Voltage Rating of Capacitors in Series

[SimpleFix]

Can you increase the voltage rating of capacitors by putting them in series? For instance if you have two 10uF 25V caps in series, could you use up to 50V? The capacitance would be halved, but that's not too big of a deal.

Thanks.

[Dean Huster]

Yes. That's a common practice, especially these days when we're restoring a lot of vacuum tube equipment with high B+ voltages. For instance, I did that with a Knight-Kit KG-670 RC tester that had a 500v rating on its 10µF filter cap. Those can be harder to find, so I used two 22µF caps in series rated at 350v. Now what you have to watch is the values of the caps. They'll split the applied voltage evenly only if they're the same value. Don't expect a 2.2µF 50v cap in series with a 10µF 50v cap to be good for 100v.

[MrAl]

Can you increase the voltage rating of capacitors by putting them in series? For instance if you have two 10uF 25V caps in series, could you use up to 50V? The capacitance would be halved, but that's not too big of a deal.

Thanks.

Hi there,


Strictly speaking, you shouldnt even use a 50v cap up to 50v, you should use a cap that has a higher voltage than what you really need. Two 25v caps in series would not equal a 50v cap really, because as Dean mentioned any variation in capacitance and one cap gets more voltage than the other. Two 35v caps might work, but it might be a good idea to measure the two voltages to make sure.

What would work even better is ONE cap rated for 75v, which would also give you plenty of error margin

[Robert Reed]

Yes - this was common practice in the past - but beware! When seriesed up, the leakage resistance of each 'Lytic comes into play. Each capacitor should be shunted with equal value balancing resistors that swamp the leakage resistance making it negligable. About 1 meg value for each resistor should be OK if memory serves me right.

[Rodney]

In general, this is not a good idea, especially if using polarized capacitors. Not only must the two capacitors be quite closely matched any heating caused by ripple currents can upset the balance. In some cases, paralleling each capacitor with a large value resistance will help with the voltage balancing if you can stand the leakage current through the resistors; use 1 to 10 megohm resistors.

[dacflyer]

do i understand right.. when caps are in series the UF is divided and the voltage capicity is doubled.
i know what they do when in parallel..

[Robert Reed]

Yes - If they are the same value and voltage rating.

[dacflyer]

ok, thanx