Dump circuit for servo motor drive

[draftex]

Hi,
I am looking for a simple circuit to dump the electricity generated by servo motors while decelerating. I just burned one of my servo drives because of this problem. Thanks,

[Al_The_Man]

What type servo's? what make?
Al.

[draftex]

This is a PIC-SERVO 3 phase brushless servo drive (DC) running an electrocraft brushless DC motor at 36V DC

[Al_The_Man]

One method is to make a shunt regulator with a voltage comparator LM311 etc and use it to switch a IGBT or HexFet with a suitable resistive load to dissipate this energy, I have used a similar circuit to this to regulate a 240vdc generator field, this might work in this application.
BTW was it this that caused the failure or the current limit not being set right on the drive?
Al.

[skippy]

Al (or anybody), without getting into whether or not draftex's problem was caused by not having a circuit that "dumps the electricity generated by servo motors during deceleration", would the average gecko or rutex, servo motor driven router (or whatever) have need for such a circuit? Do geckos and rutex take care of this phenomena or isn't it something the average person should worry about?

[ESjaavik]

@Skippy: Keep your retardation slope within reason. If you retard faster, you will increase the bus voltage. If there is nowhere to burn it off (dump resistor) either the drive will limit the retardation, and you get a following error. Or it will signal the situation with smoke and sometimes a bang. You can also use a smoothing capacitor with a higher capacitance. It will store more energy with less voltage increase. You can measure the maximum bus voltage. If it gets close to the drive rating, you're in the danger zone. If you keep to a more gentle retardation, more of the energy will be scrubbed off in frictions (slide, screw, gears...) and thus not reach the motor.

But most hobby machines does not push the retardation to such limits. Otherwise more smoke would surely have been reported here on the forum. Look around on the Gecko site. There is a smoke test of a "clone" that have a bit theory on this, and what can happen.