Reversing Rotation The direction of rotation of the shaded-pole motor is determined at the factory by placing the shaded poles on one side or the other of the main poles. A left-side position produces a CCW rotation, and a right-side position produces a CW rotation. The placement of these poles cannot be changed in the field. Reverse rotation can be achieved only if the rotor can be physically removed and reversed (reinstalled so the shaft exits the oppo- site end of the motor). Rotor reversal is not always possible. 25.3.2 Split-Phase Motor In the split-phase motor, a start winding is installed in the stator to produce a magnetic field out of step (phase) with the main winding. The start winding is rather delicate because it is made of a small wire. Since it is such a small wire, it has higher resistance. The start winding also has more wraps per coil. The start winding assists the motor in getting started but begins to interfere with the magnetism of the run winding at about 75% of normal speed. The conflict of magnetic fields will cause the motor to burn out if the start winding is not promptly taken out of the circuit. Application The split-phase motor has fairly low starting torque but good running torque. Open-type split- phase motors are popular for fans or blower motors where the load is too large for a shaded pole motor. Split-phase motors are popular in hermetic compressors on systems using a capillary tube, such as domestic refrigerators and window air conditioners. During the off cycle, the capillary tube permits some high-side pressure to bleed over (unload) to the low-pressure side of the system. Bleedover helps reduce head pressure and makes it possible to use a less-costly motor with low starting torque for the compressor. To allow time for head pressure to drop, a capillary tube system should not be restarted for two to five minutes after it is stopped. Open-Type Split-Phase Motor On open-type motors, a terminal board for making electrical connections to the motor wind- ings is located just inside the end bell (lead end). See Figure 25‑18. The manufacturer connects the The shaded pole is constantly energized when the motor is running, but such a small amount of energy is only a factor at start-up. Shaded-pole motors are available from 1/100 hp to 1/6 hp. If a shaded-pole motor malfunctions, it is usually cheaper to replace it than repair it. Making electrical connections is simple because only two wires are involved. A power supply is connected to each end of the motor winding. L1 L2 L1 L2 S S N N S S N N Shading coil Shading coil Rotor rotation Rotor rotation Goodheart-Willcox Publisher Figure 25‑17. The shaded-pole motor uses small “shading coils” on each pole to provide the necessary impetus for starting. Direction of rotation is determined by location of the shading coils on the poles. Chapter 25 Motors 495 Copyright Goodheart-Willcox Co., Inc.