Anyone know what the older bridgeport boss 5 steppers inductance was. I think mine are sigma.

I have been running them on 70V dc with larkens full amps I think 10 and I'm wondering if it may be too much voltage. They seem to do very well for what I need but they do tend to sing at verying frequencys when stopped. motors run very cool.
I have them hooked up half winding, would use of all windings be better?

Thanks for your time.
Stephen