I found a DC power supply among the stuff that I had. This is a Syncor
PP-1659A/G military power supply called "battery charger". It is a multitap
transformer and a rectifier. Goes up to 150 volts and up to 20 amps.
I fixed up whatever physical damage it had (missing banana plug) and
now it seems to work well, except that on some settings it does not
seem to have good contact. Probably needs some multitap contacts
Anyway, I can set it to, say, 76 volts DC and just user it? Do I need
to put in any capacitors, since this is a pretty bare rectifier?
ok, to run servos you don't need all that much filtering, but how much
depends on the specific amplifier topology - you can try it unfiltered, and
so long as you stay below the limits of the transistors, you will do no
harm - if the system seems sluggish or unstable, add filtering - the caps do
more than just remove ripple, they also provide a surge current capability
Are you using the existing amplifiers? If so, do they have a power supply
On my EMC2 conversion I was able to use the existing amplifiers, servos,
encoders, power supply, I just changed the control, saved some money. Looks
like you have some hopefully good encoders on the way, especially if they
fit where the old encoders were.
I do not yet know. I have existing amplifiers, and also three AMC
amplifiers that I bought inexpensively.
I am not sure how I wuold figure out the wiring for existing
amplifiers, but there is a chance that I can do so.
The hope that I have in gutting the existing stuff, is that I can also
switch to single phase and end up with a system that I understand.
I hope so.
Oversize the diodes; large rectifier bridges are dirt cheap. I've buit
many supplies for AMC and Copley servo amps with just a transformer,
rectifier bridge and cap and never had a problem. Oh, and don't forget
a bleed resistor for the cap.
It may work great, but if you didn't remove any resistors from it you
may find that it has poor regulation under a varying load. Most battery
chargers need some sort of current limiting; you can do this in the
transformer by designing in a healthy amount of leakage inductance
(microwave oven power transformers usually have a slug of transformer
material wedged or spot-welded into the core between primary and
secondary for this purpose). So you may find that the transformer it
inherently incapable of good regulation.
And poor regulation to your servo amplifiers could cause all sorts of
I'd try it, but I wouldn't be surprised if it wasn't good enough.
And yes, put some filter caps in there.
Yes. That's the test for voltage sag. Testing it without the filter
caps will measure the sag from the transformer. With filter caps you
have an effect that can either be described as "ripple causing sag" or
"ripple that looks like sag" depending on your point of view, but which
is, in either case, a ripple whose high-voltage point doesn't change
much but whose low-voltage point sags more and more with increasing current.
You'll be measuring a pulsating DC voltage; some (really cheap) digital
voltmeters will jump around a lot measuring that, others will be steady
(analog voltmeters will be rock steady). If you voltmeter jumps around
a lot then try another one, or post again and I'll show you a low-pass
filter that'll steady it out.
The servo amplifiers will be able to tolerate some sag -- they're
designed to work with power supplies that have considerable ripple, and
to them ripple and sag are the same thing. But they'll also have some
input voltage limit below which they're just not going to work right,
and that input voltage is going to be reached when you're asking for the
most torque from your motors.
Basically, you want the lowest instantaneous voltage out of the supply
to be above whatever the amplifiers needs, without letting the highest
instantaneous voltage out of the supply exceed whatever the amplifiers
can stand. You can compensate for some amount of sag by putting in
honking big filter caps -- that'll reduce the ripple, which gives you
more room for sag. The best part is that the more current limiting you
have in the transformer, the more you can just load in the filter caps
without worrying about the power factor of the current, because the
transformer will be taking care of that.
The OmniTurn CNC controls have a big toroid transformer, a moderate
sized bridge rectifier and a decent sized single cap to run the servos.
Works just fine with both AMC and Copely amps. Also the Glentec amps are
the current amps supplied. Very versitile amp.
One could not be a successful Leftwinger without realizing that,
in contrast to the popular conception supported by newspapers
and mothers of Leftwingers, a goodly number of Leftwingers are
not only narrow-minded and dull, but also just stupid.
If the transformer really does have poor voltage regulation as theorized
in other parts of this thread, then the oversized rectifiers would be
Bleed resistors take much of the excitement out of life.
After a bit of thinking, I began to realize that the whole setup is
limited by the transformer, and so, putting lathe caps on output would
not be likely to ruin the existing diodes. I will try turning it off
and on a few times. If the diodes fail I will oversize them.
Ha ha ha. I can't tell you how many fairly decent "injuries" loaded
caps have caused. Not from the voltage you catch, but from the
mechanic reaching into a controller cabinet, getting a "zap" and then
REALLY banging or scraping or even slicing an elbow or their head or
something else when they "jerk" that body part out and hit the cabinet
or a bracket or a screw or some other hard/sharp part of the
controller cabinet !!! Stitches required a number of times.
Lot of caps are used as timers on elevators, so don't have the bleeder
resistor, and when the power is pulled the normal discharge path is
opened, so they stay charged. I think maybe the fact that the power
is supposedly "off" is what causes the violent reaction....makes you
think, in that less than a split-second, that maybe you hadn't turned
everything off, and that maybe you got into the 575 volts or
ps....of course, it's never happened to me. Yeah!! Riiiigghhhtttt !!