On 2/13/2013 11:18 AM, Gene Heskett wrote: > 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 >
>>Since I can't do anything about my birthday,I may as well poke fun at it as >>long as I can. :) I agree.. Unfortunately I recognize all of that except the Magic twanger.. ;-) I worked with a guy named Charley McCarthy for a while and I thought his parents were very cruel until I met his father - Charley McCarthy senior! :-) 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
