A/C motor running backwards

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zappa

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Howdy folks!

I went to use my 6" Delta wood planer yesterday which usually stays dormant and unused. It had a heck of a time turning on this time and continued to trip either the 20Amp breaker at the panel or its own circuit breaker. I got it to turn on just once by rapidly turning the switch on and off. I investigated to possibility of both the blade drum and/or the motor getting hung up or sticky but neither was the case. With the belt off I tried to turn on the motor and noticed the motor trying to turn backwards!!! It would get a couple of revolutions in and then trip the breaker - very bizarre!!!

I fiddled with the switch for a few more minutes and then got a large spark and flash from the motor area under the tool - but it did not trip anything. Now the thing works perfectly every time - Weird huh? Whats up? I'm not asking you to fix this stuff - I'm just asking you to explain it.
 
From what you are posting, I'd bet on dirt/dust being on the "start-capacitor switch". When the motor stops that centrifugal switch should close, allowing the start circuit to energize the next time the motor starts.
When you "messed with" the motor, especially if you manually turned the shaft, you cleaned things enough for the switch to make properly..possibly burining a little dust as it did :D
my opinion for what its worth.
 
ultramegabob said:
I believe a weak capacitor will intermittently make some AC motors spin backwards.
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I believe the only way to reverse rotation is to reverse the start winding connections. The capacitor just provides the phase shift in the direction set by the polarity of the start winding.
 
augie47 said:
From what you are posting, I'd bet on dirt/dust being on the "start-capacitor switch". When the motor stops that centrifugal switch should close, allowing the start circuit to energize the next time the motor starts.
When you "messed with" the motor, especially if you manually turned the shaft, you cleaned things enough for the switch to make properly..possibly burining a little dust as it did :D
my opinion for what its worth.
Click to expand...

Possible. But would that trip the 20A breaker?
Intermittent ground fault maybe?
 
your inrush would stay pretty high without motor turning, the 20 would trip most often I'd think.
 
augie47 said:
From what you are posting, I'd bet on dirt/dust being on the "start-capacitor switch". When the motor stops that centrifugal switch should close, allowing the start circuit to energize the next time the motor starts.
When you "messed with" the motor, especially if you manually turned the shaft, you cleaned things enough for the switch to make properly..possibly burining a little dust as it did :D
my opinion for what its worth.
Click to expand...
The switch is in series with the start winding so if it stayed open, the motor wouldn't start just hum and draw lots of current.

Can't understand how any amount of dust, dirt or whatever could cause a motor reversal without a short. Of course. it did trip the breaker.
 
wptski said:
The switch is in series with the start winding so if it stayed open, the motor wouldn't start just hum and draw lots of current.

Can't understand how any amount of dust, dirt or whatever could cause a motor reversal without a short. Of course. it did trip the breaker.
Click to expand...

I'm not a "motor-man", just worked on a buch of them. I think the OP indicated he was manually turning the shaft at one point. I have had the experience on a single phase motor, with the start windinng not energized, where I have tuened the shaft opposite of the normal rotation and had the motor start turning that direction. Unless my old feeble mind is completely shot which is a distinct possibility.
 
augie47 said:
I'm not a "motor-man", just worked on a buch of them. I think the OP indicated he was manually turning the shaft at one point. I have had the experience on a single phase motor, with the start windinng not energized, where I have tuened the shaft opposite of the normal rotation and had the motor start turning that direction. Unless my old feeble mind is completely shot which is a distinct possibility.
Click to expand...
Yeah, they say that one can spin a shaft in either direction and it will start. I tried that one time and it didn't work for me. Not sure how fast you have to rotate the shaft by hand to start?

The OP said that the shaft made a rew revs in reverse only and stopped. Was he rotating it in reverse? Not clear on that.
 
If you have a capacitor start motor, check the condition of the capacitor and its connections.

You can easily reverse a single-phase motor by simply reversing the starting winding connections.
 
zappa said:
Howdy folks!

I went to use my 6" Delta wood planer yesterday which usually stays dormant and unused. It had a heck of a time turning on this time and continued to trip either the 20Amp breaker at the panel or its own circuit breaker. I got it to turn on just once by rapidly turning the switch on and off. ....
I'm just asking you to explain it.
Click to expand...

Why would U sit there and flash the Disconnect ?

Your complete service is marginal at best and your sitting there at the switch!

How many times did you Fire the Circuit Breaker?

I don't like surprises, I think before I blink!
 
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