that the mechanical parts turn or move freely.

    Some have built in infra-red heat which may just be a set of small light bulbs run at low voltage to provide mostly heat and little light (a filter may screen out most of the light as well). Obviously, individual light bulbs can go bad - if they are wired in series, this will render all of them inert.

    At least one brand - Conair - has had problems with bad bearings. Actually, poorly designed sleeve bearings which fail due to the eccentric load. If you have one of these and it becomes noisy and/or fails, Conair will repair (actually replace) it for $5 if you complain in writing and send it back to them. They would like a sales receipt but this apparently is not essential.

    Hair dryers and blow dryers

    A heating element - usually of the NiChrome coil variety - is combined with a multispeed centrifugal blower.

    First determine if the problem is with the heat, air, or both.

    For heat problems, check the element for breaks, the thermal protector or overtemperature thermostat (usually mounted in the air discharge), the connections to the selector switch, and associated wiring.

    Newer models may have a device in the plug to kill power to the unit should it get wet. See the sections: "What is a GFCI?" and "The Ground Fault Circuit Killer (GFCK)".

    For air problems where the element glows but the fan does not run, check the fan motor/bearings, connections to selector switch, and associated wiring. Confirm that the blower wheel turns freely and is firmly attached to the motor shaft. Check for anything that may be blocking free rotation if the blower wheel does not turn freely. The motor may be of the induction, universal, or PM DC type. For the last of these, a diode will be present to convert the AC to DC and this might have failed. See the appropriate section for problems with the type of motor you have.

    The Ground Fault Circuit Killer (GFCK)

    Note: I have heard that the official name for these disasters is: Appliance Leakage Circuit Interrupter (ALCI). I like mine better. :)

    This safety 'enhancement' must have been designed by engineers with too much time on their hands (or the wrong sort of incentive bonus plan). Get a few drops of water on one of these appliances and it goes in the garbage.

    The irony is that once the GFCK blows, the owner is likely to just cut off the GFCK plug and replace it with a normal plug (rather than throwing the appliance away or having it properly repaired, as was no doubt the intent), thus eliminating the protection altogether!

    The GFCK (my designation) is a device contained in an oversize plug which is part of the cordset of some newer hand-held (at least) appliances that may be used in wet areas like kitchens and baths but where there may be no GFCI protection (see the section: What is a GFCI?. I first ran across one of these on a late model Conair blow dryer (which is why this section on GFCKs is here rather than with the GFCI information).

    In a nutshell, the GFCK permanently disconnects power to the appliance - at the plug - should electrical leakage of more than a few milliamps be present within the appliance. Unlike a GFCI, ther is NO reset button and no way to get inside short of drilling out the rivets holding the plug together! In fact, the unit I dissected uses an SCR to grossly overdrive and blow out a normal resistor which by its placement holds a mechanical latch in place for a pair of contact releases that disconnect the plugs prongs from the wires of the cord. With the resistor gone, the prongs of the plug go nowhere so everything beyond them becomes totally dead, electrically - forever. Thus, even if dropped into a bathtub, the appliance will not cause electrocution. Sorry, these can't be used as part of murder mystery plots!

    Admittedly, the GFCK works regardless of whether the outlet the appliance is plugged into is 2-prong, 3-prong, correct or reverse polarity, or GFCI protected, and thus provides a high level of safety. But, this may be taking cost reduction to an extreme rather than providing a resettable basic GFCI (just H-G faults). Having said that, there is merit to disabling the appliance permanently since there is no way to know how much damage may have been done internally by the water (or whatever caused the GFCK to trip) and its safety may always be suspect.

    All this is mounted inside the plug:

                 <------------------------ Plug ---------------------->|<- Cord ->
                  ___                                                  :
     Plug (H) <---o o---+-----------------------------------------------o H
                  CB1*  |     =====        R1*                         :
                        +-----^^^^^-------/\/\-------------+-------+   :
                        |      L1                          |       |   :
                        |  120 T, #26, 3 layers       Q1 __|__     |   :
                        |  .1"x1" ferrite core    T34557 _\_/_     |   :
                        |                                / |       |   :
                 MDC +--+--+   +-----+------+------+----'  |   C2 _|_  :
                Z251 | MOV |   |     |      |      |       | .1µF ---  :
                     +--+--+   |     /      |      |       | 250V  |   :
                        |      |  R2 \  C1 _|_ D1 _|_      |       |   :
                        |      | 300 / .22 ---    /_\      |       |   :
                        |      |     \  µF  |      |       |       |   :
                        |      |     |      |      |       |       |   :
                        +------|-----+------+------+-------+-------+   :
                  ___   |      |                1N4004                 :
     Plug (N) <---o o---+---------------------------------------------------o N
                  CB2*         |             R3  1K                    :
                               +--------------/\/\-------------------------o G
    * R1 is positioned to hold the latch for CB1 and CB2 in place until it vanishes in a puff of smoke. It is interesting to note that R1 is NOT a flameproof resistor - it looks like an ordinary 1/8 W carbon composition type.

    The Ground wire in the cord (G) goes from the circuit in the plug back to the metal parts of the dryer (though as usual with a modern appliance, it is mostly made of plastic). Note that there is no Ground wire to the outlet - just to the appliance. The theory goes that should the device get wet, current is more likely to flow to the nearby metal parts and via the cord's Ground wire to the GFCK than to some other earth ground (including a person touching an earth ground). In fact, this device does NOT sense a current imbalance like a true GFCI - just leakage to its internal Ground wire, but under realistic circumstances, this should be a reliable indication of a fault.

    A fault condition would result in current flowing between H and G in the cord. When this exceeds about 3 mA, the SCR (Q1) triggers putting R1 essentially across the line (maybe limited a bit by L1). R1, which was physically holding the latch for the plug circuit breakers CB1 and CB2, now explodes releasing both these contacts. Power is shut off to the appliance - permanently! Hopefully, the plug doesn't catch fire in the process! :)

    As noted, cutting off this fancy plug and replacing it or the entire cordset with a conventional one provides the same level of safety IF AND ONLY IF the appliance is used ONLY in a GFCI protected outlet (the cord Ground wire is left disconnected in this case or can be attached to the third prong of a three prong plug). The alternative of installing a 3-prong plug on the appliance and then only using it in a properly grounded 3-prong outlet doesn't provide the same protection as there can still be enough leakage to be lethal without blowing a fuse or tripping a breaker (and the ground wire in the sample I have wouldn't be adequate to carry a major fault current anyhow).

    And, guess what? This Conair blow dryer died not because the GFCK had been activated, but because the soldering to the R1 was defective and it pulled loose!

    Curling irons

    These are just a sealed heating element, switch, and thermal protector (probably). Check for bad connections or a bad cord or plug if there is not heat. A failed thermal protector may mean other problems. While these are heating appliances, the power is small so failures due to high current usually do not occur.

    VCR cassette rewinders

    Cassette rewinders typically consist of a low voltage motor powered from a built in transformer or wall adapter, a belt, a couple of reels, and some means of stopping the motor and popping the lid when the tape is fully rewound.

    Note that some designs are very hard on cassettes - yanking at the tape since only increased tension is used to detect when the tape is at the end. These may eventually stretch the tape or rip it from the reel. I don't really care much for the use of tape rewinders as normal use of rewind and fast forward is not a major cause of VCR problems. Sluggish or aborted REW and FF may simply indicate an impending failure of the idler tire or idler clutch which should be addressed before the VCR gets really hungry and eats your most valuable and irreplaceable tape.

    Problems with tape rewinders are usually related to a broken or stretched belt or other broken parts. These units are built about as cheaply as possible so failures should not be at all surprising. The drive motor can suffer from any of the afflictions of similar inexpensive permanent magnet motors found in consumer electronic equipment. See the section: Small permanent magnet DC motors. A broken belt is very common since increased belt (and tape) tension is used to switch the unit off (hopefully). Parts can pop off of their mountings. Flimsy plastic parts can break.

    Opening the case is usually the biggest challenge - screws or snaps may be used. Test the motor and its power supply, inspect for broken or dislocated parts, test the power switch, check and replace the belt if needed. That is about it.

    Vacuum cleaners, electric brooms. and line powered hand vacs

    Despite all the hype surrounding vacuum cleaner sales, there isn't much difference in the basic principles of operation between a $50 and $1,500 model - and the cheaper one may actually work better.

    A vacuum cleaner consists of:

    1. A cordset: Broken wires or damaged plugs are probably the number one problem with vacuums as they tend to be dragged around by their tails! Therefore, in the case of an apparently dead machine, check this first - even just squeezing and bending the wire may produce an instant of operation - enough to verify the cause of the problem.

    2. A power switch: This may be a simple on/off toggle which can be tested with a continuity checker or ohmmeter. However, fancy machines with powered attachments may have interlocks or switches on the attachments that can also fail. Where multiple attachment options are present, do your initial troubleshooting with the minimal set as this will eliminate potential sources of additional interlock or switch complications. With 'microprocessor' or 'computer' controlled vacuum cleaners, the most likely problems are not the electronics.

    3. A high speed universal motor attached to a centrifugal blower wheel: As with any universal motor, a variety of problems are possible: dirt (especially with a vacuum cleaner!), lubrication, brushes (carbon), open or shorted windings, or bad connections. See the section: Problems with universal motors.

    4. A belt driven carpet brush (uprights):. The most common mechanical problem with these is a broken rubber belt. (One person who shall remain nameless, mistook the end of the broken belt for the tail of a mouse and promptly went into hysterics!). Replacements for these belts are readily available.

    5. Power nozzles and other powered attachments: Some of these are an attempt to give canister type vacuum cleaners the power of an upright with its directly powered carpet brush. Generally, these include a much smaller motor dedicated to rotating a brush. Electrical connections are either made automatically when the attachment is inserted or on a separate cable. Bad connections, broken belt, or a bad motor are always possibilities.

    6. A bag to collect dirt: Vacuum cleaners usually do a poor job of dust control despite what the vacuum cleaner companies would have you believe. Claims with respect to allergies and other medical conditions are generally without any merit unless the machine is specifically designed (and probably very expensive) with these conditions in mind. If the vacuum runs but with poor suction, first try replacing the bag.

    Vacuum cleaner mechanical problems

    1. Poor suction: Check the dirt bag and replace if more than half full. Check for obstructions - wads of dirt, carpet fibers, newspapers, paper towels, etc.

    2. Poor pickup on floors: Broken or worn carpet brush belt. There should be some resistance when turning the carpet brush by hand as you are also rotating the main motor shaft. If there is none, the belt has broken and fallen off. Replacements are readily available. Take the old one and the model number of the vacuum to the store with you as many models use somewhat similar but not identical belts and they are generally not interchangeable. To replace the belt on most uprights only requires the popping of a couple of retainers and then removing one end of the carpet brush to slip the new belt on.

    3. Vacuum blows instead of sucks: First confirm that the hose is connected to the proper port - some vacuums have easily confused suction and blow connections. Next, check for internal obstructions such as wads of dirt, balls of newspaper, or other items that may have been sucked into the machine. Note that it is very unlikely - bordering on the impossible - for the motor to have failed in such a way as to be turning in the wrong direction (as you might suspect). Furthermore, even if it did, due to the design of the centrifugal blower, it would still suck and not blow.

    4. Broken parts: Replacements are available for most popular brands from appliance repair parts distributors and vacuum/sewing machine repair centers.

    Vacuum cleaner electrical problems

    1. Bad cord or plug: This is the number one electrical problem due to the abuse that these endure. Vacuum cleaners are often dragged around and even up and down stairs by their tails. Not surprisingly, the wires inside eventually break. Test with a continuity checker or ohmmeter. Squeezing or bending the cord at the plug or vacuum end may permit a momentary spurt of operation (do this with it plugged in and turned on) to confirm this diagnosis.

    2. Bad power switch: Unplug the vacuum and test with a continuity checker or ohmmeter. If jiggling the switch results in erratic operation, a new one will be required as well.

    3. Bad interlocks or sensors: Some high tech vacuum cleaners have air flow and bag filled sensors which may go bad or get bent or damaged. Some of these can be tested easily with an ohmmeter but the newest computer controlled vacuum cleaners may be more appropriate to be repaired by a computer technician!

    4. Bad motor: Not as common as one might think. However, worn carbon brushes or dirt wedged in and preventing proper contact is possible and easily remedied. See the section: Problems with universal motors.

    5. Bad internal wiring: Not that likely but always a possibility.

    Vacuum cleaner hose damage

    "We have been quoted a price of $100 to replace the hose on our Panasonic (Mc-9537) vacuum cleaner. It has a rip in it; next to the plastic housing where the metal tubing starts. Does anyone know if there is a more economical way to solve this problem?"

    I have always been able to remove the bad section and then graft what is left back on to the connector. Without seeing your vacuum, there is no way to provide specific instructions but that is what creativity is for! :-) It might take some screws, tape, sealer, etc.

    $100 for a plastic hose is obviously one approach manufacturers have of getting you to buy a new vacuum - most likely from some other manufacturer!

    Note: Some vacuum cleaners with power nozzles use the coiled springs of the hose as the electrical conductors for the power nozzle. If you end up cutting the hose to remove a bad section, you will render the power nozzle useless.

    High tech vacuum cleaners?

    Excerpt from a recent NASA Tech Brief:

    "The Kirby Company of Cleveland, OH is working to apply NASA technology to its line of vacuum cleaners. Kirby is researching advanced operational concepts such as particle flow behavior and vibration, which are critical to vacuum cleaner performance. Nozzle tests using what is called Stereo Imaging Velocity will allow researchers to accurately characterize fluid and air experiments. Kirby is also using holography equipment to study vibration modes of jet engine fans."

    I suppose there will be degree-credit university courses in the operation of these space age vacuums as well! --- sam

    Dustbusters(tm) and other battery powered hand vacs

    These relatively low suction battery powered hand vacuums have caught on due to their convenience - certainly not their stellar cleaning ability!

    A NiCd battery pack powers a small DC permanent magnet motor and centrifugal blower. A simple momentary pushbutton power switch provides convenient on/off control.

    Aside from obvious dirt or liquid getting inside, the most common problems occur with respect to the battery pack. If left unused and unplugged for a long time, individual NiCd cells may fail shorted and not take or hold a charge when the adapter is not plugged back into the wall socket. Sluggish operation is often due to a single NiCd cell failing in this way.

    See the appropriate sections on "Batteries" and "Motors" for more information.

    Dustbusters left on continuous charge and battery problems

    The low current trickle charger supplied with these battery operated hand-vacs allow Dustbusters and similar products to be be left on continuous charge so long as they are then not allowed to self discharge totally (left on a shelf unplugged for a long time). Older ones, in particular, may develop shorted cells if allowed to totally discharge. I have one which I picked up at a garage sale where I had to zap cells to clear a shorts. However, it has been fine for several years now being on continuous charge - only removed when used.

    While replacing only selected cells in any battery operated appliance is generally not recommended for best reliability, it will almost certainly be much cheaper to find another identical unit at a garage sale and make one good unit out of the batteries that will still hold a charge. It is better to replace them all but this would cost you as much as a new Dustbuster.

    The NiCd cells are soldered in (at least in all those I have seen) so replacement is not as easy as changing the batteries in a flashlight but it can be done. If swapping cells in from another similar unit, cut the solder tabs halfway between the cells and then solder the tabs rather than to the cells themselves if at all possible. Don't mess up the polarities!

    In the case of genuine Dustbusters, where a new battery is needed and you don't have a source of transplant organs, it may be better to buy the replacement cells directly from Black and Decker. They don't gouge you on NiCd replacements. B&D is actually cheaper than Radio Shack, you know they are the correct size and capacity, and the cells come with tabs ready to install. They'll even take your old NiCds for proper re-cycling.

    Floor polishers

    A relatively large universal motor powers a set of counter-rotating padded wheels. Only electrical parts to fail: plug, cord, power switch, motor. Gears, shafts, and other mechanical parts may break.

    Heating pads

    Heating pads are simply a very fine wire heating element covered in thick insulation and then sealed inside a waterproof flexible plastic cover. Internal thermostats prevent overheating and regulate the temperature. The hand control usually provides 3 heat settings by switching in different sections of the heating element and/or just selecting which thermostat is used.

    There are no serviceable parts inside the sealed cover - forget it as any repair would represent a safety hazard. The control unit may develop bad or worn switches but even this is somewhat unlikely. It is possible to disassemble the control to check for these. You may find a resistor or diode in the control - check these also. With the control open, test the wiring to the pad itself for low resistance (a few hundred ohms) between any pair of wires). If these test open, it is time for a new heating pad. Otherwise, check the plug, cord, and control switches.

    Extended operationg especially at HIGH, or with no way for the heat to escape, may accelerate deterioration inside the sealed rubber cover. One-time thermal fuses may blow as well resulting in a dead heating pad. One interesting note: Despite being very well sealed, my post mortems on broken heating pads have shown one possible failure to be caused by corrosion of the internal wiring connections after many years of use.

    Electric blankets

    As with heating pads, the only serviceable parts are the controller and cordset. The blanket itself is effectively sealed against any repair so that any damage that might impact safety will necessitate replacement.

    Older style controllers used a bimetal thermostat which actually sensed air temperature, not under-cover conditions. This, it turns out, is a decent measurement and does a reasonable job of maintaining a comfortable heat setting. Such controllers produced those annoying clicks every couple of minutes as the thermostat cycled. Problems with the plug, cord, power switch, and thermostat contacts are possible. The entire controller usually unplugs and can be replaced as a unit as well.

    Newer designs use solid state controls and do away with the switch contacts - and the noise. Aside from the plug and cord, troubleshooting of a faulty or erratic temperature control is beyond the scope of this manual.

    Sunbeam warming blanket saga

    I have had 4 Sunbeam warming blankets in the last 10 years or so. None has lasted more than 2 years of (seasonal) use without requiring repair. Fortunately, they all had 5 year warranties. (The exact durations of how long they worked are from memory so they may not be totally accurate.):

    1. After 2 years, no heat. Repaired under warranty. Another year or two, no heat, repaired under warranty. Another year or so, no heat. Out of warranty.

    2. After 2 or 3 years, no heat. Repaired under warranty. Still working after several years but definitely not as strong heat-wise as it was when new.

    3. Worked fine for 2 years and set aside. Two years later, wanted to use it in place of the weaker #2, no heat. Repaired under warranty:

      I contacted Sunbeam through their Web site with model, date of purchase, lot number codes, and so forth. "Reply may take up to 3 business days.". After 3 days, received canned email that assumed I was an idiot and listed tests to make sure it wasn't my error. "Plug it in, make sure outlet is live, turn on control, fold in 3 to check for heat, etc.". I replied I had done all that and also measured the power being consumed and there was almost none. Nothing so far except an automated reply that it may take up to 3 business days. Really? I would assume that a company that cares about customer satisfaction would be able to handle this is a quicker manner, at least after the first canned reply. Perhaps their assessment was correct, I was an idiot for continuing to purchase Sunbeam blankets!

      After 4 days of not getting any reply, I went through the Web site again and re-entered all the information. Three days later, the reply was that the blanket was purchased in 2006 and out of warranty. So I don't know if they made a mistake or I entered some code incorrectly, I'll give them the benefit of the doubt. But I did give up on doing this via the Web and went the old fashioned way - by phone. That worked much better with relatively minimal wait times except once where they simply suggested trying at a later time due to high call volume.

      But after getting by the auto-attendant aroid - which wasn't bad as all it asked was what type of inquiry this was (warranty) and the type of product (bedding) - an actual genuine human being was on the other end of the line. This went smoothly and with a bit of prodding, he even offered to send a prepaid shipping label for returning the blanket.

      And what was sent back to me was an entirely new blanket with a more modern controller.

    4. Worked fine for 1.5 seasons, though I do think the heat is a bit lower than when new, fingers crossed on it dying completely. Of course, next season was definitely much weaker. Now attempting to get it repaired under warranty as the heat is down by at least 75 percent. The initial (when first turned on) original current was over 1 A; now it's around 0.25 A. No free shipping label though.

      This one was also replaced. For the record: Tested out of the box on Dec 27, 2016. Measured 2 A when first turned on dropping to around 1 A after a couple minutes with the blanket rolled up. I am currently using the replaced #3 so will not know how this one ages for awhile (hopefully). :)

    In all the cases of warranty repair so far, the remedy was listed as "Replaced Module" or "Replaced Blanket". As far as the module, there is a small circuit board in the plastic wart near the connector. After giving up on a warranty repair on #1, I opened the "module". There are perhaps a half dozen simple parts on the board, all tested good. I suspect bad connections to the heater wiring, or just deterioration of the wiring itself. (More on this malady below.) NONE of these blankets had been mistreated, gotten wet or even damp accidentally, or laundered. It's interesting that #3 and #4 were simply replaced instead of being repaired. That would make sense if it was heater wiring deterioration.

    For most of the repairs, I had to pay for shipping to the repair depot ($10-12) but Sunbeam paid for the return. On one, they sent a prepaid shipping label. Apparently that is at the local manager's discretion. They would not pay in the last instance.

    For #2-4, I measured the power used by the blankets when new to have something to compare to if they broke. When there was no heat, it dropped to almost zero. The controls behaved normally but had no effect on power. So this was NOT the normal reduction in heating over time that has been reported on some reviews of the Sunbeam blanket technology. For #4, the current was much lower than when originally tested.

    Sunbeam apparently uses what's known as "Positive Temperature Coefficient" or PTC material for the heater wiring. This provides a sort of self regulation - as it gets warmer, its resistance increases and limits the power and is touted as a safety feature. But apparently whatever they use does deteriorate with use. "Designed to degrade." :) Go figure. And for the technodweebs reading this, the heater seems to be driven with a very slow pulse width modulation having something like an 80 second cycle. So, on a control with 20 positions (L to H or 1 to 20) for example, when set to "L" or "1", the heat is on for 4 seconds and off for 76 seconds;) at "10", it 40 on and 40 off; on "H" or "20" or "PH" (if available), it's on continuously. Amazingly, this slow on-off is not detectable as any variation in warmth. This may be different when first turned on where it may run at around half power for a minute or so regardless of where the control(s) are set. The electronic controls are silent and there is no reliable way to know when it is actually drawing power without measuring it. The PAC 0530 Style X85A controllers are really nice with automatic time-of-day turn on with Preheat and selectable duration, but setting it up is confusing and the manual is pretty useless.

    Conclusions: Sunbeam heated blankets work really well when they work but expect them to have a 2 year life before needing repairs or replacement.

    How can Sunbeam remain the most popular brand? One reason is probably that reviews on sellers like Amazon are heavily weighted to satisfaction shortly after the purchase - most buyers don't write follow-up reviews when something breaks.

    My previous blankets were Fieldcrest. They lasted 15 to 20 years without any problems. These had mechanical controls which made periodic clicking sounds, there were lumpy over-temp thermostats in the wiring, but they kept on working. Eventually one failed from an open connection. The other started leaking blue-green goo from the thermostat lumps. :( :)

    My most recent one is from Soft Heat. It's kind of a step backwards without the fancy control, but is more conventional using high frequency PWM of current from a low voltage DC power supply.

    Update March, 2023: Sunbeam #4 is still working, though possibly slightly weaker than when new. "If it ain't broke, don't fix it." ;-) But now it does appear to finally be on its last legs.


    There are three common types:
    1. Wet pad or drum: A fan blows air across a stationary or rotating material which is water soaked. There can be mechanical problems with the fan or drum motor or electrical problems with the plug, cord, power switch, or humidistat.

    2. Spray: An electrically operated valve controls water sprayed from a fine nozzle. Problems can occur with the solenoid valve (test the coil with an ohmmeter), humidistat, or wiring. The fine orifice may get clogged by particles circulating in the water or hard water deposits. In cleaning, use only soft materials like pointy bits of wood or plastic to avoid enlarging the hole in the nozzle.

    3. Ultrasonic: A high frequency power oscillator drives a piezo electric 'nebulizer' which (with the aid of a small fan) literally throws fine droplets of water out into the room. Problems with the actual ultrasonic circuitry is beyond the scope of this manual but other common failures can be dealt with like plug, cord, fan motor, control switches, wiring, etc. However, if everything appears to working but there is no mist from the output port, it is likely that the ultrasonic circuitry has failed. See the section: Ultrasonic humidifiers for more details.

    Ultrasonic humidifiers

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (

    The components of the typical $45 unit are:

    The piezo transducer sets up a standing wave on the surface of the water pool. The level is sensed with a float-switch to ensure no dry-running (kills the piezo) and the blower/fan propels the tiny water droplets out of the cavity. A few manufacturers are nice enough to include a silly air filter to keep any major dust out of the 'output' - do clean/check that once in a while.

    Common problems:

  • Low output:

    CAUTION: Unless you know what you are doing (and have gotten shocked a few times in your life) DO NOT play with the piezo driver module. Most run at line voltage with sometimes 100+V on heatsinks - which are live.

  • No output:

    Note: piezo's in general are driven with voltage, as opposed to current. This explains why you can expect high voltages - even in otherwise low-voltage circuits. Case in point: the Polaroid ultrasonic sonar modules.

    (From: Dave VanHorn" (

    The Devilbiss units I used to repair, used about 1 W at 1 MHz (if I recall correctly into a thick barium titanate transducer. Their most common problem was cracked transducers.

    There was a shaped cavity above the transducer, I would guess some sort of Helmholtz resonator. You had to tune the operating frequency around to maximize the plume, and then trim for a certain plume height with the output drive.

    Don't stick your finger in the plume. Although the water is not hot, you will discover that your finger is mostly water. It's kind of like slamming your finger in a car door.

    (From: ActiveParticle.)

    Thinking about the above info on ultrasonic humidifiers and their power output, I decided to experiment with an ultra-cheap ultrasonic humidifier (useless for its intended application) and the clear polystyrene front cover of a CD jewel case. With the water level correctly set, placing the plastic sheet at the tip of the plume (cone shaped tip of the water) just above the transducer resulted in a cone-shaped section of material deforming outwards from the center of the wave. In normal operation, a mist of water is ejected from this location. The bottom of the sheet intersects the cone, and the truncated part of the wave doesn't like this and melts its way through. With the sheet in motion, a cut/trough about 3 mm wide appears. Moving slowly results in a slightly larger amount of material being displaced, up to about 5 mm. It doesn't go all the way through the plastic for some reason. The effect is the same as pressing a hot piece of metal against the plastic. The process is continuous and you can draw patterns by moving the material around on top of the standing wave. The deformed plastic was only warm, not hot, though it may have been cooled by contact with the water.

    After seeing this firsthand, you will never feel the urge to stick your finger in the plume again! I would not want to discover the effects of a larger humidifier or ultrasonic cleaner on parts of your body. This was with a $25 unit from a store closing special, so imagine what a larger, more powerful one could do!

    As an aside: Jewel cases are made from two kinds of polystyrene: General Purpose Polystyrene (GPPS) and High-Impact Polystyrene (HIPS). GPPS is crystal- clear but very brittle, and is used to mold the front and back covers. HIPS is translucent to opaque but more flexible, and is used to mold the tray. The tray needs to be flexible so that the tray hub can grab the disc hub without breaking off. It's unfortunate that the hinged part of the jewel case is made of such a brittle material, as it's always the first thing to break ;)

    Ultrasonic waterfalls?

    I don't suppose you are likely to encounter these but if you do, servicing procedures will be similar to those described in the section: Ultrasonic humidifiers.

    (From: Roger Vaught (

    At a local shop they sell small water fall displays made from limestone in a marble catch basin. These are made in China. They use a small water pump for the flow.

    When I first saw one I thought the store had placed dry ice in the cavity where the water emerged as there was a constant stream of cloud flowing from it. Very impressive. It turns out they use the ultrasonic piezo gizmo to make the cloud. The driver is a small 3 X 5 X 3 inch box with a control knob on top. If you look into the cavity you can see the piezo plate and a small red LED. The water periodically erupts into vapor. I haven't been able to get a close look at the driver so I can't tell where it is made or if there is a product name or manufacturer. They will sell that part of it for $150!

    Ultrasonic cleaners

    Ultrasonic cleaning is a means of removing dirt and surface contamination from intricate and/or delicate parts using powerful high frequency sound waves in a liquid (water/detergent/solvent) bath.

    An ultrasonic cleaner contains a power oscillator driving a large piezoelectric transducer under the cleaning tank. Depending on capacity, these can be quite massive.

    A typical circuit is shown below. This is from a Branson Model 41-4000 which is typical of a small consumer grade unit.

                   R1        D1
     H o------/\/\-------|>|----------+
             1, 1/2 W  EDA456         |
                   C1         D2      |
              |  .1 µF   |  EDA456    |  2  
              |  200 V   |      +-----+---+ T1      +---+------->>------+
              |    R2    |     _|_ C2      )::  o 4 |   |               |
              +---/\/\---+     --- .8 µF D ):: +----+   |               |
              |   22K          _|_ 200 V   )::(         +               |
              |   1 W           -      1 o )::(          )::           _|_
              +-----------------+---------+ ::( O        ):: L1        _x_ PT1
              |           R3    |        7  ::(          )::            |
              |      +---/\/\---+   +-----+ ::( 5       +               |
             C \|    | 10K, 1 W     |    F ):: +---+    |               |
           Q1   |--+-+--------------+  6 o )::     |    |               |
             E /|  |  D3     R4       +---+        +----+------->>------+
              |    +--|<|---/\/\--+  _|_
              |           47, 1 W |  ---       Input: 115 VAC, 50/60 Hz
              |                   |   |        Output: 460 VAC, pulsed 80 kHz
     N o------+-------------------+---+
    The power transistor (Q1) and its associated components form an self excited driver for the piezo-transducer (PT1). I do not have specs on Q1 but based on the circuit, it probably has a Vceo rating of at least 500 V and power rating of at least 50 W.

    Two windings on the transformer (T1, which is wound on a toroidal ferrite core) provide drive (D) and feedback (F) respectively. L1 along with the inherent capacitance of PT1 tunes the output circuit for maximum amplitude.

    The output of this (and similar units) are bursts of high frequency (10s to 100s of kHz) acoustic waves at a 60 Hz repetition rate. The characteristic sound these ultrasonic cleaners make during operation is due to the effects of the bursts occuring at 60 Hz since you cannot actually hear the ultrasonic frequencies they use.

    The frequency of the ultrasound is approximately 80 kHz for this unit with a maximum amplitude of about 460 VAC RMS (1,300 V p-p) for a 115 VAC input.

    WARNING: Do not run the device with an empty tank since it expects to have a proper load. Do not touch the bottom of the tank and avoid putting your paws into the cleaning solution while the power is on. I don't know what, if any, long term effects there may be but it isn't worth taking chances. The effects definitely feel strange.

    Where the device doesn't oscillate (it appears as dead as a door-nail), first check for obvious failures such as bad connections and cracked, scorched, or obliterated parts.

    To get inside probably requires removing the bottom cover (after pulling the plug and disposing of the cleaning solution!).

    CAUTION: Confirm that all large capacitors are discharged before touching anything inside!

    The semiconductors (Q1, D1, D2, D3) can be tested for shorts with a multimeter (see the document: Basic Testing of Semiconductor Devices.

    The transformer (T1) or inductor (L1) could have internal short circuits preventing proper operation and/or blowing other parts due to excessive load but this isn't kind of failure likely as you might think. However, where all the other parts test good but the cleaning action appears weak without any overheating, a L1 could be defective (open or other bad connections) detuning the output circuit.

    Where the transistor and/or fuse has blown, look for a visible burn mark on the transducer and/or test it (after disconnecting) with a multimeter. If there is a mark or your test shows anything less than infinite resistance, there may have been punch-through of the dielectric between the two plates. I don't know whether this could be caused by running the unit with nothing in the tank but it might be possible. If the damage is localized, you may be able to isolate the area of the hole by removing the metal electrode layer surrounding it to provide an insulating region 1/4 inch in diameter. This will change the resonant frequency of the output circuit a small amount but hopefully not enough to matter. You have nothing to lose since replacing the transducer is likely not worth it (and perhaps not even possible since it is probably solidly bonded to the bottom of the tank).

    When testing, use a series light bulb to prevent the power transistor from blowing should there be a short circuit somewhere (see the document: Troubleshooting and Repair of Consumer Electronic Equipment) AND do not run the unit with and empty tank.

    Here are some comments on ultrasonic cleaner repair. These would appear to be more for larger units but some of the info should apply to the small ones as well:

    (From: B. Clark (

    I spend a great deal of time repairing ultrasonic generators from sinks in medical use. I can tell you this. While different manufacturers use different circuits, the basic design is the same everywhere. The most common failure mode is that the switching transistor(s) are shorted. When this happens, does the fuse blow in your case? If this is true, replace the rectifier bridge. If the circuit contains extra diodes, check those for shorts as well. Always replace both transistors at the same time. You can use ECG/NTE equivalents, so long as both are the same - don't count on a new 2N6308 and an ECG283 working together in this case.

    Assuming the fuse never blows and the output frequency is around 40 to 50 khz, that rules out most of the small caps and resistors. Most generators that I have worked on produce a wave around 45 khz. A bad cap or resistor would cause it to be off frequency. The transducers should test as open. If they test as anything other than open on an multimeter (after allowing for settling as they are sensitive to vibration), then they could be bad. Transducer failure in my experience is not that common. It may suggest that your customer has been running the unit with the tank empty or only partially full.

    The circuit is tuned. 100% of all generators sent to me have one or more shorted transistors. The customer complaint is usually "No ultrasonic action" or "Weak ultrasonic action". 99.999% of the time, using an ohmmeter and replacing shorted semiconductors corrects the problem. I have had one unit where a precision cap was out of tolerance and detuned the circuit. One nearby hospital has sent in three 500 watt units that were ran without the transducers connected. In all cases, the fuse didn't blow, however each of the three caught on fire. One of these has a 1/8 in hole through a coil in the transformer.

    If any part drifts out of tolerance, the transistor will short. I have seen perfectly fine circuits short switching transistors when the unit is ran with no water in the tank. Do not attempt to run with one transducer. You will meet with failure. You should attempt to replace with the exact oem part when available. If you cannot find the original and have determined a adequate substitute, replace both of them.

    I keep mentioning transistors realizing that small units have only one. The units I work on have 4 to help generate 500 watts of power.

    Fog machines

    If you don't know what a fog machine does, you probably don't need to read this section!

    (From: Lance Edmonds (

    Essentially, a fog machine consists of a heater unit and a pump, plus electronics to control the heater temperature, and control how much fog juice is pumped through the heater.

    Most common failures are severed remote control leads, burned out pumps, or heating unit blockages.

    I've never seen one with a fan, but many folks use a fan to disperse the fog to the desired locations across a stage, etc.

    Unlike dry-ice, fog from a "fogger" rises and disperses quite quickly unless there is no ventilation... you can add some perfume (a few drops to the large tank) to reduce the "flavor" of the fog... when it's thick it tastes and smells horrid!


    I have examined a couple machines just out of personal curiosity. what I found was, and keep in kind that these were the lower end series, was basically a high power heater and a small fluid pump.

    From what I have seen , and can deduce, is that a high wattage heater block constantly is heating a 'transition' tube. Temperature is unknown, but it is damn hot. Temperature was controlled by a simple bimetal strip that looks like it activated a triac or similar device. Heater power was supplied by the triac. The fog fluid was pumped from the reservoir by a small fluid pump that ran on 6 to 12 VDC. The amount of fog produced was controlled by a large rheostat that had 12 volts applied to it, thereby creating a variable voltage divider. Activation of the 12 volts to the pump for fog was through a small relay that was able to be activated either through a switch added to the fog machine that completed a circuit, or the machine was set on a timer (internal) for fixed interval. Switch voltage was also 12 volts. Fog fluid was injected into the transition tube, and the output nozzle was significantly larger than the input. Estimated age of the machines was about 14 years or so.

    After I saw the insides of these things, I am amazed that they are able to demand $300 to $400 price tags. I am thinking about making one of these out of a water-cooled resistor and gravity feeding a gallon jug of the juice through an older 24 VAC sprinkler valve. One of those rainy day projects.

    From: (Don Klipstein)

    I once fixed a "Ness" brand "Mini-Fogger". Turned out there was a broken solder joint where the jack for the plug-in "remote" button went into a circuit board.

    Also sometimes, the pump sticks. Tapping the pump with a screwdriver while attempting to run it may unstick it.

    This thing is simple enough and made of parts that are reliable enough, with the possible exception of the pump. I would mostly look for broken connections or bad solder joints or clogs.


