Bridge voltage rating: Re: Power supply for Servos - bridge and caps

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <dave_mucha@y...> wrote:
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "sciciora"

> > wrote:
> > >
> > > A small bit of trivia: in general, the higher the voltage

> > of a
> > > diode, the higher it's voltage drop. So for high current
> > > applications, you don't want to get too carried away with

> > > rating, because the higher voltage bridge will get hotter than

> > > lower voltage one. I'm no expert, but for me, I think I'd pick
> the
> > > 200V one, depending on how well it was going to be heat sunk.
> > >
> > > Steven Ciciora
> >
> >
> > Interesting.
> >
> > So, if one transformer is 55volt, 800 VA, AND that can handle 3

> > these motors, then the max current will be around 10 amps.
> >
> > Therfore the selection of bridge would only need to be, say, 15
> amps,
> > and as you mentioned, 200volt.
> >
> > If there is any motor speed problems caused by pulling too much
> from
> > the circuit, a second transformer could be added easiy to make

> > power supply 20 amps.
> >
> > That then makes a 25 amp bridge a nice fit.
> >
> > Would a 25 amp, 200 volt bridge be a good candidate for a 20

> 78
> > volt power supply ?
> >
> > That then also begs the question of caps.
> >
> > if the 800 watts discussed is fine, then 800 watts at 78 volts is
> > only the 10 amps.
> >
> > using the 1k uF it would indicate only one 10k uF cap would be
> needed.
> >
> > using Mariss's formula, then (80,000 x 10 ) / 78 = 10,258 uF, so

> > 10k uF cap is selected for that.
> >
> > This would mean a second transformer would need a second cap,

> > like adding systems.
> >
> > It seems that my plasma and Brady's mill will put these to two
> > different tests.
> >
> > I'll post the results and layout and pictures when we get one of
> > these running.
> >
> > Dave
>
>
> The 400volt bridge is used so the inductive spikes caused by
> switching do not harm the bridge.
>
> Wally