DC Servo motor getting hot

[ScottI2R]

Hello all,
I am in the process of finding a new servo amp for a dc brush "pancake" motor. The previous drive was a Kollmorgen kxa-175. These have been discontinued since Danaher Motion (the Carl Ichan of motion control) bought Kollmorgen. Sorry if i offend any Danaher people , but that was a bad business move. We have 100's in the field.
We run these motors in velocity mode with tach feedback with a single ended +/-10V dc command voltage. Very small load. The motor output from the drive goes into an edge filter to increase the inductance. The pancake armature inductance is less than 100uH where as the minimum required by the amp is 800uH@160V. Oh, DC bus is 83Vdc.
PROBLEM: While sitting stationary, the motor gets hot. Not very hot but the Boss says too hot when you consider that the kxa amps never caused the motor to even get warm.Even the AMP connector gets warm.
Drive gain is at minimum, tach is 1/8 turn from minimum. Balance is set to be stable with no command signal. Amplifier is an Aerotech BA20-160. 10A cont. 20A pk.

It may be a little early to ask why because I just started it up today and I really have more t-shooting to do in the morning but I figured I might as well post now.
While watching the current monitor on the drive (6.5A/Volt) I have noticed that the voltage will sit at about 10mV for a while and then run up to + or - .5V... .3V and for 30-40 seconds and then drop back toward 10-20mV. The motor stays stationary. I think the command signal may be noisy and this in turn is making the amp try to track this. Oh, maybe a noisy tach..Scope time! In the a.m. I am going to kill the input signal to the amp and see if it gets hot like that. The problem STILL is that the kxa doesn't do this. If it does turn out that this IS the problem, does anyone have any suggestions?

Oh well, wish me luck and send any ideas you may have please...

Thanks,
Scott

In a hundred years, it isn't going to matter anyway.

 

[Skogsgurra]

As you said, scope time.

I would look for "ultra-audio" (>15 kHz) voltage across motor and inductance. Frequency too high to be heard by people, but heating iron. The 800 uH core should also be quite hot if this is the problem.
BTW, is the extra inductor a new typ that you haven't used before with these motors?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottI2R]

You got it Gunnar,

Looks like the "edge filter" only adds about 100uH in series with the <100uH of the motor armature. Quite a bit shy of the 800uH required of the amp. Really noisy current waveform. Nasty. Oh, I did the test w/o the command signal and the results were the same. It took almost as long to explain to the Boss (Mein Fuhrer) why I wanted to do the test.
In regards to the filter, it is one that we purchased for another drive as recommended by that manufacturer. It worked fine with that drive. We should have kept that drive but we never got it tuned properly for our application. This was mainly because of the high impedance factor created by micro-management syndrome.
I have a couple 1mH inductors on order now. That should do it. I hope it doesnt effect the overall response of the system too much. Heavens forbid I get anytime to tune or test it...

Yes. Im bitter. ( Does anyone remember that poem about the train and not being allowed to ring the bell but let the thing jump the tracks and see who catches...)

Thanks for the assistance Skoggs,
Scott

In a hundred years, it isn't going to matter anyway.