    Electric dehumidifiers use a refrigeration system to cool a set of coils which condenses water vapor. The heat is then returned to the air and it is returned back to the room. On the surface, this seems like an incredible waste of energy - cooling the air and heating it back up - but it is very effective at removing moisture. A typical large dehumidifier will condense something like 30 pints in 24 hours - which, unless you have it located over a drain - then needs to be dumped by hand.

    There is supposed to be a cutoff (float) switch to stop the dehumidifier when the container is full. Hopefully, it works (and you didn't neglect to install it when the unit was new!)

    Common problems with these units are often related to the fan, humidistat, or just plain dirt - which tends to collect on the cooling coils. The sealed refrigeration system is generally quite reliable and will never need attention.

    An annual cleaning of the coils with a soft brush and a damp cloth is a good idea. If the fan has lubrication holes, a couple of drops (but no more) of electric motor oil should be added at the same time.

    The fan uses an induction motor - shaded pole probably - and may require cleaning and lubrication. See the section: Problems with induction motors.

    The humidistat may develop dirty or worn contacts or the humidity sensing material - sort of like a hot dog wrapper - may break. If you don't hear a click while rotating the control through its entire range, this may have happened. If you hear the click - and the dehumidifier is plugged into a live outlet - but nothing happens, then there is probably a problem in the wiring. If just the fan turns on but not the compressor, (and you have waited at least 5 minutes for the internal pressures to equalize after stopping the unit) then there may be a problem with the compressor or its starting relay (especially if the lights dim indicating a high current).

    A very low line voltage condition could also prevent a refrigeration system from starting or result in overheating and cycling. A sluggish slow rotating or seized fan, or excessive dirt buildup may also lead to overheating and short cycling.

    A unit that ices up may simply be running when it is too cold (and you don't really need it anyway). Dehumidifiers may include sensors to detect ice buildup and/or shut off if the temperature drops below about 60 degrees F.

    Modern dehumidifiers are microprocessor-controlled so some of the timing may appear somewhat counter-intuitive, but it is designed to protect the compressor motor from rapid restarts.

    Frigidaire Dehumidifier

    The Frigidaire model FAD504DWD is microprocessor-controller with a single PCB with most of the smarts on it. The following probably also applies to the FAD301DWD, FAD704DWD, and other models manufactured around the same time (mid 2010s).

    A common problem with this unit is that the compressor will never stop running even if the unit is set to "Off". This turns out to be an easy fix but does require getting inside, which is not like it was in the good old days where there were just 4 screws and the cover came off. ;( ;-)

    Here is the general disassembly procedure, only steps 1-3 may be required to fix the compressor problem:

    1. Unplug the unit, remove the bucket and filter, and disconnect the hose if present.

    2. Remove 8 screws securing the back panel, which will then come off easily.

    3. Remove 4 screws securing the right-side panel. Tilt it out and press down to release the locking clips. Be gentle for this and similar steps below - these are cheap plastic!

    4. Remove 4 screws securing the left-side panel. Tilt it out and press down to release the locking clips. For some reason this one was more difficult to detach.

    5. Remove 4 screws securing the top and front panel. Jiggle these free as one unit and then disconnect the black multi-conductor connector between the control panel and control PCB.

    6. There are 3 interlocking posts holding these together. Use a suitable tool to gently press them out individually. Just attempting to separate the two parts will probably break them.

    7. Remove the black cover over the Control PCB by pressing on the two locking tabs and then sliding it toward the back of the unit.

    Reassemble in reverse order.

    Now for the repair:

    After step 3, above, a pair of Phillips head screws will be visible at the lower right of the evaporator coils. They will probably be somewhat corroded due to water dripping on them during normal operation, resulting in a bad ground connection between the two wires and the case. What brainiac design it that way? ;( ;-) Like wouldn't it make more sense to put the screws above the evaporator coils?

    Remove the screws and then carefully scrape off as much corrosion as possible with a file or other suitable tool. The best solution is to re-terminate the two wires into a single connection since the original crimps may be corroded inside. I used an AWG 14-16 #6 ring lug along with a pair of star washers on front and back with the original (cleaned up) screw to assure a solid connection. Coating the screw assembly with RTV may be beneficial to prevent water from messing it up again.

    If this doesn't cure the compressor always on problem, it may be that one of the relays on the Control PCB is intermittent or there are cold solder joints to it on the PCB. In that case, tapping on the relay may cause the problem to go away at least temporarily. I didn't see any cold solder joints on mine and reworking the screw connection seemed to fix the problem so I didn't pursue the relay issue.

    There are YouTube videos for these repairs but the camera work on some of them is so jerky that it's difficult to figure anything out. And one YouTuber commented that these dehumidifiers are impossible to get into non-destructively and throw-away, which is definitely bogus. It is under 5 minutes to remove all the covers without damaging anything.

    Garbage disposals

    A garbage disposal is just an AC induction motor driving a set of centrifugal hammers (they use to use sharp cutters but these were even more dangerous). The cutters throw the food against an outer ring with relatively sharp slots which break up the food into particles that can be handled (hopefully) by the waste system. However, always use generous amounts of cold water (which helps to cool the motor as well) and let it run for a while after there is nothing left in the disposal and it has quieted down. This will assure a trouble free drain. Otherwise, you may be inviting your friendly plumber over for a visit!

    Common problems with garbage disposals relate to three areas:

    Unless you are the truly die-hard doit-yourselfer, repair of disposals is probably not a good use of your time. The ultimate reliability of all but the most obvious and simple repairs is usually unknown and could be very short. However, other than time, there is nothing to be lost by at least investigating the source of the problem.

    Garbage disposal pops reset button but nothing blocked

    Even if nothing is stuck in it, is the rotor free - not too tight? If you have that little wrench that comes with many disposers , you should be able to turn the rotor relatively easily (I would say about 1 foot-pound of torque or less if your arm is calibrated). A tight bearing may be the result of a shaft seal leak - see the next section: Garbage disposal seizes repeatedly.

    The red reset button is a circuit breaker. Either the motor is drawing too much current due to a shorted winding or a tight bearing or the breaker is faulty. Without an ammeter, it will be tough to determine which it is unless the rotor is obviously too tight.

    If you have a clamp-on ammeter, the current while the motor is running should be less than the nameplate value (startup will be higher). If it is too high, than there is likely a problem with the motor. As an alternate you could try bypassing the circuit breaker with a slow blow fuse of the same rating as the breaker (it hopefully will be marked) or a replacement breaker (from another dead garbage disposal!. If this allows the disposer to run continuously your original little circuit breaker is bad. These should be replaceable.

    If the bearings are tight, it is probably not worth fixing unless it is due to something stuck between the grinding disk and the base. Attempting to disassemble the entire unit is likely to result in a leak at the top bearing though with care, it is possible to do this successfully.

    Garbage disposal is stuck - hums but does not turn

    Here are typical problems:

    "I need help. Our garbage disposal is stuck. It hums but doesn't turn. If I leave it on for more than a few seconds it trips the circuit breaker on the unit. Any tips on how to solve this shy of buying a new unit? The unit is 7 years old."

    "I have an ISE In-Sink-Erator (tm), Badger I model. I tried turning mine on a few minutes ago, the motor started then stopped and now nothing happens when I flip the wall switch, not even a click."

    Of course, first make sure there is nothing jamming it - use a flashlight to inspect for bits of bone, peach pits, china, glass, metal, etc. Even a tiny piece - pea size - can get stuck between the rotating disk and the shredder ring. WITH THE DISPOSAL UNPLUGGED OR THE BREAKER OFF, work the the rotor back and forth using the hex wrench that came with the unit or a replacement (if your unit is of the type that accepts a wrench from below. If it is not of this type, use the infamous broom handle from above.)

    The internal circuit breaker will trip to protect the motor if the rotor doesn't turn. Turn off the wall switch, wait a few minutes for the circuit breaker and motor to cool, and then press the red reset button underneath the disposal. If it does not stay in, then you didn't wait long enough or the circuit breaker itself is defective. Then, turn on the water and try the wall switch again (in-sink switch if it is a batch feed model).

    Assuming it is still tight with nothing stuck inside and/or jams repeatedly:

    (From: Rob-L (

    That's about how long it takes for the nut to rust away on the shredder disc of Insinkerator/Sears units. My comments will address ISE/Sears deluxe models with the stainless disc, for those who might have one.

    When the nut/washer rusts away, the disc will wobble and get jammed. With the power off, try to rock the disc inside the unit. You might need to wiggle the motor shaft with a 1/4" hex wrench under the unit.

    If you can free things up, and the disc can be rocked, it's the nut/washer. When that goes, so does the gasket, and unfortunately it requires total disassembly of the grinding chamber to replace the little gasket, because the disc will not come out otherwise. And if you don't replace the gasket, water/gunk will run down the motor shaft and into the motor. When those units go, you're better off to get a new disposer.

    I think they intentionally use a non-stainless steel nut, because otherwise the units would last a long time. Even the replacement nuts will corrode. The motor shaft will also corrode, but not as fast as the nut. With a stainless shaft and nut/washer, the disposer would give many more years of service. And that's why they don't make 'em that way. :)

    One part that is worth replacing is the mounting gasket. It's the part with the flaps that you feed things through. It gets cut-up and damaged by chlorine from sink cleaning or dishwasher discharge. (brittle, rough) It's a $4 part, usually available at Home Depot next to the new disposers, and it slips on in a matter of minutes -- you just disconnect the trap, then drop the disposer down by undoing the retaining ring. Swap the gasket, re-attach things, and your sink drain looks brand new.

    Garbage disposal seizes repeatedly

    A garbage disposal that doesn't have anything stuck in the cutting chamber but seems to be hard to turn or will work with effort until left alone for a day or two probably has a bad bearing caused by a leak at the shaft seal. Of course, water gushing out of the lower part of the disposal (or *any* amount of water dripping from inside the motor housing) is one indication that there is a leak! This also represents a safety hazard so the disposal should be left unplugged and not be used even if it still runs.

    By the time the leak is detected, it is probably too late to save the disposal as corrosion of the steel shaft, excessive wear of the bronze bushing, as well as possible electrical damage has already occurred.

    Realistically, there is nothing that could have likely been done in any case. It is virtually impossible to repack such a bearing in such a way to assure that a leak will not develop in the near future.

    Garbage disposal replacement (or upgrade)

    My general recommendation is to get the approximately $100 1/2-3/4 Hp Sears Kenmore (ISE In-Sinkerator™ manufactured) unit when it is on sale (which is about every week). These now have at least a 4 year warranty.

    If your previous garbage disposal was an ISE In-Sinkerator or Sears, then replacement is usually a 10 minute job if the under-sink plumbing is in reasonably good condition (doesn't crumble to dust when you touch it). If the part that mounts to the sink is not corroded and not leaking, I just leave it alone. The only tools required are a screwdriver and wire strippers (possibly) to move the power cord or cable to the new unit and a screwdriver or socket driver and a large adjustable wrench or pliers to unscrew the drain pipe and dishwasher connection (if used). Complete instructions should be provided with the replacement unit.

    But note that ISE and Kenmore disposals may NOT be 100 percent physically compatible in terms of the distance and height of the outlet to the waste pipe. I just replaced a 20 year old Kenmore with an ISE Badger and the connection had to be cobbled together with outlet pipes from old disposals, a piece of bicycle inner tube, and pipe clamp. ;( ;-)

    Sump pumps and utility pumps

    Sump pumps come in two major varieties:
    1. Pedestal: A motor on top of a 3 foot or so pole drives an impeller at the bottom of its long shaft. Only the base may be submerged.

      These motors are quite reliable but the bearing can rot/rust/sieze at the base where it may be under water or at least in a humid environment.

    2. Submersible: A motor, usually totally enclosed in a sealed pump housing within an oil bath drives an impeller. The entire unit is designed to be fully or partially submerged in the sump hole.

      The casing may leak at the bearing (if not magnetically coupled) or at the wire connections. Repair of these motors is probably not worth the effort.

    Utility pumps are often of the submersible variety.

    Three types of automatic switches are commonly used:

    1. Float/weight on a wire, rod, or string pulls on a spring action toggle type switch. The length of the linkage is adjusted for the appropriate low and high water settings. These will be used mostly with pedestal pumps. If properly sized, this type of switch can be quite reliable - I have a sump pump using this type of switch which is easily 30 years old at this point without ever having any problems with the switch.

    2. Mercury tilt switch sealed inside a rubber float. By fastening its connecting wire to a suitable location, the level of the water will cause the float to pivot from horizontal the more vertical. An enclosed mercury switch then controls power to the pump motor. These are not serviceable but replacements are readily available.

    3. Diaphragm pressure switch designed to sense the depth of the water from the trapped pressure. As above, these are not really serviceable but can be easily replaced by the same or a mercury type (2).
    Most common problems are with switches that are no longer reliable or totally broken. Universal replacements are generally available since the switch is not usually an integral part of the motor/pump unit.


    Since there are a semiinfinite number of variations on electrically powered toys, the only comment I have is that these are almost always combinations of small PM motors, switches, batteries, light bulbs - and totally impossible to identify electronic components. With small kids, physical destruction is probably a much more common occurrence than a part failure!

    Incorrect response for remote control toys

    The following may apply when there is no response or an uncontrolled response for certain commands like turn left or move backwards:

    (From: Pete Peterson (

    I've repaired a couple with the same problem and its been the motor driver transistors each time. There are two or three direct coupled transistors from each side of the motor (probably equates to an H bridge) and one or all of these go open. Probably under designed for the current they carry. Just trace the wires from the motor out through the circuit and check the first several transistors you come to.

    Garage door operators

    Typical garage door operators use a 1/3 to 3/4 horsepower induction motor with a belt drive chain or screw mechanism to move the 'trolley' that actually grabs the door. A switch or pair of switches activated at each end of travel stops the motor and toggles the state (up or down) of the controller. Door blockage sensors detect obstructions and stop or reverse travel. A light turns on with motor start and stays on for 3-5 minutes thereafter, controlled by a simple timer.

    Parts of a typical garage door operator (chain drive). Details may differ on operators with worm screw or other drive schemes.

    1. Motor: Single-phase induction motor of about 1/2 horsepower at 862 or 1,725 (or so) RPM. It is electrically reversible with a large ratio V-belt drive (probably about 25:1 for a 1725 RPM motor between motor shaft and chain sprocket).

    2. Chain or screw drive: This often needs lubrication. Make sure grease will not harden at low temperatures if relevant (e.g., Lubriplate).

    3. Limit switches set top and bottom positions of door.

    4. Safety stop: A means of sensing when excessive force is required to move the door. Some types use a compliant motor mount such that excessive torque will result in a twist which closes a set of contacts to reverse or stop the door.

    5. Logic controller: The 'brains' which consists of some relays or a microcontroller.

    6. Remote receiver: A radio receiver tuned to the frequency of the hand unit. Logic here or in the controller checks the transmission to determine if the codes match. More sophisticated units employ a pseudo-random code changing scheme to reduce the chance of code theft. This is usually in a box on the wall connected to the motor unit by a pair of wires.

      On units with DIP switches, both transmitter and receiver settings must match exactly. In addition, for older units in particular, the contacts on the switches may be dirty and/or oxidized so flipping each switch back and forth a few times may be needed to make a reliable connection. I have also seen a situation where one bit wouldn't work in one position - the other position was fine.

    7. Light bulbs and timer: In many Sears as others, the timer is a bimetal strip heated to operate a set of contacts. The on-time is determined by how long it takes for the bimetal strip to cool. These fail after about 10 years but replacements are readily available. More modern units may switch and time the light from the microcontroller.

    AAA Remotes is a replacement parts supplier but also has exploded diagrams and parts lists for a variety of Chamberlain, Genie, and LiftMaster models.

    General garage door operator problems

    1. No response from remote or local buttons. Test power to both the motor unit and control box (they may be separate) outlets. The operator or some other device might have blown a fuse or tripped a circuit breaker. Verify that the connection between the wall box and the motor unit is in tact - check the screw terminals on the motor unit - a wire may have fallen off. Check the circuit breaker (red button) on the motor unit - an overload or an undetected cycling condition (an obstruction causing the door to keep going up and down continuously) may have tripped it. Warning: pressing this button may result in the door starting to move immediately.

    2. Local (inside) buttons work but remote unit is dead. Check and/or replace batteries in the remote unit, confirm that the the code settings have not accidentally changed (unit dropped, for example), go through the set up procedure outlined in your users manual. Find a cooperative neighbor with the same model and try their remote unit (after writing down their settings and reprogramming it for your door). If this works, your remote unit is bad. If this does not work, you have a receiver problem.

    3. Remote unit has reduced range. Of course, first replace the batteries. If possible check with an identical model remote set to the same code to see if it is a problem with the hand unit or the receiver. Make sure any antenna wire (remote and/or receiver) hasn't fallen off or become disconnected. It is also possible that radio frequency emissions from something in the area is interfering with reception. Have you added any electronic equipment or even just rearranged its location recently - even a VCR or TV? What about your neighbors?

    4. Motor operates (you can hear it) but door does not move. This can be caused by a broken or loose belt, snapped door counterbalance spring, locked door, disconnected or broken trolley, logic problems causing the motor be turning in the wrong direction, and other mechanical problems. If the motor runs for about the normal time, then the trolley is probably moving but not attached to the door. If it runs until forever or the overload pops, then a broken belt is likely.

    5. Door opens or closes part way and reverses, stops, or twitches back and forth:

      • The tracks may need lubrication, there may be an obstruction like a broom that fell over into the vertical rails.

      • The gear timing may be messed up. The upper and lower limits may be determined by switches operated from a cam separate from the trolley that moves the door. If you just reassembled the mechanism, this is a likely possibility.

      • The safety stop sensors may be set to be too sensitive.

      • In extremely cold weather, the grease may simply be too viscous or just gummed up.

    6. Door opens and closes at random. There can be several possible causes:

      • A neighbor has a similar model and has selected the same code (probably the factory default - did you actually ever pick your own code?).

      • Interference from nearby high power amateur, CB, or military or commercial radio transmitters may be confusing the receiver. Suggest to them that they relocate. :-)

        Are there such things as IR remote controls for garage door openers instead of the usual radio frequency variety?

      • The push button switch on your one of your remotes or receiver module is defective - a weak or broken spring - and it is activating the door due to vibration or just because it feels like it. Test the switches. On the hand units, you can just remove the batteries for a day and see if the door stops misbehaving.

    Garage door operator light does not work correctly

    Assuming the unit otherwise operates normally and you have tried replacing the light bulb(s):

    For many types (Sears, Genie, etc.), there is a thermally operated time delay consisting of a coil of resistance wire, a bimetal strip, and a set of contacts. When the operator is activated, power is applied to the heater which causes the bimetal strip to bend and close the contacts turning on the light. Due to the mass of the bimetal strip, it takes a couple of minutes to cool down and this keeps the light on.

    The most common failure is for the fine wire in the heater to break at some point. If you can locate the break, it may be repairable at least as a temporary solution. You cannot solder it, however, so a tiny nut and bolt or crimp will be needed. However, sticking contacts resulting in a light that does not always go off are also possible. Cleaning the contacts may help.

    This part is very easily accessed once the sheetmetal cover is removed. It is probably somewhere in the middle of the unit fastened with three screws. Just remember to unplug the operator first!

    Depending on the manufacturer, the original part may be available. I know that it is for Sears models.

    You could also use a time delay relay or a solid state circuit (RC delay controlling a triac, for example) but an exact replacement should be just a whole lot less hassle.

    Garage door operator loses track of where it is

    You press the button to close the door and it works fine. However, next time you press the button to make the door go up and it tries to go down into the ground.

    When it gets to the end of the track - be it at the top or bottom, there must be something that it trips to shut down the motor. At the same time, this is supposed to set things up so that the next activation will reverse the door.

    Does the door stop and shut off when it reaches the end or does it eventually just give up and trip on the safety?

    When it trips the switch to stop at the end of its travel, some mechanism is toggled to change the 'state' of the door logic so that it knows to go up the next time it is activated. It is probably this device - be it a latching relay, mechanical two position switch, or a logic flip flop - that is not being properly toggled.

    I would recommend attempting to determine what device that switch is actually supposed to toggle - it probably is in the operator unit itself (not the control box).

    Garage door remotes behave differently

    "I've got 2 Genie garage door remotes. One of them works from about 100 yards away; the other I almost have to be right next to receiver. I suspect that the antenna is the problem; either too short, or blocked by something."

    First compare the antennas on the two remotes. If they are the same and there are no broken connections, your problem lies elsewhere. The chance of the wire itself being bad is pretty slim.

    It could also be that the receiver and transmitter frequencies are not quite identical. If the remote units have been abused, this is more likely. I don't know about Genie but my (old) Sears has trimmers and I was able to adjust it *very* slightly to match that of the receiver and boost sensitivity.

    CAUTION: If you try this (1) mark the exact position where it was originally and (2) do it only on the transmitter that has the problem. This will minimize the possibility of shifting the frequency to where it might interfere with other devices. See the section: Adjusting garage door operator remote unit for more information.

    Adjusting garage door operator remote unit

    This situation may arise if one hand unit operates normally but the other has a very short range. If you have only one hand unit, it might also be the problem though not likely to have just happened on its own - either it was improperly set up at the factory (if new) or hand unit was dropped once too often.

    It should not work at all if the switches are set improperly. In such a case, first test and/or replace the battery. If this does not help, check the switch settings.

    The tuning is done via a variable capacitor trimmer (probably).

    There will probably be a trimmer inside the hand unit (don't touch the one in the receiver). Position yourself at a reasonable distance and use a plastic tool to adjust it until the door operates while holding the button down. The door will respond at increasing distances as you approach the optimal setting.

    Note: mark the original position first in case this has no effect!

    This assumes there is an adjustment - if there is none, you may have an actual electronic failure, bad connections, etc.

    Improving sensitivity of garage door openers receivers

    Where a garage is constructed with aluminum siding, the remote signal may be significantly attenuated and of insufficient strength to activate the receiver module (inside the garage) of the opener at any useful distance or at all. Assuming the system operates normally otherwise (i.e., activation is normal with the door open), two approaches (either or both together) can be taken to solve this problem:
    1. Locate the receiver module (well, actually, its antenna) in an area of unsided wood, glass window, or other non-metallic area of the building. Note that construction insulation may use aluminum foil as part of its vapor barrier so there could be problems even in an area with no siding.

    2. Extend the antenna on the receiver module. This may not always work but is worth a try. A 1 or 2 foot length of copper wire may help dramatically.

    3. There are external antenna kits available for some door openers. The antenna goes outside, and connects to the receiver through a hole in the wall using coaxial cable. You will probably have to go directly to the manufacturer of your garage door opener or a garage door opener service company.

    Universal remote/receiver units for garage door operators

    So you lost your garage door remote or it got run over by your 4x4 :-). Or, it just expired due to age. There are alternatives other than an entire new operator if the remote is no longer available:

    (From: Kirk Kerekes (

    Go to a home center, and wander over to the garage door openers. Nearby, you will find GDO accessories, and among the accessories will be a universal replacement remote kit that includes a receiver, a transmitter and possibly a power supply. For about $40, you can by and install the receiver in place of the existing receiver. If your home center carries Genie openers, you can even get an Intellicode add-on unit that uses Genie's scanner-proof code-hopping technology.

    Garage door operator doesn't work reliably in cold weather

    First, check the lubrication. The most common problem is likely to be gummed up grease in the chain drive (if used) or the bearings of the rollers. Note: the track itself generally doesn't require lubrication.

    Increasing the safety override force settings may help but are not a wise solution as the door will then be more of a hazard to any legitimate obstructions like people and pets.

    Another possibility is that the motor start/run capacitor has weakened and is not permitting the motor to provide the proper torque. You can test the capacitor if you have a DMM with a capacitance scale or LCR meter. Better yet, just replace it.

    Chamberland garage door opener repair?

    "My remote broke for my very old (defunct) chamberlain automatic garage door opener.

    Chamberlain tech support told me they suggest I buy a whole new unit. Is there any other way to make my door usable with a different remote, or some other arrangement?"

    (From: Panayiotis Panayi (

    Which Chamberlain operator is it, i.e., which model number. You can buy the handsets for Chamberlain operators up to 5 years old. If it is older you will have to buy a new Rx & Tx for it. Most operators have three screw terminals on the back for the attachment of Rxs. The old Chamberlain operators conformed to this. The new ones have the Rx built onto the main PCB inside the operator and have 4 screws externally for pushbuttons and infra red safety beams. If yours has 4 screws you will have to provide a separate PSU for the new Rx or solder two pieces of wire after the step down transformer on the PCB. You must do it before the rectifiers. Otherwise the current drain from the Rx will be too big for them. Besides almost all modern separate Rxs take 24 VAC.

    Garage door operator security

    While manufacturers of garage door operators make excellent claims of security, this is of no value if you don't take advantage of whatever features are included in your unit.

    If there is access to your house from the garage, this security is even more critical. Once inside the garage, a burglar can work in privacy at their leisure - and a nice set of tools is probably there for their convenience in getting through your inside door! Filling up a good sized car or truck with loot - again in complete privacy - drive out and close the door behind. No one will be the wiser until you get back.

    1. DIP switches. Many garage door operators use a set of 8, 12, 16, or more little switches to set the codes of the remote and base unit. If you have never set these, then your are probably still using the manufacturer's default - and all instances of the same model probably have the same code! Change it to something random - pick a number out of a random page in a telephone directory or something like that. Do not select something cute - others, perhaps with not totally honest intentions - will think the same way. You don't have to remember it so an arbitrary totally random setting is fine. However, even the types with 24 switches - that is over 16 million possible codes - can be sniffed: a relatively simple device can monitor your transmission as you open the door and program a special remote unit to duplicate it.

    2. More sophisticated units incorporate a scheme whereby the codes change each time the operator is used in a pseudo-random manner which is almost impossible to duplicate. Even sniffing such a code is of no use as the next instance is not predictable.

    3. Don't leave your remote unit prominently displayed in your car - it is an inviting target. Theft is not necessary - just a moment to copy down the switch settings may be enough. Lock your car! Also, leave a bogus remote unit in plain view (from your previous operator).

    4. Just because the codes are secure doesn't mean that you are safe. The keylocks that are present on many operators to open the door from the outside are pretty pathetic. They can be picked in about the same time it takes to use a key - with ordinary tools - or often with any key that will fit the keyhole. My advice: replace with a high quality pick resistant keyswitch. A well designed electronic lock may be best. When going away for an extended period, use the physical lock on the garage door itself as added protection and unplug the garage door operator.

    Identifying unknown transformer ratings in garage door operator

    In a garage door operator, the transformer likely powers the controller and receiver. If you can look at where its outputs go, you may be able to infer something about the voltage even if the transformer is a charred mass.

    Electromechanical doorbells and chimes

    Most of these consist of a low voltage transformer powered directly from the house wiring providing 10 to 20 VAC at its output, one or more switches for the front door(s), one or more switches for the back door(s), and an electromagnetic chimes unit.

    All of the switches for a given location (i.e., inside and outside the storm door) are wired in parallel. There will be three terminals on the chimes unit - Common (C), Front (F), and Back or Rear (B or R). This notation may differ slightly for your unit. Typical wiring is shown below. An optional second chimes unit is shown (e.g., in the basement or master bedroom - more can be added in parallel as long as the bell transformer had an adequate VA rating.)

                 Bell Transformer                         Chimes
              H o----+                                     Unit
                      )||       X      _|_ Front door        F
                      )|| +-----+------- --------------------o
                      )||(      |  
           115 VAC    )||(      |      _|_ Back door         B
       (Junction box) )||(      +------- --------------------o
                      )||(      Y                            C
                      )|| +----------------------------------o
              N o----+

    Where the pushbuttons are lighted, a small incandescent bulb is wired across the switch contacts and mounted inside the button unit. It is unlikely that this bulb will ever burn out since it is run at greatly reduced voltage. However, if the button does not light but the bell works, this has happened. Replace the pushbutton/light combination - locating a replacement bulb may not worth the effort though Radio Shack is supposed to have something that will work.

    Most 'not-chiming' problems are due to the one or more of the following:

    Weak or erratic mechanical chimes

    This can be due to several things:

    Adding an additional set of chimes

    There are at least two ways of doing this (though the first one is more straightforward and intuitive and therefore generally preferred).
    1. Locate the wires going to the first chimes unit. There will be either 2 or 3 (both front and back door). Connect the new chimes unit to these same wires in parallel:

                   Bell Transformer                         Chimes    Chimes
                H o----+                                    Unit 1    Unit 2
                        )||       X      _|_ Front door        F         F
                        )|| +-----+------- --------------------o---------o
                        )||(      |  
             115 VAC    )||(      |      _|_ Back door         B         B
         (Junction box) )||(      +------- --------------------o---------o
                        )||(      Y                            C         C
                        )|| +----------------------------------o---------o
                N o----+

      The only concern is whether the existing transformer that operates the chimes has enough capacity - you may need to replace it with one with a higher 'VA' rating (the voltage rating should be the same). These are readily available at hardware and electrical supply stores and home centers.

      Some people might suggest just paralleling an additional transformer across the original one (which may be possible if the output phases match). I would really recommend simply replacing it. (This is probably easier mechanically in any case.) Unless the transformers output voltages as designed are identical, there will be some current flowing around the secondaries at all the times. At the very least, this will waste power ($$) though overheating is a possibility as well.

    2. Each additional chimes unit or group of chimes units can use its own transformer but share the doorbell pushbuttons. Just wire point 'X' of the transformers together and each point 'Y' separately to the C (common) terminal on its respective chimes unit(s):

                   Bell Transformer                         Chimes    Chimes
                H o----+                                    Unit 1    Unit 2
                        )||       X      _|_ Front door        F         F
                        )|| +-----+------- --------------------o---------o
                        )||(      |  
             115 VAC    )||(      |      _|_ Back door         B         B
         (Junction box) )||(      +------- --------------------o---------o
                        )||(      Y                            C         C
                        )|| +----------------------------------o    +----o
                        )||                                         |
                N o----+        From output Y of identical o--------+
                                 second bell transformer
                                 (H, N, X, wired in parallel)

      However, since the 'Y' outputs of the transformers are connected at all times to the 'C' terminals of the of the chimes units AND the 'X' outputs are tied together, any voltage difference between the 'Y' outputs will result in current flow through the chimes coils even if no button is pressed. Thus, the transformers must be phased such that there is no (or very little) voltage between 'Y' outputs. Test between 'Y' outputs with a multimeter set on AC Volts after you have the transformers powered: if you measure about double the transformer voltage rating (e.g., 32 VAC), swap ONE set of transformer leads (input or output but not both) and test again. If it is still more than a couple volts, your transformers are not matched well enough and you should purchase identical transformers or use the approach in (1), above.

    Note: For either of these schemes, beyond some number of chimes units, the current rating of the pushbutton switches will be exceeded resulting in early failure. However, this should not happen unless your house is similar in size to Bill Gates' mansion.
    1. Another alternative: If you have an unused baby monitor type intercom (your kid is now in college and you remembered to remove the old batteries which might otherwise now be a congealed mass of leaked goo), stick the transmitter next to the main chimes and put the receiver in your workshop or wherever you want it :-).

    How to add an addition button to a door bell

    Refer to the diagram in the section: Electromechanical doorbells and chimes.

    Another button can be added in parallel with any of the existing ones (i.e., between points X and F or X and B in the diagram). The only restriction is that you may not be able to have more than one lighted button in each group as the current passing through the lighted bulbs may be enough to sound the chimes - at least weakly.

    If you cannot trace the wiring (it is buried inside the wall or ceiling) the only unknown is which side of the transformer to use. If you pick the wrong one, nothing will happen when you press the button.

    Wireless doorbells or chimes

    The transmitter and receiver portion of these units are virtually identical to those of garage door operators. See the relevant sections on those units for problems with activation.

    The bell or chimes portion may be either an electromechanical type - a coil forming an electromagnet which pulls in a plunger to strike a gong or bell. See the section: Electromechanical doorbells and chimes.

    Others are fully electronic synthesizing an appropriate tone, series of tones, or even a complete tune on demand. Repair of the electronics is beyond the scope of this document. However, there are several simple things that can be done:

    Doorbell rings on its own

    Old garage door operator guts for wireless chime

    Don't toss the electronic remains of that old garage door operator. It would probably be possible to use it as the basis for a wireless doorbell. Instead of starting the motor, use its output to enable an electronic chime or buzzer. The RF transmitter and receiver for a wireless chime is virtually identical to that of a typical garage door operator.

    TV antenna rotators

    These consist of a base unit with some sort of direction display and knob and a motor unit to which the TV antenna is mounted. Of course, the troubleshooting of these installations is complicated by the remote and somewhat inaccessible location of the motor unit. :-( Before climbing up on the third story roof, confirm that you haven't lost power to the motor unit and/or base station and that the connections between them are secure.

    A common type of motor that may be used in these is a small AC split phase or capacitor run induction motor. The relative phase of the main and phase coils determines the direction. These probably run on 115 VAC. A capacitor may also be required in series with one of the windings. If the antenna does not turn, a bad capacitor or open winding on the motor is possible. See the chapter: Motors 101 for more info on repair of these types of motors.

    The base unit is linked to the motor unit in such a way that the motor windings are powered with the appropriate phase relationship to turn the antenna based on the position of the direction control knob. This may be mechanical - just a set of switch contacts - or electronic - IR detectors, simple optical encoder, etc.

    Here is some info on connections for some types:

    (From: Will Shears (

    The rotor is operated on 24 volts AC. The wires are used like this:

    This was connected to a knob switch, which also turned. Scenario is: the unit is pointed halfway through the circle. turn the knob left, the rotor turns and the indicator turns with it. when the rotor turns the same number of "clicks" as you turned the knob, it stops. same for reverse.

    OR, the third lead was a meter lead, and the rotor turned a pot that changed the meter reading according to the position of the pots' turning. The rest is the same.

    Inside the box was a 70 µF, 50 V or so NON POLARISED capacitor, or an AC capacitor. Usually the capacitor was connected across the #2 and #3 lead. It provided a phase shift for the motor, and you put 24 volts from #1 to #2 for forward, and to #1 and #3 for reverse. The other lead will either pulse as the rotor turns, or the voltage will change between the #1 & #4 lead, assuming there is a load resistor across the terminals. I would try a 470 ohm 1 watt resistor to start, and probably a 100 to 200 will be right. If you have a VOM, check for resistance across 1 and 4, if you get some, not a short, it is the second type, if you get a short or open, it is a pulse type.

    (From: Al Cunniff (

    Here is one place that is devoted to antenna rotors if you give up:

  • Norm's Rotor Service
    5263 Agro Drive
    Frederick, MD 21703
    Phone 301-874-5885

    Note: They don't have email built into their site, but the site tells you just about everything else you need to know about their business and service. It has a good rotor FAQ section too.

    I'm not connected in any way with Norm's,

    Induction cookers and cooktops

    An induction cooker or cooktop (sometimes called a "Hob") uses a rapidly changing electromagnetic field to heat the pot or pan directly instead of a gas flame or electric resistance element. A coil is excited with high frequency AC (18-25 kHz is typical) and the bottom of the pot or pan acts both as the secondary of a transformer and its core resulting a large current flow which heats it directly, avoiding the middle-person so-to-speak. This results in a boost in energy efficiency. The top plate of the induction cooker never gets hotter than the cookware sitting on it.

    To be suitable for use with an induction cooker, the bottom of the cookware must be made of a ferrous (magnetic) metal, so copper or aluminum will not work - the cooker will sense that and display an error. Usually this means iron or stainless steel. But not all stainless steel is magnetic - confirm that a magnet is attracted to any candidates if they don't have induction embosssed or a sort of coil logo on the bottom. The bottom must also be fairly flat so Woks are out. ;(

    Portable induction cookers are somewhat similar in appearance to electric hotplates, are lightweight, and plug into normal 15 or 20 amp 115 VAC outlets (in the USA, adjust for your country). Most have a single position for a pot or pan. There are double ones but their total power is limited by the available current from a 15 or 20 A circuit. So they are usually programmed internally to limit total power. It's not clear under what conditions the maximum power is specified for any of these. On those where the line current was measured, the readings were significantly below their ratings. For example, an iSiLER CHK-CCA02 rated 1,800 W read only 13 A at maximum power using a tea kettle load. That's only about 1,460 W assuming a line voltage of 120 VAC and power factor of 1. The Duxtop 9600LS did come closer at slightly over 1,700 W with a large diameter pot on a dedicated outlet with a line voltage of 122 VAC. Perhaps it is a combinatiion of a large pot with optimal ferrous base, the line voltage at the upper limit of 126 VAC, and a full moon. ;-)

    Nothing is entirely free, energy-wise. The conversion from AC line power to high frequency induction power isn't 100 percent efficient - 80 to 90 percent is typical. So the benefits in lower energy use may not be that dramatic. And for something like boiling a single cup of water, a microwave oven is faster and uses less energy. But if boiling 4 quarts of water, the induction cooker will win out.

