Air compressor motor works fine on 120v but not 240v like it was designed for...

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Old 11-13-12, 11:55 AM
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Air compressor motor works fine on 120v but not 240v like it was designed for...

I have a GE 5kcr49un2401y ?hp 230v 60hz 14amp 3450rpm Craftsman air comp motor that only works connected to 120v. I know this is bad for the motor since it's not designed for 120v, but I was trying to troubleshoot and just plugged the white and black into the 120v outlet to check. What could be bad on the motor? starter/run capacitors? switches?

There are is a white, black, and green wire. white and black each have 120v and green is grounded. When connected to 240v the capacitors each have 120v but nothing happens even if I give the motor a spin.

There is a red thermal? reset type switch on the motor, but I'm not sure how to check it. There is also a centrifugal switch that opens up when the motor spins a certain speed to trigger the run capacitor.

I'm just confused as to why the motor runs on 120v but not 240v and where to go from here

Please help,
Rob
 
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Old 11-13-12, 12:25 PM
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Here's my guess: there is a misprint on the label, this is a 120v motor. This is not a dual voltage motor and a 14 amp 230 motor would not be a 56 frame.
 

Last edited by markiz37; 11-13-12 at 12:46 PM.
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Old 11-13-12, 12:46 PM
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The weird part is the compresser was hard wired into 240v in this shop. Someone could have replaced the original 240v motor from Craftsman and just said screw it when it didn't work. At least this one mounts perfectly to the frame like the original so just a simple power swap may do it....hopefully this motor was to the original compressor motor specs....lol
 
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Old 11-13-12, 12:47 PM
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I may be jumping to conclusions here. What size pump is it, how many cfm? Does it run ok on 120? Can you measure the amp draw when it runs?

Ps
I take back what I said before. Apparently this is a 230v motor
 

Last edited by markiz37; 11-13-12 at 01:46 PM.
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Old 11-13-12, 05:29 PM
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15cfm, 60gal, 7hp/cv

Here are the stickers on the tank.

If it runs on 120v then why not 240v? Maybe they wired it wrong....the 2 120v IN black wires have connections for the white and black motor wires, while the negative white from the wall is grounded. Am I missing a wire?

Seems to run fine on 120v, but I only have it on my workbench. I'll have time check the amp draw tomorrow.

Thanks again!
 
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Old 11-13-12, 05:37 PM
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I also found this manual and parts catalog from sears: http://www.searspartsdirect.com/part...dMod=919184190

It has the same part # as my motor...hmm
 
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Old 11-14-12, 05:21 AM
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I determined that the 2-120v in lines both had 30 amp fuses...those fuses were also connected to a set of 20amp breakers which one was tripped to only show 20v. When the breaker doesn't blow the motor runs awesome on 240v!

Should the set of 30amp fuses be hardwired in and bypass the 20amp breakers or should I up the 20ampers to 30+ampers?

Thanks for walking me through this...
 
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Old 11-14-12, 11:24 AM
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2 20amp breakers? Not a double pole breaker? Funky wiring, but I guess it works for all intents and purposes. Up the breakers to 30 and never look back. Just make sure the wire is 10 gauge.
 
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Old 11-14-12, 08:31 PM
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You've got issues there. They are:
1) A 14 amp 240 vac motor should not be tripping a 20 amp breaker.
2) You have two single breakers protecting that motor. You stated one breaker tripped. The motor can not run if one of the breakers is tripped. If it does you had better double check your wiring and quickly.
3) Do not upgrade to 30 breakers.
4) Use a double pole breaker because if someone goes to service the compressor and only turns off one breaker there could be a shock hazard.
 
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Old 11-15-12, 05:14 AM
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The tag on the motor you are having problems with is a 3450 rpm motor.
You need to check to make sure that the original wasn't 1725 rpm.
If it is that would likely be your problem.......you are spinning the pump twice as fast as it should go.

If this is the case you would need a motor end pulley half the diameter of the current one.
 
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Old 11-16-12, 12:18 AM
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I added a new 20 amp double pole breaker and it works like a charm....now to line up the pulley so that the belt stops falling off. Maybe a new belt is in order as well.

Thanks for everyones guidance!

Rob
 
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Old 11-16-12, 01:04 AM
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Belts pop when the two pulleys are not perfectly inline with each other. Sometimes just loosening up the motor and twisting it can help to get it lined up.
 
 

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