I have an AC motor from an old TCL 160 Boxford NC Lathe, it has three wires named U V and W.
I thought that incorparating the original driver to a modern control interface card would be difficult or unreliable, so I got the motor out and wired it to a Lovato VE1 04 A240 3-phase AC motor driver for tests.
Motor is free on a table and shaft is not connected to anything. When I run the motor using that driver, between the frequencies 20 and 40 Hz, motor starts to shake heavily as if there is an eccentric disk on the motor shaft. But on the other frequencies, 0-20 Hz and 40-100 Hz, there isn't any shake it runs considerably smoothly so I think it's not related to a mechanical problem like a bearing failure.
The original driver was a 0.43 kW one and the one I'm testing is 0.4 kW, and I set the maximum current to 1.5 A just to be safe.
I don't know if the motor is an AC synchronous or AC asynchronous, the only guess I can make is that the motor is AC synchronous because it feels like if the rotor wasn't able to catch up with the frequency fed into it and is shaking like a stepper motor. Also it runs at 1500 RPM with 50 Hz input, and 3000 RPM with 100 Hz input, as far as I can measure with my smartphone stroboscope.
What do you think the reason would be? What would I do to make it run correctly?