On Tuesday 27 July 2021 16:10:40 Earl Weaver wrote: > On 7/27/2021 1:43 PM, Gene Heskett wrote: > > Actually, the torque goes up as the speed goes down, because they > > run at the speed determined by the counter emf generated by varying > > the current in the field winding, and the higher current actually > > causes it to slow down, but at the same time, the torque rises > > because the field magnets get stronger, generating the balancing > > back emf at a lower armature speed. Unfortunately for those motors, > > the non-grain oriented steel used in those motors is saturated > > magnetically, at around 1/4 of the magnetic field we can make with > > todays magnetic materiel. Not very efficient and it shows in the > > power bill to run it. > > > > My bet is that since this is a very old tech, the power supply will > > have both selenium rectifiers and wet electrolyte filter capacitors, > > and one, or the other or both have reached their retirement age, > > like me a long time back, and like me, are no longer working very > > well. > > > > Where are your digs located Earl? I am in north central WV. > > > >> **Earl Weaver > >> Email: [email protected] <mailto:[email protected]> > >> > >> > >> _______________________________________________ > >> Emc-users mailing list > >> [email protected] > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > > Cheers, Gene Heskett > > Gene, > Yes, this is an approx. 1984 machine.
That new? I would have guessed 1934, the year I was born. That means of making a variable speed motor is ancient tech because its not very efficient. An AC motor and a vfd should cut the energy bill in half compared to that. > I suspect the drive has seen it's better days. The lathe comes out of > a tech school, hasn't been used much. Probably sat unused for "years?" > I converted it from an old Fanuc controller to LinuxCNC. > Is there a good option for replacing the DC Drive and using the > existing DC Motor, or am I better off changing to AC VFD? I think I'd put a 3 phase 5 to 7 horse or so motor in it, geared down by about 4/1, with a 7.5 horse vfd, and let the vfd do the speed control. I'm doing that twice here from linuxcnc. You can take that 5 or 7 horse to at least 200 hz, which will run it a bit more than 3x its normal speed. I have a smaller sheldon, an 11x54, that came original with a 3/4 horse single phase and a batch of shiftable belts. I put a 50 yo 1 horse in it after putting fresh bearings into the pair of them I got for a 50 dollar bill aat a local recyclers yard. Driven from a 250 volt powered single phase line, I've shifted it up to 2nd gear once. I can do from about 20 rpm to around 600 without shifting gears. And 600 is fast enough to start a fire with the flying swarf. But you will have to learn how to program the vfd, they are horribly badly tuned straight OOTB. One of the secrets there is I don't self disable the vfd until its down to 5HZ, and its programmed to not exceed the motors nameplate FLA. And while that slow kills the effectiveness of its cooling fan, I can run it at the limit for half an hour and still lay my hand on the motor w/o burning it. My Sheldon, with that 1 horse motor has had the vfd tweaked, and I can watch the overshoot in turns with an 8" 4 jaw mounted so an m4 reversal turns it around, measuring the turn from the time motion issues the command while its running at 100 revs fwd, to the encoder issuing the first reverse motion, and its rarely over .25 turns, usually about .235. At 500 revs its several full turns, but I don't tap that fast. > I'm located up here in central Wisconsin, moved here in 2008 from > Pennsylvania. > I've been through West Virginia already. Mountainous? I still like the > mountains out east! Went thru the Dells, 70 years ago. Rode the tour in a surplus duck. Nice trip. But I came here in '84, the CBS affiliate needed a Chief Engineer, so I finished out my working time there, retiring in the middle of 2002. So in addition to the 1st phone, I am also a CET, and those are a lot rarer. We here in WV generally price level dirt by the cost of the dozer operator plus the gallons of #2 he burnt making it level. Very little naturally level land here. But first, lets measure the range of this motors FIELD currant so we can maybe figure out why its missbehaving. > **Earl Weaver > Email: [email protected] <mailto:[email protected]> > Take care Earl. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
