AC Generator Construction
Rotor The rotor assembly consists of a drive shaft, coil, and two pole pieces (Figure 19-4). A pulley mounted on one end of the shaft allows the rotor to be spun by a belt driven by the crankshaft pulley.
The rotor is a rotating magnetic field inside the alternator. The coil is simply a long length of insulated wire wrapped around an iron core. The core is located between the two sets of pole pieces. A magnetic field is formed by small amount (4.0 to 6.5 amperes) of current passing through the coil winding. As current flows through the coil, the core is magnetized and the pole pieces assume the magnetic polarity of the end of the core that they touch. Thus, one pole piece has a north polarity and the other has a south polarity. The extensions of the pole pieces, known as fingers, form the actual magnetic poles . A typical rotor has fourteen poles, seven north and seven south, with the magnetic field between the pole pieces moving from the N poles to the adjacent S poles(Figure 19-5).