STARTER FOR TWO VALUE CAPACITOR TYPE SPLIT PHASE MOTORS

This type of split phase motors have two capacitors of different values in the auxiliary winding. The motors develop a high starting torque with one capacitor of a higher value and gives a quite running performance with the other capacitor of comparatively lower value. The circuit for forward / reverse operation of a two value capacitor motor has been shown in Figure.

Figure Forward/reverse starter for a two value capacitor motor

In the circuit shown an electrolytic capacitor has been used for starting purpose and an oil filled capacitor has been used for continuous running operation. During starting both the capacitors are in the circuit. When the motor picks up speed the electrolytic capacitor gets disconnected due to opening of a relay contact. The circuit operation is as follows:
When the START-push button is pressed the M contactor is energized which in turn energizes both the main and the auxiliary windings (with both the capacitors in the auxiliary winding circuit) due to closing of contacts M₂ and M₃. A thermal timer TR is also energized along with the contactor.

This thermal timer consists of a heater coil wound on a bimetallic strip. After a pre-set delay the bimetallic strips bends and closes contact TR₁. Closing of contact TR₁ causes energization of relay R which then gets hold through its own contact R₂. At the same time relay R disconnects the electrolytic capacitor from the auxiliary winding circuit due to opening of its normally closed (NC) contact R₃. The thermal timer gets de-energized as soon as relay R is energized due to opening of its contact R₁.