    Induction ranges have multiple positions in their top surface - 4 to 8 or more - which may differ in size to optimize coupling to various diameter cookware. There are also versions with many small induction coils spread under the entire surface so cookware can be placed anywhere. How well these actually perform is questionable as none are really optimally located.

    The electromagnetic radiation emitted by these devices is currently (no pun...) considered to be safe, though there are usually warnings in the user manuals about use near people with implanted devics like pacemakers. That's probably just to satisfy the lawyers though - the intensity of the field drops off very rapidly moving away from the coil.

    Here are general comments about these devices some of which will not be found in any reviews on-line:

    If only there was such a thing as an induction oven, though how it would work and what its benefits might be are unclear.....

    With the recent push to phase out or outright bad gas heating appliances, what can be done technically at least to make this as painless as possible? Aside from paying off the fossil fuel industry ;-), it probably comes down to control of power and response to changes in power so that the positive aspects of the experience is as gas-like as possible:

    User manuals for common induction cookers are easily found on-line.

    For the actual measurements, input power is used as the dependant variable because it really isn't possible (or at least easy) to measure the output power delivered to the load. The value is based on line voltage x (line current - idle current). This assumes a power factor of unity, which means the actual power may be slightly smaller if it is actually leading as is likely. Exactly why all the results are at least 10 percent lower than the specifications is not yet known. Two clamp-on AC ammeters agree with each-other quite closely.

    What follows is a discussion of induction cooker circuits and repair considerations followed by descriptions of several common models including the Duxtop repair saga. ;-)

    Induction Cooker Driver Circuits

    If one searches for "induction heater" on eBay, mostly what will turn up are circuits based on the so-called "ZVS" (Zero Voltage Switching) self oscillating resonant design. There are versions of various ratings up to several kW where power control is primarily determined by input voltage. These are extremely simple and are used for numerous applications. But all the induction cookers I'm aware of use what may be described as synchronous resonant drive where power is controlled by Pulse Width Modulation (PWM) - both low speed and high speed. The input is usually the full wave rectified line voltage with very little filtering so it does vary widely over a half cycle with the power into the induction coil varying more or less proportionally, but that isn't used to regulate power - it's the same all the time. The microprocessor-based user interface generates the PWM signals directly or controls circuity to do it. At higher power, a PWM frequency typically between 17 and 27 kHz is used to chop the full wave rectified input. But at low power (typically less than 25-50 percent of maximum), slow PWM is used similar to how most microwave ovens control power - the drive is turned on and off over a cycle of several seconds with a fixed power when on equal to the value at the threshold where slow PWM kicks in. For example, with power settings of 1-10, settings 5-10 use fast PWM and 0-4 use slow PWM switching the power on and off at the setting 5 value. One might ask why simple chopping of the rectified AC input cannot be used? Well, this isn't a resistance heater - there are very specific requirements for an induction coil driver both to be efficient and to prevent failure of the high power components.

    The primary active component in the power circuits is a solid state switch usually consisting of one or more Insulated Gate Bipolar Transistors (IGBTs). These are controlled with a voltage signal like a MOSFET but with a Bipolar Junction Transistor (BJT) output.

    The power circuit topology is closely related to a flyback driver and operates as follows over one cycle:

    1. T=0: The switch turns on and current builds up in the induction coil approximately linearly with respect to time. The on-time is determined by control circuit based on the desired power. The longer the on-time, the more energy is stored in the coil.

    2. T=T1: The switch turns off and current is diverted into the parallel resonating capacitor(s) resulting in a buildup of voltage across the switch with a shape of slightly more than a half cycle at the resonant frequency of the LC combination of the induction coil and parallel capacitors. Because of the parallel capacitor(s), the current in the coil varies smoothly over the entire cycle.

    3. T=T2: For optimal performance, the switch should turn on again just as the voltage across the switch is back to where it started. Tests show that this is done fairly accurately. It is not known if there is any feedback involved in controlling the waveforms.

    A full cycle of T2-T0 is then equal to T1-T0 + (k+π)*sqrt(LC) and thus the operating frequency is affected by the specified output power. k represents a factor to increase the coverage to greater than a half cycle because of the energy storage in the induction coil and associated capacitors.

    Now it is a wee bit more involved than this. In the steady state, current is already flowing in reverse through the body diode inside the switching device when it is turned on and doesn't change direction until later. So the turn-on time is not critical but the turn-off time is.

    Here is an animated GIF from a simulation based on the parameters for the Duxtop 9600LS unit described below. The schematic is the same as this: CircuitLab Simulation Schematic for Duxtop 9600LS except that an ideal diode was added in series with the IGBT to block current through its internal body diode so that the forward and reverse currents could be plotted separately. (The CircuiLab MOSFET model that is being used has a built-in body diode but it's not possible to plot the forward and reverse current separately.) There are 10 plots with the duty cycle stepping from 10% to 90% but using the optimal drive frequency for 50% of 20.6 kHz: Duxtop 9600LS Induction Cooker Simulation of PWM Duty Cycle from 10-90%. The GIF dwell time is 2 seconds for all plots. Note: The vertical scaling is not the same for some plots. The top plots show the voltage for the IGBT drive (blue), IGBT collector (orange), and the power rail (tan). The bottom plots show the current in the induction coil (orange), parallel capacitors (blue), IGBT C-E (forward, tan), and IGBT body diode (reverse, green). It is interesting that the plots show duty cycles of 30-50% resulting in virtually the same behavior: The voltage on the IGBT is negative and the body diode is passing current in the reverse direction when the IGBT gate goes high. Then about halfway between the voltage pulses, the IGBT starts passing current in the forward direction. It is the turnoff of the IGBT that does the heavy lifting. ;-) The behavior is essentially unchanged down to around 25%. Outside this range, really impressive current spikes can be seen in the plots - note the scale change! These may be potentially destructive. In summary there is a fairly wide range which is safe - from 25-50%. But nasty things may happen if the PWM percent and drive frequency don't track each-other even for a single cycle. Similarly, for the optimal frequency at other duty cycles, reducing the pulse width down almost to half will also be acceptable in the steady state.

    See Duxtop Model 9600LS Induction Cooktop Simulation - PWM Drive Waveforms Annotated for the gory details. This is with the optimal parameters for a PWM of 50 percent but the waveforms and performance are almost unchnaged down to 25 percent- IGBT gate drive turning on anywhere within the shaded blue area.

    Then the cycle repeats in the steady state. The first few cycles after startup are quite different and careful control of the PWM percent may be needed to avoid undesirable "events". ;( ;-)

    Note that the shape of the voltage waveform across L2 is nearly a flipped version of the voltage on Q1-C except that it is offset positive by around 25 percent so that the current through the coil averages to 0. Else the current in the coil would increase over time and bad things would happen.

    Interestingly, the "cookware detection" pings appear to be very close to the 25% pulse width, perhaps depending on the transition to nasty behavior affected by the presense of ferrous metal. ;-) But that is a single cycle whereas the above only applies in the steady state.

    More on the simulation below.

    Induction cooker repair

    WANTED: Broken or non-functional induction cooktops/cookers in almost any condition for analysis and documentation here.

    Despite induction cookers being devices with high power semiconductors constructed as inexpensively as possible, they appear to be remarkably reliable appliances. This conclusion has been determined by a very scientific method based on the availability of broken ones on eBay. ;-) So far, only the Duxtop described below was certifiably defective performance-wise (and that wasn't even noticed by the seller). Some with cracked top plates or other physical damage turn up but that's not the same and no fun unless the price is really low. There are a few YouTube videos of induction cooker repair but with little explanation of possible causes of the failures.

    An noted below, probing these live is a risky proposition both for the device and the humans involved since they are high power and line connected, and may have voltages approaching 1,000 V peak present on the induction coil and associated components. It's also a challenge to arrange the circuit boards and induction coil in such a way that the bottom of the power PCB is accessible for probing with with something in place to serve as a load, needed to get the thing to turn on.

    However, if the device does more than just turn on the display, it is possible to detect the AC magnetic field from the induction coil to monitor much about its health including waveforms of the PWM control at lower power settings and variable amplitude at higher settings, as well as the cookware detection pings. Think of it as induction cooker EKG. ;-) My induction field sensor consists of an 8 turn coil of insulated wire 1.75 inches in diameter with red and green LEDs wired anti-parallel, a 220 ohm resistor in series for current limiting, and a pair of 5.1 V zeners with opposite polarity in series across the entire thing to limit voltage. None of this is at all critical. It is shown operating with the "naked" Duxtop 9600LS induction cooker at LED Induction Field Sensor on Duxtop 9600LS and in Closeup of LED Induction Field Sensor in Operation. And yes, the pot is sitting on a piece of Plexiglas™ acrylic sheet substituting for the missing ceramic/glass top plate. ;-) More below. For this to work, the cookware must be small diameter or slightly off-center. The strongest response is with the coil standing up next to the side of the cookware where the magnetic field lines loop out of the coil. At a position where the LEDs are not on fully, only red or green will light due to the asymmetric waveform. A scope - or meter that responds at the switching frequency - could be used in place of the LEDs but that would not be nearly as cool. ;-) In fact for the scope, a sense coil isn't even needed as there is enough electric field - which can approach 1 kV across the coil - to be detected using a 10:1 probe with its tip simply floating. With a scope, the duty cycle can be determined, which is the percent of the cycle during which the switch (IGBT) is conducting current in either direction. This is usually longer than the actual gate drive percent due to the IGBT body diode conducting in reverse. The gate drive waveform cannot be sensed remotely.

    Even the "pings" these send out to detect the presence of cookware can be easily sensed with an LED widget or scope. They are typically a single cycle of the high frequency waveform with an on-time that is low enough to avoid excessive current through the switching device with no ferrous material in place.

    Note that it is possible to light high wattage incandescent lamps and drive other devices with significant amounts of power using a modest size pancake coil in place of a pot or pan. And there are YouTube videos showing stunts like this. The load alone may be sufficient to fool the "cookware-in-place" detection. If not, a small steel plate would suffice (while siphoning off some of the power). But serious safety precautions are necessary since the input can approach 1.8 kW and the output power using a coil like the one in the induction cooker can be similar! A quick test with the coil wound for my home-built mini-hotplate consisting of a 25 turn pancake coil of #14 AWG wire with an ID of 1-1/4 inches and an OD of 4-3/8 inches sandwiched between a pair of 1/8 inch acrylic sheets used with a 100 W incandescent lamp on the iSiLER model CHK-CCA02 induction cooker. This worked, sort of. cookware sensor would display the EO error and shut off on anything above the 300 W setting with its 50 percent duty. This did shut power off entirely, just drive to the coil for a short time. However, the actual power delivered to the lamp was only around 30 W. Using the induction coil from a 220 VAC cooker resulted in excessive power to the 100 W lamp - perhaps equivalent to 150 or 200 W. A pair of 100 W lamps in series each lit at around 30 W equivalent brightness. But in all cases, the iSiLER still produced the EO error if run at more than the 300 W setting. However, this seemed to be more of a timing issue - 3 seconds or so ON was needed to realize it was unhappy. ;-) If run at higher settings (above where low speed PWM was used), it would still shut off and display E0 after about 3 seconds, though the actual power to the lamp might be higher or lower.

    Being high power devices, there are ample opportunities for common failures like cracked solder joints, burnt screw connections, and blown IGBT(s). I am not aware of any real service information on specific models but they should be generally similar in the design of the power electronics which usually consists of a large bridge rectifier for the AC input, one or two 1,200 V 15 or 20 A IGBTs, 1 or more high current inductors, high voltage film capacitors, and the actual induction ("Work") coil. THESE ARE TOTALLY LINE CONNECTED WITH NO ISOLATION so take appropriate precautions if probing live. But at least there are usually no high value high voltage electrolytic capacitors to hold a lethal charge after power has been removed. The largest HV capacitors are typically under 10 µF for a line filter and another after the bridge rectifier. There will be HV capacitors associated with the work coil having typical ratings of 0.33 µF at 1,200 V but they cannot hold any charge after power is removed.

    Finding failures in the power section will generally be straightforward, possibly with the help of a magnifying glass and smoke. ;-) At least the circuits can be traced relatively easily. But while the control section is basically simple, tracing it will be more of a challenge. And some attempt may have been made to obsure part numbers on the ICs. There will be a microcontroller for the user interface (probably on a separate PCB) and a bunch of discrete parts for the IGBT driver(s) and power feedback. A current transformer may be used to sense the AC line current and there may be a small power transformer for the DC supplies for the control circuits.

    If any of the power semiconductors fail shorted, the main fuse will blow. While it is possible for the control circuitry to force the IGBT(s) on and blow the fuse, this is less likely but also possible. A 15 or 20 A IGBT can handle a much higher surge without itself blowing. So this is a case where the fuse may blow to protect an expensive part. After replacement testing the series light bulb (or series space heater!) may be prudent.

    Replacement parts are of course available by cannibalizing a similar model, though as noted, finding one that can be an organ donor may not be easy.

    (The "L" under AWG denotes Litz wire.)

    Having covered all that, many failures - especially where the main fuse has NOT blown - are not due to the high power components as I found out attempting to repair the Duxtop 9600LS.

    The next several sections include some very basic information on several specific models, but the only one to be explored inside in depth so far is the Duxtop 9600LS and it is therefore most detailed including a partial repair. For more complete user information, search for the specific model. Many induction cookers appear to use a similar power control scheme with slow PWM at the lower-end and amplitude control via high speed PWM at the higher-end. The user interfaces and case style are where most of the observable differences will be found. However, there can be variations in the number of power levels and step sizes. And note that I really have only documented performance with respect to constant power, not heating based on temperature.

    Duxtop model 9600LS induction cooker

    The Duxtop 9600LS (which also goes by BT-200DZ) is typical of single position induction cookers at the medium $120 price point. The model 9610LS is the same but in a case with more black. The model P961LS is the "professional" version. It also appears to be functionally identical but in an ugly but sturdier stainless steel case at more than double the cost. ;-) Twin position versions are also available but are limited in total power by the maximum current from a 15 or 20 amp outlet.

    There is a Web Album at Duxtop 9600LS Induction Cooker Tear Up (Full resolution versions of the photos may be displayed by replacing the filename with the name of the photo below its thumbnail and adding a ".jpg" to it.) The first photo is just what is found on various Web sites selling this thing. The next 3 are of the actual device missing the black glass/ceramic cook surface plate, originally secured with black adhesive. Next are the major sub-assemblies: Control PCB, Power PCB, and Induction Coil. The cooling fan consists of the typical brushless DC motor and blade assembly as shown, with the couling being part of the bottom of the unit.

    In order for any of these devices to turn on heating power, their microbrain must think there is suitable cookware in place - or a steel plate or perhaps even a DIY secondary coil with a load attached. The last photo shows the E0 error code when heat is called for but nothing is present. More on this below.

    General information from manual and observations:

    Other Duxtop models have slight variations in features and style but probably use nearly identical power circuitry.

    A sense coil with 6 turns approximately 3 inches in diameter placed almost anywhere near the unit was initially used to obtain the power control and switching frequency waveforms. Later, a scope probe was found to be much more sensitive. The waveforms are very similar but both must be responding to the electric field because that is what the shape agrees with. The magnetic field is a smooth curve because it comes from an inductor whose current cannot change instantaneously.

    The following data were obtained using a new correctly functioning sample of the Duxtop 9600LS. The values are approximate:

      Setting(s)  Frequency  Duty Cycle  Amplitude  Power Input
       0.5-5.0    22.0 kHz      40%         1.0         802 W
         7.5      19.4 kHz      50%         1.2       1,233 W
        10.0      18.0 kHZ      60%         1.5       1,709 W

    Specific power input values here and elsewhere taken at the same power settings may differ because they were taken at different times with different pots and water temperature as well as different electrical outlets that may have more or less voltage drop and the line voltage wasn't checked each time. There are also variations simply due to the cooker's control electronics and heating of various electronic components - as well as the phase of the moon and other random factors originating in a universe far-far away. So some averaging and fudging may have been required. ;-)

    The power computation is based on a constant line voltage of 122 VAC. As noted above, settings 0.5-5.0 use slow on-off PWM to control power with the same parameters as power setting 5.0. The high frequency waveforms are unchanged. For the Duty Cycle, "%" is when the waveform is low (flat line) and the IGBTs are turned on with their drive high or their body diodes are conducting. Thus it is not necessarily directly related to the gate drive waveform. The Relative Amplitude changes almost in lock-step with the PWM Ratio. Since that is a voltage, the power is roughly proportional to its square, but the Frequency is lower at a setting of 10.0 (Relative Amplitude of 1.5, square of 2.25) so the actual power only doubles.

    In general, the drive frequency must track the PWM percent so that the trailing edge of the fractional cycle coincides with turn-on of the PWM. If the PWM off-time is too long, power will be wasted in the free-wheeling body diodes of the IGBTs. If it is too short, power will be wasted in the IGBTs pulling down the voltage. The values above are therefore NOT arbitrary but must be specified by the microcontroller. Whether this is actually done via feedback is not known, though there is a current sense transformer that may play a role.

    Some of these values are affected by the size of the bottom of the cookware used. For example, the line current increases by 0.5 to 1.0 A at a setting of 10.0 based on whether a small or large pot is used.

    For actual measurements using a large diameter stock pot, see Duxtop 9600LS Induction Cooker Input Power versus Power Setting. Compare this to what is in the user manual: Duxtop 9600LS Induction Cooker Input Power versus Power Setting from User Manual.

    I have not found any more complete technical information on-line for this or other common induction cookers. A search for "Duxtop Induction Cooker Circuit Diagram" or the like will return some schematics that are promising but no exact matches. If anyone has one, please contact me via the Sci.Electronics.Repair FAQ Email Links Page. I do not have the determination to trace the complete circuit presently, though that time may come. ;-) However, a schematic of most of the circuitry on the Power PCB may be found at: Duxtop 9600LS Power Circuits Schematic. Some part numbers, types, and values are guesses at this point. Most of the discrete components are easily identified and even labeled on the PCB, but the bridge rectifier and IGBTs are concealed under the heatsink and the ICs have their tops coated. It is assumed that when the IGBTs are turned on, current builds up in the induction coil (L2); when the IGBTs turn off the current continues to flow due to its inductance and charges the parallel capacitors (C2/C13 and C12) going through slightly more than one half cycle at its resonant frequency. A longer on-time would result in a higher pulse amplitude during the off-time but the drive frequency must track the PWM off-time for optimal performance and to avoid undershoot (with current through the IGBT body diode) and overshoot (a hard turn-on before the zero-crossing). The control circuit mostly takes care of that although it's not perfect.

    A basic simulation has been performed on the power circuits in the schematic using Circuit Lab. This is a particularly easy to use but somewhat limited Web-based tool. (Or I haven't found out how to exploit its hidden capabilities.) However, the simulation probably does a decent job for this simple circuit with only minor fudging. ;-) The Duxtop power circuit has so few parts that it can probably be replicated using the free trial version of CircuitLab. There is no standard symbol for an IGBT with body diode so a MOSFET with separate diode was used. CLK1 which is a digital (5 V) PWM generator and the amplifier (AMP1) which boosts its output to 15 V for driving the MOSFET gate stand in for the Duxtop control circuitry. With minor exceptions, the power components themselves have the same part numbers and values as those in the actual unit. Under some as yet to be determined conditions, the presence of the smoothing inductor (L1, 54T on 1-1/4"OD x 5/8"ID x 1/2"T core) would result in a low frequency instability that is definitely not present in the actual system. However, that may have been an artifact of the simulator sample rate The value of 25 mH was estimated by physical inspection and shouldn't be far off. But there was trouble even using a low value like 100 µH. The value of the induction coil had to be increased to 55 µH from 44 µH based on the pancake coil formula, though part of that could be due to the ferrite pole pieces. That value was fine tuned so the resulting waveform at a 50% duty cycle agreed with the measurements. The simulated waveforms and frequencies at other duty cycles then correlated with the measurements quite closely. Of course it could all be bogus.... See: CircuitLab Simulation Schematic for Duxtop 9600LS. The results are shown in Duxtop 9600LS Simulated Drive Waveforms. From top to bottom they correspond to power settings of roughly 4.0 (if it ran continuously rather than with slow PWM at a setting 5.0), 7.5, and 10.0. Note that the vertical scaling of the 3 plots is NOT the same.

    Faulty Duxtop 9600LS induction cooker

    If you don't want to get totally confused as I was, it might be best NOT to read the following paragraphs and just skip to the conclusions near the end.

    The unit used for the Web Album was acquired without the top plate, poor thing. ;-) It worked perfectly except that the input (and presumably output) power were slightly less than half of what they should be. The previous owner hasn't been able to shed a lot of light on what happened. Apparently the adhesive securing the top plate deteriorated and it stuck to a pot when lifted off the cooktop. Whether the top plate then smashed to the floor is not known but it was not included with the unit. Nor is it known whether the power was low before the incident, though the owner didn't think so and only tested it afterwards to confirm heating did something to be able to say so in the eBay listing. So no repair attempt was made and thus a twiddled trim-pot is ruled out. It's possible that the trauma of the top plate incident resulted in collateral damage to the circuitry but that would be a real stretch and there is nothing obvious. A slow power decline over time that wasn't noticed may be most likely.

    Compare the plots of the Duxtop 9600LS Induction Cooker Input Power versus Power Setting and Faulty Duxtop 9600LS Induction Cooker Input Power versus Power Setting. The plots are fairly similar except for the scale, as are the drive frequencies and waveforms (though not identical). It's not clear what can fail in the power circuitry to result in such behavior without something getting really toasty. :( There is a single unmarked 500 ohm trim-pot that looked very tempting to twiddle but I didn't want to do that initially. If that controlled maximum power, any significant change in its setting would likely have seriously impacted the waveform and that hasn't happened. Not only is it virtually impossible to turn without removing the induction coil, but not knowing what it does, there is a risk that any major change could cause the thing to melt down or blow up. The trim-pot is in the vicinity of the current sense transformer (CT1) so it probably was assumed to have something to do with power. But a 50 percent loss of power is unlikely to be due an incorrect adjustment or slight drift in value. More on the trim-pot below. The solder joints for all the high current devices on the Power PCB have been touched up. Nothing appears burnt or loose.

    A YouTube video of another similar Duxtop model shows that main switch parts may be similar to IHW15N120R3 15 A, 1,200 V IGBTs. This unit has a pair in parallel which is a bit shady since the parts are not likely to share the load evenly if they are both driven at the same time. But as they say: "If it works, use it". ;-) Or perhaps not. If one failed shorted, the main fuse would blow. If one failed open, the other one would have to handle the full load and might then fail shorted and blow the main fuse. But neither has occurred and low cooking power is not a likely result in either case. It would be no cooking power. ;-) A few shorted strands in the Litz wire of the induction coil would have little to no impact. And change in value of one of the large capacitors (C3/C13 or C12 on the schematic) or inductor (L1) would result in a significant difference in the waveforms as the resonant frequency would be higher. Or perhaps the smoothing capacitor after L1 (C2/C11) failed open resulting in less available current to the coil. But they were found to be fine. And no, it's not just jumpered for 230 VAC as there are no such jumpers. And in any case, half the voltage would result in around one quarter the power.

    To reiterate for the bad unit:

    1. The cooking power as deduced from the speed to boil water and the line current is slightly less than half the expected value.

    2. Nothing appears to be getting hot. A good fraction of the lost power would be showing up as heat and/or smoke and no such symptoms are present even after running for a while. Nor has the behavior changed which would indicate something intermittent like a bad solder joint.

    3. The drive frequency and waveforms as measured via an external probe are similar to those of the working unit but not identical.

        Unit   Power Setting  Frequency  Duty Cycle  Power Input  Power Ratio
        Good        5.0       22.4 kHz      45%          802 W       2.40
         "          7.5       19.5 kHz      54%        1,233 W       2.25
         "         10.0       18.2 kHz      61%        1,709 W       2.05
        Weak        5.0       25.0 kHz      32%          334 W       0.42
         "          7.5       22.0 kHz      45%          549 W       0.44
         "         10.0       20.3 kHz      55%          833 W       0.49

      The "Power Ratio" is for the good unit compared to faulty one and vice-versa. The greater than 2:1 power rato at 5.0 could be mostly accounted for by the difference in duty cycle - 45% versus 32%. (45/322 = 1.98.) The frequency difference should largely cancel as the the IGBT on-time is inversely proportional to frequency. So a higher frequency results in a larger number of pulses but each with less energy. Perhaps. ;-) However, the data at a power setting of 10.0 is way off with a ratio of only around 2.05. And where the PWM percent is similar for the two units at 45% at nearly the same frequency, the power input differs by ~1.46:1; at 54/55% it's ~1.48:1. For the same line voltage and PWM frequency, the PWM percent IS the only parameter controlling input power. This implies that there is something bad in the power circuitry and was thought to rule out anything like a twiddled trim-pot.

      But what if it was actually a control problem since the waveforms were only checked at the peak of the 120 Hz full wave rectified input because that's the only place it was convenient to trigger the scope. It's possible that a different portion of that envelope encompassing the high frequency PWM could be used. In other words, perhaps incorrect PWM percentages are being used at various parts of the 120 Hz half-cycle. But a subsequent comparison of the waveform envelopes didn't show any noteworthy differences. AND the amplitude of a single PWM cycle at the peak of the envelope also seems to be identical for both units with the scope probe carefully positioned in the same location. So this is a possibility.

      A careful examinatino of the measured waveforms show that the PWM percent is too large and/or the frequency is too high at a power setting of 5.0 so the IGBTs appear to be turning on slightly too soon. At a power setting of 10.0, there is no similar anomoly. But this is also true of the good unit, so it's a feature, not a bug and argues for the power circuitry being OK. I should complain to the designers. ;-)

      So this was totally confusing......

    Using the same simulation as for the good unit, parameters were varied for all the key components. The only ones that resulted in the observed behavior were the rectified line voltage (V3) and the ESR of L1. With V3 set to around 122 VDC XOR the ESR of L1 set to 20 ohms, the power was approximately cut in half (based on the amplitude of the voltage pulses on Q1C) and the waveforms were otherwise unchanged. Setting the ESR of the induction coil to 2.75 ohms resulted in a similar reduced amplitude with only a slight distortion of the waveform. However, none of these represents a realistic failure mode without a major meltdown as there would be a large amount of power dissipated in those components. ;-( And no, the bridge rectifier is not acting like a half-wave rectifier.

    Grasping at straws, the cover with the control panel (and its PCB) and top plate from the good unit was installed on the bad one with no change. Some simple tests by probing the Power PCB might be able to resolve this quickly but that could be quite a challenge. Not only would the high power line connected circuitry be dangerous but just arranging the sub-assemblies to provide access to the underside of the Power PCB AND at the same time having a pan or ferrous plate on the coil as a load is next to impossible. With fewer than a dozen relevant parts that can be bad (many of which have been ruled out), the cause should be deducible if not intuitively obvious without resorting to actual tests or calling in Sherlock Holmes! ;-) Of the power components, only L1, the IGBTs, and the induction coil are likely though as there are no other possibilities.


    And then there was a partial Eureka moment. ;-) And it definitely wan't something obvious. Out of desperation I figured it wouldn't hurt to check the trim-pot for any obvious damage and measure its value. It should be low risk to adjust it by a small amount on either side of where it's set to see what if anything happens. And Voila! The trim-pot turned out (no pun...) to just be misadjusted but quite sick. The resistance value in-circuit started at 555 ohms but then increased to above 600 ohms for no apparent reason. When removed, it tested at around 2K ohms and the wiper position made no difference. How that could happen is not at all obvious. It agrees with the PCB labaling, shows no signs of trauma, but is seriously dead.

    So the trim-pot was replaced with a new 500 ohm trim-pot. Problem solved? Not so fast. ;( ;-)

    Here are the data for various new trim-pot (clock face) positions:

                 Input Power at
      Trim-Pot  Power Setting of
      Position    5.0    10.0
        9:00     714 W  1148 W
       10:30     749 W  1204 W
       12.00     656 W  1172 W
       12:30     630 W  1401 W
        1:00     606 W  1412 W
        1:15     625 W  1401 W
        1:30     583 W  1218 W
        3:00     521 W  1197 W
    (Again, these power values may not be precisely the same those shown elsewhere due to measurement variation/uncertainty.)

    No position of the replacement trim-pot resulted in rated power, though it's much closer than before. The trim-pot setting for maximum power at a power setting of 10.0 (trim-pot at 1:15) results in an input power of slightly over 1,400 W or around 84% compared to the good unit. At 5.0, the actual power is only around ~600 W so the slope below 5.5 is slightly smaller than above. But that's a feature, not a bug as the table in the user manual shows similar dual slope behavior. Therefore, the primary purpose of the trim-pot may in fact be to fine tune the slope of the power settings from 5.5 to 10.0 (though it does affect the power at 5.0 as well). And it is very sensitive to wiper position so could really only be done properly by being able to monitor power during the adjustment process. I don't have that luxury although I've gotten fairly adept at powering down, unplugging from the electrical outlet, removing the pot, removing the top plate, moving the induction coil out of the way, tweeking the trim-pot, then reassembling in reverse order. Whew! ;-) But the trim-pot has no dramatic effect on the maximum power at either extreme of wiper position. So that must be limited by some other component and that component is faulty. The result now is still not too shabby and is probably as good as it will get since there is no other adjustment and troubleshooting the control circuitry just isn't going to happen unless possibly if I acquire a spare Power PCB to compare to. ;-) The data are shown in Repaired Duxtop 9600LS Induction Cooker Input Power versus Power Setting. If the plots of the data from the 9600LS user manual, the good unit, and repaired unit are scaled so their maximum power is equal and compared, they appear very similar. With enough fiddling, they could be matched more closely but that's not going to happen either.

    So one of the conclusions from this saga is as usual to not immediately suspect the high power expensive parts! In this case, they are almost certainly in perfect health, thank you. While there is still something not quite right, it's almost certainly a 5 cent part in the control circuitry, possibly even one of those dreaded "Select on Test" parts that was selected incorrectly upon testing and the thing is actually performing like it was when new. A maximum power ~15 percent lower than normal would not likely be noticed without actually measuring it or comparing with another similar unit. Even less likely for lower power settings. But the part is probably not directly in series or parallel with the trim-pot. And exactly how a trim-pot can fail without any evidence of overheating or abuse, and certainly not from excessive use is not at all clear. It's just a rheostat with the wiper and one end tied together, but stuck at high resistance. And contact cleaner hasn't helped. Even a dissection of the trim-pot revealed nothing except that the track seemed to have the correct resistance but was in contact with only the one terminal that was connected on the PCB to the wiper. Perhaps the delayed effect of a manufacturing defect.

    One clue suggesting the power being low but not being noticed was that the defective unit arrived in the original box for a Duxtop model P961LS - the "professional" version in a stainless steel case that is believed to have the same power specifications as the 9600LS. when asked about this, the owner replied something like "I wanted one with higher power".

    And now for the final numbers for now and probably forever. ;-)

        Unit   Power Setting  Frequency  Duty Cycle  Power Input  Power Ratio
        Good        5.0       22.4 kHz      45%          802 W       1.29
         "          7.5       19.5 kHz      54%        1,233 W       1.23
         "         10.0       18.2 kHz      61%        1,709 W       1.19
      Repaired      5.0       22.5 kHz      42%          621 W       0.76
         "          7.5       19.5 kHz      55%        1,002 W       0.81
         "         10.0       17.5 kHz      61%        1,429 W       0.84

    The duty cycle and frequency of the two units are now remarkably close, and the differences could be largely due to measurement error.

    iSiLER model CHK-CCA02 induction cooker

    This iSiLER model goes for about half the price of the DUXTOP 9600LS, above, but appears to do the job. It has a sleeker look than the others and seems to be just as good for basic tasks. At first I thought the lack of a BOIL button would be a disadvantage, but then realized that touching the MENU button twice switches to TEMPERATURE mode, which defaults to 380°F and seems to do basically the same thing. My only complaint is that the buttons do not respond in a consistent way requiring a delay between some selections. That's probably designed to minimize mistakes but takes some getting used to.

    The iSiLER CHK-CCA05-US is generally similar but has fewer settings for power and temperature, is slightly smaller, and even less expensive.

    FWIW, the iSiLER CHK-CCA02i is what I now use to boil water for tea, noodles and the like, cook pot roasts, and make flawless scrambled eggs. ;-) For these types of tasks, I haven't used my electric stove top elements in several months except where more than one position was required. A cloth under the pot or pan prevents scratching of the top plate and minimizes smudges. If I ever do replace my 70 year old classic GE electric stove ;-) it would be one with an induction cooktop and double electric oven. Too bad there isn't such a thing as an induction oven. But unlike stovetops, electric ovens are already about as efficient as Physics permits. Except for a heat pump oven, of which there have been feasibility studies for industrial applications at least, if not actual practical implementations.

    General information and observations:

    This is the one I currently use. The slow PWM period of 6 seconds is one half or less that of the others which is definitely an advantage. My only complaint is that the granularity of the increments is just barely adequate at the low end. But that isn't significantly worse than any of the others tested (only the Duxtop had smaller increments at 80 instead of 100 W) and much better than some. Why aren't these things programmed for constant percent increments instead of constant power increments?

    Avantco model IC 1800 induction cooker

    This Avantco model goes for about double the price of the DUXTOP 9600LS, above. It is called a "professional" model, which really seems to mean that it is in an ugly but sturdy case. ;-)

    General information and observations:

    Here are typical measurements:

      Setting(s)  Frequency  Duty Cycle  Amplitude  Line Current
         1-5      18.0 kHz      55%         1.0         6.6 A
         10       17.5 kHz      60%         1.1         8.7 A
         15       16.0 kHz      67%         1.3        11.6 A

    As with the others, lower settings use a constant power but cycled on and off at low speed. For the Avantco, the period is around 16 seconds. That's really too long for low mass cookware.

    Breville / PolyScience CMC850BSS "The Control Freak" Induction Cooking System

    This may be the Porsche or Cadillac (depending you your preference) of induction cookers given the typical $1,200 price tag. But at first glance it appears to be very strange. Based on the 45 page user manual (and that's all in English, not 45 different Languages!!), this thing is intended to be used for the most part with its temperature sensor and not by direct selection of power, which is counter to what most people are used to with a stove-top or hotplate. So there are only Low, Medium, and High "intensities" as power settings are called, essentially there only for the Luddites who refuse to figure out how to use the temperature sensor with computer control. But at least it apparently can be used to boil water without programming, though even that may require studying the manual. And firmware updates may be required at some point via a USB thumb drive (which can also store cooking programs and appears to be included). ;-) I wonder how many of these are sitting in attics because the users couldn't figure out the programming.

    Reviews seem to be bipolar. Those who like it rave about its ability to maintain a constant temperature. Those who dislike it nit-pit about trivialities like the lack of leveling feet.

    I may have the opportunity to test one in the near future for basic functions to document techno-dweeb type info at least (similar to the others). ;-)

    Stay tuned.

    Sam's Mini Induction Hotplate 1

    This was intended as a hotplate capable of similar tasks as an induction cooker but on a smaller scale. But due to some minor issues, the best that the final result can be called is a warm plate. ;-) The initial version uses one of the "ZVS 1000W Low Voltage Induction Heating Board" found on eBay for under $15, a 24 VDC 10 A power supply, and voltage and current monitor. The schematic is virtually identical to Backyard Scientist: Simple Induction Heater and a zillion others found with a Web search. The parts are even the same except for IRFP260s instead of IRFP250s, 1 mH for each of the inductors, and a pair of 0.3 µF, 1,200 V capacitors in parallel for the capacitor bank. Whether it's really capable of 1,000 W without blowing up is not known. But at the much lower power levels involved here, it has been very reliable, except that the barrier strip solder connections for the output promptly melted during initial testing and were replaced with a screw and cable clamp arrangement.

