On Monday, November 25, 2013 11:13:33 PM UTC-6, teegee wrote:
Hi all,



When I bought my second hand watchmaker's lathe years back I got a small Russian motor with it. It turned out to be a three phase induction motor with six leads wired in a single-phase 240V configuration with start capacitor. There was no obvious speed control possible, so I used a sewing machine motor instead to run the lathe.



A while ago I bought a cheapie Chinese VFD to see if I could use the Russian motor instead. I configured the 6 leads in delta configuration after figuring out what the coil wire pairs were. There was no marking on the wires other than C1 to C6, so I had to guess (and test) the coil polarities.



Some pictures are he https://www.dropbox.com/sc/d8czpdqcvf9x0gn/HE0rbKAkgi



My problem now is that the motor seems to run well and reacts to frequency changes well, but I can stop the pulley by hand with not much finger pressure. I would have expected friction burns and lost fingerprints when doing that..



The WW lathe doesn't need much torque, but surely this motor should be more powerful than a lousy sewing machine motor? I can barely use the lathe as is, it slows down too much or stalls when applying graver pressure, especially if I use the smaller spindle pulleys.



I don't have another motor to test with. Reconfiguring the wiring (swapping coil polarities, or the three delta leads) all lead to even worse performance.



There seems to be no obvious way to open the thing. The only screws besides the mounting ones are to keep a bearing cap in place. I wanted to look inside to see how many poles there are.



Does anyone have any idea what could cause the poor torque? Or am I just expecting too much of it?



Cheers,



Rob

How slow are you trying to run the motor? I purchased one of these cheap (and junk) VFDs, at slow speeds, I could stall the motor out with hand force, and I was playing with a 4HP 3Kw motor and VFD. By slow I'm talking less then 5Hz VFD output. These are not vector drive VFDs, which would drive high torque smoothly at very low Hz output.
Your description makes me think the end housings are spot welded directly to the motor laminations. (sorry, but dropbox requires sign in, so consider this unviewable).
I'm surprised the motor is delta, I assume you ohmed it out and did not find a common Y connection, but 6 isolated windings. Is there 12 terminations?
Sorry I can't be more help.