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Single phase motor changes direction on start

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#1 Alex


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Posted 03 February 2005 - 10:37 PM

I have just wired a NEMA frame 56 GEC single phase motor to a stop/stop circuit and a reversing Drum switch. All the wiring checks out. I use the drum switch to reverse the starter winding in relation to the main winding. Unfortunatley the motor starts in a random direction! I don't have any load on the motor and the cabling to the motor is about 3 yards. Can this be a problem with the cable length upsetting the phases? Any suggestions for fixing it or further tests?

#2 Alex


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Posted 07 February 2005 - 09:08 AM

Well guys, I fixed it myself!
After a lot of reading to understand the configuration of my single phase motor I got out the DVM and found the start winding to be open circuit. Fortunately this was caused by the centrifugal switch being slightly open even when the motor was stopped. I simply adjusted the contacts and now all is well!
Regards Alex

#3 marke


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Posted 14 February 2005 - 10:01 AM

Hello Alex

Thank you for posting the solution.
I was at a bit of a loss to give3 an answer from your description. Usually, an open start winding will cause the motor to vibrate and draw lots of current, but not rotate in any direction. This is due to the single phase field being effectively two fields that are equal in amplitude, rotating in oposite directions. The start winding adds a second phase and causes a net rotating field in one direction only.

Best regards,

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