Abstract: A chopper motor-controller for regulating a lift truck traction motor incorporates means for detecting faults which may cause the truck to run out of control, such as the high speed bypass contacts which shunt the semiconductor power switch being welded closed, and for disabling the controller in response thereto and also has time delay means for preventing a directional contactor from closing in on a fault before the fault detecting means can operate to disable the controller. The disclosed controller may alternatively be connected to require the operator to relax the accelerator foot pedal when starting or changing direction or to permit change of direction while the foot pedal is depressed.

Abstract: A pulse width modulation chopper controller for a D.C. traction motor has plug sensing means which monitors the voltage across the motor armature on a pulse-by-pulse basis and is responsive, only when the power switch is turned on, to the motor acting as a generator to limit the "on-time" of the power switch before current of high magnitude can flow in the motor.

Abstract: A forced commutation chopper control for regulating speed of a DC series tractive motor limits peak motor current by sensing the voltage across the commutation capacitor during the on-time of the current pulses and gating the commutation SCR on in response to a predetermined magnitude of sensed voltage to thereby terminate current pulses to the motor.