DC drive output voltage beyond rating

[unsaint32]

Our DC drive L1 and L2 got shorted due to bad motor. We didn't have an exact replacement of the DC drive. So we are using another DC drive that has the same input voltage rating (120v)and same output voltage is rating (0 - 90 vdc). But when we hook up to the motor (no load) the motor seems to spin too fast, and the drive actually produces 145vdc. The speed pod, Accel & decel settings don't make any difference. Why is the output voltage so high?

 

[Gene Bond]

A DC drive is a simple amplifier. If the speed reference is 0v the output should be 0v, assuming the minimum speed is set to 0 as well.

If not, the drive is bad.

Try disconnecting the pot completely. Turn the IR Comp and Min Speed all the way down. If the output is not ~ 0, then the drive is bad.

 

[thingstodo]

There's no 'current mode' on DC drives, is there?

I remember there being a current mode on some of the older Vehicle motor controllers, where you can sort of test the controller with a smaller motor, but the throttle signal is *VERY* sensitive.

Another question - is it possible that you are connected to the DC bus or Inductor terminals instead of the output terminals? That will also give you no throttle response. Some of our smaller DC drives had ... interesting .. terminal labels. It was not obvious what the output was. We actually connected a motor to the inductor terminals once and it took us a while to figure out. I don't remember the symptoms, but the speed reference did not operate very well.

 

[Gene Bond]

I suppose it would help to know the make/model of the drive...

 

[kekrahulik]

Motor - permanent magnet or field?

If you have field windings, I would check that the field is getting full field voltage (from your description, I would assume 90Vdc). To overspeed a DC motor, you weaken (or reduce) the field, so a bad connection or low field voltage would cause your motor to overspeed. I would measure voltage directly at the motor.