Pontiac FIREBIRD 1972 Service Manual page 782

6E-20 1972 PONTIAC SERVICE MANUAL
Capacitor C1 smooths out the voltage across R3, resistor
R4 prevents excessive current through T R l at high tem-
peratures, and diode D-2 prevents high-induced- voltages
in the field windings when TR1 turns off. Resistor R2 is
a thermistor which causes the regulated voltage to vary
with temperature, thus providing the optimum voltage for
charging the Energizer.
Transistor TR3 provides circuit protectiaa in the event
the circuit to terminal No. 2 becomes open. TR3 will turn
off and block the flow of current from terminal No. 1 and
TR1.
10 DN GENERATOR REGULATOR
DESCRIPTION
A double contact voltage regulator unit and field relay
unit make up the regulator assembly (Fig. 6E-27). The
voltage regulator unit operates to limit generator voltage
to a pre-set value whereas the field relay connects genera-
tor field winding to the battery through the regulator
contacts. When the ignition switch is first turned on the
charge indicator lamp lights. Then, when generator begins
to charge, the indicator lamp goes out, indicating system
is operating normally. If lamp should come on when the
generator is in operation, trouble in system is indicated.
GENERATOR
C T I O N BLOCK
\
-
IGN I N ~ C A T O R
LAMP
MECHANICAL REGULATOR
Fig. 6E-27 10 DN Regulator in Charging Circuit
OPERATING PRINCIPLES
When ignition switch is closed, before engine has started,
the indicator lamp lights to indicate generator is not
charging. The current flow can be traced from battery to
"BAT" terminal on switch, through indicator lamp and
resistor which is in parallel, and then through voltage
regulator contacts. From here it continues to flow on
through generator field winding to ground, completing
the circuit back to battery. Current through this circuit
energizes the field windings sufficiently to insure voltage
build-up in stator windings when engine starts. The volt-
ages generated in stator windings are then changed or
rectified by the rectifier bridge to a d.c. voltage which
appears at the "BAT" or output terminal on the genera-
tor. The resistor allows more current to flow through the
field windings to insure voltage build-up in stator wind-
ings.
As the generator begins to operate, voltage from the "R"
or relay terminal is impressed through the regulator No.
2 terminal across field relay winding, causing relay con-
tacts to close. This connects the regulator No. 4 terminal
directly to battery through the field relay contacts, caus-
ing the indicator lamp to go out. Generator field current
then flows from battery to regulator No. 3 terminal, and
then through field relay contacts and voltage regulator
lower or series contacts to field winding.
As the speed of generator increases, the voltage at " B A T
terminal of generator also increases. This impresses a
higher voltage through the field relay contacts and across
the voltage regulator shunt windings. The increased mag-
netism created by this higher voltage across winding
causes the lower or series contacts of relay to separate. The
field current then flows through a resistor which reduces
field current. This reduced field current causes generator
voltage to decrease thereby decreasing the magnetic pull
of voltage regulator shunt winding. Consequently, the
spring causes the contacts to reclose. This cycle repeats
many times per second to limit the generator voltage to a
pre-set value.
As the generator speed increases even further, the resistor,
connected across contacts, is not sufficiently high value to
maintain voltage control with lower contacts. Therefore,
as the voltage increases the upper or "shorting" contacts
close. When this happens, the generator field winding is
shorted and no current passes through the winding. With
no current in the field winding, the generator voltage de-
creases, which also decreases the magnetism in the shunt
winding and upper contact'points open. With these points
open, field current flows through the resistor and field
winding. As the voltage increases, the contacts reclose.
This cycle then repeats many times per second to limit the
generator voltage to a pre-set value at high generator
speeds. The voltage regulator unit thus operates to limit
the value of generator voltage throughout the generator
speed range. Consequently the electrical accessories are
protected from excessive voltage which could cause dam-
age.