# How do I calculate the size of a capacitor?

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• #28760
Trappsy
Participant

I have a question, my Son is harping on about the calculating the size of a capacitor……. I’m in the building trade and guess what not my field! give me tape measure and a couple of bricks and I’ll create something:-)

I do remember that Capacitors are calculated in Farad’s and resisters in Ohm’s but that is it!

So our question is :
A voltage of 12 V is connected to a fully discharged capacitor through a resistance of 470kOhms. After 2 seconds the the voltage across the capacitor is 7.72V. The voltage (Vc) across a charging capacitor at any time (t) is given as: Vc=Vo (1-e -t/Rc)
Therefore –
1. How do I calculate the size of the calculator?
2. How do I calculate the time constraint for the circuit?

#28761
Windell Oskay
Keymaster

The time constant is the “RC” in your equation, and the “C” in that RC is the “size” of the capacitor, at least as measured in Farads. The physical size of the capacitor depends on other things including the voltage tolerance and the type of the capacitor that you are using.

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