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Repairing a VFD motor drive. Caps are bulging.

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fastline

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I am working on a variable speed water pump drive. I was told the drive works until put under full load, then it trips out with "ground fault". A quick visual inspection shows bulging of all 4 main filter caps which are 470uf/400V. They are not leaking and not showing a short "yet".

Just curious if anyone has experience repairing these? Just not sure if replacing these caps should get this thing going or if the cap bulging is indication of something deeper? This unit just uses 1 bridge rectifier that tests good in circuit at this time. I am temped to replace and test but thought I might search for some experience on this one.
 
Age and environment might help. High ripple current can also do it.

Make sure the PRV rating and amp rating of the bridge is appropriate for the supply. I once worked on an ARC lamp supply that put out about 40 A at 22V. The mfr had a 10 A bridge in it. They had to replce the transformer with a new one and change the full wave bridge to a half-wave. This was a free replacement that we go because I said that their older model was junk when I opened it up. I had to modify their spark ignitor just to get it to work. Again the company offered, for free, to retrofit the lamp housing for an intenal ignitor. This was a 1KW arc lamp source. 40 kV to start, 22 V 40 A or so to run.
 
If the capacitors are really bulging it's a sign they are already faulty, you would need an ESR meter to check them.

It's the obvious first thing to change, make sure you use high quality, 105 degree, low-ESR replacements (if you can find them!).
 
I have never encountered problems with ripple current, but bad capacitors are usually the el-cheapo ones. Cheap caps fail even when their ripple current ratings are not exceeded!

Fastline, what brand are the caps?
 
Since posting, I have determined that the coating that was applied to the entire board apparently reacted with the caps and distorted them. After removing the plastic film, you can see the actual Al cap is just fine and they are testing out good as well. I think false alarm on this find.
 

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