Abstract: A pulse controller for a reversible d.c. series motor is provided, in place of the conventional freewheel diode across the armature and field and plugging diode across the armature, with a unidirectional current path connected across the armature and field and containing sufficient impedance to prevent build-up of motor current in interpulse periods when the motor is in a plugging mode, and switch means for shorting out the impedance during normal motoring.

Abstract: A thyristor pulse controller in which current supply to each of a plurality of d.c. loads is controlled by respective main thyristors and a single commutating capacitor common to all the main thyristors is provided, the capacitor being connected across the main thyristors to commutate them one at a time at intervals not less than the time required to forward charge the commutating capacitor from the d.c. source and to reverse the charge on the capacitor.

Abstract: A thyristor pulse controller having an electromagnetically actuated shorting contactor comprising an actuating coil and an armature which moves on energization of the actuating coil to close the contactor tips and which moves on de-energization of the coil to open the contactor tips and to create an air-gap in the magnetic circuit of the coil, is provided with an interlock circuit comprising a voltage sensing circuit connected in parallel with the contactor actuating coil, the voltage sensing circuit being adapted to provide an output signal when the modulus of the voltage across the actuating coil exceeds a predetermined value which is lower than the modulus of the voltage across the coil at the instant when the contactor tips open. A unidirectional current path, which may be provided by the interlock circuit itself, is connected across the actuating coil to discipate inductive energy in the coil when the contactor opens.