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Single phase motor problem

Discussion in 'Electronic Basics' started by Fred, Feb 9, 2004.

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  1. Fred

    Fred Guest

    I have an old single phase 110V 5.6amp 1/3HP 1200rpm induction motor
    that operates a scroll saw..The motor ran well in the past but now it won't
    It just sits there drawing current. If I spin the motor by quickly moving
    the belt
    it will start.

    It has capacitor start and the cap measures 84 mfd. Can't read the cap
    rating clearly
    but it looks like its a nominal rating of 72 mfd. I'm assuming the cap is OK
    I can measure what seems to be a reasonable value.

    Any ideas what the problem could be?

    I apologize if this is not the right news group for this post.
  2. Bill Vajk

    Bill Vajk Guest

    Some motors have an internal cenrifugal switch that
    disconnects the capacitor after the motor has started.
    Could be yours has one and the switch is shot.

    Otherwise the start winding itself could have failed.
  3. The capacitor may have dried out and though showing almost nominal
    capacitance, may have so mush series resistance that it cannot pass
    the expected current. If you can verify the start switch function and
    start winding continuity, replacing the cap is the next step.
  4. Jamie

    Jamie Guest

    in the back of the motor there should be a weight switch that ingauges
    the starter field.
    when the motor gets spinning up to a speed enough to throw the switch
    open it should do so thus disconnecting the starter field.
    i don't know what kind of starter you have in that motor but you could
    have a constant field starter which stays on all the time or a shaded
    pole type field. in either case i would say that you have an open widing.
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