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How to determine the voltage rating of an unknown capacitor?

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AndyC_772:
I think it's worth revisiting what the voltage rating of a capacitor actually means.

With a ceramic, as we've discussed, it's primarily to do with the fall-off of capacitance with voltage. It's a limit imposed by the useful functional performance of the device. Exceed it and the part just doesn't do its job properly - and that's easily defined and measured.

With other types it's not so clear cut, though. Tantalums catch fire and go bang, so I'd be very wary indeed of trying to measure the rated voltage of one at all.

Other types may simply suffer a reduced lifetime at higher voltage, so you might find that a 10V cap works perfectly well at 20V for a while, but dies prematurely. A test instrument won't tell you that, unless you specifically set out to perform long-term reliability testing.

Personally I still think the cheapest, easiest way to get a capacitor of known value and rating for a project is to buy a new one from a reputable supplier - but I applaud the academic exercise nonethelsss.

ftransform:

--- Quote from: AndyC_772 on January 25, 2013, 06:50:21 pm ---I think it's worth revisiting what the voltage rating of a capacitor actually means.

With a ceramic, as we've discussed, it's primarily to do with the fall-off of capacitance with voltage. It's a limit imposed by the useful functional performance of the device. Exceed it and the part just doesn't do its job properly - and that's easily defined and measured.

With other types it's not so clear cut, though. Tantalums catch fire and go bang, so I'd be very wary indeed of trying to measure the rated voltage of one at all.

Other types may simply suffer a reduced lifetime at higher voltage, so you might find that a 10V cap works perfectly well at 20V for a while, but dies prematurely. A test instrument won't tell you that, unless you specifically set out to perform long-term reliability testing.

Personally I still think the cheapest, easiest way to get a capacitor of known value and rating for a project is to buy a new one from a reputable supplier - but I applaud the academic exercise nonethelsss.

--- End quote ---

me and insanity are chinese quality control. :-DD

I think I am going to do some experiments in order to measure these guys tonight.

robrenz:
Don't forget the dielectric is an insulator and has a breakdown voltage where it will puncture. A higher voltage capacitor is going to have a thicker dielectric.

Fraser:
I bought a Duoyi DY294 Semiconductor analyser a couple of years ago that also claims to provide the breakdown voltage of capacitors. I have never used it for such but suspect it works on the leakage across the dielectric as the voltage is ramped up to 200V  :o I don't like causing a breakdown in a dielectric....it just seems the wrong thing to do somehow. I suppose if the capacitor is sacrificial and not for use it is of little consequence.

I have attached the DY294 manual

A review is here:

http://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-1/

http://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-2/

http://www.jestineyong.com/review-of-the-dy294-digital-transistor-tester-part-3/

For GBP30 delivered, it wasn't a bad buy.

Regards

Fraser


(In)Sanity:
Well one thing I can say about breaking down the dielectric on a capacitor.   If you thought it was rated at say 200 volts and it goes up in smoke at 150 volts then clearly you were mistaken.   If on the other hand it survives to 930 volts like one of mine did,  then it might be anything from 1 volt to 500 volt rated :)   Yep I know..so helpful isn't it. 

Jeff

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