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Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
hi,
i have bought some new capacitors for my coilgun: 10X 2200uf 400v, and they are NOS, so im reforming them and i have connected one to the supply through a 47K resistor, and after about 30 mins, there is 5v across the resistor and 270v across the capacitor, is this good? and should i increase the supply voltage to 400v? and finally, would the capacitor be happier if i would charge always charge it up through a resistor? or would this make no difference...
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Never charge a cap up directly to it's specs. Always do a little below their voltage, otherwise you may run the risk of damaging them. Not all caps are made equal.
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
alf wrote ...
hi,
i have bought some new capacitors for my coilgun: 10X 2200uf 400v, and they are NOS, so im reforming them and i have connected one to the supply through a 47K resistor, and after about 30 mins, there is 5v across the resistor and 270v across the capacitor, is this good? and should i increase the supply voltage to 400v? and finally, would the capacitor be happier if i would charge always charge it up through a resistor? or would this make no difference...
thanks. Alf.
Sounds like they're good to me. Reforming is done to prevent shelved capacitors from failing dead-short. Yours are holding the charge so they're probably good. But to be safe you should charge them to their rated voltage to make sure there aren't any problems.
They shouldn't fail at their rated voltage unless they are seriously crappy. If you want to play it extra safe, do the reforming outside since they will most likely fail by spewing fumes everywhere and maybe a little fire too. If you're reforming a bank, failures could cause an explosion so use shielding or an enclosure of some kind.
Finally, yes capacitors are always happy when being charged through a resistor, or by some sort of current limiter. Excessive currents can cause damage, refer to data sheet for limitations.
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capacitor reforming?
