Variac to drive a PWM 3 phase motor?

controlling of speed of AC motor by voltage control is not preferable because of unstable torque and increase of losses in winding. speed variation is not possible at low speeds. for better and smart speed variation PWM controller is preferable

Your motor is a synchronous 3ph PM servo. If connected while stopped with AC power of not progressively increasing frequency, it will almost definitely NOT synchronize . Use other approaches to test it, like testing waveforms on windings and the 12bit absolute encoder outputs while turning it with an external variable speed motor. S.M.

Thank you for that input. I have put 5 volts on the encoder and turned the motor. A and A- seems to be an open circuit so I think the encoder is bad. I was just looking for a way to test the motor part. A simple way to turn it without buying another driver to varify the motor or the driver. But I gather from these replys it can't be done. Could I turn the motor and see that a voltage is generated across the windings?

Thanks for the answers.

According to servo data you gave 04UWBL, this spacific servo has a 12bit absolute, not incremental encoder. So wher's the A+ and A-? . Anyway turn the motor and verify generated voltages phase to phase are within ~20% and that no abnormally high torque is needed to turn it (unconnected) as speed increases. Thas would be a sign of shorted turns S.M.