Start control arrangement for split phase induction motor

Abstract

A control arrangement for a reversible alternating current split phase induction motor of the type having a start winding electrically connected in parallel with a run winding, which controls the duty cycle of current in the start winding to selectively initiate rotation of the motor in the desired direction. In one form of the invention, a thyristor switching device is connected in series with the start winding to phase control the start winding current. An electronic controller triggers the thyristor into conduction at a first firing angle to initiate motor rotation in one direction and at a second firing angle to initiate motor rotation in the other direction. The first firing angle is less than 45.degree. and preferably in the range of 25.degree.-45.degree. relative to the supply voltage signal and the second firing angle is preferably in the range of 90.degree.-135.degree. relative to the supply voltage signal. In another form of the invention, the control arrangement additionally includes a monitoring circuit which monitors the phase angle between line voltage and run winding current. The controller is responsive to the monitoring circuit to inhibit thyristor trigger signals to the start winding thyristor when a predetermined relationship exists between the phase angle and a reference value, thereby effectively switching the start winding out of the circuit when the motor gets up to speed.