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In Reply to: Re: caps...rated at 660VAC, will they withstand 950VDC?! posted by kjt on October 31, 2001 at 21:11:24:
Why the extra 2 factor ?Isn't Vmax = sqrt(2)*Vrms ?
Then we would have Vmax = 1.4*Vrms so for these caps Vmax = 1.4*660 = 924V hence, no, they can't be used for 950V.I've got the 'same' problem, I've got loads of caps rated at 300V dc. I thought they were rated for AC when I bought them and now I'm not sure what to do with them..
Just like to be cautious with these things - I wouldn't like them to explode when there's people around.
There's two solutions: either sell them or use them at a much lower voltage.
Stelios
Follow Ups:
the "2 * 1.4 * ac" comes from the total max difference P-P of the rms AC waveform... so a cap with 660VAC RMS will actually have a max potential P-P difference of 1848V you have to realize that that potential only exists for a fraction of time, and not continuosly like DC so some caution is needed...i have run some 370VAC caps at 1KV and they do tend to short, but thats right at the edge of that 2.8 number... i suspect the 660VAC caps should be OK for the voltages you want... make sure the whole thing is fused properly, and make sure the cans are attached to ground... i think the 1.4 number is a safe one.. it gives you a factor of 2 for "derating" and of course if possible do as vry says and check with the manufacturer....
dave
If you look at the P-P of an AC waveform, you're seeing the potential of one line as referenced to itself at a different point in time.
But a capacitors only experiences the voltage across the two terminals at the same instant.
For 660VAC RMS signal (with no DC bias) the potential to the reference at the waveform peaks is only 1.4 x 660.
Now, how that translates exactly to the AC ratings of caps, I am not sure, but I don't think an AC rated cap is meant to handle 2.8 x V, certainly not DC.
Charlie G
i actually haven't purchased them yet (so that is good). they are on ebay. my problem is that i am trying to come up with a power supply for some 211s, and it is tricky to find the parts i need. i have a good design done up in duncan's power supply program...but now i'm trying to source the caps!sonofabitch.
well...i guess i'll keep looking!
ryan_
Try these two places. They have some high voltage stuff, some new, some old. I imagine there are others like them.Fair Radio
Surplus Sales of NebraskaJohn
Check out the Axon Novas at Micheal Percy 1200v 20uf.
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