Need help with a motor running at excessive speed.

Discussion in 'The Projects Forum' started by BestAppliance, Mar 21, 2016.

  1. BestAppliance

    Thread Starter New Member

    Mar 21, 2016
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    I own an appliance repair company and had an unusual call. Had a customer that has an over the range hood whose motor runs much faster than normal. It is a "squirrel cage" type blower, 120 volt. It has 3 speeds and is borderline violent at high speed. He bought it open box on sale, and has been like this since its initial install this week. I didn't do the install, he called when the motor had problems. Interestingly, if the capacitor is disconnected after start up, the run speed drops to normal. Could this be the issue? I'm almost positive that it is a start capacitor. Also when i test the voltage at the motor harness terminations, the motor is running at almost 180 volts, yet the line in voltage remains at 120 volts. Im pretty good with appliances, but this is puzzling me. Any and all help is appreciated. Thanks in advance.
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
    811
    224
    I would say that the motor isn't connected properly.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,510
    2,369
    Did you try the motor on 120v direct?
    Also if a squirrel cage type fan, is the inlet or outlet blocked? If so it will remove the load from the fan.
    Max.
     
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  4. #12

    Expert

    Nov 30, 2010
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    6,762
    Most range hoods aren't strong enough to need a capacitor. Tell more. Is there a centrifugal switch inside the motor to disconnect the capacitor when the motor gets up to speed?
     
  5. BestAppliance

    Thread Starter New Member

    Mar 21, 2016
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    I checked all the wiring by the wiring schematic and everything appears correct. Unless there is a short somewhere I haven't found.
     
  6. BestAppliance

    Thread Starter New Member

    Mar 21, 2016
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    0
    If there is a centrifugal switch, I do not hear it disengage when the unit reaches speed. Based on the wire schematic I do not believe there is. It is very unusual for a range hood to have a capacitor, but this is a very large range hood.
     
  7. BestAppliance

    Thread Starter New Member

    Mar 21, 2016
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    That is something I didn't fully check. I hear the dampener falling shut when the unit is cut off, and the duct work expand and contract, so some air is moving, but that no guarantee of proper air flow. I'll check it out.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Also if a induction motor of what ever flavour it will not run higher than just below synchronism regardless of the voltage you give it!
    The violence would not be due to out of balance by any chance?
    Max.
     
    Last edited: Mar 22, 2016
  9. #12

    Expert

    Nov 30, 2010
    16,257
    6,762
    That might be the whole problem...or it might be that the fan noise is concealing the "click".
    ps, a centrifugal switch would be inside the motor. Got more than enough wires for the 3 speeds? Check for complicated circuitry.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,510
    2,369
    Most likely similar to the PSC motor on the right.


    [​IMG]
    Max.
     
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