Chevrolet Light Duty Truck 1973, Service Manual

Page: 546 / 979

6 Y - 1 8 E N G IN E E L E C TR IC A L
Because of this blocking action, the need for a cutout
relay in the circuit is eliminated. Generator field current
is supplied through a diode trio which is also connected
to the stator windings.
THEORY OF
The typical passenger car integral charging system is
made up of two components—a Delcotron generator with
a built-in solid state voltage regulator and an Energizer
(battery). These components work together to supply
electrical power for ignition, lights, radio, cranking
motor, etc. A typical wiring diagram is illustrated in
Figure 2C. The basic operating principles are explained
as follows.
When the switch is closed, current from the energizer
flows to the generator No. 1 terminal, through resistor
Rl, diode Dl, and the base-emitter of transistor TR1 to
ground, and then back to the battery. This turns on
transistor TR1, and current flows through the generator
field coil and TR1 back to the energizer. The indicator
lamp then turns on. The resistor in parallel with the
indicator lamp reduces total circuit resistance to provide
higher field current for initial voltage build-up when the
engine starts.
With the generator operating, a.c. voltage is generated in
the stator windings, and the stator supplies d.c. field
current through the diode trio, the field, TR1, and then
through the grounded diodes in the rectifier bridge back
to the stator. Also, the six diodes in the rectifier bridge
A capacitor, or condenser, mounted in the end frame
protects the rectifier bridge and diode from high
voltages, and suppresses radio noise.
OPERATION
change the stator a.c. voltages to a d.c. voltage which
appears between ground and the generator “BAT”
terminal. As generator speed increases, current is
provided for charging the energizer and operating
electrical accessories. Also, with the generator operating,
the same voltage appears at the "BAT" and No. 1
terminals, and the indicator lamp goes out to indicate
the generator is producing voltage.
The No. 2 terminal on the generator is always connected
to the energizer, but the discharge current is limited to a
negligible value by the high resistances of R2 and R3. As
the generator speed and voltage increase, the voltage
between R2 and R3 increases to the point where zener
diode D2 conducts. Transistor TR2 then turns on and
TR1 turns off. With TR1 off, the field current and system
voltage decrease, and D2 then blocks current flow,
causing TR1 to turn back on. The field current and
system voltage increase, and this cycle then repeats many
times per second to limit the generator voltage to a pre­
set value.
Capacitor Cl smooths out the voltage across R3, resistor
R4 prevents excessive current through TR1 at high
temperatures, and diode D3 prevents high-induced
voltages in the field windings when TR1 turns off.
LIGHT DUTY TRUCK SERVICE MANUAL