An eddy-current braking crane-hoist controller with variable brake excitation

An a-c crane-hoist controller for a wound-rotor induction motor and an eddy-current brake is described. The brake serves as an artificial load for the motor. Emphasis is placed on the desirability of using speed-responsive excitation for the brake to cause its torque to increase so rapidly with speed that flat speed-load characteristics are obtained. A magnetic amplifier responsive to a signal voltage taken from the secondary circuit of the motor is a simple and reliable means for controlling the brake excitation.