# Motor Rotation Changing



## CheapCharlie (Feb 4, 2011)

We are at a loss here at work. Yes we could just buy a new motor (and did), but no one can figure out how a single phase motor can change directions randomly. It is a H137 motor. Every once in a while when starting it will change rotation directions. Not every time, randomly.

Any ideas?


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## JRaef (Mar 23, 2009)

Bad starting cap or sticking centrifugal switch. Or both.

If it's a pump or fan and there is flow making it spin backward before you energize it, it will keep tuning that direction if the centrifugal switch is getting satisfied. 

Single phase motors don't "know" which way to turn, the starting cap creates a virtual phase shift that determines the rotation direction. Anything that interferes with that process sets up unpredictability.


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## Bird dog (Oct 27, 2015)

Can you change rotation by changing taps? You may have a bad motor. Something inside might be intermittently shorting.


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## Cow (Jan 16, 2008)

I had a small 3 phase motor a few years back on a manure conveyor that would randomly change directions when it was started. I remember it smoked almost immediately after I got there to check it out though.

That's the only motor I've ever seen do that.


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## Galt (Sep 11, 2013)

jr nailed it


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## frenchelectrican (Mar 15, 2007)

also check the voltage when you start up the motor sometime when it get low enough it can actually change rotation too.

I have see that couple time before..

as JR posted he did make a good point on that..


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