SETUP OF MESA 5I20/7I29 FOR DC SERVO MOTORS

PWM rate does not play into encoder scale.
PWM rate _MUST_ be properly set for the daughter card used.

encoder scale means encoder pules per unit of movement (say inches assuming imperial lathe) including gearing and lead screw lead.

If you know your gearing ,encoder counts and lead screw pitch you can calculate it.
or you can manually figure it out:
zero the scale and move the axis exactly 1 inch that is your scale ( though it may be off slightly it is hard to move exactly 1 inch but the number you get could help you figure out the real scale)

In the open loop test if you are just manually moving the encoders then only the encoders will show changes.
I f you enable the amps and press the plus or minus keys then the other boxes should show changes.
set the DAC number low to start with there is no ramping up or down in an open loop test.

Great, that is just what I was doing, think I have it pretty close.

Yes you need a large electrolytic capacitor on the output of the rectifier to absorb reverse energy from the motor inductance(s) Probably on the order of 10000 uF. Its not safe to run without this capacitor

OK, I will get one ASAP!

Will adding this jump up the voltage at all?

I see one at Mouser, 100VDC, 10,000 uF, looks about right.

Reason I ask is I am at 90V currenty, don't want to add the capacitor and have it jump up over the capacitor's 100V rating.

Thanks!

What is the voltage rating of your transformer?
if its 90VAC then the DC bus will be around
127V So you would need at least a 150V capacitor

If you have a three phase transformer/bridge,
the measured DC voltage with no filter will
be close to your final DC filtered voltage (127 with 90VAC)

Transformer is running at 60VAC 3PH output, then it goes to the rectifier bridge, (no capacitor) comes to 90VDC (so 30V jump).

So, looks like the 90VDC unfiltered should remain close, and if I get a 100VDC capacitor, I should be fine, or should I upsize a little?

I've never really dealt with DC capacitors, how does it get hooked in the line, accross +/- in parallel or series on the +?

Thanks!

So at 90VDC you have some more margin so 5000 uF is fine,
but I would use a higher voltage, so you have some margin for motor inductive energy dump
and deceleration probably at least a 150V capacitor
You may be better of with a couple of smaller capacitors instead of one big one
These connect across the DC output of your rectifier (parallel) and polarity is very important

Another issue is ripple current capability, this will probably force you to use a large capacitor
search.digikey.com/scripts/DkSearch/dksu...36D161HPN153MDA5M-ND
is a nice 15000 UF cap

Well, I suppose this conversation is going to go on forever!

I've got the capacitor coming, I ordered one with 100V, 10,000uF from Mouser before your final post, but I may go ahead and order another from digikey too, if recommended. The Mouser one said it takes high ripple current and can take 20% +/- on voltage, so I thought it would work.

How will I know it is working properly, put a tester on the leads and monitor voltage?