# Capacitor Measurement

I was looking at some of my capacitors, and realized there is no correlation between the farad amount, and the voltage it can carry. One is 10 uf and 25V the other is 100 uf and 50V. So what does farad do?

-eLion101

Faraday was a scientist find more about him here- Michael Faraday - Wikipedia
About Capacitors - Capacitor - Wikipedia
Look at above links and ask us if you are stuck.

-Malhar

Farad represents the real unit why we use a capacitor. It's the stored capacity.

The voltage is an extra rating because a higher voltage may damage a small capacitor. It's the same with fuses. Next to there A rating the also specify the voltage. That's the max voltage the manufacturer gives you that's safe to use with that fuse.

Actually it's kind of the same with a resistor as well but most of the time we don't come a cross a situation it matters. But mains (230VAC) across a 0805 resistor isn't safe, meanly because of the distance. And in a capacitor the distances are very small.

So get the capacity rating you need and a voltage rating that's bigger then the biggest voltage it's ever going to see. In normal cases (an not talking low ESR, RF, SMPS etc) it's perfectly fine to use a 100V cap for a 3V3 rail. But the 100V one is going to be much much bigger then the 10V capacitor of the same rating.

@septillion Two typos, did you mean Safe insted save ?

Yes I did, thank you! Time for more coffee...

Thank you @septillion! that helped.

I was looking at some of my capacitors, and realized there is no correlation between the farad amount, and the voltage it can carry.

There is some correlation with physical size... Higher value (uF) capacitors tend to be larger and higher voltage capacitors tend to be larger.

You might find a high-value low-voltage capacitor that's the same size as a low-value high-voltage capacitor.

But... You might find a 25uF/50V capacitor that's the same physical size as a 10uF/50V capacitor... Or, the 25uF one might even be smaller if it's from a different manufacturer or from a different product line.

The voltage is an extra rating because a higher voltage may damage a small capacitor. It's the same with fuses. Next to there A rating the also specify the voltage. That's the max voltage the manufacturer gives you that's safe to use with that fuse.

@septillion Two typos, did you mean Safe insted save ?

?
LOL ;D

(if someone is using the phrase "max voltage" and the word "safe" in the same paragraph, it stands to reason they are talking about what voltage you can run the cap without blowing it (or yourself) up.)

All things being equal (ie same type of capacitor), expect the volume of a capacitor to depend on
capacitance times voltage-squared. That's because the stored energy = 1/2 CV^2