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single phase induction motor in grinder

Discussion in 'Troubleshooting and Repair' started by KennyMcCormick, Nov 15, 2013.

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  1. KennyMcCormick

    KennyMcCormick

    20
    0
    Sep 8, 2013
    I have a problem with a 4x36" belt grinder. I was using it and smoke started comeing out so i turned it off to clear away the metal dust which I though was makeing the smoke and when i turned it back on again it runs for about 5 seconds and then stops. after then, any time i try to turn it on it just hums and the lights in the shop go dimmer. I think it was the start capacitor because I tested it and it was bad, except why would the start cap fail when the machine had already started and was running at full speed?
    So i put in a cheap replacement to see if i was lucky and it was just the cap, but now nothing at all happens. the switch doesnt even click on.
    so is it the switch? I was thinking maybe the centrifugal switch (if it even has one) but am i perhaps right to assume it might be the start button or something that stuck on and caused the start cap to stay in circuit?
    But would any such problem result in the motor stopping? I would think it would run fine and you only would know of the problem the next time you tryed to turn on the machine.
    What is likely my problem now that the switch does nothing at all?
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The capacitor could be a start capacitor or a run capacitor. A start capacitor will be used on a larger motor.

    The motor should run without a capacitor if spun to start with no load.

    If there is no action at all, then you will have to go through the circuit from plug connection to plug connection and find the break. It may be the switch, a fuse or thermal fuse or an open winding. You talk about a start button, how does this operate? One method is for the start button to connect the main winding and a start winding via a capacitor. This eliminates the unreliable centrifugal switch. Presumably the start button operates a contactor which could be faulty.
     
  3. KennyMcCormick

    KennyMcCormick

    20
    0
    Sep 8, 2013
    Ok, maybe forget the bit about the switch. I just checked the fuse and it was blown. So I tryed to turn it on to see if only replaceing the start capacitor had been a success but it immediately blew the new fuse. it wasn't doing this before. I think I must take in entirely to pieces and hope is not the motor that is dead or it may be easier to just buy another grinder. Is really not much in there just motor, start capacitor, run capacitor, on off switch and a little transformer looking dealie by the switch which i assume has something to do with how it stays on when it doesnt seem to be a latching switch. maybe is just some kind of relay i dont know.
    How do I test to see which is main coil and which is auxilarry, and how to test if a coil is shorted? what is a normal kind of resistance to expect to read?
    How do I know if a centrifugal switch is in tehre? or do I just have to take the motor to pieces as well
     
    Last edited: Nov 15, 2013
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