understanding capacitor voltages

[neilwight]

hi guys,

looking for some info to help my general understanding.

how does the voltage spec on a cap effect its performance? is it a max voltage or an operating voltage or none of the above?

as an example, i bought up parts for a GSSL and the large caps i got were 1000uF 63v as per the bill of materials
my PCB however has the spec noted at 1000uF 35v.

not a problem as i can easily get others however it got me thinking about the above and no amount of google-ing could provide any answers.

on switches,resistors etc the voltage is a max value however with capacitors also storing as opposed to just merely passing and effecting i'm a little unclear if the same applies.

any info would be very much appreciated

 

[daArry]

how does the voltage spec on a cap effect its performance? is it a max voltage or an operating voltage or none of the above?

Max voltage ye. You'll be fine using ya 1000uF/63V's so go'ed

 

[neilwight]

thanks for that.

thats nice and straight forward too if its just max voltage like everything else.

 

[SSLtech]

Yup. It's the voltage that they recommend you "take cover" at, when you slowly ramp up the voltage across the cap!
:wink:
Keith

 

[neilwight]

haha,

:grin:

or should it be :shock:

 

[WJS]

I think this is the 3rd time i've answered this, but all in different topics.

the voltage rating on a cap is the maximum voltage which the cap should see. for example if you have a resister with 3VCD across it and you want to connect a cap across the resister, it should be rated for atleast 3 volts. anything over 3, be it 4, 400 or 4K. they will all function.

the voltage rating is the number which will make the caps go poof ( or fiiiizzzzzt, depending on the brand)

while on the subject of caps, be aware of connecting electrolytics and other polarized caps backwards.

another quick note.. I have heard it argued that higher voltage rated caps do have more leakage current, but i dont know this to be true (yes? no?) and if it is I dont think its enough to worry about at all.
best of luck
Bill

 

[CJ]

Capacitor voltages , hmmmmm.
Depends on the type and location.
If they are in the eq filter section of a Pultec equalizer, you might actually be able to scope out some sonic differences between a 50 volt cap and a 400 volt cap. A rumor I heard right here at the forum. So the voltage rating takes on an entirely different aspect other than breakdown ratings.

If the caps are in a filter sction of a power supply, then voltage breakdown is the main issue. In the old days of electrolytics, teachers used to tell you to use a filter cap with a 100 percent safety factor, example, if you have 100 volts dc on a supply, use a 200 volt cap. Nowdays, I think a 50 percent factor would be plenty. So 150 volt cap on a 100 volt supply. Size becomes an issue also. If you want to double the voltage rating, you will probably come close to doubling the size of the cap, which might be an issue with a circuit board project, so always wire point to point. (just kidding!)

Start up voltages in a tube power supply may go high until everybody gets warm, so that is another reason for using a high voltage cap.

Coupling caps- in a amplifier, you have ac and dc. The dc on the tube of the plate, and the ac imposing a signal on the grid. This grid swing has the potential to give a plate swing at the coupling cap of close to zero volts (tube saturation) or you B+ volts (tube cutoff or tube removed from the socket or miswired DIY project) so it's nice to have a coupling cap rated for at least the B+ supply voltage.

For transtitor circuits, use a voltage rating of 1/2 the supply voltage. That way, when your transistors cook, you will come over to the politically correct world of tube audio. :grin:

Did you see American Dad and Family Guy last night? Talk about sick. :green: