Re: power supply question

> Hi Barry,
>
> I think we are all curious about why a cap may be too big.
>
> Since we do know that there are systems that need that size cap and
> there people who use that size, we do know it can be used.
>
> If it is not recomended, I for one, would be interested.

Me too.

>
> There are arioius inrush limiting technologies or circuits that
> people use when using that big of a cap with a torid transformer.

I've got a toriod 160va/120vac/20vac transformer and a 20,000mfd cap
in my power supply. Am I using the wrong cap? It's out of my
Camtronics psu, I swapped transformers so I could get down to 28vdc
for my Xylotex board. 4 axis, 2.5a/phase possible.

My calcs:
160va/20vac=8amps
C=(8*80,000)/28=22857 (this formula from Mariss' stepper white paper)

>
> We also know that Mariss's circuit is designed to have an

acceptable

> ripple, not to eleminiate any ripple.
>
> I started using a couple smaller ones to reduce the space needed in

a

> box, and to reduce the ESR from one large one.

Would I be better off with several smaller caps? There is a
schematic for a psu on one of the groups I watch that has 5-6 smaller
caps, in parallel I think.

Thanks,
Monte