Large Capacitors burned up

Thread Starter

Smurfturf

Joined Apr 14, 2013
5
I am having a problem with the wiring for an electric motor attached to a compressor. I recently purchased this compressor. The paperwork with the compressor stated it was 2.2kw / 3hp, 220v/50hz, 230v/60hz, single phase. There were three ten gauge wires, so I ran a 30A circuit with ten gauge wires. After about fifteen minutes, I noticed smoke coming out of the circuit box that was plugged into the outlet. The two large capacitors had been on fire. I know that one of them is the motor start capacitor. They are 220-275VAC 200uF +/- 30% and 40uF +/-5% 450VAC 50Hz. I ordered replacement capacitors, but can someone help me understand why the first set caught fire? I initially thought it was reverse polarity, but that can't be the case with 240v. I tested each leg and they are each about 118v.
 

#12

Joined Nov 30, 2010
18,210
First guess: The 200uf capacitor was not disconnected as it should be, after the motor started. Those are, "dry electrolytics" and they have a short run time before they puke.

The 40uf cap is an oil filled capacitor and you can plug that sucker right into the 230 volt power line all day and it will not heat (unless it was bad in the first place).

Then you have the opportunity to mis-wire something....
 

Thread Starter

Smurfturf

Joined Apr 14, 2013
5
The compressor was new and the capacitors were wired at the factory. According to the hour meter the whole setup has only run for about an hour. It almost looked like most of it started with the 40uF capacitor. It was much worse than the 200uF.
 

Thread Starter

Smurfturf

Joined Apr 14, 2013
5
I went ahead and ordered new capacitors, but I thought I would ask advice if there was some underlying root cause that someone happened to know. Unfortunately, I purchased this compressor overseas and it would be very difficult to return it.
 

#12

Joined Nov 30, 2010
18,210
I made a guess, but there is no way we could know what went wrong without doing measurements and knowing how the motor is built.
 

Rbeckett

Joined Sep 3, 2010
208
Smurf,
Once the new caps arrive and you get them installed, you should insure the start cap turns off after spin up and the run cap is being supplied the correct voltage. Both of these tests will be power on, so you really need to exercise extreme caution to insure that you do not somehow become a part of the circuit. If you are not super comfortable working with mains voltages you might want to seek a professional electrician to do those tests for you at least. This will hopefully confirm that everything is hunky dory so you dont burn up another set of caps or burn down your shop area either. So be carefull and verify that everything is correctly installed and working properly before you button it all up and call it good. Another thought too is that the caps had begun to dry out and aged prematurely due to non use. Did you happen to look at the caps you are removing to see if you could get some idea of the date they were made? Just some thoughts and some cautions so you can continue to hang around and be a member of the gang..

Bob
 

Thread Starter

Smurfturf

Joined Apr 14, 2013
5
Bob,
Thanks for the insight. I was planning on having my neighbor, a professional electrician, come over and help me when they arrive. I am with you on not burning down my shop. Especially since this is a natural gas compressor.
Clark
 
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