Robin Szemeti wrote: "More obviously, run the motor at its rated speed, change one of the pulleys to give you your desired spindle speed." While that is true, my thinking is that if i gear it up so that 1700 RPM -> 2000 spindle RPM then I lose mre torque at low speeds through the gearring. On the other hand if the gearing is left as is then I just lose torque when the drive is running at say 120 hz due to field weakening. But if the lathe is running that fast I am probably turning something small in DIA and really don't need a lot of torque or HP So that is why I ask if it seems OK to run a 1700 RPM motor around 2X its nameplate speed (its not an inverter duty motor) and I am a hobbyist. Is there really much difference in the construction of a 3400 RPM induction motor vs a 1700 RPM motor other than the number of poles? I mean the rotor and bearings are probably similar?
Todd Z wrote: "At 320amps, that 300? stall torque is certainly not in in/lbs." That 320 says max peak amps so I don't think that is the continuous stall current, I mean, like no way can it be. While 300 in*lbs or 25 Ft.Lbs seems like a reasonable stall for a motor that size. Im guessing that stall current would be somewhere around 30-40 amps? Anyway that would be some pretty big power devices to assemble into my DC drive maybe too much work for me. My smaller DC drives that I have made are really made from repurposed drive hardware that I had on hand. On Thu, Mar 24, 2022 at 2:33 PM gene heskett <ghesk...@shentel.net> wrote: 0 * 47/30 = 3133 RPM. I don't have much > I'm using 2 of these but in the 1.5 horse sizing here, and they work > extremely well when controlled totally by linuxcnc. For a 5hp, you'll > need a 25 amp breaker in your service box. Thats a bit north of 10 gauge > romex for a feed, so I'd use 8 gauge in conduit just to keep the > inspectors happy. You might get by with a 20 amps and 10 gauge, but > nuisance trips might be frequent, depending on how you have it tuned, and > they don't come OOTB with anything like an optimum tune. They can be sped > up for speed and direction changes by several orders of magnitude. My > 1.5hp can reverse a 1hp, in first gear belt position, turning the 35lb > spindle 100 rpms, in .25 of a turn. Thats somewhere between pretty fast, > and damned fast. Belts slip if the pulleys are worn and bellyed out. > > Because the motors have inductance which limits the current at higher > hz's, you'll find that 5hp is pretty well out of torque at 200 hz. You > won't hurt the motor doing it unless its cooling fan is weak, it might > explode. And if you limit the low speed boost to the motors FLA rating, > you'll reduce the nuisance trips, and gain the ability to run it at 5hz > for long enough to get the job done w/o burning your hand on the motor. A > 4 pole motor, running at 400hz, will if it has enough torque, run at > 12,000 rpms, about 2x faster than it can actually turn. 6 grand, aka 200 > hz, s/b be considered the red line. Thanks Gene this is really helpful info to me. I don't think I would run the drive faster than 2X the motor rated speed (120 hz) for the reasons you state as well as for being nice to the lathe spindle bearings. The lathe also has a 3 speed gearbox in the headstock. When I built my new shop I had 200A service put in. I use Hubble Wireway around the shop so it is easy to add or modify wiring and it keeps things neat. I plan on putting the VFD drive close to the motor and well away from my other linuxCNC controls. Hopefully this will help with noise. Are you using line input filters with your drives? Regards, John Figie _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
