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Air compressor capacitor keeps blowing

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by Andy
(Northeast wisconsin)

I am an electrician that has done electrical work for an automobile repair shop this winter.

They have a large air compressor that blows the capacitors often. I replaced them once while there and they have (blown again) since then.

I believe they may have voltage drop problems not sure.



by: Doug in s.d.ca

I’m not gonna say it’s impossible, but I suppose low voltage could be a problem. More likely, I think, would be high voltage spikes taking out the caps.

Were the replacements as spec’d for the motor, or did you replace with what was on it?

Also unclear: is one or two caps you replaced?


Capacitors blowing
by: Andy

Thanks for input Doug.

The motor has more than one capacitor but only replaced one at a time. I am not sure how many it has two maybe three.

Also I just replaced with the ones that they said went with this motor. I should check again to make sure. I was wiring an addition at the place and didn’t spend a lot of time on this problem. However I would like to fix it for them.


by: Doug in s.d.ca

I know how you feel – Is this 3-phase?

Keep us posted please.


Capacitors blowing
by: Andy

No the air compressor is single phase. The building is served with a single phase 120/240 service. However they do have what looks to me a rotary phase converter made with a three phase motor and capacitors.

When you mentioned voltage spike this set up came to mind. It is running a lathe and tumbler that cleans discs for automatic transmissions.


3 phase
by: Doug in s.d.ca

A motor-generator for three phase?

That shouldn’t be a problem unless it’s really squirrelly and feeds back to single phase somehow.


Capacitors blowing
by: Andy

I finally got to the air compressor. They had tripped the breaker because the wire vibrated off the capacitor.

I replaced all the ends on the wiring of the capacitor box. They must vibrate lose then get hot and the temperature changes the strength of the stab on crimps.

I am guessing this was the whole problem. The motor was also poorly grounded.

I talked with a motor guy who has worked on it and supplied the capacitors he said they should be correct. The motor is a GE and could not find the nameplate. When I left it was running fine.


by: Doug in s.d.ca

Sounds like something could/should be done about the vibration –

Maybe secure the wires to the box such that they don’t move at the connector, and/or maybe solder ’em on.

Visit our Air Compressor Capacitor Guide for more information on capacitors.

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By Bill Wade

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