How to calculate the value u farad of a dc capacitor?

Question

If a dc voltage generated by a bridge rectifier & dc capacitor is 250vdc & has to be loaded about 3A,what is the u farad of the dc capacitor needed?

How to calculate?

Thanks!!

Answer 1

It is recommended to have around 2000 mic per amp of current. You would be using this purely as a filter cap by the sound of it.  2000 mic per amp is more than sufficient for a nice o/p voltage.

Answer 2

A lot goes into this.  How much ripple can you live with.  The less ripple, the more current in the rectifier and the larger the capacitor needed.

If you need very clean DC, then you need to consider something better than just a rectifier and capacitor.

Answer 3

Depends on how much ripple you can have. And on the frequency.

If I assume you want only 1 volt P-P of ripple and the frequency is 60 Hz, then:

The period is 8ms, and the cap will discharge at a rate determined by

CV =  it

C = 3*8ms/1 = 24mF or 24000uF

this is an optimistic formula and will come out with a larger cap than needed, by perhaps 25%, as it assumes the cap discharges for the full half cycle of 8ms, whereas it starts recharging before that time. But it gives you a starting point.