On 2/12/2013 10:47 PM, Gene Heskett wrote: > On Tuesday 12 February 2013 22:36:22 Przemek Klosowski did opine: > > >> On Tue, Feb 12, 2013 at 10:57 AM, Dave<[email protected]> wrote: >> >>> I have a large CNC lathe that has contactors wired in between the >>> servo drives and the motors and on an Estop, the contactors drop out >>> and the 3 phase servo motor windings are shorted together to stop the >>> motors. >>> >> I thought this is a no-no---opening of the circuit causes the servo >> driver stage to abruptly change from high-current to zero current >> flow, bound to cause transients in every inductance in the system. >> THere's a standard warning for the people rewiring their equipment >> with VFDs to take the reversing drum switch out from next to the >> motor, and replace it with something that commands the VFD to reverse. >> >> Is it one of those things that shouldn't be done routinely but is OK >> in an emergency? >> > Generally its a big "no" on that. The VFD probably assumes there is a > motor out there, and using a switch to interrupt would be a bit hard on it > because the average switch breaks dirty, going on& off for 5 to 10 > milliseconds, and re-closing the switch at an unknown position in the VFD's > output sequence stands a very good chance of letting the magic smoke out of > it, and we all know things don't work without that magic smoke. Do ALL > your starting and stopping via the input controls on the VFD, so that it > can handle the sequences properly. > > This is also true for stepper drives. The most solidly connected wires in > the system should be between the motor and the driver. A flaky connection > there will blow the tops off the chips in the driver. Instantly in terms > of human time. > > Cheers, Gene >
>>I thought this is a no-no---opening of the circuit causes the servo >>driver stage to abruptly change from high-current to zero current >>flow >>Generally its a big "no" on that. The VFD probably assumes there is a >>motor out there, and using a switch to interrupt would be a bit hard on it That is what I thought also.. however that is the way that lathe is wired. It uses Siemens servo drives for the feeds and the spindle and the drives are original. I would not recommend doing that to any random servo drive, but it seems to work with these Siemens drives. Dave ------------------------------------------------------------------------------ Free Next-Gen Firewall Hardware Offer Buy your Sophos next-gen firewall before the end March 2013 and get the hardware for free! Learn more. http://p.sf.net/sfu/sophos-d2d-feb _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
