Charging System: Description and Operation

CHARGING SYSTEM DESCRIPTION
Voltage regulation is necessary on all vehicles that have a charging system with an alternator. All voltage regulators limit the voltage the vehicle's charging system produces. The need for this regulation is most critical on vehicles with electronic devices, such as an engine controller, body controller, or ETR radio. Inconsistent voltage levels or excessively high or low voltage levels have a negative effect on the performance and durability of electronic components.

There are two basic functions of a voltage regulator:
1. To maintain a constant system voltage regardless of the vehicle's electrical load requirements or its engine speed.
2. To regulate system voltage to keep the battery at an optimum state of charge.

The engine controller contains the voltage regulator function. The engine controller uses the battery voltage sense, the battery temperature sensor, and its own program to determine the charging system's voltage goal. The voltage goal is adjusted by the controller based on changes in the voltage sense and temperature values.

The basic voltage regulating function is to keep the charging system voltage between 12.9 and 15.0 volts. The voltage regulator accomplishes this by controlling the current flow through the rotor. Since the rotor is electromagnetic, controlling the current through the rotor effectively limits the strength of the magnetic field and the output of the alternator.

BATTERY VOLTAGE SENSE
The battery voltage sense is the sensor value that establishes the basic charging rate of the alternator. The voltage level sensed is used by the engine controller to determine the vehicle's electrical load condition and the battery's state of charge.

The engine controller controls the alternator's field ground based on how close the battery sense voltage is to the voltage goal. If the battery sense voltage is below the voltage goal, the engine controller initiates the grounding of the field. If the battery sense voltage is above the voltage goal, the module stops grounding the field, thus effectively disabling the magnet and stopping output.

BATTERY TEMPERATURE SENSOR
The battery temperature sensor signal is a voltage used by the engine controller to report the temperature under the hood. This temperature is used to indicate the battery temperature. The battery's temperature is critical to its state of charge and to determining the charging rate.