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How did this motor die and can it be fixed?

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  • How did this motor die and can it be fixed?

    I was just given- they even delivered it- a big Hobart meat grinder with a bad motor. The local motor shop apparently took it apart, said it wasn't worth fixing, and so the owner "donated" it to my scrapheap.

    The question is, can it be saved? We don't really need it, since we already have a 3HP grinder that'll mulch a whole moose, antlers and all, if you can just get 'is front hoof into it. But the packrat in me can't stand to see good junk go to the dump. Gearbox is in fine shape, rest of the housing is okay, the grinder itself is a little rusty but easily salvageable.

    Now, some pics:

    The commutator- Burned/overheated. Can it be turned down a few thou and largely cleaned up?

    The Motor numbers- They mean anything, other than the 60Hz/230VAC/1Ph line?

    The Brushes- Only two are left. Of the other two, one is gone entirely and the other is worn down to about 1/4" thick. Any good suppliers that might have these badboys on hand? Also, all four appeared to be grounded to the housing ring... I admit I don't know much about AC motors, but that didn't seem right to me.

    The curious part- There were a bunch of these little tapered, L-shaped bits of copper in there. After a little head-scratching, it appears, from the burned/arced portions, they fitted the comm about like this. Never seen that sort of thing before- what are they, if anything, and do they mean the wound is fatal?

    They appear to fit together like this, being extensions of the comm laminations. There appears to have been a bunch of arcing/burning as they sheared off (or melted off?)

    Some of them had a tab that appeared to have accepted this plate. Again, for what reason, I don't know.

    And finally, inside the brush-end bell, are these smears of solder that appear to have been slung out of the commutator, or near it. Perhaps where the windings are connected to the comm laminates?

    And last, the motor ID plate which is actually on the sheetmetal outer housing of the grinder case, not the motor itself.

    So, the question is, how did it die, and somewhat more importantly, can it be made to run again, with minor expenditures in time and effort? I'll assume it'll never be top-notch again, but if it can be made funtional enough to use or sell, it ought to be worth a little time.

    To me- again, not knowing much about AC motors- it looks like if I just turned about 20 thou off the comm, and found some new brushes, the thing just might work. I just don't know what's up with those L-shaped tabs or the disc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    I think he's dead Jim, er.. I mean Doc.
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    • #3
      Looks like a repulsion start, induction run motor. The L shaped bits hold the shorting ring away when at rest. When up to speed they overcome the garter spring though centrifugal force and allow the shorting ring to short out the comutator to essentially turn it into an induction motor.

      This allows for massive starting torque without drawing large current flow.

      Doesn't look like its worth trying to fix.
      Better off trying to fit another motor to it.

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      • #4
        Yes on all accounts,shame too,those are damn good motors.

        Remember on those old motors go through the hp calculation-amps x volts < 746 = hp,those brush motors develope nearly double the torque per hp than an induction motor.Trust me I know,I replaced a motor on a ice cream mixer with a equal hp motor and it toasted in short order,thats when my motor supplier told me what happened
        I just need one more tool,just one!

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        • #5
          I agree with YF. Looking at the first picture, It looks like the rotor is universal/induction combination design.

          Few questions.

          - can you post a picture showing the rotor and stator
          - how many leads in the field winding?
          - is there a capacitor?

          Few comments.

          - commutator doesn't look that bad. You should be able to turn it down until it's clean

          - you may be able to run the motor as a pure induction motor. Since there is no starter winding (I'm guessing), you'll have to start the rotation with your finger. You can completely ignore the rotor winding, commutator, and brush

          - you can wire it so that instead of using those L-shaped tabs to automatically switch off the rotor winding, you can wire a momentary push button or even better a relay with a timer. Some old refrigerator motors use this.

          - If after few hours, you can't get it to run I wouldn't waste any more time.

          Good luck.

          Albert

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          • #6
            I hear taps playing softly in the background

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            • #7
              On the plus side the motor windings still have a good color to them and don't appear to have overheated. The solder has melted out of the commutator so some motor windings may be open there. You'll feel much more hope after you clean up the commutator and meter out the windings. There won't be much resistance in windings of that gauge but you still should be able to determine if they are internally shorted.

              If you get it running be sure to give the standard evil scientist yell "It's alive,..IT'S ALIVE!!"

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              • #8
                YF and wierd have identified the motor correctly, I think. These are good motors, especially for high starting torques. All four brushes are grounded, and the grounds need to be good grounds (Large wire, clean joints). The brush holder should shift a few degrees. The motor is reversed by shifting the plate, and can be burned up by mis-adjusting the plate. It is probably a very old motor but, In the right place, very good trading material. BTW, the end play is kind of critical, too much and the motor "hunts"
                for a good running position- and the torque seems to vary so the speed kind of varies too. Normally not a problem. You may have trouble finding a repairman who understands the motors. I did not get your pics to come up, but you may have (those tapered pieces) a bunch of broken shorting bars- if so junk the motor unless you have an immediate need for a high torque (at starting) motor.

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                • #9
                  Steve,

                  The shorting bars look they are melted off. Something went badly wrong like a big piece of bone fed in.
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                  • #10
                    I think it got Mad cow disease

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                    • #11
                      Pics came up today. I would say the motor is beyond economical repair.

                      Were I trying to determine WHY the motor failed, I would suspect that the brush shifting plate was mis-adjusted. Some of these motors have a lever to reverse direction. If the lever is set to the "neutral position, the rotor acts as a single turn shorted winding on a transformer. Extremely high currents flow through the brushes, starting torque is zero- the solder melts or brushes burn or commutator burns- some thing happens to reduce the current to zero (including blown fuses).

                      You know these motors are going to fail because of brush placement when they make lots of noise while starting- sounds like a shorted buzz box welder. The starting torque is very low, often the mechanical load is rebuilt to make it turn easier. The motors are just uncommon enough to be strange to the repairman (through no fault of his) and common enough to be an expensive source of motor replacements.

                      When the brushes are properly located,The starting torque is 200 to 300 percent of the the running torque so they are good for starting heavy loads. Some of them have speed characteristics similar to a DC series motor so they need a load or may self destruct.

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                      • #12
                        Hi;
                        From the looks of the comminator I have the same style of motor on my home brewed chop saw. The motor got to the point that it would not start. On inspecting the motor, the garter spring was in pieces. Paid $15 for a new spring, they saaw me comming, but the motor is back in operation now. Well worth the price of the spring.
                        charlie
                        Don\'t ask me to do a dam thing, I\'m retired.
                        http://home.earthlink.net/~kcprecision/

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