Hi Chris, although I haven't had a chance to test it in 'anger' so to speak I have a voltage clamp circuit across the power supply. Mine uses a small PIC micro-controller and it's also used to bleed the 105VDC power supply.
Henrik Olsson published a circuit back in 2008. I searched google and came up with this link which may help. https://www.cnczone.com/forums/uhu-servo-controllers/67118-regenerative-powe r-dump-circuit.html The Power FET generally has a diode in the opposite direction so negative back emf is automatically clamped. The circuits sense when the voltage goes too high and turn on the FET to bleed down the voltage. Mariss from Gecko also posted some circuits that sense current back into the power supply and also serve as a bleed. John Dammeyer > -----Original Message----- > From: Chris Albertson [mailto:[email protected]] > Sent: June-14-18 4:41 PM > To: Enhanced Machine Controller (EMC) > Subject: [Emc-users] Protection from back EMF? > > This is a general motion controller question.... > > A couple days ago I blew up a pair of mosfets What I think happened > was I had a motor going forward then switched to reverse. Basically > slammed over. The motor likely developed it's full stall current of > 21 amps. This blew the fuse I had on the power supply. Then I'm > guessing the motor finds itself inside a powerful magnetic field and > has open circuit leads and puts some large voltage across the mosfet > H_bridge letting some smoke out. > > I think that is the physics. basically a motor and some attached > rotational mass trying to act as a generator powering a high impedance > circuit. Not 100% sure I understand this well enough to calculate > voltages. > > Question: This must be a common problem. Is it common to use some > kind of diode voltage clamp to limit the volts across the controller? > I've also heard of placing a reversed diode in parallel with the power > supply fuse to basically sort the back EMF. > > What are people doing with DC brushed motors that work with currents > up to a couple tens of amps? > > What is the maximum back EMF current? I'm guessing that a motor can > only generate current up to it's stall current. > > Why did the motor go from full forward to full reverse? In this case > it was dutifully following a hand controller but it could result from > other dumb things like an error in programming > > I can think of all kinds of solutions but I figure some have been > tested by time and are well known, > -- > > Chris Albertson > Redondo Beach, California > > ---------------------------------------------------------------------------- -- > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