    The first induction coil was 13 turns of #10 AWG magnet wire sandwiched between a piece of 1/4 inch clear acrylic and wood panel. The ID is around 1 inch and the OD is around 3.5 inches resulting in an inductance around 9.6 µH. See: Sam's Mini Induction Hotplate 1. The lower photo is supposed to show it boiling water though it's hard to make out any bubbles.

    So this one does work but unfortunately the resonant frequency is 150 kHz and there is little control over that. So the RF skin depth is only around 0.17 mm out of the 2.6 mm wire diameter. That increases the resistance significantly making it similar to that of #16 AWG wire or worse. There is noticeable heating in the coil even with no load and that increases with load. In fact, it gets hot enough to soften the acrylic and brown the wood. ;-( Proper cooling and Litz wire is really needed - or water cooling! Or a different driver circuit.

    The lower photo shows it with a somewhat bedraggled 4 inch steel saucepan running with a power input of around 200 W. But only perhaps one half to two thirds of that ends up as useful heating since it is 35-40 W with nothing in place. And thick acrylic top plate reduces the coupling efficiency. This is similar to low simmer on an induction cooker. As noted, the coil does get hot due to its resistance and also being sandwiched between thermal insulators. They should be perforated at least and the coil should be fan-cooled - or wound with Litz wire or both. But the ZVS driver dissipates relatively little at this power level.

    In an attempt to avoid the acrylic totally melting, it was replaced with a piece of glass along with a fan underneath the coil for cooling. Unfortunately, this turned out to not be entirely successful. :( ;-) Since the glass plate was thinner than the acrylic, coupling was better and heating was faster. But about when the water was about to start boiling, there was a LOUD SNAP which I first feared was a capacitor blowing up or some other electrical failure. But heating continued just fine. It turned out that the glass plate had cracked cleanly into three pieces. Whether due to the coil getting hot, the pan getting hot, or some other thermal stress is not known. But using ordinary plate glass may not be advisable for these stunts. :( ;-) As a side note, the fan which was mounted below the coil apparently has enough ferrous metal in close enough proximity to increase the power input by several watts, so it was probably getting hot as well but continued to run. Oh well, on to Plan B - Litz wire.

    My initial attempt at Plan B was only slightly more successful than Plan A. I had a mostly full spool of #14 AWG magnet wire purchased as part my TMS project from over 5 years ago. So 4 strands of #14 wire were twisted together to form a length of #8 Litz wire of sorts. This resulted in a 10 turn coil of approximately the same diameter as the one above. With fewer turns and lower inductance, the no-pan current was a bit higher than the previous coil. But this still became hot enough to soften the acrylic plate and brown a piece wood backing. Its peak temperature in the vicinity of the coil while attempting to boil water exceeded 170°C! The water never really did boil, just a few occasional bubbles at 80-90°C using an IR thermometer. ;( So on to Plan C.

    Plan C consists of a very nicely wound (thank you!) 25 turn classic pancake coil of #14 AWG wire with an ID of 1-1/4 inches and an OD of 4-3/8 inches sandwiched between a pair of 1/8 inch acrylic sheets. With its much higher inductance of around 40 µH (calculated and measured), this one draws about two thirds of the DC input current of the first version (only 5.5 A when cold) and thus is much lower power but doesn't melt down as quickly either. So it's currently more accurately described as a mini induction warm-plate as opposed to a hotplate or cooker, which was the original intent. ;-)

    The simplest least expensive way to acquire suitable Litz wire may be to salvage it from an induction cooker coil. These can be had on eBay as replacement parts for some unidentified make and model for $15-$20 and would have enough Litz wire for several of these mini hotplates. ;-) Search on eBay for "Induction Cooker Coil Cooking Component Heating". Buying only the Litz wire would be costlier and home-built Litz wire would be much more work as I found out with Plan B. And likely more expensive as well. The cost of magnet wire seems to have at least doubled in the last few years.

    These eBay induction cooker coils have 27 turns of something like #12 AWG Litz wire (around 0.08 inches in diameter) with an ID and OD of approximately 1.75 and 7.5 inches, respectively. The calculated inductance is around 85 µH while the measured inductance is 99 µH unloaded. The large difference may be due to the 6 ferrite blocks on one side of the winding. The inductance goes up to 110 µH with a pot that covers the entire area of the coil. This compares to an ID and OD of 2.0 and 6.75 inches with 20 turns and a calculated inductance of 44 µH for the Duxtop 9600LS coil.

    This was powered using the same ZVS driver with a 10 inch diameter stock pot as the load. The power input to the ZVS driver with no load was ~18 W. With the stock pot, it started at ~150 W dropping to ~134 W as its temperature increased. The resulting ZVS drive frequency was 22.3 kHz with a slightly distorted sinewave of 125 V p-p across the coil. Over that range of loading, the frequency varied between around 22.3 kHz and 24.0 kHz, though the maximum didn't appear to be with no load. Interestingly, the sensed waveform using an open scope probe had alternating high and low half sinusoidal bumps where the total period corresponded to the measured frequency. But it couldn't even achieve a temperature much above 60°C even with less than 1/2 cup of water in the pot, mostly due to convection losses. The coil temperature never exceeded 44°C and that was probably high only because the pot was sitting right on the coil. With a 1/4 inch spacing, the power input dropped to 100 W. Using a coil intended for 115 VAC such as the 20 turn Duxtop with an inductance of ~44 µH should have better performance, though the frequency would increase significantly and the losses in the coil would be greater. That may be attempted at some point in the future. But my first attempt at disconnecting the Duxtop induction coil to be able to make measurements proved unsuccessful. The screws would not budge.

    I am planning on constructing a driver for this induction coil using a single IGBT (Onsemi FGA25N120 - 1,200 V, 25 A - which is way overkill for this but new/NOS 5 pieces were found on eBay for $10). The controller may eventually be Arduino-based using my mLMA1 platform (Mini Laser Mode Analyzer 1) which includes a 3 button user interface and color LCD. It would be tested on the same 24 VDC 10 A power supply (though one with a higher voltage may be required to achieve the same power). But the frequency will be much lower so the RF skin effect would be greatly reduced. A simulation similar to the one used for the Duxtop 9600LS was implemented: CircuitLab Simulation Schematic for Sam's Mini Induction Warm Plate 1. The inductance of the coil is based on the standard pancake formula and confirmed by a measurement. The other component values and frequency of 9 kHz were selected based on what was available in my junk drawers on eBay. 9 kHz isn't exactly ideal being below the upper limit of middle-age human hearing, which could be annoying since there is bound to be some vibration. ;( ;-) But perhaps it will chase the squirrels away...... The value of C2 can be adjusted in approximately the ratio of 4:1 versus frequency if needed. At 1 µF, the frequency would be 18 kHz (like the Duxtop). I have several values of induction cooker capacitors on order. For unknown reasons, the simulation blows up at exactly 10 kHz but that appears to be a bug in CircuitLab since it works at 9.999999 and 10.000001 kHz and other values nearby as long as they are exactly 10 kHz. There is nothing that would result in a singularity at exactly 10 kHz. Is also works at any other value tested that isn't a round number but also fails at 40 kHz in a similar way. This was tested on two different PCs on two different Browsers. So it's not like the infamous Pentium CPU floating point bug in the 1990s, but I wonder if it is a result of using fixed point arithmetic for round numbers. ;-)

    It will be interesting to see what happens, particularly if the simulation bears any relation to reality. The tests will use a 555 timer for frequency and an LM393 comparator for generating the PWM, not the Arduino though for now. ;-) The capacitors were originally scrounged but then it was decided to use proper induction cooker capacitors due to the required low ESR and resulting high AC current. The inductor L1 was wound and is lower in value than the one in the Duxtop but according to simulation, that makes no difference over a wide range.

    Stay tuned.

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Power Tools

    Types of motors found in power tools

    A variety of motor types are used depending on the type of tool. AC powered portable tools usually use a universal motor due to it high power/weight ratio and ease of electronic speed control. Cordless tools usually use a high performance permanent magnet DC motor. Stationary power tools almost always use some form of AC induction motor except where variable speed is required.

    See the sections on these types of motors for more details than the following summaries provide.

    Motors in AC line operated portable tools

    Line operated portable (corded) power tools usually use a universal type AC motor providing 3,000 to 30,000 RPM at the motor shaft. For the same power rating, these will be significantly lighter than an induction motor.

    A single or multiple stage gear reducer drops the relatively high speed at which these motors are most efficient to whatever the tool actually requires, increasing the torque as well.

    Universal motors can also be speed controlled relatively easily using a variant of a simple light dimmer type circuit. Excellent torque is maintained over a very wide range extending to nearly 0 RPM.

    Motors in cordless power tools

    These are usually high performance permanent magnet DC motors using advanced high strength and exotic magnetic materials. They are very compact and light weight for their power output. As with all DC (brush type) motors, brush wear is a common problem.

    Speed control is easily accomplished by low cost electronic circuits which chop the power (pulse width modulation) rather than simply using a rheostat. This is much more efficient - extremely important with any battery operated device.

    Motors in stationary power tools

    Stationary power tools which do not require continuous speed control will generally use some type of AC induction motor - split phase or capacitor start/run. The motors generally operate at a fixed speed of around either 1725 or 3450 RPM (U.S., 60 Hz power). Stepped pulleys or continuous mechanical speed/torque changers are used to obtain (usually) lower work piece speeds.

    For example, a typical drill press may have one or two sets of stepped pulleys providing 3 to 15 or more speeds by changing belt positions. A continuously variable cone drive is also available as an option on some models. This is extremely convenient but does add cost and is usually not found on less expensive models.

    An internal thermal overload protector may be incorporated into larger motors. WARNING: this may be self resetting. If the tool stops on its own, switch off and unplug it before attempting to determine the cause.

    Generally, these induction motors are virtually maintenance-free though cleaning, tensioning, and lubrication may be required of the drive system.

    However, electronic speed control of induction motors, while possible, is relatively complex and expensive requiring a variable frequency variable voltage power supply. Therefore, universal motors may be used on stationary tools like scroll saws with continuously variable electronic speed control.

    As technology marches on, there will be increasing use of electronically controlled motors in all sorts of appliances and power tools. Greatly increased efficiency and finer control are possible by using 3 phase permanent magnet motors - similar to larger versions of brushless DC fan motors - with integrated power control electronics. But, for these applications, that is largely in the future (currently: Spring 2000).

    About horsepower ratings

    One horsepower is equal to 746 watts of electrical power (100% efficiency). Therefore, the most you can get continuously from a normal 115 V 15 A outlet is about 2 HP. Any claims (for air compressors, for example) of higher ratings on a normal outlet are totally bogus. Companies such as Sears (Craftsman) like to specify 'Reserve Power' for their power tools which as best as I can determine refers to the power available for a short time and may relate to the mass - and inertia - of the rotating parts but not the continuous power available. This may be useful to help saw through a tough knot in a piece of hardwood but may not be terribly meaningful for a wet/dry vacuum! Therefore, pay most attention to the continuous power ratings if they can be found anywhere. A good indication is probably the maximum amps required for the electrical service.

    As with over-the-counter drugs, extra strength does not necessarily translate into faster relief, higher current does not always mean better performance, and horsepower ratings much above what you would compute from V x A may be more of a marketing gimmick than anything really beneficial.

    Cords for AC line operated portable power tools

    Really old power tools had two wire cord plugs and no safety ground yet were of all metal (solid and heavy!) construction. I would recommend that as a matter of policy, these be retrofitted with a 3 wire grounded cordset.

    Newer ones have the grounded cordset while the newest 'double insulated tools' are of mostly plastic construction and are back to a 2 wire ungrounded cord.

    As with any electrical appliances, inspect cords regularly and repair or replace any that are seriously damaged - if the inner wiring is showing, nicked, or cut; if the plug is broken or gets hot during use, or where the cord is pulled from or broken at the strain relief.

    Portable drills

    The portable electric drill (now the rage is cordless) is probably one of the two first tools that any handyman should own (the other being a saber saw). It is used for many things in addition to drilling little holes - drilling large holes, sanding, polishing, driving screws, etc. Therefore, these tools get a lot of use - and abuse.

    AC line powered drills

    An AC line powered electric drill is just a universal motor with a two stage (typical) gear reduced powering a chuck to hold the drill bit or attachment. A continuous range speed control with a reversing switch is now standard on most AC line powered drills.

    Typical problems include:

    Upgrading the bearings on a Craftsman drill

    Very inexpensive models (like the $30 Father's day specials) may use sleeve bearings in various locations instead of better quality longer lived ball or roller bearings. One particular bearing tends to deteriorate rapidly, especially if the drill is used for sanding or in dusty work environments (as opposed to clean rooms :-) ). This is the motor bearing at the handle end. The lubrication dries out or is absorbed by dust particles, the bearing runs dry, wears, and fails with an ear shattering squeal. Even if you use ear plugs, the speed and power are not adequate as the motor is laboring and overloaded and motor failure would result from prolonged operation.

    I have upgraded a couple of these drills to ball bearings. The substitution is straightforward requiring disassembly of the drill - removing of the front gear reducer and then one side of the case. At this point, the old sleeve bearing is easily freed from its mounting (just the plastic of the case) and pulled from the shaft. The shaft is likely undamaged unless you attempted to continue running the drill even after going deaf.

    The drills I upgraded had bearings that were 7/8" OD, 5/16" thick, and with a 5/16" ID center hole. The old ones were worn by almost 1/32" oversize for the center hole but the motor shaft was undamaged. I found suitable replacement double sealed ball bearings in my junk box but I would assume that they are fairly standard - possibly even available from Sears Parts as I bet they are used in the next model up.

    If the gear reducer needs to come apart to access the motor, take note of any spacer washers or other small parts so you can get them back in exactly the correct locations. Work in a clean area to avoid contaminating the grease packing.

    The bearing should be a press fit onto the shaft. Very light sanding of the shaft with 600 grit sandpaper may be needed - just enough so that the new bearing can be pressed on. Or, gently tap the center race with hammer (protected with a block of wood). Make sure that the bearing is snug when mounted so that the outer race cannot rotate - use layers of thin heat resistant plastic if needed to assure a tight fit (the old sleeve bearing was keyed but your new ball bearing probably won't have this feature).

    These drills now run as smoothly as Sears' much more expensive models.

    Cordless drills

    Cordless drills use a permanent magnet DC motor operating off of a NiCd (usually) battery pack. Manufacturers make a big deal out of the voltage of the pack - 6, 7.2, 9.6, 12, 14, 18, etc. - but this really isn't a sure measure of power and time between charges as a motor can be designed for any reasonable voltage. A gear reducer follows the motor driving a chuck for holding the drill or screwdriver bit, or attachment. These are most often have a single or two speeds with reverse.

    In addition to the problems listed in the section: AC line powered drills, these are also subject to all the maladies of battery operated appliances. Cordless tools are particularly vulnerable to battery failure since they are often use rapid charge (high current) techniques.

    Other direct drive tools

    Saber saws, reciprocating saws

    These use a universal motor which drives a gear reducer and reciprocating mechanism. Better models have a variable speed control so that the sawing rate can be optimized to the work. All but the most inexpensive allow the head to be rotated or rotate automatically based on feed direction adding a bit of complexity.

    A reciprocating saw is very similar but uses a much larger motor and beefier gearing.

    In addition to motor problems, there can be problems with damage, dirt, or need for lubrication of the reciprocating mechanism.

    Electric chain saws

    WARNING: Read and follow all safety instructions using any type of chain saw.

    These have a high power universal motor and gear reducer. Most have the motor mounted transversely with normal pinion type gears driving the chain sprocket. A few models have the motor mounted along the axis of the saw - I consider this less desirable as the gyroscopic character of the rotating motor armature may tend to twist the saw as it is tilted into the work.

    Inexpensive designs suffer from worn (plain) bearings, particularly at the end of the motor opposite the chain since this is exposed to the elements. Normal maintenance should probably include cleaning and oiling of this bearing. A loud chattering or squealing with loss of speed and power is an indication of a worn and/or dry bearing Replacement with a suitable ball bearing is also a possibility (see the section: Upgrading the bearings on a Craftsman drill since the approach is identical.

    Keep the chain sharp. This is both for cutting efficiency and safety. A dull chain will force you to exert more pressure than necessary increasing the chance of accidents. Chains can be sharpened by hand using a special round file and guide or an electric drill attachment. Alternatively, shops dealing in chain saws will usually have an inexpensive chain sharpening service which is well worth the cost if you are not equipped or not inclined to do it yourself.

    One key to long blade and bar life is the liberal use of the recommended chain oil. Inexpensive models may have a manual oiler requiring constant attention but automatic oilers are common. These are probably better - if they work. Make sure the oil passages are clear.

    The chain tension should be checked regularly - the chain should be free to move but not so loose that it can be pulled out of its track on the bar. This will need to snugged up from time-to-time by loosening the bar fastening nuts, turning the adjustment screw, then retightening the nuts securely.

    There may be a slip clutch on the drive sprocket to protect the motor if the chain gets stuck in a log. After a while, this may loosen resulting in excessive slippage or the chain stopping even under normal conditions. The slip clutch can generally be tightened with a screwdriver or wrench.

    Circular saws, miter, and cutoff saws

    These have a high power universal motor either directly driving the blade or driving a gear reducer (high torque/large blade variety).

    Miter and cutoff saws are similar but are mounted on a tilting mechanism with accurate alignment guides (laser lights in the most expensive!).

    Grinding wheels

    A dual shaft induction motor drives rotating grinding stones (or other tools like wire brushes). Most common are fixed speed - usually around 3450 RPM but variable speed operation is highly desirable to avoid overheating of tempered metal during sharpening. All but the most inexpensive use sealed ball bearings requiring no routine maintenance.

    Small light duty grinders may be 1/4 HP or less. However, this is adequate for many home uses.

    Wet wheels may run at much slower speeds to keep heat to a minimum. Being in close proximity to water may in itself create problems.

    Polishers, rotary sanders

    A gear reduced universal motor drives a rubber (usually) mounting plate to which a sanding disk or polishing pad is attached.

    Due to the nature of their use, sanders in particular may accumulate a lot of dust and require frequent cleaning and lubrication.

    Orbital sanders and polishers

    In addition to the usual universal motor and its bearings, the orbital mechanism may require cleaning and greasing periodically.

    Belt sanders, power planers

    A typical portable belt sander uses a gear or belt reduced universal motor driving one of the rollers that the sanding belt rotates on under tension. In decent quality tools, these should use ball or roller bearings which require little attention.

    A power planer is similar in many ways but the motor drives a set of cutters rather than a sanding belt.

    Air compressors

    A direct or belt drive induction motor (probably capacitor start) powers a single or multiple cylinder piston type compressor. Typical continuous motor ratings are between 1/4 and 2 HP (for a 115 VAC line). Over and under pressure switches are used to maintain the pressure in an attached storage tank within useful - and safe - limits. Most will include an unloading valve to remove pressure on the pistons when the compressor stops so that it can be easily restarted without damage to the motor and without blowing fuses or tripping circuit breakers.

    I much prefer a belt driven compressor to a direct drive unit. One reason is that a motor failure does not render the entire compressor useless as any standard motor can be substituted. The direct drive motor may be a custom unit and locating a replacement cheaply may be difficult.

    Drain the water that collects in the tank after each use.

    Inspect the tank regularly for serious rust or corrosion which could result in an explosion well.

    Paint sprayers

    Traditional air powered paint sprayers may simply be an attachment to an air compressor or may be a self contained unit with the compressor built in. Since the active material is paint which dries into a hard mass (what a concept!), cleaning immediately after use is essential. Otherwise, strong solvents will be needed to resurrect a congealed mess - check your user's manual for acceptable deadly chemicals.

    Portable airless paint sprayers use a solenoid-piston mechanism inside the spray head itself. There is little to go wrong electrically other than the trigger switch as long as it is cleaned after use.

    Professional airless paint sprayers use a hydraulic pump to force the paint through a narrow orifice at extremely high pressure like 1000 psi.

    With all types, follow the manufacturer's recommendations as to type and thickness of paint as well as the care and maintenance before and after use and for storage.

    Warning: high performance paint sprayers in particular may be a safety hazard should you put your finger close to the output orifice accidentally. The pressures involved could be sufficient to inject paint - and anything else in the stream - through the skin resulting in serious infection or worse.

    Heat guns

    These are similar to high performance hair dryers and subject to the same problems - bad cord or switch, open heating element, defective thermostats, universal motor problems, and just plain dirt and dust buildup.

    Paint strippers

    These are just a high power heating element attached to a cord. If there is no heat, check for a bad plug, cord, or open element with your multimeter.

    Soldering irons

    Simple pencil irons use an enclosed heating element is attached to the 'business' end in some manner - screw thread, set screw, clamping ring, etc. Failure to heat may be due to a bad plug, cord, bad connections, or defective element.

    Some types package the heating element and replaceable tip in a separate screw-in assembly. These are easily interchangeable to select the appropriate wattage for the job. Damage is possible to their ceramic insulator should one be dropped or just from constant use.

    High quality temperature controlled soldering stations incorporate some type of thermostatic control - possibly even with a digital readout.

    Soldering guns

    The common Weller Dual Heat soldering gun is a simple transformer with the tapped primary winding in the bulk of the case and a single turn secondary capable of 100 or more amps at around 1.5 V. The soldering element is simply a piece of copper (possible with a shaped tip) which is heated due to the high current passing through it even though it is made mostly of copper. The 'headlight(s)' (flashlight bulbs) operate off of a winding on the transformer as well.

    Possible problems include:

    Note: a soldering gun is not a precision instrument and should not be used for fine electronics work - you will ruin ICs and printed circuit boards.

    Hot melt glue guns

    The typical consumer grade hot melt glue gun is about as simple an electrical tool as it gets. A heating element heats a metal or ceramic chamber where the hot melt glue stick material (technically a thermoplastic adhesive) melts and is pushed out the front as a semi-liquid.

    There are no doubt countless variations on implementation. Two that I've seen are:

    The most common problem will be no heat:

    Given the low cost of these things, repair beyond fixing broken wires or swapping parts from identical units is probably not worth it. There is no way to fix either type of heating element or thermostat other than by replacement.

    Wet-dry vacs, yard blowers/vacs

    A powerful universal motor driving a centrifugal blower is all there is in this equipment. Unfortunately, many common models use cheaply made motors which may fail simply due to use or from the dust and proximity to liquids. The blower sucks air and whatever else into the holding tank. A filter is supposed to prevent anything from getting through. The motor itself should be sealed against direct contact with the dust/liquid section of the machine.

    Problems occur with bad cords, switch, motor brushes, bearings, or a burnt out motor from excessive use under adverse conditions.

    As with inexpensive electric drills, sleeve bearings (usually, the top bearing which is exposed somewhat) in the motor can become worn or dry. Replacing with a ball bearing is a worthwhile - but rather involved - undertaking if this happens. See the section: Upgrading the bearings on a Craftsman drill as the technique is similar (once you gain access - not usually a 10 minute job).

    Hedge trimmers

    A gear reduced universal motor drives a reciprocating mechanism not too dissimilar to a saber saw. In addition to the usual motor/electrical problems, lubrication may be needed periodically. Should you accidentally try to trim a steel fence instead of a bush, damage to one or more teeth may occur. In this case, light filing may be needed to remove nicks and burrs.

    Of course, you probably will not get away without cutting the power cord a couple of times as well! See the sections on power cords. One way to avoid the humiliation (other than being half awake) is to wrap a cord protector around the first 2 or 3 feet of cord at the tool. This will make the cord larger in diameter than the inter-tooth spacing preventing accidental 'chewups'.

    Electric lawn mowers

    A large universal or permanent magnet DC motor drives one or two sets of rotating blades. A load or dead short may be thrown across the motor to act as a dynamic brake when stopping. As usual, when the mower does not operate, check for bad plug, cord, switch, brushes, dirt, etc. See the sections on motors.

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Incandescent Light Bulbs, Lamps, and Lighting Fixtures

    Editor's note: More information on incandescent light bulbs can be found at: Don Klipstein's Lighting Web Site.

    Incandescent light bulbs - single and three way

    The basic incandescent lamp operates on the same basic principles as the original carbon filament lamp developed by Thomas Edison. However, several fundamental changes have made it somewhat more efficient and robust. However, modern bulbs are hardly efficient at producing lighte. Typically, only about 3 to 7 percent of the electrical energy used by a typical incandescent light bulb is turned into useful (visible) light. The rest goes to waste (usually) as heat.

    Tungsten replaced carbon as the filament material once techniques for working this very brittle metal were perfected (Edison knew about tungsten but had no way of forming it into fine wire). Most light bulbs are now filled with an inert gas rather than containing a vacuum like Edison's originals. This serves two purposes: it reduces filament evaporation and thus prolongs bulb life and reduces bulb blackening and it allows the filament to operate at a higher temperature and thus improves color and brightness. However, the gas conducts heat away so some additional power is wasted to heating the surroundings.

    Incandescent lamps come in all sizes from a fraction of a watt type smaller than a grain of wheat to 75 kW monster bulbs. In the home, the most common bulbs for lighting purposes are between 4 W night light bulbs and 250-300 W torch bulbs (floor standing pole lamps directing light upwards). For general use, the 60, 75, and 100 W varieties are most common. Recently, 55, 70 and 95 W 'energy saving' bulbs have been introduced. However, these are just a compromise between slightly reduced energy use and slightly less light. My recommendation: use compact fluorescents to save energy if these fit your needs. Otherwise, use standard light bulbs.

    Most common bases are the Edison medium (the one we all know and love) and the candelabra (the smaller style for night lights, chandeliers, and wall sconces.

    Three-way bulbs include two filaments. The three combinations of which filaments are powered result in low, medium, and high output. A typical 3-way bulb might be 50 (1), 100 (2), and 150 (1+2) W. If either of the filaments blows out, the other may still be used as a regular bulb. Unfortunately, 3-way bulbs do tend to be much more expensive than ordinary light bulbs. There may be adapters to permit a pair of normal bulbs to be used in a 3-way socket - assuming the space exists to do this safely (without scorching the shade).

    The base of a 3-way bulb has an additional ring to allow contact to the second filament. Inexpensive 3-way sockets (not to be confused with 3-way wall switches for operation of a built-in fixture from two different locations) allow any table lamp to use a 3-way bulb.

    Flashlight bulbs are a special category which are generally very small and run on low voltage (1.5-12 V). They usually have a filament which is fairly compact, rugged, and accurately positioned to permit the use of a reflector or lens to focus the light into a fixed or variable width beam. These usually use a miniature screw or flange type base although many others are possible. When replacing a flashlight bulb, you must match the new bulb to the number and type of battery cells in your flashlight.

    Automotive bulbs are another common category which come in a variety of shapes and styles with one or two filaments. Most now run on 12 V.

    Other common types of incandescent bulbs: colored, tubular, decorative, indoor and outdoor reflector, appliance, ruggedized, high voltage (130 V).

    Why do my light bulbs seem to burn out at warp speed?

    The lifespan of an average incandescent bulb is 750-1000 hours which is about 1.5 months if left on continuously or roughly 4 months if used 8 hours a day. So, if you are seeing a 3-4 month lifespan, this may not be that out of line depending on usage. With a lot of bulbs in a house, you may just think you are replacing bulbs quite often.

    Having said that, several things can shorted lamp life:

    1. Higher than normal voltage - the lifespan decreases drastically for slight increases in voltage (though momentary excursions to 125 V, say, should not be significant).

    2. Vibration - what is the fixture mounted in, under, or on?

    3. High temperatures - make sure you are not exceeding the maximum recommended wattage for your fixture(s).

    4. Bad switches bad connections due to voltage fluctuations. If jiggling or tapping the switch causes the light to flicker, this is a definite possibility. Repeated thermal shock may weaken and blow the filament.
    A bad neutral connection at your electrical service entrance could result in certain circuits in your house having a higher voltage than normal - multimeter would quickly identify any.

    It may be possible to get your power company to put a recording voltmeter on your line to see if there are regular extended periods of higher than normal voltage - above 120 to 125 V.

    To confirm that the problem is real, label the light bulbs with their date (and possibly place of purchase or batch number - bad light bulbs are also a possibility). An indelible marker should be satisfactory.

    Of course, consider using compact or ordinary fluorescent lamps where appropriate. Use higher voltage (130 V) bulbs in hard to reach places. Bulbs with reinforced filament supports ('tuff bulbs') are also available where vibration is a problem.

    Halogen bulbs

    (From: Don Klipstein (

    A halogen bulb is an ordinary incandescent bulb, with a few modifications. The fill gas includes traces of a halogen, often but not necessarily iodine. The purpose of this halogen is to return evaporated tungsten to the filament.

    As tungsten evaporates from the filament, it usually condenses on the inner surface of the bulb. The halogen is chemically reactive, and combines with this tungsten deposit on the glass to produce tungsten halides, which evaporate fairly easily. When the tungsten halide reaches the filament, the intense heat of the filament causes the halide to break down, releasing tungsten back to the filament.

    This process, known as the halogen cycle, extends the life of the filament somewhat. Problems with uneven filament evaporation and uneven deposition of tungsten onto the filament by the halogen cycle do occur, which limits the ability of the halogen cycle to prolong the life of the bulb. However, the halogen cycle keeps the inner surface of the bulb clean. This lets halogen bulbs stay close to full brightness as they age. (recall how blackened an ordinary incandescent bulb can become near the end of its life --- sam).

    In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may not adequately vaporize or fail to adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass".

    Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual. This slows down the evaporation of the filament. In addition, the small size of the bulb sometimes makes it economical to use premium fill gases such as krypton and xenon instead of the cheaper argon. The higher pressure and better fill gases can extend the life of the bulb and/or permit a higher filament temperature that results in higher efficiency. Any use of premium fill gases also results in less heat being conducted from the filament by the fill gas, meaning more energy leaves the filament by radiation, meaning a slight improvement in efficiency.

    Efficiency, lifetime, and failure modes of halogen bulbs

    A halogen bulb is often 10 to 20 percent more efficient than an ordinary incandescent bulb of similar voltage, wattage, and life expectancy. Halogen bulbs may also have two to three times as long a lifetime as ordinary bulbs, sometimes also with an improvement in efficiency of up to 10 percent. How much the lifetime and efficiency are improved depends largely on whether a premium fill gas (usually krypton, sometimes xenon) or argon is used.

    Halogen bulbs usually fail the same way that ordinary incandescent bulbs do, usually from melting or breakage of a thin spot in an aging filament.

    Thin spots can develop in the filaments of halogen bulbs, since the filaments can evaporate unevenly and the halogen cycle does redeposit evaporated tungsten in a perfect, even manner nor always in the parts of the filament that have evaporated the most. However, there are additional failure modes which result in similar kinds of filament degradation.

    It is generally not a good idea to touch halogen bulbs, especially the more compact, hotter-running quartz ones. Organic matter and salts are not good for hot quartz. Organic matter such as grease can carbonize, leaving a dark spot that absorbs radiation from the filament and becomes excessively hot. Salts and alkaline materials (such as ash) can sometimes "leach" into hot quartz, which typically weakens the quartz, since alkali and alkaline earth metal ions are slightly mobile in hot glasses and hot quartz. Contaminants may also cause hot quartz to crystallize, weakening it. Any of these mechanisms can cause the bulb to crack or even violently shatter. For this reason, halogen bulbs should only be operated within a suitable fully enclosed fixture. If a quartz halogen bulb is touched, it should be cleaned with alcohol to remove any traces of grease. Traces of salt will also be removed if the alcohol has some water in it.

    Use of dimmers with halogen bulbs

    Dimming a halogen bulb, like dimming any other incandescent lamp, greatly slows down the formation of thin spots in the filament due to uneven filament evaporation. However, "necking" of the ends of the filament remains a problem. If you dim halogen lamps, you may need "soft-start" devices in order to achieve a major increase in bulb life.

    Another problem with dimming of halogen lamps is the fact that the halogen cycle works best with the bulb and filament at or near specific optimum temperatures. If the bulb is dimmed, the halogen may fail to "clean" the inner surface of the bulb. Or, tungsten halide that results may fail to return tungsten to the filament.

    Halogen bulbs should work normally at voltages as low as 90 percent of what they were designed for. If the bulb is in an enclosure that conserves heat and a "soft-start" device is used, it will probably work well at even lower voltages, such as 80 percent or possibly 70 percent of its rated voltage.

    Dimmers can be used as soft-start devices to extend the life of any particular halogen bulbs that usually fail from "necking" of the ends of the filament. The bulb can be warmed up over a period of a couple of seconds to avoid overheating of the "necked" parts of the filament due to the current surge that occurs if full voltage is applied to a cold filament. Once the bulb survives starting, it is operated at full power or whatever power level optimizes the halogen cycle (usually near full power).

    The dimmer may be both "soft-starting" the bulb and operating it at slightly reduced power, a combination that often improves the life of halogen bulbs. Many dimmers cause some reduction in power to the bulb even when they are set to maximum.

    (A suggestion from someone who starts expensive medical lamps by turning up a dimmer and reports major success in extending the life of expensive special bulbs from doing this.)

    The humorous side of light bulbs

    Also see the document: Engineering, Science, and Other (Pretty Clean) Jokes Collection for all the light bulb jokes you could never want.

    (From: Susanne Shavelson (

    People have often mentioned experiencing epidemics of light-bulb-death after moving into a new (to them) house. The same thing happened to us for a few months after moving last year into a 55-year-old house. After most of the bulbs had been replaced, things settled down. I am persuaded by the theory advanced by David (?) Owen in his wonderfully informative and witty book "The Walls Around Us" that houses undergo a sort of nervous breakdown when a new occupant moves in, leading to all sorts of symptoms like blown bulbs, plumbing problems, cracks in the walls, and so forth. Now that the house has become more accustomed to us, the rate at which strange phenomena are occurring has slowed.

    Notes on bulb savers

    These are usually either Negative Temperature Coefficient (NTC) thermisters or simple diodes.

    When cold, NTC thermisters have a high resistance. As they warm up, the resistance decreases so that the current to the light bulb is ramped up gradually rather than being applied suddenly.

    With a properly selected (designed) thermistor, I would not expect the light output to be affected substantially. However, while reducing the power on surge may postpone the death of the bulb, the filament wear mechanism is due to evaporation and redeposition of the tungsten during normal operation. This is mostly a function of the temperature of the filament.

    A thermistor which was not of low enough hot resistance would be dissipating a lot of power - roughly .8 W/volt of drop for a 100W bulb. Any really substantial increase in bulb life would have to be due to this drop in voltage and not the power-on surge reduction. The bulb saver (and socket) would also be heating significantly.

    The bulb savers that are simply diodes do not have as much of a heat dissipation problem but reduce the brightness substantially since the bulbs are running at slightly over half wattage. Not surprisingly, the life does increase by quite a bit. However, they are less efficient at producing light at the lower wattage and it is more orange. If you are tempted to then use a higher wattage bulb to compensate, you will ultimately pay more than enough in additional electricity costs to make up for the longer lived bulbs.

    My recommendation: use high efficiency fluorescents where practical. Use 130 V incandescents if needed in hard to reach places where bulb replacement is a pain. Stay away from bulb savers, green plugs, and other similar products claiming huge energy reduction. Your realized savings for these products will rarely approach the advertised claims and you risk damage to your appliances with some of these.

    Can you prove that bulb savers do not work?

    No, sorry, I don't have conclusive proof. I would love to be proved wrong - I could save a lot on light bulbs. However, new bulbs do not fail upon power on. Old bulbs do. If you examine the filament of a well worn light bulb, you will see a very distinct difference in surface appearance compared to a brand new one. The surface has gone from smooth to rough. This change is caused by sustained operation at normal light bulb temperatures resulting in unequal evaporation of the filament.

    Reducing the power on surge with a thermistor will reduce the mechanical shock which will postpone the eventual failure. 5X or even 20 % increase in life is pushing it IMHO.

    I do believe that Consumer Reports has tested these bulb savers with similar conclusions (however, I could be mistaken about the kind of bulb savers they tested - it was quite awhile ago).

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Motors 101

    Small motors in consumer electronic equipment

    A large part of the functionality of modern appliances is based on the use of motors of one form or another. They are used to rotate, blow, suck, sweep, spin, cut, grind, shred, saw, sand, drill, plane, time, and control.

    Motors come in all shapes and sizes but most found in small appliances can be classified into 5 groups:

    1. Universal motors: Run on AC or DC, speed may be varied easily. Relatively efficient but use carbon brushes and may require maintenance.

