RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Voltage Regulator: Description and Operation
VOLTAGE REGULATOR
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the Powertrain Control
Module (PCM). 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 (refer to Battery Temperature Sensor for more information). 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. Also refer to Charging System Operation for additional information.
