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Is the motor fried?

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  • Is the motor fried?

    I pulled off my ear protection and didn't here the dust collector - just a loud HUMMMMMMMMMMMMMMMM.

    I unplugged the dust collector (haven't put a switch on it yet) and the HUMMM stopped.

    Went outside. It's a 3hp 220v 1Ph TEFC motor, pulling the air through a cyclone. The motor was too hot to touch, but it didn't fry spit. Took of the fan cover, and the motor turned OK. No bearing siezed.

    Opened up the J-box on the motor and there was one very fried capacitor and a pile of soot.

    I have no idea of the specs on the capacitor, so where do I go from here?

    1. Forget it. It's fried. Pay some exhorbitant sum to buy the motor as a part from JET. (special shaft for the dust collector fan)

    2. Go to a motor ship which will magically know just what capacitor to give me, take it home and try it.

    3. Take the motor in so the motor shop can make sure the insulation didn't break down somewhere. (Will they charge to check it?)

    In the past, I've always had some spare motor lying around when one fries, so this is the first time I've had to get serious about it.


    Ed Bryant

  • #2
    Take the nameplate specs to a motor shop and buy a new cap for a coupla bucks. Chances are very high that this is your prob. I have 54 similar induction motors at work. (18 AMF pinspotters) Always replacing caps.
    Rgds, Lin


    • #3
      I would ask myself what fried the cap. If the motor never came up to speed it would have stayed in the start position, same if the centrifugal (if it has one) switch is stuck.


      • #4
        From the melted terminals on the capacitor, I am guessing that it vibrated in some way that permitted a short.

        It had been running a while, with no evidence of low power or low rpm.
        Ed Bryant


        • #5
          True enuff. I shoulda mentioned that almost all the centrifugal switches have been replaced with electronic starters. My fault for presuming that switch (if any) had been checked


          • #6
            What is to check on the centrifugal switch, just that it moves freely?

            Ed Bryant


            • #7
              Yeah, that it moves freely and hang a multimeter across it to check contact open/close.


              • #8
                I'll do that as soon as it is cool enough to pick up. AND I won't run it again until I have a magnetic thermally protected switch on it !! (Assuming the cap fixes it.)

                Ed Bryant


                • #9
                  Yeah, ah klixon is a VERY good idea


                  • #10

                    After getting the motor up on the bench, I find that two wires shorted just inside the motor case. I am able to get the end cap off and pull the wires out that way. I could splice them with a crimp-type butt splice, but do I need a special kind of wire?

                    It gets worse. The varnish on some of the windings have turned black. Is this the end?


                    [This message has been edited by elbryant (edited 06-11-2005).]
                    Ed Bryant


                    • #11
                      The only true way is to have the insulation tested. A motor shop can do that for you. Unless you know some one with a megger ( a machine that will check the insulation).
                      Don\'t ask me to do a dam thing, I\'m retired.


                      • #12
                        If you can get to that fan without doing a job on your fingers give the motor a spin and it should take off. If it runs after you start it by hand it's the starter circuit if it smokes replace/rewind the motor. I have been hand starting a bench grinder for years.
                        my two cents worth
                        Herm Williams


                        • #13
                          Can anyone explain simply how a centrafugal switch works to me .
                          this fritz im doing up has some sort of doofer bolted to the end of the armature shaft on the outside of the motor that looks like a mini generator with what looks to be like a comutator in the middle with two magnets on the outside.
                          the comutator bit does not have any feed or return electrically......dont know whats behind the magnets .....but wiring exits from behind them.....and the wiring then goes into the main electrical cupboard.
                          how does this lot work ...i need to know because someone has bi-passed a lot of stuff in the electrical cabinet.
                          all the best..mark