    2. Single-phase induction motors: AC, fairly fixed speed except by switching, windings, very quiet. Quite efficient and low maintenance.

    3. Shaded pole induction motors: AC, somewhat fixed speed, very quiet, not very efficient and low maintenance.

    4. Small permanent magnet DC motors: DC, variable or constant speed, often cheaply made, fairly quiet, prone to problems with metal brushes.

    5. DC brushless motors: DC usually (but some may have built in rectifiers to run on AC), somewhat variable or fixed speed, very quiet, low maintenance.

    6. Synchronous timing motors: Constant speed absolutely tied to power line. The long term accuracy of clocks based on the AC line exceed that of most quartz oscillator based time pieces since the ultimate reference is an atomic frequency standard.
    Each type of motor has its advantages and disadvantages. More than one type may be suitable for any particular application.

    Identifying type of unknown motor

    Determining the actual type of motor is the first step toward being able to test to see if it is being powered properly or if there is a fault in the motor itself.

    Open frame motors in line operated appliances with a single coil off to one side are almost always shaded pole induction motors. To confirm, look for the copper 'shading rings' embedded in the core. There will usually be either 1 or 2 pairs of these. Their direction is determine by the orientation of the stator frame (position of the shading rings).

    For enclosed motors, first check to see if there are carbon brushes on either side of a commutator made of multiple copper bars. If so, this is almost certainly a series wound 'universal' motor that will run on AC or DC though some may be designed for DC operation only.

    If there are no brushes, then it is likely a split phase induction or synchronous motor. If there is a capacitor connected to the motor, this is probably used for starting and to increase torque when running.

    Where there is a capacitor, it is likely that how this is wired to the motor determines the direction of rotation - make sure you label the connections!

    Very small motors with enclosed gear reducers are usually of the synchronous type running off the AC line. Their direction of rotation is often set by a mechanical one-way clutch mechanism inside the casing.

    Motors used in battery operated tools and appliances will usually be of the permanent magnet DC type similar to those found in toys and electronic equipment like VCRs and CD players. Most of these are quite small but there are exceptions - some electric lawnmowers use large versions of this type of motor, for example. These will be almost totally sealed with a pair of connections at one end. Direction is determined by the polarity of the DC applied to the motor.

    For universal and DC permanent magnet motors, speed control may be accomplished with an internal mechanical governor or electronic circuitry internal or external to the motor. On devices like blenders where a range of (useless) speeds is required, there will be external switches selecting connections to a tapped winding as well as possibly additional electronic circuitry. The 'solid state' design so touted by the marketing blurb may be just a single diode! A similar approach may also be used to control the speed of certain types of induction motors (e.g., ceiling fans) but most are essentially fixed speed devices.

    Once identified, refer to the appropriate section for your motor.

    Universal motors

    The Universal motor is the most common type of high speed motor found in appliances and portable line operated power tools. Typical uses include vacuum cleaners, floor polishers, electric drills, routers, and sewing machines. They are likely to be found anywhere medium power, high speed, and/or variable speed control are required capabilities. Note that quiet operation is NOT a feature of these motors. Therefore, they will not often be found in electronic equipment.

    Construction consists of a stationary set of coils and magnetic core called the 'stator' and a rotating set of coils and magnetic core called the 'armature'. Incorporated on the armature is a rotating switch called a 'commutator'. Connection to the armature is via carbon (or metal) contacts called 'brushes' which are mounted on the frame of the motor and press against the commutator. Technically, these are actually series wound DC motors but through the use of steel laminated magnetic core material, will run on AC or DC - thus the name universal.

    Speed control of universal motors is easily achieved with thyristor based controllers similar to light dimmers. However, simply using a light dimmer as a motor speed controller may not work due to the inductive characteristics of universal motors.

    Changing direction requires interchanging the two connections between the stator and the armature.

    This type of motor is found in blenders, food mixers, vacuum cleaners, sewing machines, and many portable power tools.

    Problems with universal motors

    These motors can fail in a number of ways:

    Sometimes, there is a thermal fuse buried in the windings that will blow due to overheating before any serious damage has occurred. If so, cleaning and relubing the bearings or remedy of whatever other problem caused the overload and replacement of the thermal fuse may be all that is needed. See the section: Thermal protection devices - thermal fuses and thermal switches for precautions when replacing these and the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    WARNING: Don't just bypass the protection device or the next time you may be dealing with your fire insurance company!

    Testing of universal motors

    Test the field coils for continuity with an ohmmeter. An open winding is bad and will require replacement of the entire stator assembly unless the break can be located. Compare the resistance of the two windings - they should be nearly equal. If they are not, a short in one of the windings is likely. Again, replacement will be necessary.

    Also test for a short to the frame - this should read infinity. If lower than 1 M or so, the motor will need to be replaced unless you can locate the fault.

    An open or shorted armature winding may result in a 'bad spot' - a position at which the motor may get stuck. Rotate the motor by hand a quarter turn and try it again. If it runs now either for a fraction of a turn or behaves normally, then replacement will probably be needed since it will get stuck at the same point at some point in the future. Check it with an ohmmeter. There should be a periodic variation in resistance as the rotor is turned having several cycles per revolution determined by the number of commutator segments used. Any extremely low reading may indicate a shorted winding. Any erratic readings may indicate the need for brush replacement or cleaning. An unusually high reading may indicate an open winding or dirty commutator. Cleaning may help a motor with an open or short or dead spot.

    A motor can be tested for basic functionality by disconnecting it from the appliance circuit and running it directly from the AC line (assuming it is intended for 115 VAC operation - check to be sure).

    CAUTION: series wound motors can overspeed if run without a load of any kind and spectacular failure may result due to centrifugal disassembly of the armature due to excess G forces. In other words, the rotor explodes. This is unlikely with these small motors but running only with the normal load attached is a generally prudent idea.

    About commutators and brushes in universal motors

    A commutator is essentially a rotating switch which routes power to the appropriate windings on the armature so that the interaction of the fixed (stator) and rotating (armature) magnetic fields always results in a rotational torque. Power is transferred to the commutator using carbon brushes in most motors of this type. The carbon is actually in the form of graphite which is very slippery as well. Despite that fact that graphite is a relatively soft material, a thin layer of graphite is worn off almost immediately as the motor is started for the first time and coats the commutator. After this, there is virtually no wear and a typical set of carbon brushes can last thousands of hours - usually for the life of the appliance or power tool.

    A spring presses the brush against the rotating commutator to assure good electrical contact at all times. A flexible copper braid is often embedded in the graphite block to provide a low resistance path for the electric current. However, small motors may just depend on the mounting or pressure spring to provide a low enough resistance.

    The typical universal motor will have between 3 and 12 armature windings which usually means a similar number of commutator segments. The segments are copper strips secured in a non-conductive mounting. There are supposed to be insulating gaps between the strips which should undercut the copper. With long use, the copper may wear or crud may build up to the point that the gaps between the copper segments are no longer undercut. If this happens, their insulating properties will largely be lost resulting in an unhappy motor. There may be excessive sparking, overheating, a burning smell, loss of power, or other symptoms.

    Whenever checking a motor with a commutator, inspect to determine if the commutator is in good condition - smooth, clean, and adequately undercut. Use a narrow strip of wood or cardboard to clean out the gaps assuming they are still present. For larger motors, a hacksaw blade can be used to provide additional undercutting if needed though this will be tough with very small ones. Don't go too far as the strength of the commutator's mounting will be reduced. About 1/32 to 1/16 inch should do it. If the copper is pitted or worn unevenly, use some extra fine sandpaper (600 grit, not emery cloth or steel wool which may leave conductive particles behind) against the commutator to smooth it while rotating the armature by hand.

    Since the carbon brushes transmit power to the rotating armature, they must be long enough and have enough spring force behind them to provide adequate and consistent contact. If they are too short, they may be unstable in their holders as well - even to the point of being ripped from the holder by the commutator causing additional damage.

    Inspect the carbon brushes for wear and free movement within their holders. Take care not to interchange the two brushes or even rotate them from their original orientation as the motor may then require a break-in period and additional brush wear and significant sparking may occur during this time. Clean the brushes and holders and/or replace the brushes if they are broken or excessively worn.

    An appliance, vacuum cleaner, or motor repair shop may have replacement carbon brushes. However, even if you cannot locate an exact replacement, buy a set of slightly larger ones. They can usually be filed down to fit rather easily (the graphite is soft but messy).

    I don't know whether the following approach is viable but it may be worth a try if you can't locate a proper replacement carbon brush. I wonder if the brand of battery matters? :-)


    Why on earth would you not make new brushes yourself from the carbon rod from the center of a cheap battery. You can file or grind the graphite to just the size you need. Free too.

    I have done this many times with motors as small as an electric shaver to ones as large as vacuum cleaners. There is very little difference I can see in both the life of the new brushes and of the commutator segments they bear on. Electric drills are hard on brushes if you use them a lot and they get hot. I have re-brushed several drills and they are all still in service.

    Repairing small universal motors

    Too bad that the Sears lifetime warranty only applies to hand (non-power) tools, huh?

    Which part of the motor is bad? The armature or stator? How do you know? (A smelly charred mess would probably be a reasonable answer).

    Rewinding a motor is probably going to way too expensive for a small appliance or power tool. Finding a replacement may be possible since those sizes and mounting configurations were and are very common.

    However, I have, for example, replaced cheap sleeve bearings with ball bearings on a couple of Craftsman power drills. They run a whole lot smoother and quieter. The next model up used ball bearings and shared the same mounting as the cheaper sleeve bearings so substitution was straightforward.

    Single-phase induction motors

    Where a fixed speed is acceptable or required, the single-phase induction motor is often an ideal choice. It is of simple construction and very robust and reliable. In fact, there is usually only one moving part which is a solid mass of metal.

    Most of the following description applies to all the common types of induction motors found in the house including the larger fractional horsepower variety used in washing machines, dryers, and bench power tools.

    Construction consists of a stationary pair of coils and magnetic core called the 'stator' and a rotating structure called the 'rotor'. The rotor is actually a solid hunk of steel laminations with copper or aluminum bars running lengthwise embedded in it and shorted together at the ends by thick plates. If the steel were to be removed, the appearance would be that of a 'squirrel cage' - the type of wheel used to exercise pet hamsters. A common name for these (and others with similar construction) are squirrel case induction motors.

    These are normally called single-phase because they run off of a single-phase AC line. However, at least for starting and often for running as well, a capacitor or simply the design of the winding resistance and inductance, creates the second (split) phase needed to provide the rotating magnetic field.

    For starting, the two sets of coils in the stator (starting and running windings) are provided with AC current that is out of phase so that the magnetic field in one peaks at a later time than the other. The net effect is to produce a rotating magnetic field which drags the rotor along with it. Once up to speed, only a single winding is needed though higher peak torque will result if both windings are active at all times.

    Small induction motors will generally keep both winding active but larger motors will use a centrifugally operated switch to cut off the starting winding at about 75% of rated speed (for fixed speed motors). This is because the starting winding is often not rated for continuous duty operation.

    For example, a capacitor run type induction motor would be wired as shown below. Interchanging the connections to either winding will reverse the direction of rotation. The capacitor value is typical of that used with a modest size fan motor.

          Hot o------+------------+
                     |             )||
                     |             )|| Main winding
                     |           2 )||
      Neutral o---+---------------+ 
                  |  |
                  |  |    C1     3         C1: 10 µF, 150 VAC
                  |  +----||------+
                  |                )||
                  |                )|| Phase winding
                  |              4 )||

    Speed control of single-phase induction motors is more complex than for universal motors. Dual speed motors are possible by selecting the wiring of the stator windings but continuous speed control is usually not provided. This situation is changing, however, as the sophisticated variable speed electronic drives suitable for induction motors come down in price.

    Direction is determined by the relative phase of the voltage applied to the starting and running windings (at startup only if the starting winding is switched out at full speed). If the startup winding is disconnected (or bad), the motor will start in whichever direction the shaft is turned by hand.

    This type of motor is found in larger fans and blowers and other fixed speed appliances like some pumps, floor polishers, stationary power tools, and washing machines and dryers.

    Shaded pole induction motors

    These are a special case of single-phase induction motors where only a single stator winding is present and the required rotating magnetic field is accomplished by the use of 'shading' rings which are installed on the stator. These are made of copper and effectively delay the magnetic field buildup in their vicinity just enough to provide some starting torque.

    Direction is fixed by the position of the shading rings and electronic reversal is not possible. It may be possible to disassemble the motor and flip the stator to reverse direction should the need ever arise.

    Speed with no load is essentially fixed but there is considerable reduction as load is increased. In many cases, a variable AC source can be used to effect speed control without damaging heating at any speed.

    This type of motor is found in small fans and all kinds of other low power applications like electric pencil sharpeners where constant speed is not important. Compared to other types of induction motors, efficiency is quite poor.

    Problems with induction motors

    Since their construction is so simple and quite robust, there is little to go bad. Many of these - particularly the shaded pole variety - are even protected from burnout if the motor should stall - something gets caught in a fan or the bearings seize up, for example.

    Check for free rotation, measure voltage across the motor to make sure it is powered, remove any load to assure that an excessive load is not the problem.

    If an induction motor (non-shaded pole) won't start, give it a little help by hand. If it now starts and continues to run, there is a problem with one of the windings or the capacitor (if used).

    For all types we have:

    If any of these faults are present, the motor will need to be replaced (or rewound if economical - usually not for typical appliance motors). The only exception would be if the location of the open or short is visible and can be repaired. They usually are not.

    For capacitor run type:

    For larger induction motors with centrifugal starting switches:

    Disassembling and reassembling a universal or induction motor

    The description below assumes that the construction is of an enclosure with an integral stator and brush holder. For those with an internal structural frame, remove the outer casing first.

    For the case of induction motors, ignore any comments about brushes as there are none. With shaded pole motors, the entire assembly is often not totally enclosed with just stamped sheet metal brackets holding the bearings.

    Follow these steps to minimize your use of 4 letter expletives:

    1. Remove the load - fan blades, gears, pulleys, etc. If possible, label and disconnect the power wiring as well as the motor can them be totally removed to the convenience of your workbench.

    2. Remove the brushes if possible. Note the location of each brush and its orientation as well to minimize break-in wear when reinstalled. Where the brushes are not easily removable from the outside, they will pop free as the armature is withdrawn. Try to anticipate this in step (6). (Universal motors only).

    3. Confirm that there are no burrs on the shaft(s) due to the set screw(s) that may have been there. For motors with plain bearings in particular, these will need to be removed to allow the shaft(s) to be pulled out without damage to the bushing. For ball bearing motors, the bearings will normally stay attached to the shaft as it is removed.

    4. Use a scribe or indelible pen to put alignment marks on the covers so that they can be reassembled in exactly the same orientation.

    5. Unscrew the nuts or bolts that hold the end plates or end bells together and set these aside.

    6. Use a soft mallet if necessary to gently tap apart the two halves or end bells of the motor until they can be separated by hand.

    7. Remove the end plate or end bell on the non-power shaft end (or the end of your choice if they both have extended shafts).

    8. Remove the end plate or end bell on the power (long shaft) end. For plain bearings, gently ease it off. If there is any resistance, double check for burrs on the shaft and remove as needed so as not to damage the soft bushing.

    9. Identify any flat washers or spacers that may be present on the shaft(s) or stuck to the bushings or bearings. Mark down their **exact** location and orientation so that they may be replaced during reassembly. Clean these and set aside.
    Inspect all components for physical damage or evidence of overheating or burning. Bad bearings may result in very obvious wear of the shaft or bushings or show evidence of the rotor scraping on the stator core. Extended overloads, a worn commutator, or shorted windings may result in visible or olfactory detected deterioration of wire insulation.

    While it is apart, brush or blow out any built up dust and dirt and thoroughly clean the shaft, bushings, commutator, and starting switch (present in large induction motors, only).

    Relubrication using electric motor oil for plain bearings and light grease for non-sealed ball/roller bearings.

    CAUTION: cleanliness is absolutely critical when repacking bearings or else you will be doing this again very soon.

    Badly worn ball bearings will need replacement. However, this may be better left to a motor rebuilding shop as they are generally press fit and difficult to remove and install.

    Reassemble in reverse order. If installation of the brushes needs to be done before inserting the armature, you will need to feed them in spring end first and hold them in place to prevent damage to the fragile carbon. Tighten the nuts or bolts evenly and securely but do not overtighten.

    Wiring up a capacitor run induction motor

    The following assume that the wires are unmarked and the motor is for use on 110 VAC, 60Hz (make appropriate changes if 220 VAC):

    Measure the resistance between each pair of windings to determine the common. That goes to the AC Neutral.

    The one with the higher resistance is probably the phase winding. The other winding goes directly to the AC Hot. If the resistances are similar, it doesn't matter which you use. If the resistances are very different, it may be a split phase induction motor that doesn't even need a capacitor. (It won't hurt to try it without for a short time. If the motor has enough torque and doesn't overheat, no cap is needed.)

    Select a capacitor value so that its impedance at 60 Hz (1/2pifC) is between 1 and 2 times the resistance of the winding. It has to be a cap rated for 250 VAC, continuous duty. The value I gave is sort of a guess but will get it running. The idea is to maximize the phase shift while still getting useful power to the phase winding. For a small motor, a few µF should work. The cap goes between AC Hot and the phase winding.

    This should get it going. If torque is too low, the µF value of the cap may need to be increased. Check that the motor isn't overheating once you have it running.

    Also see the section: Single-phase induction motors.

    Determining wiring for multispeed induction motor

    Many motors have a wiring diagram on their nameplate. However, where this is not the case, some educated guessing and experimentation will be necessary.

    Here is an example for a common multispeed furnace blower motor. In this case there is no capacitor and thus there are few unknowns.

    "Here's the problem - I have a squirrel cage fan that I would like to wire up. Unfortunately, there's only these four wires hanging there and I would hate to burn it up trying combinations. Here's what I know:

                  White   Black   Blue   Red
          White    0      1.5     2.2    2.9
          Black    1.5    0        .7    1.3
          Blue     2.2     .7     0       .7
          Red      2.9    1.3      .7    0

    So, how do I connect the motor?"

    From the resistance readings, it would appear that the Black, Blue, and Red are all taps on a single winding. My guess (and there are no warranties :-) would be: White is common, black is HIGH, blue is MEDIUM, red is LOW.

    I would test as follows:

    If it does not make any effort to start turning - just hums, go to plan B. It may require a starting/running capacitor and/or not be a 3 speed motor.

    Small permanent magnet DC motors

    These are constructed like small versions of universal motors except that the stator field is provided by powerful ceramic permanent magnets instead of a set of coils. Because of this, they will only operate on DC as direction is determined by the polarity of the input voltage.

    Small PM DC motors are used in battery or AC adapter operated shavers, electric knives, and cordless power tools.

    Similar motors are also used in cassette decks and boomboxes, answering machines, motorized toys, CD players and CDROM drives, and VCRs. Where speed is critical, these may include an internal mechanical governor or electronic regulator. In some cases there will be an auxiliary tachometer winding for speed control feedback. This precision is rarely needed for appliances.

    As noted, direction is determined by the polarity of the input power and they will generally work equally well in either direction.

    Speed is determined by input voltage and load. Therefore, variable speed and torque is easily provided by either just controlling the voltage or more efficiently by controlling the duty cycle through pulse width modulation (PWM).

    These motors are usually quite reliable but can develop shorted or open windings, a dirty commutator, gummed up lubrication, or dry or worn bearings. Replacement is best but mechanical repair (lubrication, cleaning) is sometimes possible.

    Problems with small PM motors

    These motors can fail in a number of ways:

    Testing of small PM motors

    An open or shorted winding may result in a 'bad spot' - a position at which the motor may get stuck. Rotate the motor by hand a quarter turn and try it again. If it runs now either for a fraction of a turn or behaves normally, then replacement will probably be needed since it will get stuck at the same point at some point in the future.

    Check across the motor terminals with an ohmmeter. There should be a periodic variation in resistance as the rotor is turned having several cycles per revolution determined by the number of commutator segments used. Any extremely low reading may indicate a shorted winding. An unusually high reading may indicate an open winding or dirty commutator. Cleaning may help a motor with an open or short or dead spot as noted below. Erratic readings may indicate the need for cleaning as well.

    Also check between each terminal and the case - the reading should be high, greater than 1M ohm. A low reading indicates a short. The motor may still work when removed from the equipment but depending on what the case is connected to, may result in overheating, loss of power, or damage to the driving circuits when mounted (and connected) to the chassis.

    A motor can be tested for basic functionality by disconnecting it from the appliance circuit and powering it from a DC voltage source like a couple of 1.5 V D Alkaline cells in series or a DC wall adapter or model train power pack. You should be able to determine the the required voltage based on the battery or AC adapter rating of the appliance. If you know that the appliance power supply is working, you can use this as well.

    Identifying voltage and current ratings small PM motors

    If the carcass of the device or appliance is still available, the expected voltage may be determined by examining the original power supply - batteries, voltage regulator, wall adapter, etc.

    The following applies to the common DC permanent magnet (PM) motors found in tape players and cassette decks used for the capstan.

    Motors without internal speed regulators are used for many functions in consumer electronics as well as toys and small appliances. The wire color code will probably be red (or warm color) for the positive (+) lead and black (or dark cool) color for the minus (-) lead.

    Reviving a partially shorted or erratic PM motor

    Dirt or grime on the commutator can result in intermittent contact and erratic operation. Carbon or metal particle buildup can partially short the motor making it impossible for the controller to provide enough voltage to maintain desired speed. Sometimes, a quick squirt of degreaser through the ventilation holes at the connection end will blow out the shorting material. Too much will ruin the motor, but it would need replacement otherwise anyway. This has worked on Pioneer PDM series spindle motors.

    Another technique is to disconnect the motor completely from the circuit and power it for a few seconds in each direction from a 9 V or so DC source. This may blow out the crud. The long term reliability of both of these approaches is unknown.

    WARNING: Never attempt to power a motor with an external battery or power supply when the motor is attached to the appliance, particularly if it contains any electronic circuitry as this can blow electronic components and complicate your problems.

    It is sometimes possible to disassemble the motor and clean it more thoroughly but this is a painstaking task best avoided if possible. See the section: Disassembling and reassembling a miniature PM motor.

    Disassembling and reassembling a miniature PM motor

    Note: for motors with carbon brushes, refer to the section: Disassembling and reassembling a universal or induction motor. This procedure below is for those tiny PM motors with metal brushes.

    Unless you really like to work on really tiny things, you might want to just punt and buy a replacement. This may be the strategy with the best long term reliability in any case. However, if you like a challenge, read on.

    CAUTION: disassembly without of this type should never be attempted with high quality servo motors as removing the armature from the motor may partially demagnetize the permanent magnets resulting in decreased torque and the need to replace the motor. However, it is safe for the typical small PM motor found in appliances and power tools.

    Select a clean work area - the permanent magnets in the motor will attract all kinds of ferrous particles which are then very difficult to remove.

    Follow these steps to minimize your use of 4 letter expletives:

    1. Remove the load - fan blades, gears, pulleys, etc. Label and disconnect the power wiring as well as the motor will be a whole lot easier to work on if not attached to the appliance or power tool. Note: polarity is critical - take note of the wire colors or orientation of the motor if it is directly soldered to a circuit board!

    2. Confirm that there are no burrs on the shaft(s) due to the set screw(s) that may have been there. For motors with plain bearings in particular, these will need to be removed to allow the shaft(s) to be pulled out without damage to the bushing.

    3. Use a scribe or indelible pen to put alignment marks on the cover so that it can be replaced in the same orientation.

    4. Make yourself a brush spreader. Most of these motors have a pair of elongated holes in the cover where the power wires are connected to the commutator. These allow the very delicate and fragile metal brushes to be spread apart as the armature is removed or installed. Otherwise, the brushes will get hung up and bent. I have found that a paper clip can be bent so that its two ends fit into these holes and when rotated will safely lift the brushes out of harm's way.

    5. Use a sharp tool like an awl or dental pick to bend out the 2 or 3 tabs holding the cover in place.

    6. Insert the brush spreader, spread the brushes, and pull the cover off of the motor. If done carefully, no damage will be done to the metal brushes.

    7. The armature can now be pulled free of the case and magnets.

    8. Identify any flat washers or spacers that may be present on the shaft(s). Mark down their **exact** location and orientation so that they may be replaced during reassembly. Clean these and set aside.
    Inspect all components for physical damage or evidence of overheating or burning. Bad bearings may result in very obvious wear of the shaft or bushings or show evidence of the rotor scraping on the stator core. Extended overloads, a worn commutator, or shorted windings may result in visible or olfactory detected deterioration of wire insulation.

    Check that the gaps in the commutator segments are free of metal particles or carbonized crud. Use a sharp instrument like an Xacto knife blade to carefully clear between the segments. Clean the brushes (gentle!), shafts, and bushings.

    When reassembling, make sure to use your brush spreader when installing the cover.

    DC brushless motors

    These are a variation on the small DC motors described above and uses a rotating permanent magnet and stationary coils which are controlled by some electronic circuitry to switch the current to the field magnets at exactly the right time. Since there are no sliding brushes, these are very reliable.

    DC brushless motors may be of ordinary shape or low profile - so called pancake' style. While not that common in appliances yet, they may be found in small fans and are used in many types of A/V and computer equipment (HD, FD, and CD drives, for example). Fortunately, they are extremely reliable. However, any non-mechanical failures are difficult to diagnose. In some cases, electronic component malfunction can be identified and remedied. Not that common in appliances but this is changing as the technology matures.

    Direction may be reversible electronically (capstan motors in VCR require this, for example). However, the common DC operated fan is not reversible.

    Speed may be varied over a fairly wide range by adjusting the input voltage on some or by direct digital control of the internal motor drive waveforms.

    The most common use for these in appliances are as small cooling fans though more sophisticated versions are used as servo motors in VCRs and cassette decks, turntables, and other precision equipment.

    Disassembling and reassembling a DC brushless fan

    This is the type you are likely to encounter - modify this procedure for other types.
    1. Remove the fan from the equipment, label and disconnect the power wires if possible.

    2. Remove the manufacturer's label and/or pop the protective plastic button in the center of the blade assembly. Set these aside.

    3. You will see an E-clip or C-clip holding the shaft in place. This must be removed - the proper tool is best but with care, a pair of fine needlenose pliers, narrow screwdriver, dental pick, or some other similar pointy object should work. Take great care to prevent it from going zing across the room.

    4. Remove the washers and spacers you find on the shaft. Mark down their positions so that they can be restored exactly the way you found them.

    5. Withdraw the rotor and blades from the stator.

    6. Remove the washers and spacers you find on the shaft or stuck to the bushings. Mark down their positions so that they can be restored exactly the way you found them.
    For fans with plain bearings, inspect and clean the shaft and the hole in the bushing using a Q-tip and alcohol or WD40 (see there is a use for WD40!). Check for any damage. Lubricate with a couple drops of electric motor oil in the bushing and any felt pads or washers.

    For fans with ball bearings, check the bearings for free rotation and runout (that they do not wobble or wiggle excessively). If bad, replacement will be needed, though this may not be worth the trouble. These are generally sealed bearings so lubrication is difficult in any case. On the other hand, they don't go bad very often.

    Reassemble in reverse order.

    Synchronous timing motors

    Miniature synchronous motors are used in mechanical clock drives as found in older clock radios or electric clocks powered from the AC line, appliance controllers, and refrigerator defrost timers. These assemblies include a gear train either sealed inside the motor or external to it. If the motor does not start up, it is probably due to dried gummed up lubrication. Getting inside can be a joy but it is usually possible to pop the cover and get at the rotor shaft (which is usually where the lubrication is needed). However, the tiny pinion gear may need to be removed to get at both ends of the rotor shaft and bearings.

    These consist of a stator coil and a magnetic core with many poles and a permanent magnet for the rotor. (In many ways, these are very similar to stepper motors). The number of poles determines the speed precisely and it is not easily changed.

    Direction is sometimes determined mechanically by only permitting the motor to start in the desired direction - they will usually be happy to start either way but a mechanical clutch prevents this (make note of exactly how is was positioned when disassembling). Direction can be reversed in this manner but I know of no actual applications where it would be desirable. Others use shading rings like those in a shaded pole induction motor to determine the direction of starting.

    Speed, as noted, is fixed by construction and for 60 Hz power it is precisely equal to: 7200/(# poles) RPM. Thus, a motor with 8 poles will run at 900 RPM.

    Disassembling and reassembling a small timing motor

    The best approach is usually replacement. In some designs, just the rotor and gear unit can be replaced while retaining the stator and coils.

    However, if your motor does not start on its own, is sluggish, or squeals, cleaning and lubrication may be all that is needed. However, to get to the rotor bearing requires removal of the cover and in most cases the rotor as well. This may mean popping off a press-fit pinion gear.

    1. Remove the motor from the appliance and disconnect its power wires if possible. This will make it a lot easier to work on.

    2. Remove the cover. This may require bending some tabs and breaking an Epoxy seal in some cases.

    3. Inspect the gears and shafts for gummed up lubrication. Since these motors have such low torque, the critical bearing is probably one for the main rotor. If there is any detectable stiffness, cleaning and lubrication is called for.

    4. You can try lubricating in-place but this will usually not work as there is no access to the far bearing (at the other end of the shaft from the pinion gear). I have used a small nail or awl to pop the pinion gear from the shaft by gently tapping in the middle with a small hammer.

    5. Withdraw the rotor from the motor.

    6. Identify any flat washers or spacers that may be present on the shaft. Mark down their **exact** location and orientation so that they may be replaced during reassembly. Clean these and set aside.

    7. Inspect and clean the shaft and bushings. Lubricate with electric motor oil.

    8. Reinstall the rotor and washers or spacers. Then press the pinion gear back onto the shaft just far enough to allow a still detectable end-play of about .25 to .5 mm. Check for free rotation of the rotor and all gears. Replace the cover and seal with household cement once proper operation has been confirmed.

    Motor bearing problems

    A dry or worn bearing can make the motor too difficult to turn properly or introduce unacceptable wobble (runout) into the shaft as it rotates.

    Feel and listen for a dry bearing:

    The shaft may be difficult to turn or it may turn with uneven torque. A motor with a worn or dry bearing may make a spine tingling high pitched sound when it is turning under power. A drop of light machine oil (e.g. electric motor oil) may cure a dry noisy bearing - at least temporarily.

    Runout - wobble from side to side - of a motor shaft is rarely critical in a small appliance but excessive side-to-side play may result in noise, rapid bearing wear, and ultimate failure.

    Motor noise

    If the noise is related to the rotating motor shaft, try lubricating the motor (or other suspect) bearings - a single drop of electric motor oil, sewing machine oil, or other light oil (NOT WD40 - it is not a suitable lubricant), to the bearings (at each end for the motor). This may help at least as a temporary fix. In some cases, using a slightly heavier oil will help with a worn bearing. See the section: Lubrication of appliances and electronic equipment.

    For AC motors in particular, steel laminations or the motor's mounting may be loose resulting in a buzz or hum. Tightening a screw or two may quiet it down. Painting the laminations with varnish suitable for electrical equipment may be needed in extreme cases. Sometimes, the noise may actually be a result of a nearby metal shield or other chassis hardware that is being vibrated by the motor's magnetic field. A strategically placed shim or piece of masking tape may work wonders.

    Finding a replacement motor

    In many cases, motors are fairly standardized and you may be able to find a generic replacement much more cheaply than the original manufacturer's part. However, the replacement must match the following:
    1. Mechanical - you must be able to mount it. In most cases, this really does mean an exact drop-in. Sometimes, a slightly longer shaft or mounting hole out of place can be tolerated. The pulley or other drive bushing, if any, must be able to be mounted on the new motor's shaft. If this is a press fit on the old motor, take extreme care so as not to damage this part when removing it (even if this means destroying the old motor in the process - it is garbage anyway).

    2. Electrical - the voltage and current ratings must be similar.

    3. Rotation direction - with conventional DC motors, this may be reversible by changing polarity of the voltage source. With AC motors, turning the stator around with respect to the rotor will reverse rotation direction. However, some motors have a fixed direction of rotation which cannot be altered.

    4. Speed - depending on the type appliance, this may or may not be that critical. Most induction motors run at slightly under 900, 1800, or 3600 RPM (U.S., 60 Hz power). DC motor speed can vary quite a bit and these are rarely marked.
    MCM Electronics, Dalbani, and Premium Parts stock a variety of small DC replacement motors. Appliance repair shops and distributors may have generic replacements for larger motors. Junk and salvage yard or your local dump may actually have what you want for pennies on the pound or less!

    Is motor rebuilding economical?

    So you left your electric cement mixer mixing away and forgot about it - for 3 days. Now the motor is a black charred ruin. You can rent a jack hammer to break up the cement but the motor is a lost cause. The manufacturer has been out of business for 20 years. What should you do besides give the tool a decent burial?

    Here is a possible option for, in this case, a planer:

    (From: Ed Schmitt (

    I located a person who rewinds motors and had the job done for $60.00. That was over 7 years ago, and the planer is still working. Look around and find some of our elderly craftsman who know how to rewind motors. You'll save a bundle, and have a working tool.

    (From: Michael Sloane (

    That is an interesting thought - I have a 1942 Cat road grader with burned out wiring in the 6 V wiper motor. Cat wants $200(!) for a new one, so I would like to find someone who would rewind the old one (and make it 12 V at the same time). I wouldn't even bother with the so-called auto-electric guys, all they do is replace the brushes and diodes on starters and alternators.

    Motor armature testing - or - what is a growler?

    A common fault that cannot always be reliably identified with a simple ohmmeter test is a couple of shorted turns in the winding that do not affect the total resistance significantly.

    A growler is basically an AC electromagnet exciting the windings in the armature. A shorted armature winding will act as a the secondary of a transformer resulting in a high current flow and high induced magnetic field.

    Hold a piece of spring steel like a hacksaw blade as a probe over the armature as you rotate it slowly on the electromagnet. A shorted winding will show up as a strong audible vibration of the 'probe' - thus the name growler.

    Small motor repair and replacement

    (From: mjsrnec (

    Most motor shops won't bother with the universal motors because they are much cheaper to replace than repair. However, if yours is a special be prepared to pay standard rates for the service. Email the Electrical Apparatus Service Association to find the EASA shop nearest you.

    If you think the motor may be fairly common pick up a Grainger catalog or go to: Grainger or: Grainger Universal Motor Index.

    If this is for a power tool, contact the tool manufacturer for the authorized service center nearest your location.

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Large Appliances

    Editor's note: Yes, I know this is supposed to be the "Small Appliance FAQ" but so be it. Until and if I write a "Large Appliance FAQ", this chapter will have to do. :-)

    Web resources for large appliance troubleshooting

    There are a number of Web sites dedicated to large appliance repair. Most are companies selling parts or manuals but they may also have on-line forums, replies to requests for assistance via email, or other free DIY information. However, very few, if any, have the sort of in-depth treatment of appliance repair provided by a good book on the subject. Please go to the "Appliance Sites" sections of Sam's Neat, Nifty, and Handy Bookmarks.

    The USENET newsgroups,, and may be appropriate for appliance repair questions as well.

    Electric oven calibration

    If your cakes come out all drippy or your chicken breasts end up hard as a rock and charred, this discussion is for you! It is possible that the thermostat on your oven needs calibration. However, major errors in temperature may be the result of a bad heating element, blown fuse or tripped breaker, a door that doesn't close or seal properly, etc. Confirm that the oven is in otherwise good operating condition before attempting calibration.

    The typical oven thermostat uses a bulb type thermometer/thermostat that feeds a diaphragm or Bourdon tube back at the control. A Bourdon tube is a coiled flattened tube that wants to straighten out when pressure is applied to it.

    Most ovens still use a fluid filled bulb that transmits pressure directly back to a pressure switch located in the control. When you turn the knob on the control, you are adjusting a cam that changes the position of the contacts inside.

    The sensor/sender is a larger copper tube (the bulb portion) that feeds into a capillary copper tube (your large copper wire - is a tube) that runs to the control.

    The procedure given below assumes that your oven has a mechanical thermostat which is still the most common type. For an electronic thermostat - one in which the set-point is entered via a touchpad - the adjustment (if any) will likely be on the controller circuit board rather than under the temperature knob. If you do attempt calibration of an electronic thermostat, make double sure that you have located the correct adjustment screw!

