Starting Capacitor Principles

In cases where considerably higher speeds can be achieved, which may vary between 80% and 90% of the synchronous speed on average, the torque curve with the combined windings must cross it so that, for speeds above this limit, the electric motor will develop a smaller torque. Because the curves do not always intersect at the same point, and the centrifugal circuit breaker does not always open at the same speed, it is very common for the opening to occur immediately before the curves intersect. The starter capacitor motor basically consists of a split phase comma-like machine.

Among the differences, the main one is based on the inclusion of a series electrolytic capacitor, with auxiliary starting winding. This capacitor has the ability to promote a larger angle of lag between the main and auxiliary winding currents, thereby providing high starting torques. Also in the split-phase motor, the auxiliary circuit is deactivated as soon as the motor reaches approximately 75% to 80% of the synchronous speed. In this pause of speeds, the main winding alone can develop the same torque as the combined windings.