Re: [CAD_CAM_EDM_DRO] Capacitor Sizing in Power Supplies

jmw@... wrote:

> I seem to recall a formula in some Gecko docs re capacitor sizing on
> roll your own power supplies (the xformer, bridge, cap variety). And
> I think this formula was of the form (80,000*amps)/volts = uF of cap.
> (The 80,000 is related somehow to the number of millisecs per half
> cycle of 60 cycle AC and the time it takes the cap to charge?)
>
> Suppose you wanted to build a 2VDC @ 20A supply. Without getting into
> why one might want to do that, this works out to 80,000*20/2 = 800k
> uF. That's a lot of capacitor, albeit at pretty low voltage.
>
> Is this a non-linear situation or would 800k be the proper sized cap?

If you need good regulation, these numbers might be OK. I think this
is for shunt motor field excitation? The inductance of the field windings
smooths the current such that current fluctuations will be much reduced.
Putting the fields of several motors in series would increase inductance
and lower current requirements, while raising the voltage to a much
more reasonable range. I think you will find the rectifier loss and the
current surges in the transformer secondary would be a major problem
in such a low voltage power supply.

Jon