    (Portions from:

    Most thermostats have a calibration screw located under the knob. Try pulling the knob off and look at the shaft. Some shafts have a small screw located in the center. Rotating this screw will change the trip point at which the thermostat will turn on and off. This is determined by the sensor located inside the oven itself. Some other schemes allow for the entire control to rotate with respect to the scale. You will need to identify the type used on your oven

    You can also have your oven calibrated by an appliance service technician by locating them in your yellow pages and have him/her make a house call but you wouldn't be reading this if you wanted someone else to do it!

    The following procedure can be performed by almost anyone who knows which end of a screwdriver to poke into the screw head. :-) The first procedure is for controls where the adjustment screw changes the trip point temperature:

    1. Locate 2 thermometers that are oven safe and place them inside the oven on a shelf approximately in the center of the oven. Make sure the actual sensing elements of the thermometers do not touch anything.

    2. Remove the knob from the thermostat and locate an appropriate screwdriver for the adjusting screw. Re-install the knob.

    3. Turn on the oven and set it for 300 degrees F. Allow it to come up to temperature (set light goes out). Then wait an additional 10 minutes.

    4. Look at the temperature of the thermometers (averaging the two) and determine the error amount and direction. Note: if the error is large (greater than, perhaps, 50 degrees F) then there may be a problem with the oven (such as a bad temperature sensor) which will not be remedied by calibration.

    5. Where the adjustment changes the trip point, remove the knob and adjust the screw in the shaft one way or the other depending on which way the oven set-point is off. If the direction is not marked to increase or decrease the temperature, just pick one - there is no standard. You may be wrong on the first attempt. :-(

      Rotate the adjustment in small increments!

    6. Place the knob back on the shaft.

    7. Again wait 10 minutes after the oven set light goes off.

    8. Look at the temperature of the thermometers and see how far off the error is now.

    9. Repeat the steps above until this set-point is accurate.

    10. Now set the thermostat to 400 degrees F and repeat the steps above for this setting.

    Where the adjustment only changes the knob pointer position, the procedure is much simpler:

    1. Locate 2 thermometers that are oven safe and place them inside the oven on a shelf approximately in the center of the oven. Make sure the actual sensing elements of the thermometers do not touch anything.

    2. Remove the knob from the thermostat and locate an appropriate screwdriver for the screws that lock the control. Re-install the knob.

    3. Turn on the oven and set it for 300 degrees F. Allow it to come up to temperature (set light goes out). Then wait an additional 10 minutes.

    4. Look at the temperature of the thermometers (averaging the two) and estimate by how much the knob would have to rotate to match that. If the temperature error is very large (greater than, perhaps, 50 degrees F) then there may be a problem with the oven (such as a bad temperature sensor) which will not be remedied by calibration.

    5. Remove the knob and loosen the lock screw(s) so the control can be rotated but is snug enough that it will retain its position.

    6. Rotate the control by the amount estimated above and place the knob on the shaft just enough to check how close it is. Adjust as needed.

    7. Now set the thermostat to 400 degrees F and confirm that it is close at this setting.

    If you really want to be the oven to be accurate, Turn the oven off and allow it to completely cool. The, repeat the above complete procedure 2 more times or until the accuracy you desire is achieved.

    Repeating this procedure may seem redundant but some thermostats because of their mechanical nature have a margin of error. Also due to the mechanical nature, some settling of the parts inside does occur.

    As long as the heating elements in the oven do not fail, the oven should maintain its accuracy for quite some time. A simple check of the oven once every 6 months or once every year will assure you that your baking temperatures will be accurate.

    Heat control in electric range surface units

    The typical electric range surface unit has two spiral elements. In older ranges, they are used in various combinations across the 120 and 240. We have a GE range like this which has 5 heat settings (and off) for each 'burner'.

    Given 2 element and 2 voltages there are 8 possible connection possibilities. I don't know which 5 my GE range uses.

    Newer ranges use a single element or just parallel the two elements and use variable power control (pulse width modulation or thyristor phase control) to obtain arbitrary heat levels and/or a thermostat to sense the actual temperature.

    BTW, this GE range is about 46 years old and still going strong (except for the 1 hour timer which died about 5 years ago.)

    (The following experiments from: Mark Zenier (

    From my multiple renovations of my mother's stove of a similar vintage:

    Warm is 120 volts applied to both elements of a burner in series.

    Low is 120 volts applied to one of the two elements. The burners are wired so that they are not the same. Half of the burners used the center element, the others used the rim element. Usually split between front burners and rear. (This is a GE, other companies used two interleaved spiral elements.)

    Third is 120 volts applied to both elements.

    Second is 240 volts applied to one element, like Low, it varies from burner to burner.

    High is 240 volts applied to both elements.

    Electric range top element does not work properly

    If all the elements are dead, check for blown fuses/tripped circuit breakers. There may be some in the range unit itself in addition to your electrical service panel.

    If one element is completely dead on all heat settings, the control is probably bad or there is a broken wire. If it is stuck on high for all control settings or is erratic, the control is bad - replacements are readily available and easily installed.

    On ranges with push button heat selection, a pair of heating elements are switched in various combinations across 120 and/or 240. If some heat settings do not work, the most likely cause is that one of the heatings elements is burnt out although a bad switch is also possible. Kill power to the range and test the heating elements for continuity. Replacements are available from appliance parts stores or the places listed in the section: Parts suppliers.

    Improvised welding repair of heating elements

    Due to the high temperatures at which they operate, welding may provide better long term reliability of heating elements than mechanical fasteners. However, in most cases, the following extreme measures are not really needed.

    Warning: only consider the following if you are absolutely sure you understand the safety implications of working directly with line voltage - it is not very forgiving. There is both an electrocution and fire hazard involved.

    (From: Donald Borowski (

    I have had success with welding heating element wires back together using a "carbon arc torch". I did this on a ceramics kiln recently.

    I extracted the carbon rods from two carbon/zinc D cell ('Classic' or 'Heavy Duty' variety, alkalines do hot have carbon rods). I filed one end to a point.

    I wired a circuit as follows:

    Then I touched the carbon rods together and drew them apart, producing a carbon arc. I moved the carbon rods and arc to position the tip of the heater wire pigtail in the arc. I slowly moved the arc in along the pigtail until a molten ball of nichrome formed between the two wires of the pigtail. When this happened, I immediately withdrew the arc.

    Of course, all safety warnings apply: Dangerous power line voltages, welder's mask needed for protect eyes, possible dangerous chemicals in D cell, etc.

    This should work for other types of Nichrome coiled or ribbon heating elements as well.

    I vaguely recall seeing many years ago a suggestion of making a paste of borax and putting it over the twisted-together ends. I guess it was supposed to act as a self-welding flux. Anyone else recall this?

    Due to the high temperatures at which they operate, welding may provide better long term reliability of heating elements than mechanical fasteners. However, in most cases, the following extreme measures are not really needed.

    Warning: only consider the following if you are absolutely sure you understand the safety implications of working directly with line voltage - it is not very forgiving. There is both an electrocution and fire hazard involved.

    Induction cooktops

    This info has moved to Induction Cookers and Cooktops since the actual technology is similar for stand-alone cookers and the individual positions on induction stoves.

    Range, oven, and furnace electronic ignition

    Many modern gas stoves, ovens, furnaces, and other similar appliances use an electronic ignition rather than a continuously burning pilot flame to ignite the fuel. These are actually simple high voltage pulse generators. The Harper-Wyman Model 6520 Kool Lite(tm) module is typical of those found in Jenne-Aire and similar cook-tops. Input is 115 VAC, 4 mA, 50/60 Hz AC. C1 and D1 form a half wave doubler resulting in 60 Hz pulses with a peak of about 300 V and at point A and charges C2 to about 300 V through D2. R2, C3, and DL1 form a relaxation oscillator triggering SCR1 to dump the charge built up on C2 into T1 with a repetition rate of about 2 Hz.
               C1                A       D1                     T1 o
        H o----||----------------+-------|>|-------+-------+       +-----o HVP+
             .1 µF     D2 1N4007 |     1N4007      |       |  o ::( 
             250 V   +----|>|----+                 |       +--+ ::(
                     |           |                 |           )::(
                     +---/\/\----+                 |       #20 )::( 1:35
                     |  R1 1M    |             C2 _|_          )::(
                     |        R2 /           1 µF ---      +--+ ::(
                     |       18M \    DL1   400 V  |     __|__  ::(
                     |           /    NE-2         |     _\_/_     +-----o HVP-
                     |           |    +--+         |     / |
                     |           +----|oo|----+---------'  | SCR1
                     |       C3  |    +--+    |    |       | S316A
                     |  .047 µF _|_        R3 /    |       | 400 V
                     |    250 V ---       180 \    |       | 1 A
                     |           |            /    |       |
             R4 2.7K |           |            |    |       |
        N o---/\/\---+-----------+------------+----+-------+
    Before you blame the ignition module for either lack of spark or continuous spark, make sure the wiring is in good condition and completely dry and clean (well reasonably clean!). Confirm that proper voltage is reaching the module with a multimeter or neon test lamp. The modules are actually quite robust: These are probably standard modules and replacements should be available from your local appliance repair shop or parts supplier. An exact mechanical match is not needed as long as the specifications are compatible.

    Oven door seal repair

    (From: Brian Symons (

    If you need a high temp silastic (e.g., for refitting glass windows in ovens) then the Black silastic sold for car windscreen sealing from the local service station or garage is the stuff. Works well. Someone here waited several months and paid $80 for what he could buy down the road for $10 - it was even the same brand.

    Freezer is normal but fresh food compartment isn't even cool ---------------------------------------------------------

    Some possibilities:

    If you are handy, you can narrow down the problem and possible fix it - a defrost timer can be easily replaced. See the section: Defrost system operation and wiring.

    Refrigerator not cooling after a week

    First, clean the condenser coils. It is amazing how much dust collects there and interferes with proper cooling.

    If you just turned it on a week ago and it is not acting up, a failure of the defrost timer is quite likely. On an old fridge, the grease inside dries out/gunks up and restarting from cold results in it not running. It takes about a week for enough ice to build up to be a problem.

    This is a $12 repair if you do it yourself or $100 or so if you call someone.

    Could be other things but that is what I would check first. On a GE, it is usually located at the bottom front and there is a hole in the front in which you can poke your finger to turn it clockwise by hand. Turn it until you hear a click and the fridge shuts off. You should not get melting in the evaporator compartment and water draining into the pan at the bottom. The fridge compressor should start up again in 10-20 minutes but I bet in your case it won't as the timer needs replacement.

    Defrost system operation and wiring

    The most common type of defrost system on a no-frost refrigerator or freezer usually consists of: Testing: It should be possible to easily identify the bad components. For the following, it is assumed that the main thermostat is set such that the compressor is on. Defrost timers are readily available at appliance parts distributors. A generic timer will cost about $12. An exact replacement, perhaps up to $35. If you call in a service person, expect to pay over $100 for the part and labor.

    Generally, the defrost timer is an SPDT switch operated by a cam on a small motor with a 4 to 8 hour cycle (depending on model). For an exact replacement, just move the wires from the old timer to the same terminals on the new unit. For a generic replacement, the terminal location may differ. Knowing what is inside should enable you to determine the corresponding terminal locations with a multimeter.

    The terminal numbering and wire color code for the defrost timer in a typical GE refrigerator is shown below:

                         Black (4)
        Gray (3)      /o---------o Normal position - Compressor, evaporator fan.
    H* o-----+------/
             |         o---o Blue (2)
           Timer           |         Defrost heater  Defrost Thermostat
           Motor (3180     o------------/\/\/\------------o/o----------+
             |    ohms)                 31 ohms          32 F          |
             |                                                         |
             | Orange (1)                                              |
             o---------------------------------------------------------+--o Common

    * H is the Hot wire after passing through the main thermostat (cold control) in the fresh food compartment.

    Since the defrost timer only runs when the compressor is powered, it will defrost more frequently when the fridge is doing more work and is likely to collect more frost. This isn't perfect but seems to work.

    Compressor starting relays

    Most refrigeration compressors use a current mode relay to engage the starting winding of their split phase induction motor. However, a PTC (Positive Temperature Coefficient) thermistor might also be used.

    A starting relay senses the current flowing to the run winding of the compressor motor (the coil is a few turns of heavy wire in series with the run winding) and engages the starting winding when that current is above a threshold - indicating that the rotor is not up to speed.

    A PTC thermistor starts with a very low resistance which increases to a high value when hot. Proper operation depends on the compressor getting up to speed within a specific amount of time.

    For testing only, you can substitute an external switch for the starting device and try to start it manually.

    CAUTION: Do not bypass a faulty starting device permanently as the starting winding is not intended to run continuously and will overheat and possibly burn out if left in the circuit.

    Assuming you have waited long enough for any pressures to equalize (five minutes should do it if the system was operating unless there is some blockage - dirt or ice - inside the sealed system), you can test for proper operation by monitoring the voltage on the start and run windings of the compressor motor. If there is line voltage on both windings and it still does not start up - the overload protector switches off or a fuse or circuit breaker pops - the compressor is likely bad.

    Refrigeration compressor wiring

    The following applies to a typical GE refrigerator compressor. YOURS MAY BE DIFFERENT! There may be a wiring diagram tucked in with your customer information, attached to the back of the unit, or hidden underneath somewhere.

    The sealed unit has 3 pins usually marked: S (Start), R or M (Run or Main), and C (Common). The starting relay is usually mounted over these pins in a clip-on box. The original circuit is likely similar to the following:

                          |<- Starting Relay ->|<---- Compressor Motor ---->|
                   ___            L      
         AC H o----o o--------------+--o/   S    S
                "Guardette"         |    o---->>-------------+
                 (Thermal           +-+                      |
                 Protector)            )||                   +-+
                            Relay Coil )||                      )||
                                       )||                      )|| Start
                                    +-+                         )|| Winding
                                    |                           )||
                                    |      M    R/M          +-+
                                    +-------->>------+       |
                                                      )||    |
                                             Run/Main )||    |
                                              Winding )||    |
                                                      )||    |
                                                   +-+       |
                                                C  |         |
         AC N o------------------------------>>----+---------+
    The Starting Relay engages when power is applied due to the high current through the Run winding (and thus the relay coil) since the compressor rotor is stationary. This applies power to the Start winding. Once the compressor comes up to speed, the current goes down and the Starting Relay drops out.

    Note the Thermal Protector (often called a "Guardette" which I presume is a brand name). This shuts off power to the compressor if the temperature rises too high due to lack of proper cooling (defective compressor/condenser cooling fan, missing cardboard baffle, or clogged up (dusty) comdensor; an overload such as a blockage in the sealed system (bad news), or low line voltage.

    Changing the temperature range of a small refrigerator

    It is simple in principle. The cold control - the thing with the knob - needs to be modified or replaced. It is a simple on/off thermostat. You may be able to figure out how to adjust its limits (mechanical) or simply locate a suitable thermostat and install it in place of the existing unit. Note: if it uses a capillary tube to a sensing bulb, don't attempt to modify that part - it is sealed and should remain that way. The mechanism it operates may still be adjustable. However, you will likely loose the low end of your temperature range.

    Washer sometimes spins

    When it should be spinning, is the motor running? Does it complete the cycle in the normal time?

    I would guess that the solenoid to shift it into spin is binding or erratic. Thus opening the door gives switches it on and off like the timer but since it sometimes works, it sometimes works by cycling the door switch.

    Clothes washer does not fill (cold or hot)

    This assumes the unit has power and otherwise operates normally. However, determining this may be difficult if the completion of the cycle is dependent on a water weight or volume sensor.

    There are several possibilities:

    1. The appropriate water inlet filter is clogged. This will be accessible by unscrewing the hose connection. Clean it.

    2. The solenoid is bad. If you are electrically inclined, put a multimeter on the cold water valve to see if it is getting power.

    3. The temperature selector switch is bad or has bad connections.

    4. The controller is not providing the power to the solenoid (even for only hot or cold, these will have separate contacts).

    Maytag washer timer motor repair

    The following applies to many Maytag models manufactured over the last 25 or 30 years. A typical example is "A106" of 1970s vintage but much more recent models use the same mechanism. After 20 or 30 years, even a Maytag washer may need a service call. :) It also likely applies to other makes of washers.

    One common failure is of the motor that drives the electromechanical controller. And, the problem may be a 2 cent plastic gear! The symptoms are that the timer never advances. The cause is that due to age, use, or gummed up grease, the pinion gear on the rotor of the timing motor cracks and the timer fails to move. As of 2001, the entire motor was available from Maytag for about $55, and generic versions from other appliance parts suppliers for around $30. (An Internet search of "Maytag parts" will turn up several possible suppliers.) However, a repair may be possible. There is no way to order just the gear but what's left of it is usually salvageable. Whether the repair lasts a week or 10 years, no guarantees but it is fairly easy. Here is the sequence of steps to perform the repair:

    Now you (or your spouse) will have no excuses to deal wtih those piles of dirty laundry!

    Window air conditioner preventive maintenance

    Very little needs to be done to get many years of service from a typical window air conditioner.

    Of course, clean the inside filter regularly. This is usually very easy requiring little or no disassembly (see your users manual). Some slide out without even removing the front cover (e.g., Emerson Quiet Kool).

    I generally do not bother to open them up each year (and we have 4). Generally, not that much dirt and dust collects inside. A cover during the winter also helps.

    Use a vacuum cleaner on the condenser coils in the back and any other easily accessible dirt traps.

    If you do take the cover off, check the fan motor for free rotation. If it is tight indicating bad bearings or lack of lubrication, it will have to be disassembled, cleaned, and lubricated - or replaced. If there are lubrication holes at the ends of the motor, put a couple drops of electric motor oil in there while you have it open.

    These units have a sealed freon system - so if anyone's been into it before - you can tell from obvious saddle valves clamped on. Generally, if it cools and the air flow is strong, it is OK.

    These units tend to be very reliable and low maintenance.

    Window air conditioner doesn't cool

    This means the fan runs but you do not hear the compressor kick in.

    It could be several things:

    Except for a bad compressor, all these are repairable relatively inexpensively but if it is real old, a new high efficiency model may be a better solution.

    Air conditioner freezes up

    When this happens, airflow is reduced greatly since ice is blocking the evaporator. Turning the unit off for a while or running it on fan-only will clear the ice but this may indicate the need for maintenance or an actual problem. Similar comments apply to window and central air conditioners as well as heat pumps.

    The three major causes of an air conditioner freezing up are:

    1. Reduced airflow due to a dirty filter or clogged evaporator. If you are not aware that there is a filter to clean, this is probably the cause :-).

    2. Low Freon. While your intuition may say that low Freon should result in less cooling, what happens is that what is there evaporates too quickly and at the input end of the evaporator coils resulting in lower temperatures than normal at that end (which results in condensed water vapor freezing instead of dripping off) but part of the evaporator will likely be too warm.

      You cannot fix this yourself without specialized equipment. For a room air conditioner that isn't too old, it may be worth taking it in to a reputable shop for an evaluation. For a central air conditioner, you will have to call an HVAC service company for repairs.

      The fact that the Freon is low means that there is a leak which would also need to be repaired. Freon does not get used up.

    3. Outside and/or inside temperature may be very low. The unit may not be designed to operate below about 65 degrees F without freezing up.
    If it is 90 degrees F and you have full air flow with the fan set on high and still get the freezup on a part of the evaporator, then low Freon is likely.

    Comments on electric clothes dryer problems and repair

    For quite a lot of useful information, do a web search for 'appliance repair'. There are a couple of decent sites with DYI information.

    (From: Bernie Morey (

    I've repaired our electric dryer several times over the years and kept it going well beyond its use-by date.

    My main problems have been:

    1. Mechanical timer failure. Easy fix.

    2. Leaking steam damaging the element. Have replaced element twice -- fairly easy job. Had to replace some stainless stand-offs at the same time. Elements readily available and equivalent of USD24 each.

    3. Bearing replacement -- have to be done carefully or they don't last.

    4. Belt replacement. (Make sure you center the belt with respect to the idler and rotate the drum by hand to double check it before buttoning things up. Else, it may pop off the first time the motor starts. --- sam).

    5. Exhaust fan bearing replacement. This was the trickiest, although far from impossible. It is a sealed unit subject to high heat and dust contamination -- not a good environment.
    The only problem for the past two years has been the dryer throwing the exhaust fan belt. Cleaning up the fluff fixes it for another year.

    Did all these without any guide -- just carefully inspecting the work before starting and making diagrams of wiring and ESPECIALLY the main drum belt. I generally have to get my wife to help me with the main belt -- hard to get the tensioner in position while stopping the belt slipping down the far side of the drum.

    These things are mechanically and electrically pretty simple -- if it's not working the fault is usually obvious.

    (From: Larry Brackett (

    Here are some things to check for a Kenmore or Whirlpool dryer not running. These things will apply to any dryer. The difference being the identification and location of these parts in different dryers. Always look at the wiring picture for your product to see what these are. The identifying numbers and letters here will not apply to all Whirlpool dryers. Please remember this.

    Dryer shuts down after a few minutes

    There are multiple thermostats in a dryer - one that sets the air temperature during normal operation (and controls power to the heating element) and one or more that sense fault conditions (and may shut everything down) such as those described below.

    (From: Bernie Morey (

    The dryer is likely cutting out because a thermostat is tripping. The fundamental reason is probably that the exhaust air is too hot. And the air flow is probably too hot because it is restricted -- lower volume of air at higher temperature. Check these things out:

    1. Lint filter. Although these can look clean (and I assume you do clean it after every load!) the foam variety can gradually clog up with very fine dust and restrict air flow. If it's a foam disk, a new one is fairly cheap.

    2. Can you feel the exhaust air? If not, the exhaust fan belt may be worn broken or slipping. The exhaust fan bearing could be partly seized -- try turning the fan by hand and check for stiffness.

    3. Air outlet blockage. Lint and dust may have built up in the exhaust side of the machine. Check for restrictions. Our machine just vents up against the laundry wall as it is too difficult to vent it to the outside.

      Outside vents are often plastic tubing with a spiral spring steel coil for stiffness -- check for kinks or obstructions.

    4. 'Clutching at straws' Dept #1: Element may have developed a hot-spot near a thermostat. Involves dismantling the machine and checking the element. NB -- if you dismantle the machine, make a diagram of how the drive belt fits over the drum, motor, and idler!

    5. 'Clutching at straws' Dept #2: The drum may be restricted from turning freely. This would slow the motor and hence the exhaust fan. Check for socks, women's knee-highs (these thing seem to breed everywhere!) & caught near the bearings (probably the front).
    You cannot completely check the thermostat with a meter -- they are either open or closed. To test it properly you would have to know the temperature at which it opens (from the manufacturer's specs), and then measure the temperature of the exhaust air with a probe while watching the thermostat.

    Why has my dryer (or other high current) plug/socket burned up?

    This sort of failure is not unusual. The brass (or whatever) corrodes a bit over time and/or the prongs loosen up. It doesn't take much resistance at 20 or 30 Amps to produce a substantial amount of heat. The hotter it gets, the more the resistance goes up, heating increases, it loosens more, and so on until something melts. The power is I*I*R (where I is current and R is the resistance) so at 20 A, a .1 ohm resistance at the contact results in 40 W - think of the heat of a 40 W light bulb.

    An exact cause would be hard to identify. However, only the plug and receptacle are involved - this is not a case of an outside cause. Such a failure will not normally blow a fuse or trip a breaker since the current does not increase - it is not a short circuit.

    It is definitely wise to replace both the plug and receptacle in such cases since at the very least, the socket has lost its springiness due to the heating and will not grip well.. Make sure that the prongs on the new plug make a secure fit with the socket.

    On plugs having prongs with a pair of metal strips, spreading them out a bit will make much better contact in an old receptacle.

    In general, if a plug is noticeably warm, corrective action should be taken as it will likely get worse. Cleaning the prongs (with 600 grit sandpaper) and spreading the metal strips apart (if possible) should be done first but if this does not help much, the plug and/or socket should be replaced. Sometimes, the original heating problem starts at the wire connections to the plug or socket (even inside molded units) - loose screws, corroded wires, or deteriorated solder joints.

    Four year old gas dryer just started popping GFCI

    Why is it on a GFCI in the first place? A grounded outlet is all the protection that is needed and any type of appliance with a motor or transformer could be a potential nuisance tripper with a GFCI (though not always).

    As to why it is now different, I assume that this is a dedicated outlet so nothing else you added could affect it. Thus you are left with something changing in the dryer or the GFCI somehow becoming overly sensitive.

    It is possible that there is now some electrical leakage in the dryer wiring just from accumulated dirt and grime or dampness. This could be measured with an AC milliamp meter or by measuring the resistance between the AC wires and the cabinet. If this test shows up nothing, I would recommend just putting on a grounded outlet without a GFCI. It could also be that due to wear, the motor is working harder at starting resulting in just a tad more of an inductive current spike at startup.

    Checking dishwasher solenoids

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (

    Greetings. Well, since it's a moist/damp environment... I'd suspect a bad connection first. You will need to pop off the front bottom panel and get at the wires that actually connect the solenoid to the timer motor (and/or wire harness). You will need an ohmmeter to check the resistance of the coil - if it's OK (20-200 ohms I would guess), that's not the problem. Well, that leaves you with pretty much the wires that connect the timer motor (a MULTI-contact switch driven by a timer motor like those found in old clocks that plugged into outlets) and the switch itself. I hope the dishwasher is unplugged... Since the dishwasher operates as a closed system (because of the "darned" water :-) it will be difficult to test it in circuit. I suggest that you try to trace the wires that come off the solenoid to their other ends... and then test the wires themselves. If you feel this is too much for you, call the repair folks - ask around... see if anyone else knows a particular service that has a good record...

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Electrical Wiring Information and Problems

    Safe electrical wiring

    This chapter is in no way intended to be a comprehensive coverage of wiring issues but includes a discussion of a few of the common residential wiring related questions. For more information, see the official Usenet Electrical Wiring FAQ or a DIY book on electrical wiring. The NEC (National Electrical Code) handbook which is updated periodically is the 'bible' for safe wiring practices which will keep honest building inspectors happy. However, the NEC manual is not what you would call easy to read. A much more user friendly presentation can be found at the CodeCheck Web Site. This site includes everything you always wanted to know about construction codes (building, plumbing, mechanical, electrical) but were afraid to ask.

    In particular, the following series of sections on Ground Fault Circuit Interrupters (GFCIs) is present at the CodeCheck web site and includes some nice graphics as well. Specifically: GFCI by Sam Goldwasser.

    What is a GFCI?

    A Ground Fault Circuit Interrupter (GFCI) is a device to protect against electric shock should someone come in contact with a live (Hot) wire and a path to ground which would result in a current through his/her body. The GFCI operates by sensing the difference between the currents in the Hot and Neutral conductors. Under normal conditions, these should be equal. However, if someone touches the Hot and a Ground such as a plumbing fixture or they are standing in water, these currents will not be equal as the path is to Ground - a ground fault - and not to the Neutral. This might occur if a short circuit developed inside an ungrounded appliance or if someone was working on a live circuit and accidentally touched a live wire.

    Continuing with the water analogy used elsewhere in this document, the Hot is equivalent to the water supply and the Neutral is equivalent to the drain. The flow rate (current) can be high and do work like running a pump as long as all the water goes down the drain. But if there is a leak and the water splashes out on to the ground, then the the water equivalent of a GFCI will trip and shut off the water.

    The (electrical) GFCI will trip in a fraction of a second at currents (a few mA) well below those that are considered dangerous. Note that a GFCI is NOT a substitute for a fuse or circuit breaker as these devices are still required to protect equipment and property from overloads or short circuits that can result in fire or other damage.

    GFCIs can be installed in place of ordinary outlets in which case they protect that outlet as well as any downstream from it. There are also GFCIs that install in the main service panel. Either will provide the same level of safety but the breaker will automatically protect everything on its circuit no matter how it is wired while the outlet version will only protect the outlet and other outlets downstream from it.

    Note that it may be safe and legal to install a GFCI rated at 15 A on a 20 A circuit since it will have a 20 A feed-through. Of course, the GFCI outlet itself can then only be used for appliances rated 15 A or less.

    Many (if not most) GFCIs also test for a grounded neutral condition where a low resistance path exists downstream between the N and G conductors. If such a situation exists, the GFCI will trip immediately when power is applied even with nothing connected to the protected outlets.

    GFCIs, overloads, and fire safety

    A GFCI is NOT a substitute for a fuse or circuit breaker (unless it is a combined unit - available to replace circuit breakers at the service panel).

    Therefore, advice like "use a GFCI in place of the normal outlet to prevent appliance fires" is not really valid.

    There may be some benefit if a fault developed between Hot and Ground but that should blow a fuse or trip a circuit breaker if the outlet is properly wired. If the outlet is ungrounded, nothing would happen until someone touched the metal cabinet and an earth ground simultaneously in which case the GFCI would trip and provide its safety function. See the section: Why a GFCI should not be used with major appliances for reasons why this is not generally desirable as long as the appliance or outlet is properly grounded.

    However, if a fault occurs between Hot and Neutral - a short in the motor, for example - a GFCI will be perfectly happy passing almost any sort of overload current until the GFCI, wiring, and appliance melts down or burns up - a GFCI is not designed to be a fuse or circuit breaker! That function must be provided separately.

    How does a GFCI work?

    GFCIs typically test for the following condition:

    1. A Hot to Ground (safety/earth) fault. Current flows from the Hot wire to Ground bypassing the Neutral. This is the test that is most critical for safety.

    2. A grounded Neutral fault. Due to miswiring or a short circuit, the N and G wires are connected by a low resistance path downstream of the GFCI. In this case, the GFCI will trip as soon as power is applied even if nothing is connected to its protected (load) circuit.

    To detect a Hot to Ground fault, both current carrying wires pass through the core of a sense coil (transformer). When the currents are equal and opposite, there is no output from its multiturn sense voltage winding. When an imbalance occurs, an output signal is produced. When this exceeds a threshold, a circuit breaker inside the GFCI is tripped.

    GFCIs for 220 VAC applications need to monitor both Hots as well as the Neutral. The principles are basically the same: the sum of the currents in Hot1 + Hot2 + Neutral should be zero unless a fault exists.

    To detect a grounded neutral fault, a separate drive coil is continuously energized and injects a small 120 Hz signal into the current carrying conductors. If a low resistance path exists between N and G downstream of the GFCI, this completes a loop (in conjunction with the normal connection between N and G at the service panel) and enough current flows to again trip the GFCI's internal circuit breaker.

    GFCIs use toroidal coils (actually transformers to be more accurate) where the core is shaped like a ring (i.e., toroid or doughnut). These are convenient and efficient for certain applications. For all practical purposes, they are just another kind of transformer. If you look inside a GFCI, you will find a pair of toroidal transformers (one for H-N faults and the other for N-G faults as described above). They look like 1/2" diameter rings with the main current carrying conductors passing once through the center and many fine turns of wire (the sense or drive winding) wound around the toroid.

    All in all, quite clever technology. The active component in the Leviton GFCI is a single chip - probably a National Semiconductor LM1851 Ground Fault Interrupter. For more info, check out National's LM1851 Specs.

    More on how the GFCI detects a N-G short

    To detect a Neutral to Ground fault there is a second transformer placed upstream of the H-G sense transformer (see the illustration of the internal circuitry of the GFCI at: A small drive signal is continuously injected via the 200 T winding which induces equal voltages on the H and N wires passing through its core.

    GFCIs and safety ground

    Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be installed in a 2 wire circuit, the GFCI does not create a safety ground. In fact, shorting between the Hot and Ground holes in the GFCI outlet will do absolutely nothing if the GFCI is not connected to a grounded circuit (at least for the typical GFCI made by Leviton sold at hardware stores and home centers). The Ground holes are only connected to the green screw on the outside of the GFCI, not to any circuitry inside the GFCI and it will trip only if a fault occurs such that current flows to a true ground. If the original circuit did not have a safety ground, the Ground Holes aren't going anywhere. What this means is that an appliance with a 3 prong plug can develop a short between Hot and the (supposedly) grounded case but the GFCI will not trip until someone touches the case and an earth ground (e.g., water pipe, ground from some other circuit, etc.) at the same time.

    Note that even though this is acceptable by the NEC, I do not consider it desirable. Your safety now depends on the proper functioning of the GFCI which is considerable more complex and failure prone than a simple fuse or circuit breaker. If it's not tested periodically, reliability is even lower. Therefore, if at all possible, provide a proper Code compliant ground connection to all outlets feeding appliances with 3 wire plugs.

    Where are 3 wire grounded outlets required?

    If you move into a house or apartment where some or all of the outlets are the old 2 prong ungrounded type, don't panic. There is no reason to call an electrician at 2:00 AM in the morning to upgrade them all at great expense. (This also applies to 3 prong outlets that don't have their third prong hooked up.)

    You don't need grounded outlets for two wire appliances, lamps, etc. They do essentially nothing if the third hole isn't occupied :-). A GFCI will provide much more protection and it is permissible retrofit these into ungrounded wiring.

    You should have grounded outlets for the following:

    In most cases, there will only be a few circuits where this is needed and only these need to be upgraded. To what extent the wiring plan of your residence separates lighting type circuits from those with outlets that will be used for 3 wire equipment will determine how easy it is to upgrade only those outlets that are affected. It may be cheaper to just add new branch circuits for specific equipment needs.

    However, if you are replacing old worn outlets anyhow, it does make sense to upgrade to 3 prong outlets if they can be properly grounded without pulling a new wire - for example, if the box is already grounded but simply not connected to the old outlet.

    In all cases, make sure that the new outlet is properly wired with respect to the ground and H-N polarity. An improperly wired 3 prong outlet may be worse than any 2 prong variety!

    Why you should NOT connect G to N

    The question often arises: "Why can't I just connect the G to the N if my outlets are only two prong?"

    For one reason, consider the 'appliance' below:

                 |                 |        Open Fault
      Hot o---------o-o----/\/\---------+------ X -----o Neutral
                 | Switch  Load    |    |
                 |  (On)           |----+ Case should be G but is connected to N
    With the appliance 'on', current passes through the internal wiring/motor/etc. of the appliance to the N but this is now connected to the case as well. If the house wiring opens (or even if the plug is loose, it is possible to have line voltage on the case.

    The 'appliance' can actually be *all* loads on the circuit upstream of the the Open Fault - all those with a grounded cabinet have it then become live!

    Testing installed GFCIs

    These tests should be performed periodically to assure that the GFCIs are providing the protection for which they were designed. It is possible for the GFCI's circuitry to go bad or for the contacts to get stuck. The usual recommendation is once a month but more frequently won't hurt.

    On most GFCIs, the built-in tester is designed to actually introduce a small leakage current so its results should be valid. Therefore, testing a single GFCI outlet with an external widget is not really necessary except for peace-of-mind. However, such a device does come in handy for identifying and testing outlets on the same circuit that may be downstream of the GFCI.

    An external tester is easy to construct - a 15 K ohm resistor between H and G will provide a 7 mA current. Wire it into a 3 prong plug and label it "GFCI Tester - 7 mA". The GFCI should trip as soon as you plug the tester into a protected outlet. On a GFCI equipped for grounded neutral detection (as most are), shorting the N and G conductors together downstream of the GFCI should also cause it to trip (push buttons for both functions would be a useful enhancement).

    Note that such a tester will only work for GFCI protected outlets that are on grounded (3 wire) circuits (unless you add an external ground connection). Thus, just using a commercial tester may falsely indicate that the GFCI is bad when in fact it is simply on an ungrounded outlet (which is allowed by Code in a retrofit situation).

    The test button will work whether or not the circuit includes a safety ground. On most GFCIs, it passes a small current from Hot on the line side, via an additional wire threaded through the sense coil, to Neutral on the load side and therefore doesn't depend on having a safety Ground. The use of the single wire introduces an imbalance in current.

    The only exception to the above that I know of is Leviton's SmartLock GFCI and any others that use the same technology. The following is from a Leviton engineer:

    "In this case, the test button mechanically trips the GFCI by simply pushing the latch which holds the contacts closed. We satisfy the UL requirements for testing the electronics when you press the reset button. When you press the reset button the test circuit described above is invoked and creates the current imbalance. If the GFCI is operating properly, it will sense this and fire the solenoid used to trip the GFCI. We use the firing of the solenoid to move shutters blocking the latching mechanism for the contacts. The result is, if the GFCI does not sense the ground fault and fire the solenoid correctly, you will not be able to reset the GFCI - no power without protection. An added benefit is that the SmartLock GFCI will also block the reset button if the GFCI is wired incorrectly."

