Re: power supply question

> > 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)

This is correct. But see what happens at 66 volts.
48VAC (less rectifier) x 1.414 = 66 volts DC

(8 x 80,000)/66 = 9,696uF cap

Lower voltage does mean larger caps.

Also, 80,000 is for 60 hz, use 100,000 if you are using 50hz

>
> > 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.

Which group ?

I have caps both ways, one huge one, and multiples. For the smaller
enclsoures I'm using, it is harder to fit in one 10,000uF/ 100V cap

Dave

>
> Thanks,
> Monte