Re:Power supply questions

[While we're on the subject of power supplies, are there any
reasonably-priced power supplies appropriate for this purpose that are
available for purchase all set up and ready to go? I'd really like to find
one in a box, with a fan installed, and (preferably) with a UL sticker
attached. Ideally it would take 110v AC input and convert it to about 60vDC
at 20 amps or so. The rest of the circuitry would be at a (relatively) low
voltage, which doesn't seem all that dangerous to play with (and probably
won't require a UL sticker), but power supplies can bite you if you're not
careful.

I can find "wall warts" that put out (nearly) enough voltage but not enough
amps (or vice versa), and also switching power supplies built for
computers, but apparently the switching function, while it reduces the
amount of wire necessary and thus the expense, can interfere with the pulse
train. (The Gecko site indicates they can be used, though, if one fits the
drives with capacitors to filter the current.) The other problem with
computer supplies is that they are meant to be mounted to the DIN rails
inside a computer, and not to be free-standing.

A third class of supplies I've looked at- bench-type laboratory power
supplies- seem ideal: they come mounted in a box, and they can be found with
sufficient voltage and amp capacity, but they're hideously expensive, and
seem fancier that what's needed, with multiple outputs and extraneous meters
and knobs, etc. Has anybody out there powered a Gecko-based servo setup
(like the one Thomas wants to build) with an off-the-shelf unit? It seems
like a major stumbling block would be removed if we didn't have to "roll our
own".]

Andrew Werby
www.computersculpture.com

"Tom Murray <thomasm923@...>" <thomasm923@...>
Subject: Power supply questions

I hate repost my recent questions, but I really need some help in
building a power supply.

Questions below:

My Taig mill is ordered, and one of the things that I have to do
while I wait the 6 to 8 weeks for delivery is make a power supply.

There's a few things that I'd like to ask the group to get me
started...

First, I am wondering if my choice of caps is correct. I will be
using a 30 volt transformer to supply power to three 24 volt servos
rated at 6 amps peak. I doubt that it will ever need to supply more
than 12 amps at once, if that much, but let's assume that the maximum
current is 15 amps. I am looking at some surplus capacitors rated at
17,000 MFD, 75 VDC. Would a pair of these in parallel be sufficient?

Second, I wonder if it is ok to attach a smaller transformer to the
same AC input that is hooked up to the main transformer to supply 5
volts to the Geckos?

[I thought the new edition of the G-320s didn't need the extra 5v input. Am
I wrong here?]

Third, how does one calculate the rating of the fuse that is needed?
I assume that it should be a slow-blow type, but what would the
correct amperage rating be? A little over the maximum current, a
little under, or dead on?

Thanks,
Tom Murray