Hello I have an AC induction motor with a stator winding (3 phase) operating with a phase shift capacitor to provide comutation. The rotor is a copper bar design with copper end rings brazed together on M19 laminations. Input is via rectified DC through a full wave bridge followed by the caps in line. Phase 1 & 2 have the same turns & wire size and phase 3 is more turns of bigger wire.
Problem is I can get this motor to generate 130 volts P-P while being back driven when connected to the bridge/cap circuit, no other electrical connections exist. Without the circuit, simply backdriving the motor produces 2.24 V P-P. Which could be resdual magnetism in the lams. As speed is raised on the back driving motor (it's a PMDC on a separate power supply) voltage on a scope will be nill until at the same speed (approx. 12800 RPMs) something happens. The voltage jumps to 130 (in a sine wave) and the speed of the back driving motor slows as if the AC motor is working as a brake. The AC get hot to the touch so something is going on electrically in the AC. The current of the generated voltage is less than 500 milliamps.
This motor has a brake (not in the circuit for this test) that is used to stop the rotation after power is cut. Motor powers an actuator (ball screw) and there is a spec for stopping time. Some motors pass some do not. The generated voltage sometimes keeps the brake from providing torque to stop in time. The 2.24 P-P witout the circuit will not keep the brake open, it should stop the shaft.
After all said how can an AC motor (induction, no magnetic field) produce produce a voltage when connected to the bridge and cap circuit but not without it ?
Whew, if anybody answers this I will be very grateful as I am stumped. Not claiming to be an AC expert. I know enough to be dangerous. My specialty is mechanical followed by DC motors. Thanks in advance, kt