Re: [CAD_CAM_EDM_DRO] Re: Re: Power supply question.....

JanRwl@... wrote:

> In a message dated 04-May-02 02:29:48 Central Daylight Time,
> mariss92705@... writes:
>
> >
> > It would be a wonderful world if capacitors were capacitors,
> > resistors were resistors and inductors were, well, inductors.
> >
> > In a perfect world they are, but not in this one.
> >
> > The reality is capacitors have a little bit of resistance and
> > inductance, rresistors have a little bit of capacitance and
> > inductance, inductors have.. you see where I'm going with this.
>
> Guess, then, I simply haven't had to deal with AMPERES through capacitors. I
> guess that largest caps/supply-amps I have ever built was, what, 68,000 uF x
> 30 amp? What kinda currents from the bridge and how large a cap. would one
> be talking about for "capacitor heat-dissipation" to become a considerable
> factor?

This one could easily be one of those cases. Assuming it really was delivering
full load of 30 A, the ripple current could be somewhere in the 30 A RMS range,
in the form of a nearly continuous 30 A DC drain, with short pulses of about
150 A during the charging cycle. Transformer leakage inductance and series
resistance would limit the peak charging current. But, a very rough guess might
be about 50 A average. If the cap had an ESR of .1 Ohm, that would be
50^2 * .1 = 250 W ! So, you must have had a good cap if this power supply was
really delivering 30 Amps continuous. the ripple current is much less when the
power supply is at partial load.

Jon