Figure 14-27. - Schematic wiring diagram of a capacitor-start capacitor-run motor.
The permanent split-phase motor has limited starting torque and is used basically with capillary tube air-conditioning equipment, such as window units. Capillary systems permit high-side and low-side pressure equalization when the compressor is not operating. A run capacitor is wired in series with the starting winding. Both the starting winding and the run capacitor remain in the circuit during operation. No start relay or start capacitor is needed. Figure 14- 28 is a schematic wiring diagram of the circuits used in this type of motor.
Split-phase motors used in hermetic refrigeration and air-conditioning applications are designed to start under load. These split- phase and capacitor motors use two sets of spiral windings: a starting winding and a running winding. The two sets of windings differ in their impedance and in their positions in the stator slots.
The starting winding has high resistance and small reactance, whereas the running winding has low resistance and high reactance. Reactance is the opposition to the flow of alternating current by inductance and capacitance. The running winding has many turns of large wire and is placed in the bottom of the stator slots. The starting winding is wound of small, high resistance wire and is placed on top of the running winding. Both windings are connected internally at one end to provide a common lead, and when starting, both are energized in parallel. The currents are out of phase with each other and their combined efforts produce a rotating field that starts the motor.
Figure 14-29 shows the starting and running windings of a two-pole motor in their 90-degree out-of-phase positions.
Figure 14-28. - Schematic wiring diagram of a permanent split-phase motor.
Figure 14-29. - View of a two-pole motor having starting and running windings.Continue Reading