Their operating characteristics, however, are not as desirable as those of other types of single-phase motors.
Due to the way they operate, they have a low power factor.
Resistance-start induction-run and capacitor-start induction-run motors are very similar in construction.
The stator winding of both motors contains both a start winding and a run winding.
Inductive loads cause the current to lag the applied voltage.The stator is constructed in thismanner to produce a phase shift between the cur- rent flowing through the run winding and the current flowing through the start winding.Both the resistance-start and capacitor-start induction- run motors start rotation by producing a rotating magnetic field in the stator winding.Alternate magnetic fields are produced in the rotor, causing the motor to con- tinue operating, as shown in Figure 11–10.This is the same principle that permits a three-phase motor to continue operating if one phase is lost and the motor is connected to single-phase power.
Applications of capacitor start single phase induction motor
Since the run winding appears more inductive and less resistive than the start winding, the current flow in the run winding will be close to 90 degrees out-of-phase with the applied voltage.The start winding appears more resistive and less inductive than the run windout-of-phase with the applied voltage, as shown in Figure 11–5.Placing the run winding deeper in the metal core material causes it to exhibit a greater amount of inductance that the start winding.Electrically, the winding appears similar to the circuit shown in Figure 11–4.The start winding is made of smaller wire and placed higher in the metal core material than the run winding, as shown in Figure 11–3.
Since the start winding is made with smaller wire than the run winding, it will exhibit a higher resistance than the run winding.The phase-angle difference between current in the run winding and current in the start winding of a resistance-start induction-run motor is generally 35 to 40 degrees.This is enough phase- angle difference to produce a weak rotating field, and consequently a weak torque, to start the motor.Recall that a rotating magnetic field cannot be produced with a single phase.The rotating magnetic field of the resistance-start induction-run motor is produced by the out-of-phase currents in the run and start windings.