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  1. #1
    Join Date
    Nov 2016
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    Confused PSC motor capacitor question

    I read that in a PSC motor the start and run winding are made 90degs out of phase with each other for greater starting torque. Once the motor has started, the run capacitor puts the start winding back in phase with the run winding. 0 degs. Then the motor runs on 180 degs oscillation from the AC.
    But I read elsewhere that this is not true. I read that the run capacitor is chosen so that the start and run windings will be somewhere between 0 to 90 degs out of phase with each other depending on how much torque you want vs run. Thus, if you needed more torque it would be more 90 degs. If you wanted more run it would more towards 0 degs.
    Which is true? Maybe both? Does anybody know a lot about motors?

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  3. #2
    Join Date
    Dec 2004
    Chicago area
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    In a PSC motor, the run capacitor is in series with the start winding, so whatever phase shift is created, is continuous.

    A capacitor has 2 functions

    The first, which everyone knows is that it stores energy, then releases when the sine wave reverses, which creates the phase shift, sort of like a time delay. The bigger the capacitor, the more the delay, and the more the phase angle shift.

    The second, which is a secret is that it acts as an amperage limiter. The smaller the capacitor, the lower the amperage.

    The bigger the capacitor, the more the amperage can be.

    In the field, capacitor size selection is not up to you, its provided to you by the motor manufacturer.

    Sent from my iPhone using Tapatalk

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  5. #3
    Join Date
    Aug 2002
    Southold, NY
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    Good read on Motors:
    Attached Images Attached Images

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