Copyright Goodheart-Willcox Co., Inc. Chapter 13 Electric Motors 253 of wire that make up the winding are wrapped around iron cores to increase the magnetic field strength. Iron cores are made of iron laminates. Laminated iron sec- tions produce a greater magnetic field than one solid piece of iron, Figure 7-2. The stator assembly is attached to the housing. Housing construction is determined by how a motor’s internal parts are cooled and where the motor is located. Because motors generate heat, there must always be means for it to dissipate. The rotor is the rotating part and is made up of staggered iron laminates to produce diagonal bars. It is attached to the shaft. See Figure 13-2. These bars act as conductors. Rings are placed at both ends of the rotor to connect the diagonal bars together and complete a circuit. The rings are called shorting rings. End bells are attached at both ends of the housing to support the shaft and rotor. The end bells contain bearings to allow rotation of the rotor. Bearing type depends on the size of the mechanical load driven by the motor. 13.2 Basic Motor Operation Electric motors require continuously changing magnetic field polarities to produce a rotating motion. Since mag- nets have a north and south pole, the stator must, at a minimum, produce two poles. These poles must also change polarity at some frequency. Alternating current automatically produces changing magnetic polarities as the current flow changes direction. See Figure 13-3. Field windings Iron core Metal bars Motor shaft DiversiTech Corporation Figure 13-2. Squirrel cage rotor showing the diagonal bars that are attached to the shaft. 1 N S + – Wire wrapped clockwise Wire wrapped counterclockwise 2 S N – + Goodheart-Willcox Publisher Figure 13-3. Magnetic poles are formed by wrapping wire around poles in different direction.