On 04/06/2011 07:32 AM, Dave wrote: > On 4/6/2011 9:18 AM, andy pugh wrote: >> I have 400V servo drives, 350V motors and 240V single-phase mains power. >> >> Is there any reason that my servo power supplies need to be anything >> more than a rectifier and caps? I will probably add a PTC and an input >> fuse too. >> >> Would a relay/resistor to discharge the caps on power-off be usual? >>
Perhaps but not enough when you are dealing with huge surges. A commercial mill had problems with burnt relay contacts which had to be replaced all the time. The owner was not amused with the downtime and cost of replacement parts. I installed RC snubber circuit which solved the problem. That was over 15 years ago. > Do you have any concerns about the drives regenerating into the power > supply during decels and causing a bus overvoltage - I'm assuming that > the drives can regenerate... perhaps they cannot? Disconnecting large currents will cause arching, ripple on power lines in other circuits, radio noise, etc. Try "snubber circuit" on search engine to find volumes on this subject. I'm sure others have solved these problems and circuits are readily available. > I don't know why a relay/resistor wouldn't be a better solution for > discharging the caps. Power goes off, the relay closes and the caps > discharge.. > > Dave > Relays are very slow in comparison to semiconductors. Better use combinations of other components like varistor inverse-series Zener diodes (transorbs), FETs, etc. which are not too expensive these days to create an effective circuit that will protect your driving systems. Circuits allow you to "ramp up" the discharge rate rather than simply short circuit it through the load. Perhaps start with a calculator for your situation: http://www.daycounter.com/Calculators/Snubbers/Snubber-Design-Calculator.phtml I wish snubber website http://www.snubberdesign.com/why-snubbers.html was available when I was looking for this kind of information. Just keep the smoke in your circuits. -- Rafael ------------------------------------------------------------------------------ Xperia(TM) PLAY It's a major breakthrough. An authentic gaming smartphone on the nation's most reliable network. And it wants your games. http://p.sf.net/sfu/verizon-sfdev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
