On Wednesday 13 February 2013 00:00:37 Dave did opine: > 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<e...@dc9.tzo.com> 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 > And they were designed which side of Fred & Wilma Flintstones wedding?
Sorry, just couldn't resist, sometimes this stone age stuff turns out to be pretty tough. It had to be when Barney Rubble was turning the cranks. ;-) I'll get me pj's & toddle off to bed now... Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> Intel Inside, Idiot Outside. I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
