RAM 2500 Truck 4WD V8-5.7L VIN D (2005)
Voltage Regulator: Description and Operation
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the PCM (Powertrain
Control Module) (within the ECM for diesel engines). The EVR is not serviced separately. If replacement is necessary, the PCM must be replaced.
The amount of direct current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series
with the generators second rotor field terminal and its ground.
Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+)
and battery temperature. It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM
grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field
up to 100 times per second (100Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If
the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output.
