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Thread: Bad capacitor maybe?

  1. #1
    Join Date
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    Bad capacitor maybe?

    I have a Craftsman 10 inch table saw that I bought used about 10 years ago. It has served me well, but now the motor has trouble starting. It will hum, but not turn. If I hit the restart button, it will sometimes come to life, but does not seem to have the power it used to.

    Could this be the capacitor instead of the motor? I hope so as I can buy one for only $8.

    As Sgt Oddball, the Sherman tank man said in the movie Kelly's Heroes - "I only ride 'em, I don't know what makes 'em work."
    "Archaeology is the science of digging a square hole, and the art of spinning a yarn from it."

  2. #2
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    Mark.....I had an old Craftsman that did that. The On-Off switch was mounted so the switch handle came through the front panel and the switch was actually mounted inside a box behind the front panel. I found that blowing out the switch and the circuit breaker (reset) with an air hose helped dramatically. Apparently sawdust was getting in there and preventing the contacts from closing completely.
    Ken

  3. #3
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    Easthampton, MA
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    Typically when a capacitor goes it's done for. Sounds more like a centrifugal switch hanging up. Bring it to your local motor shop to check it out. It maybe as simple as blowing the dust out. You didn't mention if it is totally enclosed.

  4. #4
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    A bad capacitor will not harm the motor. Turn the saw on, give the motor a spin. If it starts and runs, the cap is bad.

  5. #5
    I know that on my dads craftsman radial arm saw, probably a mid 80's vintage, it has a centrifugal switch on the back of the motor that would get clogged with saw dust and would refuse to start. It was not enclosed.

    Blowing it out with some compressed air would take care of the problem.

  6. #6
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    Thanks guys,

    I'll blow out the back of the motor and the switch area before I do anything else. I usually vacum it out after use and that has seemed to work over the years, but you never know. I have a compressor so I give it a good going over.

    Thanks again
    "Archaeology is the science of digging a square hole, and the art of spinning a yarn from it."

  7. #7
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    Quote Originally Posted by Mark Hubbs View Post
    ...now the motor has trouble starting. It will hum, but not turn. If I hit the restart button, it will sometimes come to life, but does not seem to have the power it used to.

    Could this be the capacitor instead of the motor? I hope so as I can buy one for only $8.
    ...
    Very likely, and for an $8 risk, that's the first thing I would try. I'm no electric motor expert, but I've recently had cap. failures in two different configurations of motors. One was a two cap. motor, capacitor start-capacitor run, with a centrifugal switch on an air compressor. The other was a single cap. motor without a centrifugal switch on a little 4x6 horizontal bandsaw.

    My experience with a two cap. motor was that the switch hung up and didn't drop the start cap. out of the circuit. If that's what happened in your case, the cap. will be bad also. Start capacitors are intended for only short term energization during motor starting- measured in seconds. If the switch freezes and keeps the start cap in the circuit while the motor is running, the start cap. will burn out in just a few seconds.

    Symptoms were similar to yours. Motor might or might not start - mostly wouldn't. Usually when it didn't start, it would blow the breaker on the circuit it was plugged into. Might or might not happen to you depending on the motor amperage and the breaker rating.

    The single capacitor bandsaw motor did not have a centrifugal switch. The bad capacitor resulted in a motor that wouldn't start under load. Would start fine on the bench with no load, but a light grip on the output shaft would keep it from starting.

    Note that if the motor doesn't have a centrifugal switch you MUST use a run capacitor - not a start capacitor. Run capacitors are rated for continuous usage. Start capacitors, even if with the proper mfd and voltage ratings, are for intermittent usage only, and will burn out in less than a minute if there's no switch to drop them out of the circuit when the motor starts. Been there, done that.

    Good luck.
    Tom Veatch
    Wichita, KS
    USA

  8. #8
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    Thanks Tom,

    I found a parts diagram for the motor on line. It has not centrefugal switch, and only one capacitor. If blowing out does not help it I'll order the capacitor from Sears. Bad thing is the postage costs as much as the part!
    "Archaeology is the science of digging a square hole, and the art of spinning a yarn from it."

  9. #9
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    Quote Originally Posted by Mark Hubbs View Post
    Thanks Tom,

    I found a parts diagram for the motor on line. It has not centrefugal switch, and only one capacitor. If blowing out does not help it I'll order the capacitor from Sears. Bad thing is the postage costs as much as the part!
    If the capacitor has the mfd and voltage rating on the case, you might can pick up one with the same rating (and physical size, so it'll fit in the housing) at a local motor shop. Probably be cheaper, considering Sear's postage/handling charges.

    Run and start capacitors usually have different capacitance (mfd) values, but the sizes available in each do overlap. So if you get one locally, be sure you ask for a RUN capacitor.
    Tom Veatch
    Wichita, KS
    USA

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