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

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "sciciora" <sciciora@A...>
wrote:

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

of a

> diode, the higher it's voltage drop. So for high current
> applications, you don't want to get too carried away with voltage
> rating, because the higher voltage bridge will get hotter than the
> 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 of
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 the
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 amps, 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 a
10k uF cap is selected for that.

This would mean a second transformer would need a second cap, kinda
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