Type of 120 V AC single phase motor

Discussion in 'Electronics Resources' started by fborot, Jul 12, 2018.

  1. fborot

    Thread Starter New Member

    Feb 1, 2018
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    My gate uses a single phase, 120 V AC motor with a capacitor. It has 3 wires that I refer to as:
    1- ground
    2- forward direction
    3- reverse direction

    When there is power between 1&2 the motor rotates in one direction and when power is applied between 1&3 it rotates on the opposite direction.
    I would like to properly identify this motor in case I need to find a replacement for it.

    Is "bidirectional motor" a right term? When I search for that term I find examples on how to permanently reverse the original direction of a motor (i.e from clock wise to counter clock wise or vice versa) but can't find descriptions of such a motor or where to buy a similar one.

    Also, about the capacitor: how do I know whether it is a "capacitor run" or "capacitor start" motor?

    Thank you
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It sounds like a PSC (permanent start cap) motor, is is very simple to reverse by SPDT switch with centre off.
    Google PSC motor.
    Same as a garage door opener etc.
    Max.

    [​IMG]
     
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  3. fborot

    Thread Starter New Member

    Feb 1, 2018
    13
    1
    thank you. I can see in your diagram the 3 wires ....

    help me understand it better ... it has a winding for each direction ? , I found this simplified diagram of a PSC motor on this web site:

    upload_2018-7-12_15-26-12.png
     
  4. fborot

    Thread Starter New Member

    Feb 1, 2018
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The typical PSC motor has two identical windings for run and start so they can be used alternately.
    IOW, no defined Main winding, they alternate duty.
    Max.
     
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  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    BTW, that is a bit of a poor representation of PSC motors in general.
    Max.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Incidentally, the correct term for 1- is Neutral or Common, not Ground.
    In this instance Ground would be the earth conductor to the motor frame.
    Max.
     
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  8. fborot

    Thread Starter New Member

    Feb 1, 2018
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    thank you for the correction and explanation , can you help me found a better diagram ?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you look at the DWG I posted in #2, draw a winding from CW to Common, and a winding from CCW to common, and you have it.
    Both winding serve as start and run alternatively.
    Max.
     
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  10. fborot

    Thread Starter New Member

    Feb 1, 2018
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    Thank you very much I understand it better now.
     
  11. KeepItSimpleStupid

    Distinguished Member

    Mar 4, 2014
    2,871
    505
    Here http://www.hurst-motors.com/permanentmagnetacsynchronous.html is a little blurb.

    The windings are not quite identical, but for all practical purposes they are. I ran into a paper explaining why when they were discussing speed control.

    This https://www.designnews.com/automati...l-single-phase-induction-motor/74809400841732 also confirms the windings are not the same. Search for "different electrical" on the page.

    The motors are also used in clocks and ceiling fans.

    When the capacitor goes bad, the motor generally has trouble figuring out what direction to turn when unloaded. The capacitor phase shifts the phase of the other winding.

    Check for continuity of the windings. The resistance will be close, but not identical and the condition of the bearings.

    The capacitor used MUST be non-polarized.
     
    Last edited: Jul 13, 2018
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  12. fborot

    Thread Starter New Member

    Feb 1, 2018
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    Thank you sir!
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the windings are not close then there will be a different running current in one direction over the other, this is in motors that are not intended to be reverable in use.
    In my personal experience the winding's have been the same in a dedicated reversable PSC motor.
    This statement indicates they are only talking of unidirectional motors.
    Max.
     
    Last edited: Jul 13, 2018
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