In single phase squirrel cage motors, the primary winding within the motor housing is not capable of starting a rotational motion on the rotor, but is capable of sustaining one. To start the motor, a secondary "start" winding has a series non-polarized starting capacitor to introduce a lead in the sinusoidal current. When the secondary (start) winding is placed at an angle with respect to the primary (run) winding, a rotating electric field is created. The force of the rotational field is not constant, but is sufficient to start the rotor spinning. When the rotor comes close to operating speed, a centrifugal switch (or current-sensitive relay in series with the main winding) disconnects the capacitor. The start capacitor is typically mounted to the side of the motor housing. These are called capacitor-start motors, that have relatively high starting torque. Typically they can have up-to four times as much starting torque than a split-phase motor and are used on applications such as compressors, pressure washers and any small device requiring high starting torques. COUNT 5
QSN1 What is the main winding on a squirrel cage motor capable of withstanding? ANS1 a rotational motion on the rotor QSN2 What sort of capacitors are used on the second winding of a squirrel cage motor? ANS2 series non-polarized starting capacitor QSN3 What does the capacitor on the second winding of a squirrel cage motor do? ANS3 introduce a lead in the sinusoidal current QSN4 What does the centrifugal switch do the capacitor when the rotor achieves operating speed? ANS4 disconnects the capacitor QSN5 Where is the start capacitor commonly mounted? ANS5 to the side of the motor housing