Simple Capacitance Q...

[Justin Thomas]

Hi everyone,

Sorry to ask a silly question, but in all the books I've read, I have yet to see this addressed (or I missed it.). About caps: I know that 2 or more caps in series adds the voltage handling together and that the capacitance calculates like resistors in parallel. When caps are paralleled, I know the capacitance adds like resistors in series. But what about the voltage rating of that combination?

So,
A. 20uF/500V & 20uF/500V in SERIES = 10uF/1000V, right?
B. 20uF/500V & 20uF/500V in parallel = 40uF/???V what would be the voltage here? 500?

For dissimilar voltage caps in parallel,
C. 20uF/500V & 20uF/100V = 40uF/???V

Would it be 100V, because that's the weaker part of the chain? Less? Somewhere between 100 & 500 that can be calculated?

I'm just a casual builder, and would not send out a customer's amp with mismatched caps, but on occasion for testing & prototyping, I only have certain parts on hand and would like to know how to better use them. Thanks!

Justin

[Enzo]

In parallel, the same voltage is across each. The capacitance may add, but one cap has no idea the other is there, so th voltage is whatever is across the cap.

Yes, 500v and 100v in parallel means 100v is the tops. After all, just because ther is a 500v cap next to it, the 100v cap is still only rated to see 100v across its terminals.

[52 Bill]

So,
A. 20uF/500V & 20uF/500V in SERIES = 10uF/1000V, right?
B. 20uF/500V & 20uF/500V in parallel = 40uF/???V what would be the voltage here? 500?

For dissimilar voltage caps in parallel,
C. 20uF/500V & 20uF/100V = 40uF/???V

Would it be 100V, because that's the weaker part of the chain? Less? Somewhere between 100 & 500 that can be calculated?

You are correct.

When two or more caps are paralleled each cap is subjected to the same amount of voltage so the lowest voltage rating will apply to all of the caps, as it is the weakest link.

[Justin Thomas]

Thanks Enzo - your explanations and analogies make sense for the "rest of us."

Bill - now I'm entering electronics 101... in parallel resistors, voltage stays the same and current divides, right? And the same goes for caps - hence the need to go with the lower voltage rating for safety. Makes sense.

I guess I could experiment and blow some lytics up... my sense of smell is kinda dull.

Justin

[diydidi]

Exception to the series rule: If you connect two 20uF 500V caps in series, with the negatives or positives linked to form a Non polarised cap, the rating is as follows:
10uF at 500V.
Half the capacitance and voltage rating of lowest voltage cap.