On Thursday 07 January 2016 09:10:23 andy pugh wrote: > My lathe has a 3HP motor driven by a 3hp VFD. > There is also a Kopp Variator variable speed drive, and a 2-speed > gearbox with electromagnetic clutches. > > Running at 50Hz it thus has two speeds, 10-500rpm and 80-3000 rpm. > Those ranges aren't identical, it would be 4000 rpm as a top speed otherwise.
> The VFD works fine in the lower range, but in the higher speed range, > unless the variator is wound down to a low speed, the VFD current > reaches 18A and the VFD trips out. Acc that manual, it should be able to goto 20.5 amps (from the source line), not 18. On this side of the pond that would be at least a 10 gauge circuit, possibly 8 depending on how far from the service. > I am wondering if the 1968 3hp motor was made of bigger horses than > the 2015 3hp VFD. 1 HP, I was always told, will raise a 550 lb weight 1 foot in 1 second. They do not seem to use a horsepower translation, and I don't have a clue how to compare a 1 hp PMDC motor that claims to use 9.5 amps at full song from a 127 volt AC input with that of a 3 phase motor. That 1HP, as shipped, made 2250 rpms in high gear at the spindle, BUT when fed from a 127 Volt DC supply through one of Jon's pwm servo drivers, turns 2750 at no load. The OEM controller was an scr based unit that also restricted the speed in reverse to about 110 revs, but with the pwm servo driver, is orthogonal, spinning as fast in reverse as fwd. But my gut reaction is that a 2.2kw inverter should translate to about 2.5 HP. You said electromagnetic clutches for the gear change, are these band brakes, or mechanical dogs or sliding gears that can only be changed at zero or creep speeds? I'm thinking if band brakes, the released band is dragging, and half an hours running at the higher range might disclose heating in that gearbox. There is always a possibility that the variator's higher speed ranges may have excessive friction from uneven wear. That I would think, would also result in additional, detectable, heat being developed in the variator. I also assume you've already checked those. AIUI, your normal line voltage for a single phase circuit is something in the 220 volt 50 Hz range, which could add a gauge number from what we'd use on this side of the pond, meaning that a 10 gauge feed line should be sufficient. We have more than 220 here for the full load wireing, closer to 254 these days but of course thats from a center tapped circuit giving 127 to ground for either leg. OTOH I expect you've already metered that for excessive losses. You don't miss much. > > I further wonder if I can change the V/F curve to keep the motor > current inside the limits of the VFD. Does that seem reasonable, or > will the motor simply run slower, make less back-emf and sink even > more current? I'd think that factory defaults should be the most efficient settings. I am thinking in terms of supply voltage stiffness issues, or excessive friction someplace in the drive between motor and chuck including both motor and headstock bearings. That, and the inverter could be a mite puny for 3HP. Basically, if the HP is put in, it has to be converted to heat "someplace". In this case apparently not at the cutting tool edge. > This might be a link to the manual > http://www.lovatoelectric.com/HandlerDoc.ashx?s=I365GB12_12.pdf&ic=119 Let us know what you find. 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) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
