capacitance?

[CTho9305]

if I have a 1000uF, 30V cap, I can use that as a 3000uF, 10V cap also, right?
c = q / v

edit: same for a 1200uF, 200V cap? 24000 if I run it at 10V?

 

[Krakerjak]

I say no, you can't.
I believe the 30v is the rating, meaning the capacitor will function properly up to 30 volts as a 1000uF cap.

 

[CTho9305]

after giving it some thought i agree with you .

 

[Jerboy]

Capacitance and voltage are both constants. It will only change when you start connecting multiple capacitors in parallel or series configuration.

Parallel connection is simply additive.

Series connection is much more complex and I don't know much about it.

When you connect two 200V 500µF capacitors in series, it will become 400V 250µF. Even though it doesn't look like it, it make sense, because the energy is in linear function of capacitance and square of voltage, thus 1/2 x 4=2 You have two capacitors of same energy storage and energy is effectively doubled.

J(joules)=1/2 c x v^2

C is in farad, not µF


0.5 x 5^-4 x 200^2=10joules
0.5 x 2.5^-4x 400^2=20joules

 

[jasonroehm]

I'm pretty sure that capacitors in series combine like resistors do in parallel. For instance, if you have capacitances C1, C2, and C3 in series, then the effective capacitance would be

Ceff = (1/C1 + 1/C2) + 1/C3)^-1

The "reciprocal of reciprocals" method, I've heard it called.

 

[rimshaker]

Both rating may give the same charge quantity, but being rated at 30V or 10V does make a difference in the application. So no, you cant just interchange the ratings.

 

[CTho9305]

eh, I swapped out in very very bad ways and it worked. but thx for the replies