Squirrel Cage

Most single-phase motors use a rotating armature called a squirrel cage. These types of armatures are attached to the motor shaft. The motor shaft performs the work of the device to which it is attached. A squirrel cage rotor is composed of electrically connected copper bars. It reacts to the revolving field of magnetism that is produced by the single-phase motor’s electrical windings. As the alternating current enters the motor’s windings, a magnetic field is produced. The magnetism revolves around the center of the motor shaft. Since the windings are fixed in place and the rotor is free to move, the shaft turns in accordance with the magnetic field. There is generally only one component of electrical power that enters the single-phase motor: the fixed stator or outer motor windings.

Copper Wires

Many winds of a copper wire form the collected coils of wire in a single-phase motor. Electrical power must be conducted through these windings in a continuous path. If the path is broken, the power cannot flow from the hot side to the neutral, or ground, path of the electrical circuit. All single-phase motors are fed with two wires. One wire carries the hot-side, 120-volt alternating current (VAC) and the other wire carries the power back to the neutral path. If this path is disrupted, the motor won’t run. A simple test with an ohmmeter can check to see if the path is complete for the electrical circuit. The power must be shut off to the motor and the main connections for power exposed. Switch the ohmmeter on and be sure that the switch is in the "ohm" position. The probes from the meter are touched to the motors connected to the power terminal. The meter should read a continuous path from both ends of the electrical connections. If the meter shows an "open" or "infinite ohms," then a wire may be broken inside the motor.

Noisy

If the motor runs but is overheating or makes a growling noise, you may need to replace the bearings that support the freewheeling rotor. Remove the long screws from the end bells of the motor, then pull the armature out. The bearings will simply "knock" out of the end bell. Replace them with bearings of the same type. Some older model single-phase motors may use brass Babbitt bearings in place of roller or ball bearings. These pieces of oil-impregnated brass will last for a very long time if kept properly lubricated. Once they begin to wear, though, they too must be knocked out of the end bell and be replaced. Be sure to thoroughly inspect the motor shaft for any signs of wear, which is indicated by an uneven or worn shaft. If this is the case, it may be less expensive to find a replacement motor than another rotor or armature.