My 1996 baldor dc servo drives use contactors on the outputs (Supermax mill.) The limit switches open the contactors, which disconnect the drives from the motors, and put a power resistor across the motor leads for braking. You have to manually move the drives off the limit switches. There are small degreed wheels to do this. Sort of like the degree wheels on a bridgeport but w/o the handles. Since it should never hit the limit switches this isn't a big deal.
Disconnecting a motor from drive/vfd isn't the problem. Reconnecting it while its still powered is what typ lets the magic smoke out. On Wed, Feb 13, 2013 at 9:37 AM, Dave <e...@dc9.tzo.com> wrote: > On 2/13/2013 12:05 AM, Gene Heskett wrote: > > 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 > > > > They aren't That old! 1992 Vintage. Not too long after the wheel was > invented and well after the creation of "dirt". > > So they aren't older than dirt. ;-) > > Siemens made very similar servo drives up until about 2000, but they > changed the packaging. > > 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 > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ 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
