Shaded-pole a.c. motor with dynamic brake

Abstract

Am improved shaded pole A.C. motor with dynamic brake that includes a secondary high resistance winding that is selectively connected to a D.C. source when the A.C. voltage is removed. To stop a motor the A.C. voltage applied to the motor is removed with tandem switches that apply the D.C. voltage immediately upon removal of the A.C. voltage or the D.C. voltage can be selectively applied subsequently. The brake winding produces a magnetic flux in the same core where the main stator winding produces the magnetic flux responsible for causing the rotor to move. The brake winding can be connected in parallel during the time the A.C. voltage is applied to increase of the combined windings' inductance (resulting in an overall higher torque) and/or in series when during the braking operation when the D.C. voltage is applied to increase the combined winding's resistance (limiting further the peak D.C. current or reducing the secondary winding size). Relays are used in the preferred embodiment to implement the switching functions, which require arc-suppressing circuitry. More expensive active solid-state switches can be used obviating the need for the arc suppressing circuitry. The improved shaded pole A.C. motor is capable of running and stopping, like other motor types, with a relatively simple dynamic brake circuit compatible with these inexpensive motors.