    I suppose you can purchase suitable low cost testers as well (but they are subject to the same must-be-grounded restrictions). Try your local home center or electrical supply distributor.

    The general procedure for the test is as follows. (This assumes a live GFCI circuit. If there is no power and the RESET button doesn't restore it, testing will need to be done to determine if the problem is in the GFCI, wiring, or a blown fuse/tripped circuit breaker at the service panel.):

    If any of these don't work as expected, the GFCI is defective or the outlet is miswired and there may be no protection.

    Reminder: A separate Ground connection must be provided to use a GFCI tester in an ungrounded outlet. Without one, the GFCI's TEST button must be used.

    John's comments on the use of GFI breakers

    (From: John Grau (

    I personally would not feed a subpanel with a GFI breaker. Here are just a few of the reasons:

    1. GFI breakers for personnel protection are set to trip at 5 mA (1/1000ths of an Amp). The longer the circuit conductors, the greater the potential for leakage. If you subfeed a panel, you would have the cumulative distances of all circuits connected to that panel to contend with and hope that the breaker would hold.

    2. You would not be able to connect any thing to that subpanel that would be a critical load. e.g. freezer, sump pump, well pump, furnace, etc. An unnoticed nuisance trip, could mean that you would come home to a thawed freezer, frozen pipes, flooded basement, etc.

    3. Using breakers to achieve GFI protection has 2 downsides: expense, and usually, an inconvenient location to reset the tripped device. A GFI outlet at the point of usage, is usually more convenient to reset, should it trip. Here in Wisconsin, I can buy about 6 GFI outlets for the cost of 1 breaker.
    There is no compulsory language in the National Electrical Code the forces an update to current code standards, unless you repair, replace or update the affected component. Not all changes in the 1996 code made sense, and I would not update the wiring in my own home (built in 1995) to current standards.

    Antique Electronics and GFCIs

    The following applies to a great deal of really old electronics, not just the radios described below. They were often called something like "AC/DC sets" with no power transformer, no isolation, and the metal chassis and other user accessible parts connected directly to one side of the AC line.

    (From: Jim Locke (

    Tube radios made several decades ago are now collectors' items (literally 100s are offered for auction on eBay) and they had a metal chassis which was often connected to one side of the AC line. The user would get a shock if he or she simultaneously touched the electrically hot chassis and a separate ground. There was no safe way for the plug. Commonly, the chassis would be hot when the radio was off but at ground potential when the radio was on, or vice versa, depending on which way the plug was in the outlet. Earlier radios had set screws in their knobs, which provided electrical connection from a human turning the knob to the chassis. Also, screws through the bottom of the case connected to the chassis, and the back had ventilation holes large enough for fingers to reach the chassis. So, it was easy to connect the body to the chassis. Later models provided isolated chassis, plastic shafts for the knobs, etc., but still presented a shock hazard. I would recommend that collectors of working tube radios power them through GFCI devices. Furthermore, in a collection of radios, each radio should have a separate GFCI device, to detect when a human completes the circuit between two radios! If the two radios are on the same GFCI device, it will not trip. There is still a shock hazard with either or both radios switched off, but plugged in. More information may be found at Fun With Tubes.

    Phantom voltage measurements of electrical wiring

    When making measurements on household wiring, one expects to see one of three voltages: 0, 115 VAC, or 230 VAC (or very similar). However, using a typical multimeter (VOM or DMM) may result in readings that don't make sense. For example, 2 VAC between Neutral and safety Ground or 40 VAC between a Hot wire (with its breaker off) and Neutral or safety Ground.

    The most likely reason for these strange readings is that there is E/M (electromagnetic) coupling - capacitive and/or inductive - between wires which run near one another - as inside a Romex(tm) cable. Where one end of a wire is not connected to anything - floating, the wire acts as an antenna and picks up a signal from any adjacent wires which are energized with their 60 (or 50) Hz AC field. There is very little power in these phantom signals but due to the very high input resistance/impedance of your VOM or DMM, it is picked up as a voltage which may approach the line voltage in some cases.

    Another possibility is that the you didn't actually walk all the way down to the basement to shut off power completely and the circuit is connected to a high tech switch (such as one with a timer or an automatic dimming or off feature) or a switch with a neon light built in. There will be some leakage through such a switch even if it is supposed to be off - kill power completely and test again.

    Putting any sort of load between the wires in question will eliminate the voltage if the cause is E/M coupling. A small light bulb with test probes can be used to confirm this both by serving as a visual indication of significant voltage (enough to light the bulb, if weakly) and to short out the phantom voltage for testing with the multimeter.

    There can be other causes of such unexpected voltage readings including incorrect or defective wiring, short circuits in the wiring or an appliance, and voltage drops due to high current in a circuit. However, the E/M coupling explanation is often overlooked when using a multimeter.

    I did an experiment using a Radio Shack DMM with a 10 M ohm input impedance. It was set to AC volts and the red lead was plugged into the Hot side of a live outlet:

    There may also be resistive leakage in an actual wiring installation but capacitance alone can easily mess up your multimeter readings if you have unconnected conductors! Adding any sort of load like a 25 W bulb in parallel with the multimeter will make the voltage drop nearly to zero if either of these are the cause of the phantom readings.

    Checking wiring of a 3-wire outlet

    The following assumes a simple duplex outlet, not split or switched. For each of the tests below, check both halves of the outlet.

    The easiest thing to do is use an outlet tester. This simple gadget gives a fairly reliable indication using three neon lamps. See the section: Test equipment for details.

    Or, using a multimeter set to "AC Volts":

    Or turn off the breaker for that outlet and remove the cover plate:

    Of course, the wiring could be screwed up at the service panel or an outlet upstream of this one.

    Determining wiring of a 2-wire outlet

    Connect a wire between one prong of a neon outlet tester and a known ground - cold water pipe if copper throughout, heating system radiator, ground rod, etc.

    (Experienced electricians would just hold onto the other prong of the tester rather than actually grounding it. Their body capacitance would provide enough of a return path for the Hot to cause the neon to glow dimly but you didn't hear this from me :-). Yes, they survive without damage and don't even feel anything because the current is a small fraction of a mA. DON'T try this unless you are absolutely sure you know what you are doing!)

    With one prong grounded, try the other prong in the suspect outlet:

    Outlet wiring screwed up?

    So your $6 outlet tester displays a combination of lights that doesn't make sense or one or more lights is dim. For example, all three lights are on but K and X (see below) are dim.

    The three neon bulbs are just between what should be (The first letter is how the light is marked on mine):

    I suspect at the very least that your ground is not connected at the service panel. I may run from some/all the outlets but ends somewhere. You are seeing capacitive/inductive pickup between the floating ground and the other wires in the circuit. Your N and H may be reversed as well but this cannot be determined without checking with a load between H/N and a proper ground.

    I would recommend:

    1. Determining if the ground wire for those 3 prong outlets does indeed go anywhere.

    2. Determining if the Hot and Neutral polarity is correct by testing between each of the prongs and a confirmed ground (properly connected 3 prong outlet, service panel, or a cold water pipe in an all metal water system) with a load like a 25 W light bulb. The neon lamps in the tester or a high impedance multimeter can be fooled by capacitance and other leakage paths.
    For a computer or other 3 wire appliance, you should really install a proper 3 prong outlet wired correctly. Otherwise, any power line filters and surge suppressors will not have the safety ground (which a GFCI does NOT create). Some UPSs may get away without one but then their surge suppressor and/or line filters will not work correctly.

    Some appliances like microwave ovens MUST have a proper safety ground connection for safety. This not only protects you from power line shorts to the case but also a fault which could make the case live from the high voltage of the microwave generator.

    220 V outlet reads 0 VAC between slots

    "I have a 220 outlet that I need to plug an AC unit into. The AC unit works fine in another outlet, but not in this specific outlet. I pulled out my handy dandy meter and checked the voltage across the two line slots - the meter read 0.

    But when I tried one line and the ground I got 125 V. Similarly, when I tried the other line and the ground I also got 125 V. What's the scoop? Why does the meter, and obviously the AC, think that there isn't 220 V coming in? Any help is greatly appreciated - as this room is stinking hot right now!"

    Did it ever work? It sounds like both slots are being fed from the same phase of the power from the service panel. Check with a load like a 100 W light bulb between each slot and ground. This could have happened during the original installation or during renovation.

    Another possibility is that there is some other 220 V appliance on the same line with its power switch in the ON position (and not working either) AND one side of the line has a tripped breaker or blown fuse.

    Yet another possibility:

    (From: David L. Kosenko (

    My load center is GE unit. They make both full height and half height breakers. If you use a half height breaker set for a 220 line, you must be careful to install it across the two phases. It is very easy (especially if you don't know about 220) to place the ganged breakers into a single full height slot in the load center, giving you both lines off the same phase line.

    Testing for fault in branch circuit

    This may trip the breaker or blow a fuse - or trip a GFCI if so protected. The procedure below is specifically for GFCI tripping. You will need a multimeter. Assuming the circuit is at fault: Assuming the line is separate from any other wiring: One of these will show a fault - possibly the N-G test indicating a short or improperly wired outlet since this would not result in any operational problems until a GFCI is installed (though it does represent a safety hazard).

    Locating wires inside a wall

    There are gadgets you can buy that look like test lights but sense the electric field emitted by the Hot wire. One is called 'Volt Tick' and may be available at your local home center or large hardware or electrical supply store.

    It is also possible to inject a signal into the wire and trace it with a sensitive receiver.

    However, if you are desperate, here is a quick and easy way that is worth trying (assuming your wiring is unshielded Romex - not BX - and you can power the wire). Everything you need is likely already at your disposal.

    Get a cheap light dimmer or a fixture with a light dimmer (like that halogen torchier that is now in the attic due to fire safety concerns) and plug it into an outlet on the circuit you want to trace. Set it about half brightness.

    Now, tune a portable AM radio in between stations. If you position the radio near the wire, you should hear a 120 Hz hum - RFI (Radio Frequency Interference) which is the result of the harmonics of the phase controlled waveform (see the section: Dimmer switches and light dimmers. Ironically, the cheaper the dimmer, the more likely this will work well since no RFI filtering is built in.

    I have tried this a bit and it does work though it is somewhat quirky. I do not know how sensitive it is or over how large a circuit it is effective. It is somewhat quirky and even normal power may have enough junk on the waveform to hear it in the radio. However, with a partner to flip the dimmer off and on to correlate its position with what you hear, this may be good enough.

    (From: author unknown.)

    The probe is really simple. All it consists of is a LM386 and a MPF102 JFET from Radio Shack. The MPF102 is connected as a source follower with a 4.7k load resistor from source to ground. The gate has a 10M resistor to ground and a 1M from gate to the probe tip. The drain of course connects to the plus 9 VDC. There is a 0.1 µF coupling cap between source and the input to the LM386. The LM386 is the standard circuit found in the data sheet. You can put a 5K volume control between the two pins to increase the gain. And of course you have to find a small 1.3 inch or 3 cm speaker to fit the probe. Use a 9 V battery.

    The tone generator can be anything that oscillates. You could use a hex inverter in the typical circuit. Or you could use a two transistor astable multivibrator with 2.2k collector load resistors. Whatever you use, make sure the coupling capacitor to the phone line is a 200 V or higher NON POLARIZED capacitor, so it won't make any diff how you connect it up. Remember that this little box takes a lot of beating from stray voltages and stuff, like ringing currents. So it's best to buy this and get one that's safe. I've burnt them out on occasion so I suggest you don't build it but buy it for under $30.

    (From: Bill Jeffrey.)

    Go to the electrical department at Home Depot or Lowes and buy what I call a "squeaker". More properly called, I think, a non-contact voltage tester. It looks like a fountain pen. When you squeeze the pocket clip against the body, it chirps once. Then if you hold the tip near an energized wire, it chirps continuously.

    There are two variants. One is labeled "100-250 volts". You must hold it within an inch or so of a 120 VAC wire to make it chirp, so this may not work for you if the wires are buried back between the wall studs. But there is a "low voltage version" - mine says "12-90 VAC" that can detect a 120 VAC wire from considerably farther away. This is probably what you want. Mine is made by GB Instruments, model GVD-504LV (the LV suffix meaning "low voltage").

    If you don't have a Home Depot or Lowe's near you, the standard version of these things is often available at Ace Hardware, etc - or on eBay - but I'm not sure about the low-voltage version. Still, they are not expensive, so try it out.

    Lights dim when high current load is switched on

    Heating appliances space heaters toasters draw a large current when their operating. Appliances with large motors like air conditioners and washing machines draw a very large current momentarily when starting. And, tools like bench grinders and power saws draw a large current until they get up to speed. All of these conditions increase the voltage drop of the wiring in the branch circuit they are on and thus reduces voltage to lights on the same circuit. Normally, this isn't anything to worry about but do make sure your wiring is properly rated for the equipment in use AND that the fuses or circuit breakers are of the correct rating. If the amount of dimming is erratic, it could mean that there are some corroded or loose high resistance connections due to age/use and/or aluminum wiring. These are serious conditions that can result in an electrical fire and would need to be found and repaired. Where lights brighten under these conditions, a bad Neutral connection may be the problem. See the next section.

    Bad Neutral connections and flickering lights or worse

    Residential service comes from a centertapped 110-0-110 V transformer on the utility pole. There are 3 wires into your house - 2 Hot or live wires and the Neutral which is the centertap of the transformer. If the connection between the Neutral bus in your service panel and the pole transformer centertap becomes loose and opens or develops a high resistance, then the actual voltage on either of the Hots with respect to the Neutral bus (which is divided among your branch circuits) will depend on the relative loads on either side much in the way of a voltage divider using resistors. Needless to say, this is an undesirable situation.

    Symptoms include excessive flickering of lights (particularly if they get brighter) when large appliances kick in, light bulbs that seem too bright or too dim or burn out frequently, problems with refrigerators or freezer starting due to low voltage, etc. In the worst case, one set of branch circuits can end up with a voltage close to 220 VAC - on your poor 110 V outlets resulting in the destruction of all sorts of appliances and electronics. The opposite side will see a much reduced voltage which may be just as bad for some devices.

    It is a simple matter for an electrician to tighten up the connections but this is not for the DIY'er unless you are familiar with electrical wiring and understand the implications of doing anything inside the service panel while it is live! Furthermore, the problem may actually be in the Neutral cable outside your residence and that can only be dealt with by the power company. Since it's exposed to the elements as well as squirrels and such, damage is possible. An electrician will be able to eliminate internal problems, and recommend contacting the power company if necessary.

    Here is what can happen if you don't remedy the situation:

    (From: Sinbad (

    Speaking from experience, I can tell you that if your ground goes you will have no doubt about.

    When I lost mine I was watching TV. The picture tore and then smoke came out of the back of it. I also lost two VCR's, a dryer, a scanner, a microwave, an AM/FM receiver, an amplifier (everything with a remote control since these always have power going to them), a CD player and a scanner, which also smoked.

    The incandescent bulbs that were turned on turned blue and then white before they burned out and a couple fluorescent fixtures burned out as the bulbs arced and melted and cracked.

    Fortunately, my insurance policy specifies replacement with no deductible, but I still had to run around buying new stuff (except for the dryer, which was repairable.)

    Lightning storm trips GFCIs protecting remote outdoor outlets

    "I have several outdoor 110V outlets, protected by GFCI breakers. These circuits nearly always trip when there are nearby lightening strikes. I am satisfied that there is no short circuit caused by water as:

    The electrical cables buried underground run for about 600 feet.

    Is GFCI tripping caused by electrical storms normal ? Are my GFCI breakers too sensitive ? Is there any way to modify the circuits to avoid this?"

    This doesn't surprise me. Long runs of cable will be sensitive to the EM fields created by nearby lightning strikes. Those cables probably have 3 parallel wires: H, N, G. The lightning will induce currents in all three which would normally not be a problem as long as H and N are equal. However, I can see this not being the case since there will be switches in the Hot but not the Neutral so currents could easily unbalance.

    These are not power surges as such and surge suppressors will probably not help.

    Since it happens with all of your GFCIs, it is not a case of a defective unit. Perhaps there are less sensitive types but then this would reduce the protection they are designed to provide.

    GFCI trips when it rains (hard)

    Most likely, moisture/water is getting into some portion of the GFCI's protected wiring (at the GFCI or anywhere downstream) and the GFCI is simply doing its job. You will have to trace the wiring through all junction boxes and outlets to determine where the problem is located. Yes, I know this may not be your idea of fun!

    Why a GFCI should not be used with major appliances

    A Ground Fault Circuit Interrupter is supposed to be a valuable safety device. Why not use them everywhere, even on large appliances with 3 wire plugs?
    1. A properly grounded 3 prong outlet provides protection for both people and the appliance should a short circuit develop between a live wire and the cabinet.

    2. Highly inductive loads like large motors or even fluorescent lamps or fixtures on the same circuit can cause nuisance tripping of GFCIs which needless to say is not desirable for something like a refrigerator.

    Nuisance tripping of GFCIs

    When used with highly inductive loads like motors or even fluorescent lamps, GFCIs may occasionally (or more frequently) trip due to the voltage/current spikes at power on/off. While the NEC/UL specifications apparently allow for some time delay in their response to combat this problem, it is not known if all manufacturers of GFCIs incorporate this into their product. However, the very common Leviton GFCI outlet probably does use the National chip (LM1851 Ground Fault Interrupter) referred to below. Also see the section: How does a GFCI work?.

    (From: James Phillips (

    I quit having GFCI trouble after I fixed all the bad wiring connections, and I haven't had trouble at all with GFCIs and my workshop, which I wired myself. GFCI controller chips include a time delay to reduce false tripping. I used to think GFCIs always tripped at 5 to 6 mA, but the UL allows up to a whopping 200 mA if the GFCI stops the current within 30 ms, and 6 mA leakage is allowed to last 6 seconds.

    According to National Semiconductor, their GFCI chips will stop a 200 mA fault in 20 ms, a 6mA fault in .5 sec.

    Toasters and GFCIs

    The following is a reason to use GFCIs on kitchen outlets that may not be obvious:

    (From: David Buxton (

    In addition to the usual explanations dealing with safety around water, another reason why kitchen outlets need a GFCI is the toaster. All too often people stick a butter knife in there to dislodge some bread. If the case was grounded there would be short from the element to the case. So toasters are two wire instead of 3-pronged. So, you must have a GFCI for any outlet that might take on a toaster.

    Problems with outlets getting hot

    With normal loads, electrical outlets should get at most just warm to the touch. A number of factors can result in hot or dangerously hot outlets. Check the following:

    Reverse polarity outlets - safety and other issues

    "Our new home has reverse polarity in all of the electrical outlets. The house inspector didn't seem to think this was a major problem, and neither did he think it was worth fixing. Can anyone explain how this might matter for us? The best I understand this is that when something is plugged in, even when it's not turned on, there is still a current going through it--is that true at all, or is that normal? Our biggest concern is our computers, and the possibility that our surge protectors won't be effective. If anyone could clear this up, that would be great."

    New as in brand new or new for you? If it is a totally new home, the builder should have them fixed and you should not sign off on the house until this is done. While there is no imminent danger, the house inspector was being a bit too casual for my tastes. It is not a big deal as in should stop you from going through with the purchase but it really should be fixed.

    As far as current present when the appliance is off, this is not quite true. When properly wired, the power switch is the first thing in the circuit so it cuts off power to all other parts of the internal wiring. With the reversal, it is in the return - the rest of the wiring will be live at all times. Except for servicing, this is really not that big a concern and does not represent any additional electricity usage.

    Normally (I assume these are 3 prong grounded outlets) you have the following:

    Reverse polarity means that Hot and Neutral are interchanged. (Any other variation like an interchange with the ground represents a serious safety hazard and it should be corrected as soon as possible. The outlet should not used until it is.)

    For most appliances and electronics, reversed H and N does not really matter. By design, it must not represent a safety hazard. However, there can be issues - as you are concerned - with surge suppressors and susceptibility to interference. In some cases, the metal case of a stereo could be coupled to the Neutral by a small capacitor to bypass radio frequency interference. This will be coupled now to Hot instead. While not a safety hazard, you might feel an almost imperceptible tingle touching such a case.

    Surge suppressors may or may not be affected (to the extent that they are ever effective in any case - unplugging the equipment including modem lines and the like during an electrical storm is really the only sure protection but that is another section). It depends on their design. Some handle the 3 wires in an identical manner and interchanging them makes no difference. Others deal differently with the Hot and Neutral in which case you may lose any protection you would otherwise have.

    My advice: If you are handy electrically and have experience working on residential wiring, correct them yourself. If not, get them corrected the next time you have an electrician in for any reason. It is a 5 minute job per outlet unless the wiring is extremely screwed up.

    If there are only a few outlets involved, to be doubly safe, simply don't use them. But if there are many, do get them corrected ASAP.

    And always use a properly wired outlet for your computer to be doubly sure.

    It is not an absolute emergency but I consider proper wiring to be very desirable.

    Here is another example:

    "I was checking some outlets in my apartment. As I recall, the narrow prong should be hot, i.e., there should be 120 V between it and the wide prong or the ground prong. The wide prong should be neutral, i.e., it should show no voltage relative to the ground prong. Well, it appears that the Neutral and Hot wires are reversed in some outlets. In others, they are correct."

    Well, there should be very little voltage although it may not be 0.

    Reversed polarity outlets are not unusual even in new construction.

    Reversed H and N is not usually dangerous as appliances must be designed so that no user accessible parts are connected to either H or N - even those with polarized plugs. Think of all the times people use such appliances in old unpolarized outlets or with unpolarized extensions cords. (There are exceptions like electric ranges where there may be no separate safety ground conductor but I assume you are talking about branch circuits, not permanently wired-in appliances.)

    There are a couple of instances where this may be an issue though.

    1. Replacing a light bulb: The center contact of the socket is supposed to be the one that gets switched and goes to the Hot wire of the line cord (if a plug-in lamp with a polarized plug) or the Hot of the electrical system (if a built-in lighting fixture). If due to miswiring of the lamp, outlet, or fixture, the screw part of the socket ends up being Hot, there is a potential shock hazard during the light bulb changing operation.

      As a practical matter, older lamps don't have polarized plugs, replacement cords, plugs, or sockets/switches are often installed reversed, lamps are jammed into non-polarized extension cords, and lamps often come from the factory reverse wired. For permanently installed fixtures, the incidence of reverse polarity is lower but non-zero due to simple errors or cut corners during installation.

    2. Toasters, broilers, and other heating appliances with exposed coils: Extracting a piece of burnt toast with a metal utensil is perhaps not highly recommended but who thinks about it? If the appliance XOR the outlet has reverse polarity, then unless both sides of the line are switched, the coils will be live with the switch off unless the appliance is unplugged.

    3. Really ancient "AC-DC" radios, TVs, and other equipment where one side of the line is actually connected to the chassis. My advise is to remove the line cord (so they can't be used) and throw them away, or donate them to a museum. These are a disaster waiting to happen.

    "In still others, I get some voltage between ground and either the wide or narrow prong. Ack. Should I worry? Should I do more than worry?"

    You should, of course, measure full line voltage between the H and G. The safety ground, G, does not normally carry any current but is at the same or nearly the same potential as N.

    The voltage between G and (actual) N if quite low - a couple volts or less - is probably just due to the voltage drop in the current carrying N wire. Turn off everything on this branch circuit and it should go away. However, there could also be a bad (high resistance connection) somewhere in the N circuit.

    If the voltage reads high to either H or N - say, 50 volts - and you are measuring with a high impedance multimeter, this is probably just due to an open ground: a three prong outlet was installed without connecting the ground (in violation of Code unless on a GFCI) and this leakage is just due to inductive/capacitive pickup from other wires. See the section: Phantom voltage measurements of electrical wiring.

    Full line voltage on the G conductor relative to an earth ground (like a copper cold water pipe) would represent a serious shock hazard to be corrected as soon as possible - the appliance or outlet should *not* be used until the repair is made. While unlikely, for anyone to screw up this badly, it could happen if someone connected the green or copper wire, or green screw to H instead of G.

    In any case, it would be a good idea to correct the H-N reversals and determine if the voltage on the G is an actual problem.

    Comments on whole house surge suppressors

    These are typically offered your power company:
    "I have a surge suppressor that was put between my meter and the service panel. It's rented from my power company. The advertised product is part of a 'package' that includes plug in surge suppressors. The package price is $4.95/month. I didn't want the plug in suppressors so they said that it would be $2.75/month. Is this a good deal?"
    (From: Kirk Kerekes (

    The power company just passes on the warranty of the manufacturer, which is, in turn, merely an insurance policy whose premium in included in the normal retail price of the unit. Basically, the power company is taking a product with a wholesale cost of about $30, and "renting" it to consumers for $40 to $100 a year.


    Nice work if you can get it.

    Note that most homeowner and similar insurance policies already cover lightning damage, and that the policy from the surge protector is generally written to only apply to losses not already covered by other insurance. As a result, you are paying for insurance that you will likely *never* be able to make a claim against, even if the device is totally ineffective.

    The simplest whole-house protection is to purchase an Intermatic whole house surge protector ($40 from Home Depot or Lowe's) and install it yourself (or pay an electrician to do so -- maybe 15 minutes of work). Then purchase inexpensive ($10 and under) plug-in surge protectors and surge-protected power strips and use them all over the house at sensitive equipment. Note that surge protectors and surge protected power strips protect the _other_ outlets in the house as well as the ones they contain (because the MOV's in inexpensive surge protectors are simply connected in parallel with the power line), so the more of that that you have plugged in, the more effectively protected your home is. Some power strips need to be turned "on" for the MOV's to be connected to the power lines.

    You can also buy MOV's and add your own custom protection -- but if you don't already know that, you probably shouldn't be tinkering with such things.

    Note that you should only purchase surge protectors that contain a monitor LED to tell you if the protector is still functioning -- MOV's deteriorate when zapped by large surges. This is one reason why I recommend the multiple-power-strip distributed-protection approach -- it is doubtful that all of your surge protectors/power strips will get zorched at once.

    Electric tingles or shocks from plumbing

    This it not what is meant by a stimulating shower. :-)

    Needless to say, any sensation of electricity while using the water indicates a potentially very dangerous situation. (More so, apparently, for cows but that is another story!).

    The most likely cause assuming you haven't actually wired the plumbing into the electrical system's Hot bus bar is some variation of bad or lack of connections of the electrical system's ground. What happens is that the unavoidable electrical leakage to the grounds of appliances and computer equipment with 3 prong plugs (from line filter capacitors and such) feeds into the grounding system of your house. If that is bonded to the actual earth ground via the plumbing supply system and that has a bad connection, you can get a voltage between the metal plumbing fixtures and the drain - which is pretty well grounded going into the earth. The reverse is also possible depending if there is plastic pipe at some point in your drain line.

    While a tingle is unpleasant, an actual short in an appliance would be quite deadly where such a situation exists.

    Of course, it is also possible to create a situation of electrically live pipes during renovation - by nailing a metal pipe bracket into an electrical wire without realizing it. However, this type of screwup usually takes some effort. :-)

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    All About Wire and the AWG (American Wire Gauge) Numbers

    Some types of wire

    Note: For an understanding of the AWG numbers, you may want to first see the section: American Wire Gauge (AWG) table for annealed copper wire.

    A semi-infinite variety of wire and cable is used in modern appliances, electronics, and construction. Here is a quick summary of the buzz words so you will have some idea of what your 12 year old is talking about!

    So, where did AWG come from?

    Nearly everyone who has done any sort of wiring probably knows that the AWG or American Wire Gauge number refers to the size of the wire somehow. But how?

    (From: Frank (

    According to the 'Standard Handbook for Electrical Engineers' (Fink and Beaty) the 'gauge' you referenced to is 'American Wire Gauge' or AWG and also known as Brown & Sharp gauge.

    According to above handbook, the AWG designation corresponds to the number of steps by which the wire is drawn. Say the 18 AWG is smaller than 10 AWG and is therefore drawn more times than the 10 AWG to obtain the smaller cross sectional area. The AWG numbers were not chosen arbitrary but follows a mathematical formulation devised by J. R. Brown in 1857!

    For the marginally mathematically inclined

    Each increase of 3 in the gauge halves the cross sectional area. Each reduction by 3 doubles it. So, 2 AWG 14 wires is like one AWG 11.

    It seems that everyone has their own pet formula for this (though I prefer to just check the chart, below!).

    (From: Tom Bruhns (

    As I understand it, AWG is defined to be a geometric progression with AWG 0000 defined to be 460 mils diameter and 36 gauge defined to be 5.000 mils diameter. This leads directly to the formula:

                  Diameter(mils) = 5 * 92^((36-AWG)/39)
    That is, 460 mils is 92 times 5 mils, and the exponent accounts for 39 steps of AWG number starting at 36 gauge.

    (From: David Knaack (

    You can get a fairly accurate wire diameter by using the equation:

              Diameter(inches) = 0.3252 * e^(-0.116 * AWG)
    where 'e' is the base of the natural logarithms, 2.728182....

    I don't know where it came from, but it is handy (more so if you can do natural base exponentials in your head).

    In its simplest form, the cross sectional area is:

                     A(circular mils) = 2^((50 - AWG) / 3)
    Here's a Web site that has a program to calculate most of the useful specifications based on the AWG number, diameter, or cross-sectional area: They also have a bunch of other useful CAD programs at:

    American Wire Gauge (AWG) table for annealed copper wire

    (Similar tables exist for other types of wire, e.g., aluminum.)

    (The original table was provided by: Peter Boniewicz ( I added to it above #40.)

    Wire Table for AWG 0000 to 47, with diam in mils, circular mils, square microinches, ohms per foot, ft per lb, etc.

       AWG  Dia in  Circ.  Square  Ohms per lbs per Feet/   Feet/    Ohms/
      gauge  mils   Mils   MicroIn 1000 ft  1000 ft Pound    Ohm     Pound
      0000  460.0  211600  166200  0.04901  640.5   1.561   20400   0.00007652
      000   409.6  167800  131800  0.06180  507.9   1.968   16180   0.0001217
      00    364.8  133100  104500  0.07793  402.8   2.482   12830   0.0001935
       0    324.9  105500  82890   0.09827  319.5   3.130   10180   0.0003076
       1    289.3  83690   65730   0.1239   253.3   3.947   8070    0.0004891
       2    257.6  66370   52130   0.1563   200.9   4.977   6400    0.0007778
       3    229.4  52640   41340   0.1970   159.3   6.276   5075    0.001237
       4    204.3  41740   32780   0.2485   126.4   7.914   4025    0.001966
       5    181.9  33100   26000   0.3133   100.2   9.980   3192    0.003127
       6    162.0  26250   20620   0.3951   79.46   12.58   2531    0.004972
       7    144.3  20820   16350   0.4982   63.02   15.87   2007    0.007905
       8    128.5  16510   12970   0.6282   49.98   20.01   1592    0.01257
       9    114.4  13090   10280   0.7921   39.63   25.23   1262    0.01999
      10    101.9  10380   8155    0.9989   31.43   31.82   1001    0.03178
      11    90.74  8234    6467    1.260    24.92   40.12   794     0.05053
      12    80.81  6530    5129    1.588    19.77   50.59   629.6   0.08035
      13    71.96  5178    4067    2.003    15.68   63.80   499.3   0.1278
      14    64.08  4107    3225    2.525    12.43   80.44   396.0   0.2032
      15    57.07  3257    2558    3.184    9.858   101.4   314.0   0.3230
      16    50.82  2583    2028    4.016    7.818   127.9   249.0   0.5136
      17    45.26  2048    1609    5.064    6.200   161.3   197.5   0.8167
      18    40.30  1624    1276    6.385    4.917   203.4   156.6   1.299
      19    35.89  1288    1012    8.051    3.899   256.5   124.2   2.065
      20    31.96  1022    802.3   10.15    3.092   323.4   98.50   3.283
      21    28.46  810.1   636.3   12.80    2.452   407.8   78.11   5.221
      22    25.35  642.4   504.6   16.14    1.945   514.2   61.95   8.301
      23    22.57  509.5   400.2   20.36    1.542   648.4   49.13   13.20
      24    20.10  404.0   317.3   25.67    1.223   817.7   38.96   20.99
      25    17.90  320.4   251.7   32.37    0.9699  1031.0  30.90   33.37
      26    15.94  254.1   199.6   40.81    0.7692  1300    24.50   53.06
      27    14.20  201.5   158.3   51.47    0.6100  1639    19.43   84.37
      28    12.64  159.8   125.5   64.90    0.4837  2067    15.41   134.2
      29    11.26  126.7   99.53   81.83    0.3836  2607    12.22   213.3
      30    10.03  100.5   78.94   103.2    0.3042  3287    9.691   339.2
      31    8.928  79.70   62.60   130.1    0.2413  4145    7.685   539.3
      32    7.950  63.21   49.64   164.1    0.1913  5227    6.095   857.6
      33    7.080  50.13   39.37   206.9    0.1517  6591    4.833   1364
      34    6.305  39.75   31.22   260.9    0.1203  8310    3.833   2168
      35    5.615  31.52   24.76   329.0    0.09542 10480   3.040   3448
      36    5.000  25.00   19.64   414.8    0.07568 13210   2.411   5482
      37    4.453  19.83   15.57   523.1    0.06001 16660   1.912   8717
      38    3.965  15.72   12.35   659.6    0.04759 21010   1.516   13860
      39    3.531  12.47   9.793   831.8    0.03774 26500   1.202   22040
      40    3.145  9.888   7.766   1049.0   0.02993 33410   0.9534  35040
      41    2.808  7.860   6.175   1319     0.02379 42020   0.758   55440
      42    2.500  6.235   4.896   1663     0.01887 53000   0.601   88160
      43    2.226  4.944   3.883   2098     0.01497 66820   0.476   140160
      44    1.982  3.903   3.087   2638     0.01189 84040   0.379   221760
      45    1.766  3.117   2.448   3326     0.00943 106000  0.300   352640
      46    1.572  2.472   1.841   4196     0.00748 133640  0.238   560640
      47    1.400  1.951   1.543   5276     0.00595 168080  0.190   887040

    Note: Values for AWG #41 to #46 extrapolated from AWG #35 to #40 based on wire gauge formula.

    Ohms per 1000 ft, ft per Ohm, Ohms per lb, all taken at 20 degC (68 degF). Sizes assume bare wire - insulation is extra. For hookup and similar wire, this is easy to determine. For magnet wire, the additional diameter will be a fraction of mil (0.001 inch) up to several mils depending on the wire gauge and type. When in doubt, use a micrometer to compare the original wire and the wire with insulation removed using a non-mechanical (e.g., chemical) stripper.

    Apparently, you can buy wire down (up?) to size #60 - less than .000350 inches in diameter! Check out MWS Wire Industries if you are really curious about fine wire.)

    What about stranded wire?

    (From: Calvin Henry-Cotnam (

    In addition to the cross-section area, there are a few other factors. First off, a stranded wire effectively has more surface area than a solid wire of the same gauge, but much of this surface is "inside" the wire.

    I checked out the label of a spool of #18 stranded wire and found it was comprised of 16 strands of #30 wire. Given the info above that each reduction of 3 in the gauge, then #18 has a cross-section area that is 16 times greater than #30 -- so it *appears* to translate exactly.

    Looking through a catalog for wire, I found that this more-or-less holds true, though the occasional wire might have an extra strand or two. Here is what I quickly found -- there are many more, but this is a sample:

             Overall gauge      Typical stranded wires made up of:
                #32              7 x #40
                #30              7 x #38
                #28              7 x #36
                #26              7 x #34
                #24              7 x #32    19 x #36
                #22              7 x #30    19 x #34
                #20              7 x #28    10 x #30    19 x #32
                #18             16 x #30
                #16             19 x #29    26 x #30
                #14             41 x #30
                #12             65 x #30
                #10             65 x #28
                 #8             84 x #27

    Comments on Magnet Wire and Coil Winding

    Motors, transformers, and other electrical and electronic components using magnetic fields have coils that are wound with (usually) copper wire having very thin but tough insulation, rather than the types of plastic used on building wire and hookup wire. The purpose is to minimize the space taken up by the insulation to allow for a higher packing density of current carrying conductors.

    (From: Smitty Two (

    If you're winding your own coils, start with wire that's already coated. I've wound guitar pickups, power and output transformers for tube amplifiers, and coils for magnetic bearings. I usually buy wire from MWS Wire Industries, although there are many other suppliers, too.

