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Registered Member #579
Joined: Mon Mar 12 2007, 09:45AM
Location: Burntwood, Staffs, England
Posts: 46
I have a load of compacitors from a cap bank (MMC) I think I have blown at first switch on I Hope some are OK I have thought of lots of different ways to check them but felt I need some more experienced in put So, given that I have 30 POLYPROPYLENE capacitors of 10nF and 2000V How would you test them effectively? I have No MM with cap range , no Oscilloscope I don't mind soldering a little test circuit up
Registered Member #546
Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239
If it's a CDE cap or any other well made polypro cap you'll know when it's actually dead....they don't die quietly. If it didn't burn up it's probably "ok" for the MMC still.
Check your wiring and make sure a solder joint isn't loose or melted...make sure you have the right size bleeder resistors on the MMC....check for hidden shorts. If you have a continuity function on your MM use that. you can check EVERY junction for resistance, anything over about 1 ohm is not well soldered and will be a failure point eventually.
Easy tests for SMALL caps (don't do this on anything over a few joules) Charge them to 1000v and see if they make a spark when you short the leads with a screwdriver. If they'll hold voltage for a second or 2 after you remove power from them they're probably ok. Doing this will stress them out a little, but not much more than TC use does to them, In fact probably less since you're only doing it once.
You could take one apart and look at the film, check for large holes or burn spots. If they're the CDE caps they're amazingly resilient, and even a pretty heavy strike to the caps can self heal. If the cap looks like swiss cheese or window screen it's dead... if it's got 4-5 pin holes it's fine (pushed too far, but it'll still work for an MMC)
You could get a cheap capacitor meter from Radio Shack for about $20-30...
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testing capacitors
