DC Servo Overvoltage?

I'm looking for some guidance on a dc servo setup supply. I have Baldor dc brushed servo motors (circa 1995) that are rated at 150v DC max. I would like to use a simple Bridge Rect/Cap supply off my 120AC line to create V+. However, depending on the line in voltage, it's going to be a little high (maybe 155-175DCv - probably closer to the high end).

Does anyone have opinions/experience on how tolerant DC servos are going to be of this over voltage? I can add a transformer in front to bring the line voltage down some if I have to, but it's going to be a bit space limited in the cabinet and I would really like to avoid that route if possible. I also don't want to thrash the servo motors either if in fact the 150v is a very hard limit. I know the simple answer is the datasheet says 150V, so use the mnf recommendations, but I thought I'd throw the question out for discussion.

This is on a typical 3axis BP type mill installation.

Here's a link to the motor.
www.baldor.com/catalog/MTE-4070-BLBCE

It's discontinued and I haven't found much in the way of datasheets on them. The 150V is the nameplate voltage. I'd like to find a datasheet that shows absolute max listed on it. Perhaps nameplate voltage is the abs. max???


Thanks,
Len

It's the servo drive you need to consider, not the motor - it's not going to blow up or saturate if you simply give it a 10-20% overvoltage transient. If you exceed the voltage ratings of the switching devices on the other hand, you are likely to pop them. Look at what is driving the motors and look them up instead.

You can fit a voltage clamp to limit the overshoot during decel / regen. I have one of these on my system www.shop.cncdrive.com/index.php?productID=260 It's not industrial quality but does the trick. I think there's a US distributor for those products.

Muzzer,

Thanks for the feedback and link. The drives are rated to handle the voltage, just the motors are on the edge, and the more I research on the motors, the less concerned I am that they are in any long term danger. I think the worst may be the brushes wear a little faster.

My thoughts were it would only see absolute max voltage during short periods of max accel/decels & the average would be far less than over time. I hadn't even considered that they make clamps to assist with the peaks. Thanks again for the link.

Len

Brush wear is almost entirely a mechanical affair, so won't be affected.

Note that overvoltage is due to deceleration (kinetic energy being converted back into electrical energy), not acceleration.

These clamps use the same concept seen in VFDs where you have a braking resistor. You can buy external braking modules for use with VFDs but obviously the threshold voltage will be higher than here.

Murray