As with the case of the capacitor-start motor, an start winding is used to produce additional torque. In the capacitor-run motor, however, the winding and capacitor remains in the circuit at all times. This requires a heavier winding (so as not to overheat) and a capacitor rated for full-time use.

  Although the starting torque can not be so dramatically improved as with the capacitor start technique, power factor, torque and efficiency are all improved, since the motor is basically a two-phase motor.

  Again, the capacitor will usually experience a voltage in excess of the line voltage. Also, if too much capacitance is used the start winding can become overloaded, resulting in reduced starting torque and increased heat while running.

  Typical capacitance value for this type of motor are in range of 20 to 50F.  The torque-speed characteristic for the typical motor of this type is shown in Figure 2b.

Fig. 2a

Fig. 2b

Capacitor-run induction motor