Saab SONETT III Service Manual page 53

Ii
To current-
consuming
units
Battery 12 V
F-- ---1
Voltage regulator AD 1 14 V
— Resistor 1
FITi egulat i C71
contact
Alternator
1 . K11+14 V 35 A 20
S 2221
Wiring diagram
When the ignition key is turned to the drive position (K),
the circuit is energized.
The circuit runs from the ignition switch via the charge
indicator light to terminal D+ on the voltage regulator
and thence over the breaker contact to terminal DF on
the alternator, and finally through the brushes to the ex-
citer winding, after which the circuit is grounded.
The rotor is thus magnetized and a force field is generated
in the rotor.
When the engine starts and the rotor begins to spin, an al-
ternating current is generated in the stator winding; this
cucrent is rectified as it passes the diodes and is fed into
the battery from terminal B+.
The voltage obtained from the stator winding also passes
via the exciter diodes to the voltage regulator and acts upon
the coil that controls the breaker. When the voltage rises
to 14 V or above, the magnetic field of the coil becomes
so powerful as to overcome the spring resistance of the
regulating contact and break the circuit.
The current to the exciter winding is then forced to go
through the resistance and is thus reduced, whereupon
the magnetic field strength diminishes,
and
with it the
strength of the alternating current generated in the sta-
tor winding. The voltage regulator thus governs the volt-
age to a maximum of about 14 V.
The charge indicator light is also influenced by the voltage
output from the stator winding via terminal D+ on the reg-
ulator, in such a way that the voltage is equal on both sides
of the light and the light is therefore extinguished. This is
an indication that the alternator is charging.
No current-limiting relay is needed, since the alternator
itself governs the current intensity. At high alternator
speeds, when the frequency of the alternating current is
also high, and when the intensity of the output current
reaches a given value, the resulting resistance (impedance)
assumes such a magnitude that no further increase of cur-
rent is possible.
WIRING DIAGRAM FOR A. C. ALTERNATOR
321-3
SAAB
Nov. 1972