    You have a choice of several different insulating coatings. Some will melt with the heat of a soldering iron, which makes termination easy, and others require mechanical stripping.

    Beyond the insulating varnish, you can also buy wire with an additional coating that melts in an oven, fusing the coils together and making the coil rigid without a core or bobbin. There are also coatings that melt with solvent, and pulling the wire through a damp sponge of solvent bonds the coils together.

    To keep the coils quiet, if they aren't bonded by heat or solvent, you can vacuum pot them in melted paraffin, or some commercial potting compound.

    Estimating the Number of Turns of Wire in a Coil

    Suppose you have a solenoid or relay and it would be desirable to know the number of turns on it without disassembly or even being able to measure the wire size? It is possible simply based on the resistance and the coil cross sectionall area (which may be easier to estimate).

    First assuming a square wire cross-section:

       Number of turns = N = ----
    where A is the cross sectional area of the winding (bobbin) and w is the diameter of the wire. Defining a variable called r = resistance/inch of wire:
       R = N*2*pi*D*r
    where D = average diameter of the coil and r is the resistance in ohms per unit length. So:
       N = ----------
    But r can also be expressed in terms of the wire diameter:
       r = ---
    where k is a constant dependent on the units for length and may be determined from the wire tables or the basic properties of copper. For copper magnet wire, k is 8.643x10-7 ohm-inches. Note that the value of k does not depend on the shape of the wire (round or square) as long as the packing factor of the turns is the same for both. Also:
       w = sqrt(-----)
    Then with some simple manipulation:
            A*r        R
       N = ----- = ----------
             k      2*pi*D*r
       r = sqrt(----------)
    For example, consider a solenoid with the following parameters:

    The coil area then equals 0.188 square inches.

                k*R              8.643x10-7 * 120         0.01209 ohms    145 ohms
    r = sqrt(----------) = --------------------------- = ------------- = ----------
              2*pi*D*A      2 * 3.14159 * 0.6 * 0.188        inch         1000 ft.
    Checking part of the AWG wire table:
       AWG  Dia in  Circ.  Square  Ohms per lbs per Feet/   Feet/    Ohms/
      gauge  mils   Mils   MicroIn 1000 ft  1000 ft Pound    Ohm     Pound
       30   10.03  100.5   78.94   103.2    0.3042  3287    9.691   339.2
       31   8.928  79.70   62.60   130.1    0.2413  4145    7.685   539.3
       32   7.950  63.21   49.64   164.1    0.1913  5227    6.095   857.6
       33   7.080  50.13   39.37   206.9    0.1517  6591    4.833   1364
    This would be somewhere between #31 and #32 wire. Then.
            A*r     0.188 * 0.01209
       N = ----- = ----------------- = 2,629 turns
             k         8.643x10-7
    Since this doesn't take into consideration the insulation thickness or
    circular cross-section of actual manget wire, there will need to be a
    fill factor adjustment.  This is left as an exercise for the student. :)

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Items of Interest

    Editor's note: Not all of these actually apply to small appliances but may be of use nonetheless.

    Determining electricity usage

    So, where does all the electricity (or money, same thing) go?

    You could put a watt-hour meter on every appliance in your house but that is probably not needed to estimate the expected electricity usage.

    Check the nameplate on heating appliances or those with large motors. They will give the wattage. Multiple these by hours used and the result is W-hours (or kW-hours) worst case. Appliances that cycle like refrigerators and space heaters with thermostats will actually use less than this, however.

    Multiple light bulb wattages by hours used to get the W-hours for them.

    Things like radios, clocks, small stereos, etc., are insignificant.

    Add up all the numbers :-).

    It would be unusual for an appliance to suddenly increase significantly in its use of electricity though this could happen if, for example, the door on a freezer or refrigerator is left ajar or has a deteriorated seal.

    How your electric (kW-hour) meter works

    While there have been a variety of technologies used to measure the amount of electric power used by residential and industrial customers, the most common is probably the one that uses a rotating aluminum disk to operate a clockwork mechanism with a visible readout in kW-hours.

    The implementation is quite clever - and often misunderstood. This type of meter is designed to read true power (for residential customers, at least) and operates as follows:

    There is both a current electromagnet (which passes the user load current) and a voltage electromagnet (connected across the AC line). The pole pieces of these electromagnets are mounted in close proximity to the aluminum disk and close to one-another. When the voltage and current are in phase, their magnetic fields are roughly 90 degrees out of phase. Why? Because the load current is in-phase with the AC voltage but the current in the voltage electromagnet lags by 90 degrees since its winding acts like an inductor.

    This results in a net torque on the disc which is proportional to voltage times current. The disk acts like the rotor of an induction motor and rotates, operating the dials. A permanent magnet also acts on the disk and acts to limit the rotation due to induced eddy-currents - its restraining force is proportional to speed. Rotation rate is therefore proportional to the instantaneous power being consumed with a direct readout in kW-hours.

    Where reactive power is involved and the voltage and current are out of phase, the peak current will be higher (for the same real power) but the phase angle will change resulting in reduced torque. These effects will tend to cancel so the rotation rate will be essentially unchanged. Therefore, adding capacitors or inductors to change the power factor in a house or apartment (either to legitimately improve power factor or to cheat the power company) will have little effect on the measured power usage. Note: Power factor is equal to: cos(phase angle between voltage and current).

    That's why it is called a kW-hour meter and not a VA-hour meter :-).

    (Note that large industrial customers ARE charged for reactive power since that extra current DOES stress generating and transmission facilities thus requiring excess capacity so this does not apply in that case.)

    It is quite possible that under extremely low power factor conditions, accuracy may be compromised due to friction and materials non-linearities but over the range of power factors generally encountered, these should be quite accurate.

    Taking equipment overseas (or vice-versa)

    When does it make sense to take an appliance or piece of electronic equipment to a country where the electric power and possibly other standards differ?

    For anything other than a simple heating appliance (see below) that uses a lot of power, my advise would be to sell them and buy new when you get there. For example, to power a microwave oven would require a 2kVA step down (U.S. to Europe) transformer. This would weigh about 50 pounds and likely cost almost as much as a new oven.

    There are several considerations:

    1. AC voltage - in the U.S. this is nominally 115 VAC but in actuality may vary from around 110 to 125 VAC depending on where you are located. Many European countries use 220 VAC while voltages as low as 90 or 100 VAC or as high as 240 VAC (or higher?) are found elsewhere.

    2. Power line frequency - in the U.S. this is 60 Hz. The accuracy, particularly over the long term, is excellent (actually, for all intents and purposes, perfect) - better than most quartz clocks. In many foreign countries, 50 Hz power is used. However, the stability of foreign power is a lot less assured.

    3. TV standards - The NTSC 525L/60F system is used in the U.S. but other countries use various versions of PAL, SECAM, and even NTSC. PAL with 625L/50F is common in many European countries.

    4. FM (and other) radio station channel frequencies and other broadcast parameters differ.

    5. Phone line connectors and other aspects of telephone equipment may differ (not to mention reliability in general but that is another issue).

    6. Of course, all the plugs are different and every country seems to think that their design is best.
    For example, going to a country with 220 VAC 50 Hz power from the U.S.:

    For electronic equipment like CD players and such, you will need a small step down transformer and then the only consideration power-wise is the frequency. In most cases the equipment should be fine - the power transformers will be running a little closer to saturation but it is likely they are designed with enough margin to handle this. Not too much electronic equipment uses the line frequency as a reference for anything anymore (i.e., cassette deck motors are DC).

    Of course, your line operated clock will run slow, the radio stations are tuned to different frequencies, TV is incompatible, phone equipment may have problems, etc.

    Some equipment like PCs and monitors may have jumpers or have universal autoselecting power supplies - you would have to check your equipment or with the manufacturer(s). Laptop computer, portable printer, and camcorder AC adapter/chargers are often of this type. They are switching power supplies that will automatically run on anywhere from 90-240 VAC, 50-400 Hz (and probably DC as well).

    Warning: those inexpensive power converters sold for international travel that weigh almost nothing and claim to handle over a kilowatt are not intended and will not work with (meaning they will damage or destroy) many electronic devices. They use diodes and/or thyristors and do not cut the voltage in half, only the heating effect. The peak voltage may still approach that for 220 VAC resulting in way too much voltage on the input and nasty problems with transformer core saturation. For a waffle iron they may be ok but not a microwave oven or stereo system. I also have serious doubts about their overall long term reliability and fire safety aspects of these inexpensive devices..

    For small low power appliances, a compact 50 W transformer will work fine but would be rather inconvenient to move from appliance to appliance or outlet to outlet. Where an AC adapter is used, 220 V versions are probably available to power the appliance directly.

    As noted, the transformer required for a high power heating appliance is likely to cost more than the appliance so unless one of the inexpensive converters (see above) is used, this may not pay.

    Note that if you plan to be moving between countries with different standards, it may pay to invest in appliances specifically designed for multisystem operation. However, there are all sorts of definitions of 'multisystem' - not all will handle what you need so the specifications must be checked carefully and even then, marketing departments sometimes get in the way of truth in advertising!

    For additional information, see the document: International Power and Standards Conversion.

    Controlling an inductive load with a triac

    Thyristor based controllers need to be designed with inductive loads in mind or else they may not work correctly or may be damaged when used to control a motor or even a transformer or large relay.

    There are a couple of issues:

    1. Will it switch correctly? Assuming it uses a Triac to do the switching, the inductive nature of the load may prevent the current from ever turning off. Once it goes on the first time, it stays on.

    2. Inductive kickback. Inductive loads do not like to be switched off suddenly and generate a voltage spike as a result of the rapid change in current. This may damage the Triac resulting the load staying on through the next millennium.

    3. Heating. Due to the inductive load, this will be slightly greater for the switch but I wouldn't expect it to be a major issue. However, some derating would be advised. Don't try to switch a load anywhere near the rated maximum for a resistive load.
    Where feasible, adding a light bulb in parallel with the load will decrease the effect of the inductance. There is no way of knowing whether it will be effective without analyzing the design or trying it.

    Using a relay controlled by the Triac to then switch the inductive load may work but keep in mind that a relay coil is also an inductive load - a much smaller one to be sure - but nonetheless, not totally immune to these effects.

    Dan's notes on low voltage outdoor lighting

    (From: Dan Hicks (

    Most major brands of 12V lights are "sort of" interchangeable. (Occasionally you have trouble getting the wire from one brand to connect with the fixtures of another brand, but with a little fudging it can usually be done.) So look for the brand/model that gives you most of the lights you want in the styles you want, then augment with add-ons from other brands. Be aware of the current limit of transformers, though -- some kits have small transformers not sized for add-ons, while others have quite a bit of excess capacity. I've got a (mostly) Toro system I'm semi-satisfied with, though the built-in photocell system has failed twice. (I'm going to install a separate photocell & timer and just set the transformer to "On".)

    Effects of brownouts and blackouts on electronic equipment and appliances

    Brownouts down to 100 V, maybe even 90 volts should not affect electronic equipment. It is possible that there is a no-man's land in between 0 and 90 volts (just an estimate) where strange things may happen. Whether this will cause permanent damage I cannot say. The surge, spikes, and overvoltage possibly associated with repeated brownouts or blackouts can damage electronics, however.

    Induction motors - the type in most large appliances - will run hotter and may be more prone to failure at reduced line voltage. This is because they are essentially constant speed motors and for a fixed load, constant power input. Decrease the voltage and the current will increase to compensate resulting in increased heating. Similar problems occur with electronic equipment using switching power supplies including TVs, some VCRs, PCs and many peripherals. At reduced line voltage, failure is quite possible. If possible, this type of equipment should not be used during brownout periods.

    Grounding of computer equipment

    While electronic equipment with 3 prong plugs will generally operate properly without an earth ground (you know, using those 3-2 prong adapters without attaching the ground wire/lug), there are 3 reasons why this is a bad idea:
    1. Safety. The metal cases of computer equipment should be grounded so that it will trip a breaker or GFCI should an internal power supply short occur.

      The result can be a serious risk of shock that will go undetected until the wrong set of circumstances occur.

    2. Line noise suppression. There are RLC filters in the power supplies of computer and peripheral equipment which bypass power supply noise to ground. Without a proper ground, these are largely ineffective.

      The result may be an increased number of crashes and lockups or just plain erratic weird behavior.

    3. Effectiveness of surge suppressors. There are surge suppression components inside PC power supplies and surge suppression outlet strips. Without a proper ground, H-G and N-G surge protection devices are not effective.

      The result may be increased hard failures due to line spikes and overvoltage events.

    Removing gummed labels (or other dried or sticky gunk)

    My order of attack: water, alcohol, WD40, Windex, then stronger stuff like ammonia, acetone, degreaser, flux-off, carburetor cleaner, lacquer thinner, gasoline.

    WARNING: most of these are flammable and harmful to your health - use only in a well ventilated areas away from open flames. Well, OK, except perhaps water unless you do your cleaning in a swimming pool and drown. :)

    CAUTION: Test that each of the cleaners or solvents you intend to use are safe for plastics and painted surfaces by trying some in an inconspicuous location first. Many of the ones listed above will damage or dissolve paint, varnish, and/or lacquer, and printing on the equipment itself.

    (From: Paul Grohe (

    I use "Desolv-it", one of those citrus oil (orange) based grease and "get's-the-kids-gum-out-of-your-carpet" cleaners (These are usually touted as "environmentally friendly" or "natural" cleaners).

    Spray it right on the label and let it soak into the paper for a minute or two, then the sticker slips right off (it also seems to do well on tobacco and kitchen grease residue).

    The only problem is you have to remove the oily residue left by it. I just use Windex (a window cleaner) to remove the residue, as I usually have to clean the rest of the unit anyways.

    (From: Bob Parnass, AJ9S (

    I spray the label with WD40 and let it soak in for several minutes. This usually dissolves the glue without damaging the paint and I can remove the label using my fingernail.

    Preventing radio frequency interference from whacking out appliances

    This probably applies to many of the new high tech appliances including touch lamps, smart irons and coffeemakers, etc.

    (From: James Leahy (

    My lamps were flashing each time I transmitted on 2 meters. HF transmissions don't seem to cause any trouble. (that just knocks the neighbor's TV out, har de har). Believe it or not, a simple snap-on toroidal choke with the lamp cord wrapped as many turns possible near the plug end cured it. Didn't want to bother with the several type of filter circuits one could build to fix the problem. It may be a simple fix for others with similar 2-way interference problems. One can get these chokes at Radio Shack among other sources.

    Yard lights cycling and maintenance humor

    (From: John Rowe (

    The new maintenance man at one of our customers, a rather large apartment complex in Minneapolis, had purchased from us a case of 200 watt incandescents. He returned to our office about a week later with the lamps, complaining that they 'flashed' and that the residents were really upset that these lights (used outside) were not letting them sleep.

    Under the 'customer is right' rule, I replaced them immediately, no questions asked. Of course I tested the 'bad' ones and found no defects.

    When he returned with the new batch and the same complaint, he was really upset, because the residents were now complaining to the management company (his employer) about the situation.

    I sat him down and asked him about the application. He explained that they were being used in 16" white poly pole lights, along all the footpaths around the complex.

    I asked how they were switched, and he replied that they used to be on timers but that after complaints that the lights were on during the daylight hours, he had purchased, from his local hardware store, screw-in photocells. The type into which the bulb screws. These were then, inside the globes with the bulbs.

    Of course the reflection within the poly globe was enough to prompt the photocell to switch the circuit off and cycle the lights all night.

    It took him a minute or two to comprehend his error. I was able to recommend an electrician to install more appropriate photocells. He remained a good customer for several more years after this incident.

    My amusement comes from the picture I have in my mind of the residents of this rather up-scale apartment complex looking out of their windows to see all the walkway security lights going on and off all night, and wondering what the heck was going on! I imagine it was quite a sight.

    Will a hard-wired appliance save energy over a plugged in variety?

    The resistance of the connection may be slightly lower - .05 versus .1 ohm, for example. Other than the reduced amount of power lost in this wiring, there is otherwise no functional difference.

    With fancy expensive test equipment you might be able to detect it but not in normal use. The savings of a hard wired appliance would be quite small even for a high wattage device like a space heater.

    However, the hard wired connection will be more reliable and should not deteriorate over time whereas a plug and outlet can corrode and the spring force decreases with multiple plugins and outs. The added resistance will increase the losses. So, in this regard, directly connecting the device into the house wiring is better.

    Note that if the cord and/or plug gets hot in use, this is a loss (though for a space heater, the heat is just coming from the cord/plug instead of the elements inside) - and a possible fire hazard as well and should be checked out. Sometimes, all it takes to remedy such a problem is to expand the metal strips of the prongs of the plug so it makes better contact.

    A short history of heat

    (From: Bill (

    In the beginning we had but rocks and wood, not an efficient safe or practical way to heat your home. This system was refined and did do a fair job, as long as you didn't mind cold spots or care about your safety.

    Then we got more creative and used coal and then oil. Oil was a far safer and a better controlled system. Then came gas now that's the fuel, the fuel of choice for most. It's also the one we are here to explain.

    The older systems were really very simple. You had a small pilot light which was always on. No safety, it just was lit, and we hoped it stayed lit. When the thermostat called for heat we opened a solenoid (electric valve) and allowed gas to flow in and hopefully get lit by the pilot light. If the pilot had gone out the theory was that the majority of the gas would go up the chimney and vent to the outside. This simple system, used for years did a fair job. It lacked many features we take for granted today.

    With the coming of more technology people started thinking more of safety and expected more from there equipment. A device commonly known as a thermocouple was a great start in the direction of safety. It is a union of dissimilar metals that when heated generates electricity. Now we had a way to stop gas flow if our pilot went out. By putting a solenoid in the pilot gas line we could use a thermocouple to keep it powered open by the heat of the pilot. Thus if our pilot went out the thermocouple would cool and stop producing power to hold the solenoid open, gas flow would be interrupted. Power from this control was also required prior to the main valve opening, this making uncontrolled gas flows a thing of the past.

    With the coming of the R.E.A. (Rural Electric Authority) power to every home became a reality. We now could introduce a new concept, blowers. The fan motor made forced air heat a reality. Now even the most distant room could be heated and even temperatures became a real happening.

    The addition of electricity allowed for the addition of safety controls which resulted in greatly reducing the fiscal size of a furnace. We now had the means to control running temperatures using the fan - turning it on and off by the temperature and the on and off valve of the fire. Should by chance the fan not start, the furnace would over heat and a high temperature switch would turn the fire off. No melt down! very safe.

    We all know that something simple that works well can't be left alone. Man just has to make it more labor complex. Soon came the addition of some actually neat ideas. First being the addition of humidity, in cold climates a must, that also lowers your heat bill. The ability to run the fan just to stir air, not add heat or cool. Then the electronic air cleaner. This one if you have allergy is a must. I don't have one so can't tell if it is on or off. BUT my son can tell in a matter of hours if its off.

    And let's not forget the best of all air conditioning! In my world a must. All of these additions were working steps towards our modern furnace.

    The older burners were called ribbon (they sat in the combustion chamber) and did a good job until we started going for higher efficiency. Then a major problem arrived, with colder heat exchangers came condensation. This caused the mild steel burners to rust and the size of the openings to get smaller, making for a poor air to fuel ratio and just a terrible dirty burn, lots of soot. The good news is stainless steel burners did solve this, how ever it's an expensive fix.

    Now remember what we said about something that worked? You got it! new style burners, not all bad though. With the high efficiency furnaces comes a colder stack temperature (fumes to chimney). They are cold enough that they possibly would not raise without a little help. So a venter (blower) motor is used to draw the fumes out of the heat exchanger and up the chimney. This made possible a new style burner. It is in reality a far better burner then the previous style. We call it, in shot. This burner is self adjusting for its air mixture and is positioned out side of the heat exchanger. It is more like the fire from a torch. The fire is now sucked in to the heat exchanger by the draft of the venter. keep in mind the burner sits out in mid air. In most modern furnaces the heat exchanger is basically a piece of pipe with a burner on one end and a venter on the other.

    Knowing that good things get better, next we worked over the controls. Rather then using temperature to turn on the fan we use a solid state timer. This controls all fan functions. Remember the pilot light? It's gone. We now use either a hot surface igniter or if your lucky a spark. The hot surface is much like the filament of a light bulb. It upon demand gets very hot and is used as the source for ignition, unfortunately like a light bulb it burns out. Again remember the thermal couple? Yes it to is gone. We now use a micro processor and electronically sense if the fire is lit.

    On most modern furnaces the sequence of operation is as follows:

    1. The thermostat call for heat. It starts only the venter.

    2. The venter comes to speed and if the chimney is not blocked and intake air is present it will draw a vacuum on the heat exchanger. This is sensed by a vacuum switch, it now will turn on our timer.

    3. The timer lets the ignition come on and after a delay the gas valve opens and if all is well we finally get FIRE!

    4. A rod in the fire passes an extremely small current through the fire to ground. If the microprocessor accepts the signal the fire will remain on.

    5. Our timer will soon turn on the blower.
    When the thermostat no longer calls for heat:

    Venter stops. Vacuum is lost. Fire is turned off. Blower will run till timer tells it to stop. You still have the old style over temperature switches. All of this has made new furnaces extremely small, efficient and safe. Do they require more maintenance? YES. If someone tells you different, they tell less then the truth! But I will gladly pay the cost to have my family safe and comfortable.

    About those automatic toilets

    I bet you will probably never have to repair one of these but I also bet that you were curious as to how they work. :) In addition to what is said below, I should add that only the initial push to open or close the valve comes from the solenoid. Most of thw work is done by a clever hydraulic amplifier which uses water pressure as the power source.

    (From: Hauser Christoph (

    The automatic toilets are active infrared devices. This means, you have a IR transmitter and an IR receiver basically. More sophisticated systems use more emitters and receivers or a PSD to get a triangulation. Some systems are battery-operated with lithium 2CR5, CR-P2 or simply with four AA-cells.

    Usually, the infrared system is activated every second up to every 4 seconds. If the receiver sees a response, the sampling is higher. There also several time delays included. The systems detects persons or objects in the range of 10 to 100 cm (4 to 40").

    The valve for the flush is a bistable solenoid device. With a short pulse you open the valve and with another and opposite polarity you close it. It's possible to reach about 200,000 flushes with batteries and a life-cycle of 4 years. Often PIC's (Programmable Interface Controllers - one chip micros) are used, because they have a low stand-by consumption.

    You wonder, why I know this? It's my job to develop these devices!

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

    Service Information

    Wiring diagrams

    Many larger appliances like washing machines and microwave ovens have a wiring diagram or connection diagram pasted inside the cover. However, this is rare for small appliances.

    In most cases, wiring is trivial and five minutes with your Mark I Eyeball(s) and a pencil and paper (remember those? If not, use your PC and a schematic capture software package) will result a complete schematic. There may still be some uncertainties with respect to motor, transformer, or switch wiring but testing with an ohmmeter or continuity checker should eventually prevail.

    Removing screw with stripped head

    Even if a Phillips head screw head is severely damaged, it is sometimes possible to free it just by applying enough pressure while turning with a properly shaped screwdriver. This can only be attempted if it is possible to press hard without risk of breaking or damaging anything.

    Other more drastic measures:

    1. Drill it out - the same way you would remove a rivet - with a sharp twist drill bit on slow speed. If necessary, use a metal or plastic sleeve to guide the drill bit.

    2. Use a Dremel tool with a disk cutter or fine hacksaw blade to cut a slot in the head and then use a straight blade screwdriver to remove it.

    3. Take a pair of sharp diagonal cutters and grip between the center and one edge or the entire head. Or, grab the head with a pair of miniature locking pliers (Vice-Grips(tm).)

    4. Drill a hole in the head and use a screw extractor (E-Zout(tm).)
    Take care to avoid excessive mechanical shock to delicate equipment and avoid allowing metal particles to fall into the interior of the appliance.

    Fil's tips on improvised parts repair

    (From: Filip "I'll buy a vowel" Gieszczykiewicz (

    Whenever I'm stuck with some "Unprofitable" with a broken part, I see if I can duplicate the functionality of the part. My raw materials include:

    • 5 minute 2-part epoxy (under $8 from a RC hobby store).
    • 30 minute 2-part epoxy (under $8 from a RC hobby store).
    • Wire: copper, steel, SS, "piano", spring, etc.
    • Springs (a box of 1000s from hamfests, stripped monsters).
    • Plastic stock: all types (you will learn which glue well).
    • Plastic build up kit: two parts - foul smelling polymer and "dust".
    • Aluminum stock: from thin foil to .080" to .5".
    • Brain: regular edition. :-)
    As long as you know what the part does (you need not HAVE it... as long as you can see where it goes in, what it moves, what activates it, etc).

    If it's something intricate, my parts bin door is NEVER closed.. and it gives its "body" to science :-)

    If you have part of the old plastic lever, it's usually easy to build up the broken off part. I like to heat up a segment of piano wire and insert it into the remaining part in such a way as to hit the most "meat" of the part. Then, using either epoxy or plastic build up material, I form something that does the job.

    Overall, I have about a 75% "plastic broken part" repair ratio. After a while, you will be able to judge if it's doable. "lever"s are usually easy... sliding assemblies are a pain in the @ss...

    Fixing stripped plastic threaded holes

    (From: Gordon S. Hlavenka (

    Simply set the screw on top of the hole, and press LIGHTLY on it with the tip of your soldering iron. The iron will heat the screw, which then slides into the post. After everything cools, you can take the screw out normally and the threads are as good as new! If the post is badly stripped, you may want to stuff the hole with extra plastic shaved from some non-critical area to provide additional material.

    You have to be careful not to overheat, or push too hard. But it works very well.

    Interchangeability of components

    The question often arises: If I cannot obtain an exact replacement or if I have another appliance carcass gathering dust, or I just have some extra parts left over from a previous project, can I substitute a part that is not a precise match? Sometimes, this is simply desired to confirm a diagnosis and avoid the risk of ordering an expensive replacement and/or having to wait until it arrives.

    For safety related items, the answer is generally NO - an exact replacement part is needed to maintain the specifications within acceptable limits with respect to line isolation (shock prevention) and to minimize fire hazards. However, these components are not very common in small appliances.

    For other components, whether a not quite identical substitute will work reliably or at all depends on many factors. Some designs are so carefully optimized for a particular part's specifications that an identical replacement is the way to return performance to factory new levels. With appliances in particular, may parts which perform common functions - like thermostats - utilize custom mounting arrangements which precluded easy substitution even if the electrical and thermal characteristics are an exact match.

    Here are some guidelines:

    1. Fuses - exact same current rating and at least equal voltage rating. I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm long fuse as a substitute. Also, they should be the same type - slow blow only if originally specified. A fuse with a faster response time may be used but it may blow when no faults actually exist.

    2. Thermal fuses and thermal cutouts - exact same temperature and current rating (if stated). Physical size may also be important when these are buried in motor or transformer windings. Also see the document: Notes on the Troubleshooting and Repair of AC Adapters, Power Supplies, and Battery Packs.

    3. Thermostats - temperature range must be compatible (or slightly wider may be acceptable). Electrical current and voltage ratings must meet or exceed original. With some devices, hysteresis - the tendency of a thermostat that has switched to stay that way until the temperature changes by a few degrees - may be an issue. For example, electric heaters use a thermostat which has a typical hysteresis of 3-5 degrees F. However, heating appliances like waffle irons and slow cookers may depend on the thermal mass of the castings and use a thermostat with very little hysteresis.

    4. Resistors, capacitors, inductors, diodes, switches, trimpots, lamps and LEDs, and other common parts - except for those specifically marked as safety-critical - substitution as long as the replacement part fits and specifications are met should be fine.

    5. Rectifiers - use types of equal or greater current and PRV ratings. A bad bridge rectifier can be replaced with 4 individual diodes. However, high efficiency and/or fast recovery types are used in parts of electronic ballasts and other switching power supplies.

    6. Transistors and thyristors (except power supply choppers) - substitutes will generally work as long as their specifications meet or exceed those of the original. For testing, it is usually ok to use types that do not quite meet all of these as long as the breakdown voltage and maximum current specifications are not exceeded. However, performance may not be quite as good. For power types, make sure to use a heatsink.

    7. Motors - small PM motors may often be substituted if they fit physically. Make sure you install for the correct direction of rotation (determined by polarity). For universal and induction motors, substitution may be possible but power input, speed, horsepower, direction of rotation, and mounting need to be compatible.

    8. Sensor switches - some of these are common types but many seem to be uniquely designed for each appliance.

    9. Power transformers - in some cases, these may be sufficiently similar that a substitute will work. However, make sure you test for compatible output voltages to avoid damage to the regulator(s) and rest of the circuitry. Transformer current ratings as well as the current requirements of the equipment are often unknown, however.

    10. Belts or other rubber parts - a close match may be good enough at least to confirm a problem or to use until the replacements arrives.

    11. Mechanical parts like screws, flat and split washers, C- and E-clips, and springs - these can often be salvaged from another unit.
    The following are usually custom parts and substitution of something from your junk box is unlikely to be successful even for testing: SMPS (power supply) transformers, microcontrollers, other custom programmed chips, display modules, and entire power supplies unless identical.

    Appliance repair books

    Your local large public or university library should have a variety of books on appliance repair and general troubleshooting techniques.

    Here are a few titles for both small and large appliance repair:

    1. Chilton's Guide to Small Appliance Repair and Maintenance
      Gene B. Williams
      Chilton Book Company, 1986
      Radnor, PA 19089
      ISBN 0-8019-7718-5

    2. Chilton's Guide to Large Appliance Repair and Maintenance
      Gene B. Williams
      Chilton Book Company, 1986
      Radnor, PA 19089
      ISBN 0-8019-7687-1

    3. Major Appliances, Operation, Maintenance, Troubleshooting and Repair
      Billy C. Langley
      Regents/Prentice Hall, A Division of Simon and Schuster, 1993
      Englewood Cliffs, NJ 07632
      ISBN 0-13-544834-4

    4. Major Home Appliances, A Common Sense Repair Manual
      Darell L. Rains
      TAB Books, Inc., 1987
      Blue Ridge Summit, PA 17214
      ISBN 0-8306-0747-1 (Paperback: ISBN 0-8306-0747-2)

    5. Home Appliance Servicing
      Edwin P. Anderson
      Theodore Audel & Co., A Division of Howard W. SAMS & Company, Inc., 1969
      2647 Waterfront Parkway, East Drive
      Indianapolis, IN 46214
      Telephone: 1-800-428-7267

    6. Handbook of Small Appliance Troubleshooting and Repair
      David L. Heisserman
      Prentice-Hall, Inc. 1974
      Englewood Cliffs, NJ 07632
      ISBN 0-13-381749-0

    7. Fix It Yourself - Power Tools and Equipment
      Time-Life Books, Alexandria, VA
      ISBN 0-8094-6268-0, ISBN 0-8094-6269-9 (lib. bdg.)

    8. Readers Digest Fix-It-Yourself Manual
      The Readers Digest Association, 1996
      Pleasantville, New York/Montreal
      ISBN 0-89577-871-8

      Overall, this is an excellent book which I would not hesitate to recommend as long as one understands its shortcomings. The coverage of both small and large appliances, tools, and common yard equipment, as well as a
      variety of other categories of household repair (furniture, plumbing, etc.) is quite comprehensive.

      It is very well illustrated with hundreds upon hundreds of easy to understand exploded diagrams. In fact, that is probably its most significant feature. Where the equipment is similar to yours, it is possible to use the pictures almost exclusively for understanding its construction, operation, and disassembly/reassembly procedures.

      The discussion of each type of more complex equipment provides one or more troubleshooting charts. Each entry includes the level of difficulty and identifies any needed test equipment (e.g., multimeter) for dealing with that problem or repair.

      However, this book is at best an introduction and once-over. Much of the material is presented based on one or two models of a particular type of devices while sort of implying that all the rest are similar. In all fairness, very often this is sufficient as most models of simpler differ only in details. However, for all but the most general repairs on the more complex appliances, a book with more specific information would be highly desirable before actually tackling the repair.

      One significant shortcoming is that there are NO wiring diagrams of any kind for any of the appliances. Their approach seens to be to just check parts for failure. While this will be successful in many cases. a wiring diagram would be useful when explaining appliance operation and would help in logical troubleshooting to localize the problem.

      Although there is a chapter on home electronics - audio, video, computer, security systems, etc. - don't expect anything useful beyond very general information and simple repairs like replacing belts and looking for bad connections. While it isn't surprising that the treatment of this complex equipment is superficial at best in a book of this type, in some cases it is as though the editing was based on a page limit rather than including a more complete summary but with fewer details. For example, the only repair on a CD player beyond belts and lens cleaning is to test and replace the tray loading motor (one particular model). Unfortunately, some of the specific information is not entirely accurate either and may be misleading and expensive. The safety instructions for the electronics (as well as microwave ovens) is also a bit lacking considering some of the suggestions for troubleshooting and parts replacement.

      Some errata: Testing of microwave oven HV diodes (good ones will test bad), HV discharging of TVs and monitors always (not needed) and possibly to wrong place (should be to picture tube ground, not chassis ground) but no mention of power supply capacitor discharging, not specific enough on 'good' and 'bad' resistance readings for various parts like motors.

    9. All About Lamps - Construction, Repair, Restoration
      Frank W. Coggins
      Tab Books, 1992
      Blue Ridge Summit, PA 17214
      ISBN 0-8306-0258-5 (hardback), 0-8306-0358-1 (paperback)

    10. How to Repair and Care for Home Appliances
      Arthor Darack and the Staff of Consumer Group, Inc.
      Prentice-Hall, Inc. 1983
      Englewood Cliffs, NJ 07632
      ISBN 0-13-430835-2 (hardcover), ISBN 0-13-430827-1 (paperback)

    11. Popular Mechanics Home Appliance Repair Manual
      Hearst Books, NY, 1981
      ISBN 0-910990-75-1

    12. Microsoft Home (CDROM)
      Based on the Readers Digest Complete Do-It-Yourself Guide
      The Readers Digest Association, 1991
      Microsoft, 1996
      ISBN 0-57231-259-9

      This isn't the Fix-It-Yourself Manual but I expect that is coming on CDROM if it is not out already. However, there is some information including nice diagrams relating to door chimes, telephone wiring, incandescent and fluorescent lighting fixtures, electrical switches, and heating and air conditioning systems (in addition to everything else you ever wanted to know about how your house works, tools and tool skills, materials and techniques, and home repair and maintenance).

    Manufacturer support

    Major manufacturers may provide a variety of types of support for their products including technical assistance, parts sourcing, unadvertised repair or replacement beyond the expiration of the warranty, upgrade or replacement to fix known defects whether covered by official recalls or not, etc.

    I have on several occasions been pleasantly surprised to find that some companies really do stand behind their products and all it took was a phone call or short letter. One only hears of the horror stories!

    (From: lizard3 (

    Sears sells schematics and plans of all their appliances. This includes a breakout of the entire machine with each part number. They have a toll-free number to call. All you need is the model number and a credit card. We have used their washing machine schematic a couple of times to replace some very minor parts.

    Parts suppliers

    Common parts like cordsets, plugs, wire, and some light bulbs can be found a larger hardware stores, home centers, or electrical supply houses. Small electronic components like resistors and capacitors, can be found at any electronics distributor - including even Radio Shack in a pinch.

    The original manufacturer of the appliance is often the best source for unusual or custom parts. Many are quite willing to sell to the consumer directly. Check for an 800 number and have complete information on model and a part number if possible. However, their prices may be high - possibly rendering a repair uneconomical.

    There are numerous appliance repair centers that may be able to obtain parts at lower cost - check your Yellow Pages. Their prices may be less than half of those of the original manufacturer.

    The following is a good source for consumer electronics replacement parts, especially for VCRs, TVs, and other audio and video equipment but they also carry a variety of common electronic components and appliance parts like switches, range elements, defrost timers, light bulbs, and belts

    • MCM Electronics, 1-800-543-4330,

      VCR parts, Japanese semiconductors, tools, test equipment, audio, consumer electronics including microwave oven parts and electric range elements, etc.

    • Global Micro Parts, 1-800-32584-88,

      They specialize in microwave oven parts, but also carry some other major appliance parts.

    Also see the documents: "Troubleshooting of Consumer Electronic Equipment" and "Electronics Mail Order List" for additional parts sources.

  • Back to Small Appliances and Power Tools Repair FAQ Table of Contents.

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