Charging System: Description and Operation

The Bosch alternator is a three phase type with a star wound stator, twelve pole rotor, full wave rectification and a solid state voltage regulator.
The alternator is machine sensed with an externally mounted radio suppression capacitor. An alternator load dump module is located on the inner wing valance and is used for load dump protection. This device protects the alternator and the vehicle electrical system from high transient voltages caused by the removal of the battery leads or loose battery connections.
When the ignition is switched ``On,'' the rotor winding is connected to the battery via the warning lamp and the ignition switch. A small current flows through the rotor to ground via the voltage regulator. This small current flow produces a weak magnetic field which, when the engine is started is sufficient to begin the build-up of alternator output voltage through the output diodes and the field or exciter diodes. As the alternator voltage builds up, the same amount of voltage will be applied to both sides of the warning lamp (12 volts from the alternator and 12 volts from the battery) at this point the warning lamp will be extinguished and as the alternator speed builds up the charging current will flow through the output diodes to the battery.
Regulator operation is similar to the vibrating contact type of voltage control unit, but instead of vibrating contacts to switch the rotor circuit on and off, switching is achieved by the use of transistors. When the battery voltage rises to 14 volts, the transistor located in the regulator switches on and off very quickly to maintain a steady 14 volts.