Alternators

An alternator/generator

An alternator is a device that is used to charge the battery in our automobiles. 

An alternator is comprised of the following parts:

• The Rotor - shown below, is a belt-driven computer controlled electromagnet. It has a large coil of wire, shown with red wiring, connected to the two brass slip rings shown on the left of the photograph. The coil of wire in enclosed inside of an iron frame with twelve pole pieces (the pointed shaped pieces in the photograph). The iron frame strengthens the magnetic field, and when the coil is energized with power and ground, it produces twelve very strong magnetic fields at 30 degree intervals. The rotor also has at least one cooling fan attached to it. The fan directs air across the rectifier bridge to cool it.

• The Stator - The stator is comprised of three evenly-spaced large coils of wire positioned inside a laminated iron frame.  The iron frame helps strengthen the rotor's electromagnetic field.  As the rotor is spun inside the stator, AC current is induced into the three stator windings by the rotor's magnetic field.  The even spacing of the three coils of wire of the stator allows for a three-phase voltage/current signal to be sent to the rectifier bridge.

• A Rectifier Bridge - The three-phase AC voltage/current induced into the stator by the spinning rotor is rectified into DC current with six or more diodes in the rectifier bridge.  Next, It is fed back to the battery to charge it.  Diodes and rectification will be discussed is greater detail in the next class; AUTOSV 1322.

• A voltage regulator and a set of brushes - The voltage regulator, shown below, can be a stand-alone part or be remotely controlled by an external computer like an engine computer. The voltage regulator controls the current through the coil of wire inside the rotor by controlling the ground side of the circuit.  The current is fed into and out of the rotor by the brushes and slip rings. 

• When system voltage is too low, the voltage regulator increases the current through the coil onside the rotor. This increases the magnetic field strength of the rotor, this results in more current being induced into the stator.

• When system voltage is too high, the voltage regulator decreases the current through the coil onside the rotor. This reduces the magnetic field strength of the rotor, this results in less current being induced into the stator.