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 -- "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> Hollywood is where if you don't have happiness you send out for it. -- Rex Reed 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
