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Starting Motor Without it's Starter Capacitor

  1. Sep 12, 2015 #1
    I found a motor I think is from an old AC unit in the recycle. It is a 1/4 HP, 265V, 1.20A AC motor. I've been looking to make a low-torque sander and was thinking about using this as a a drive motor. I know the starter capacitor is there to provide an initial burst of current to get it up to speed.

    My question is, If I was to power it from a regular wall-outlet (120V) without the starter capacitor (didn't find one), and start it by hand-turning it, could this create a dangerous situation where the motor pulls too much current or something? I don't see any big problems, but wanted to ask people with more experience.
  2. jcsd
  3. Sep 12, 2015 #2


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    You have a 265 VAC motor and you need to run it with 265 VAC. The starting capacitor is not there to give it an 'initial burst of current'. It is wired in series with a special starting winding and causes a phase shift in the current in that winding. This causes the appearance of a rotating magnetic field and the rotor follows it. There is a centrifugal switch that opens that starting winding once the rotor is up to speed. It is no longer needed. Typically though, if you rotate the shaft of a an AC induction motor by hand that has no current in the starting winding it will come up to speed whichever way you rotate it.
  4. Sep 12, 2015 #3


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    Why don't you calculate a starter capacitor:


    and buy one:

    http://www.grainger.com/category/capacitors/motor-supplies/motors/ecatalog/N-9yp [Broken] ?
    Last edited by a moderator: May 7, 2017
  5. Sep 12, 2015 #4


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    This is dangerous and is not recommended. I've had times when it was done in a emergency until a proper motor was installed but the chance of a motor stall because of the low power (~25% of normal) and the resultant cooking of the motor is high with no run capacitor.
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