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    Shaded pole motor failures?

    I'm trying to debug a dehumidifier and found that the blower wasn't working.

    Taking it apart, I find... a shaded pole motor.

    These things usually don't fail?

    Anyway, it's apparently a 2-speed with three wires: black red and orange.
    Orange apparently is common, and the speed is changed by applying 120V to red or orange. Black appears to be "high", red is "low".

    I see about 7 ohms DC resistance from black-orange, 11 ohms from red-orange, and about 4 ohms from red-black.

    There does not appear to be any overheating indication on the plastic covering the windings and the shaft seems to turn freely when power is disabled.

    With 120VAC from Black-Orange, the motor seems to try to turn but won't turn, I feel a bit of magnetic reluctance to turn. Spinning the rotor by hand, it still refuses to continue - always slows to a stop. When power is removed, the spindle turns freely once more. It seems to spin fewer times to stop when power is applied.

    I don't get why this thing won't spin? Seems really odd here...shorted winding? But it didn't overheat?

    I suspect I'm in the market for a new motor most likely but this is baffling.

    #2
    Re: Shaded pole motor failures?

    I know with ac induction motors, the rotor's squirrel cage bars can lose contact with the end rings. The one I saw wouldn't start form certain resting positions. Im not certain if it is possible for the copper ring on the shaded poles to fail.
    Last edited by rievax_60; 07-19-2017, 05:09 AM.

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      #3
      Re: Shaded pole motor failures?

      Interesting. I just was wondering about the possibility of that happening after doing some more research. Any ideas how many percent of rungs need to be broken before the motor stops running?

      Now is it possible to repair these disconnects, perhaps soldering the bars back to the rings, or are the welded because of possible heat/vibration issues?

      After taking apart this failed motor, solder does not seem to be an option... or at least I'm not sure how it can be soldered... Now how was this thing assembled in the first place?
      Last edited by eccerr0r; 07-19-2017, 04:06 PM.

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        #4
        Re: Shaded pole motor failures?

        I wonder if any of the shading coils are open circuit?
        With the rotor pulled out, could try put a screwdriver in and feel for the flux dead spots maybe.

        The stator coils are usually "impedance protected" so they don't care much if the motor is jammed, as long as the inductance is ok.

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          #5
          Re: Shaded pole motor failures?

          I think rievax_60 got the answer. Call it poor QC for this chinese motor. I tried "banging" the ring closer to the bars and got it to temporarily work again, but not 100% sure. Either way, pulling the rotor and putting it back sometimes got it to work again.

          I think I'll need to get a new rotor, if I can't get a whole motor.

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            #6
            Re: Shaded pole motor failures?

            Is the short loop open?
            My pc
            CPU : AMD PHENOM II x4 @ 3.5Ghz
            MB : ASUS M4A89TD PRO USB3
            RAM : Kingston ValueRAM 16gb DDR3
            PSU : Cooler Master 850W Silent Pro
            GPU : ATI Radeon HD 6850

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              #7
              Re: Shaded pole motor failures?

              Interesting failure mode. So looks like the shaded poles are open? Or perhaps shorting to the case?

              The only bad shaded pole motor I saw was from a small duct fan. It had a fuse inside it that was blown. I replaced the fuse, and got it fixed again.

              By the way, I do have a spare shaded pole motor, and it does appear to be dual speed. Not sure what it came out of (found it in an industrial dumpster), but it's a fairly large one. Also have a washing machine universal motor in anyone cares. Came from the same dumpster and also appears to work fine. In fact, most of the stuff I have gotten from there seemed to work.

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