Re: looking for a 20vac transformer resource

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Monte" <montejw@e...> wrote:

>
> I have a power supply that outputs 36vdc (24vac transformers)and I
> want to get down to 30vdc. A 20v transformer would get me 28vdc,

if I

> have the math right, which is close enough. Where can I get one (or
> 2) of these. I want to drive the 4 axis Xylotex driver board and

some

> 250 oz in steppers on my Taig mill.
>
> Or a 24-30vdc power supply would work too, if the price is right.
>
> Thanks,
> Monte

I JUST went through this same exercise. I dug through a stack of old
linear supplies (I can't bring myself to throw away transformers) and
found a 5 amp 15 regulated supply. The Raw DC was about 27 volts.
The primary was tapped for low ac so I used that tap and
wahla...30VDC on the nickle! I just tapped off the big filter cap.
If you can find a cheap 15VDC regulated DC linear supply I'll bet you
can get close to your voltage. You don't have to disconnect anything
and there were spare lugs on the output terminal strip so now I have
30VDC (unregulated) and 15VDC regulated.

A 12V supply will be too low and a 24 will be too high. The 15 was
just right. Reason: The designer has to be able to maintain
regulation down to low line (brown out) of 90VAC. It takes around 5
volts more in than out in a traditional series pass circuit figuring
in all of the voltgae drops, so he needed 20V at 90VAC. At 120VAC
that works out to about 26.6 VOlts. The booster tap on the primary
(for running in cronically low line conditions) boosts the output
about 10% in RMS volts or about 14% (30.4 VDC) which almost exactly
what I have.