On Wednesday 13 February 2013 11:06:18 Dave did opine: > 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
I shouldn't let my sense of humor out to play without a chaperon. :) A couple times recently I have been accused of being older than dirt. Since I can't do anything about my birthday,I may as well poke fun at it as long as I can. :) Hell, even the reference to Fred & Wilma dates me, I haven't seen a Flintstones program on tv in a good 30 years, so I know there are folks on this list who don't have a clue about them, or Howdy Doody either for that matter. Magic twanger? Whazzat? ;-) 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> Your supervisor is thinking about you. 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
