On Wednesday 28 July 2021 12:57:30 Earl Weaver wrote: > **I took some voltage readings on the field windings F1 and F2. > This is on the edge of my experience with electrical testing, > so you may need to coach me with getting the readings that you need. > > Motor stopped: > From Ground to F1 = +107.9 - Ground to F2 = -107.8 > Leads on F1 and F2 = 215.0 > > Motor @ 50 RPM : > From Ground to F1 = +107.5 - Ground to F2 = -107.4 > Leads on F1 and F2 = 214.4 > > Motor stalled: > From Ground to F1 = +105.7 - Ground to F2 = -105.5 > > I have noticed if the main power disconnect switch is let on the > machine for a length of time, the motor will feel hot to the touch. > Is this normal? The F1 and F2 wires show voltage anytime the main > power disconnect switch is on. > > It appears to me that this is the original motor supplied with the > lathe. > Since that motor is shown with a max field currant of 3 amps, and you have nominally 215 volts available, the resistance of that winding s/b in the 72 ohm area. Can you disconnect it and measure that ohmage?
Also as a side comment, I disable all power to the machine when motion is off, making linuxcnc running AND motion (F2) on as the power switch for the whole thing, but I get cute with time delays, so the turn on is current limited for about 4 seconds by a big high wattage resistor allowing a much smaller circuit breaker since the inrush at turn-on is limited. And in your case if the field winding is good, add an off delay for the field circuit AC power src using $11 HOYMC SSR's which you can control from a std bob card or whatever. Delay long enough that the instantly turned off AC power to the armature supply has decayed to where the spin-up by shutting down the field supply is no longer a problem. That is why they didn't turn it off at all in the first place. But its also a 645 watt load on the power bill anytime the breaker is on, and that 645 watts is the major source of the motors heating when on. A couple rough service 120 volt light bulbs of lower wattage, in series added across the 215 dc to the armature will hasten the demise of that power to a safer level by acting as bleeders, and tell you how long you need to delay the field shutdown. Say 10 seconds after the bulbs have gone dark, if that's not enough, and the motor still jerks, add another 5 or 10 to the delay time via the setp in the hal file that sets that. Or use higher wattage bulbs for a quicker drain. Get back to me if you need to when that time comes. You could get even cuter and turn the light bulbs off with a relay when the motion is enabled. No delays in that circuit needed, and the bulbs should come on and then fade with the F2 that toggles it off. And leave LinuxCNC running, or make sure the machine is dead before stopping it. I tally that stuff with pyvcp leds in my axis gui. > **Earl Weaver > Email: [email protected] <mailto:[email protected]> > > On 7/28/2021 9:47 AM, Gene Heskett wrote: > > On Wednesday 28 July 2021 05:33:46 andy pugh wrote: > >> On Wed, 28 Jul 2021 at 00:46, Gene Heskett <[email protected]> > > > > wrote: > >>>> 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. > >> > >> I think you are maybe thinking of the Ward Leonard set, as used on > >> the early Monarch 10EE, where an AC motor ran a DC generator which, > >> in turn ran a DC motor. > >> That is pretty old-tech, but a DC motor with solid state drive is > >> hardly old-school at all (only the use of field coils is slightly > >> outdated at that motor size) > > > > Even with my broadcast history, big motors in the 10 to 25 HP range > > have always been std 3 phase. I've only read about using the control > > of speed via the field currant applied, and here I probably need to > > mention just for the record that loss of field leaves the motor > > running on residual magnetism in that old steel, and if unloaded, > > will spin up till it explodes. If loaded, it will trip every breaker > > back to the fuses on the pole.\ > > > > And having some experience with that, I would not bet more than 50 > > cents that they would actually break the circuit, I've been witness > > on two occasions when it did not, the ceramic tube containing that > > fuse had blown so many times that it was metal plated on the inside > > and failed to open the 7200 volt line, eventually throwing hot > > pieces into the grass below the pole, causing fires we had to stomp > > out. We also had to replace 4 750mcm cables from the substation cans > > on the pole, into and thru the weather head, and on into the > > distribution bus inside the building. That building, which preceded > > the NEC by a couple decades, had no entrance breaker, and an open > > transmitter door by a curious new operator crowbared a 4000 lb plate > > transformer, and a GE AK-225 breaker feeding that transformer failed > > to open from old age, which led to the 7.5 amp fuse wires in the > > poles flag switches to try and open. > > > > Thank $DIETY we had a spare transformer so we were only off the air > > something under 3 days. Just one of the BTDT's over my nearly 40 > > years in broadcast engineering. > > > >>> An AC motor and a vfd should cut the energy bill in half > >>> compared to that. > >> > >> But will have less low-speed torque. Bear in mind that the lathe is > >> geared for 2500rpm and was probably running at 250rpm (steel part > >> 8" dia, carbide tooling) > > > > I had assumed a change in the gearing to address that. Probablt with > > stuff from Tractor Supply. At 2500 revs, throwing swarf, I'd want a > > metal wall between that swarf and me. That stuff would be start a > > fire hot. > > > >> A VFD would be down at 5Hz to achieve that. > > > > Which I am doing on my ancient Sheldon. With torque enough to cut a > > 10 thou chip with a carbide tool. At 100 revs, the vfd is at 16HZ. > > Bring in the backgear and I can turn the house around. > > > >> I think that a DC motor is appropriate here, but probably a PM > >> servo motor would be better. > > > > I won't argue that. Both of my brushed PMDC motors are getting long > > in the tooth and running fine on the OEM brushes. And don't have a > > minimum speed other than enough to overcome friction. And the motors > > FLA torque is available down to zero speed. Temp rise limits with > > time at low fan speeds will eventually wave a hand at you of course. > > Generally the job is done by then, but its a consideration not to be > > ignored. > > > >> Is this the motor originally supplied with the lathe? > > > > I suspect it is, but Earl would have to answer that. > > > > Cheers, Gene Heskett > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users 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
