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PART
13·2
BOSCH ALTERNATOR
13-15
Section
Page
Secdon
Page
1 Description and Operation ................ 13-15
3 Major Repair Operations
.
.
..
.
..
..
....
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.. 13-17
2 Removal and Installation ...•..........
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.. 13-17
IJ
DESCRIPTION AND OPERATION
The Bosch alternator is a three
phase alternating current (AC) gener-
ator with six integrally mounted
silicon diodes that convert the AC
into direct current (DC) suitable for
charging the battery.
A further three smaller diodes are
fitted into the rectifier pack to pro-
vide DC for field excition via the
voltage regulator.
A
remote
voltage
regulator
,
mounted on the fender apron,
IS
used to control the alternator voltage
output.
The alternator is inherently self
current limiting and the diodes pre-
vent reverse current flow from the
battery.
The alternator consists of the
following major parts:
-
1. The
Stator,
a laminated frame
which carries in slots the three phase
star connected output
winding.
2. The Rotor, comprising the slip
rings and field (exciter) windings and
is constructed of interlaced poles or
fingers which form alternate north
and south poles. The field winding is
wound concentric with the shaft
inside the claw poles and has its
ends connected to the slip rings.
3. The Rectifier Pack containing
nine diodes.
The six output diodes are arranged
in a three phase bridge connection
having three diodes of positive polar-
ity and three diodes of negative
polarity.
The three field diodes are in the
D+ circuit and allow portion of the
DC output current to be used for
indicator
light
operation
and
excitation
of the field winding
through the regulator.
4.
The two end heads which carry
the ball bearings.
The drive end head incorporates
the mounting lug while the slip ring
end head contains the brush gear and
rectifier
pack.
Alternator Terminals - Fig. 8
D+ Field diode junction for regulator
D+
and indicator lamp
DF Field terminal connection for
regulator DF.
B+ Battery connection
+ Radio suppressor terminal
OPERATION
With the ignition switch turned
on and the engine running (Fig. 3),
the flow of current through the ro-
tor
field
coil energises
the
twelve
pole rotating electro magnet.
The
rotation of the energised rotor unit
induces an A.C. voltare in the three
phase rotor winding which ia con-
verted into D.C. by the aix diode
rectifiers and conducted to the B+ terminal.
The rectifiers, which only conduct
in one direction, prevent the battery
which is directly and permanently
connected to the alternator output
terminal, from diachar&'ing through
the alternator.
This characteristic
of the rectifiers eliminates the need
for a cut-out relay, BUT IT IS
ESSENTIAL THAT
THE
BAT-
TERY MUST ALWAYS BE CON-
lii'ECTED WITH THE NEGATIVE
TERMINAL TO
GROUND.
FAIL-
URE TO CONNECT A BATTERY
WITH THE CORRECT POLARITY
WILL DAMAGE THE ALTERNA-
TOR
AND
REGULATOR.
DIS-
CONNECT ONE VEHICLE BAT-
TERY LEAD WHEN USING A
QUICK CHARGER.
Portion
of this
D.C.
is
directed
to the
field
excitation diodes, one
end
of
each
diode
being connected
to a
phase of the
stator and
the other end
to
the
D+
terminal. From
the
D+ terminal the current
is routed through
the
regulator to the
DF terminal
of
the alternator.
The
current
now passes through
the field
winding to
ground.
As the speed of
the
rotor in-
creases,
the induced vol tage in the
stator
winding
increases,
causing
more current to flow to satisfy the
load equirements. However, the in-
ductive
reactance
of
the
stator
winding provides an automatic up-
per limit on the cu.rrent output of
the
alternator.
The function of the voltage limi-
ter is to control the output voltage
of the Alternator to meet the needa
of the
vehicle
electrical system
which it accomplishes by controll-
ing the flow of current in the rotor
field coil.
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