Ford Corsar Repair Manual page 836

CHARGING SYSTEM A l t e r n a t o r -
T o complete the clrcult a return
path from the negatlve battery termi-
nal t o the alternator stator star point
must be found.
The negarive heat s ~ n k is directly
connected to the alternator housing,
therefore, the return circutt is firstly
througli the negative diodes. However,
the
negative
diode, which 1s connected
at the b r ~ d g e
connection,
is open t o
current tlow
111
this d~rection but is
opposed by the equal potential of the
phase. The remaining negative diodes
are free at this period and the circuit
back t o the star point can be c o m -
pleted through either of these diodes
and associated phases. The intercon-
nected positive diodes also have the
phase potential and resist the direct
flow of current across the bridge con-
nection. If the rotor is now moved
until the other loop of the phase
winding 1s affected, a current will flow
in the opposite direction and s o c o m -
plete the other half of the sine wave.
Actually, t h s cycle takes place very
quickly in the phases and the o u t p u t is
the collapse of the excitation the
output voltage decreases until the
zener diode blocks positive potential
from reachng the base of T 3 . T I and
T 2 now become conductive again and
the output voltage will rise until the
switching cycle 1s repeated.
Diode D1
IS
for the protection o f
transistor T I . Condenser C1 is a stabi-
l~sing condenser t o reduce any insta-
b ~ l ~ t y o f the zener diode arrangement.
ALTERNATOR
TERMINALS
D+
Exciter diode junction-connection
for indicator lamp
B+ Battery c o n n e c t ~ o n ( d ~ r e c t t o bat-
tery).
a continuous current flow.
TESTING ON
T H E T E S T BENCH
VOLTAGE
REGULATOR
OPERATION
Voltage from
D+
is supplied t o
voltage dividers
RS,
R 6 and R 7 ,
whereby R 7 is adjusted t o the correct
value during production. T h e centre
tapping of the voltage divider is taken
t o a zener diode through diode
D2
w h c h provides the necessary tempera-
ture compensation. The zener diode
controls the base of T 3 w h c h opens t o
ground when set voltage is exceeded.
This renders T 3 conductive, thereby
switctung off T 2 and T 1 w h c h are
arranged In a Darlington pair.
With tlus s w ~ t c h n g action the cur-
rent flow through the exclter winding
and T I to ground is interrupted. With
T h e alternator may only be run on
a test bench when the fan is fitted. Use
only correct sockets and cable ends for
the various alterantor connections. D o
n o t use temporary connection clips. A
12 volt battery must always be con-
nected in parallel with the machine
when it is being tested. T h e battery
acts as a buffer and eliminates voltage
peaks which occur when a load is
switched o n and off.
When voltage peaks exceed safe
limits, the rectifier action of the
diodes will be destroyed.
Set u p the alternator on an ap-
proved test bench. As the construction
of the alternator does not readily lend
itself t o clamp type mounting, a suita-
ble adapter should be used.
Connect a I?V warning lamp of at
least 2 watts between terminals D+
and B+.
Connect the test bench voltmeter
between terminals D
arid
B+ and the
ammeter in the cable t o B+. If the test
bench is not fitted with a battery load
resistor, a load resistor rated at 40A
must be connected in parallel with the
battery.
Start test b e n c h , a n d increase speed
but maintain a maximum of 14V by
adjusting the load resistor.
With a warm alternator i.e. after S
minutes operation at maximum o u t -
put values as per test instruction
should be obtained.
TESTING
ON T H E CAR
a) Ignition switch off.
b) Connzct ampmeter between
B+
connector and
B+
lead at rear of
alternator.
c) Connect voltmeter between B+
connector and earth.
d) Brldge B+ and
D+
with a
2
watt
globe.
e) Connect tachometer.
f)
Run engine a t
900
RPM.
g)
Switch o n consumers t o achieve
an output o f 2 6 a m p s
f 2
a m p s and
check that voltage is within specifica-
tions 13.6 t o 14.4 volts.
Note: If consumers a r e unable t o sup-
ply required load, connect addi-
tional load in parallel.
DISASSEMBLY
1. Mark relative positions of stator
@ and e n d plates @ and
a
with
centre punch.
2. Loosen brush holder and regula-
tors @ by unscrewing 2 screws
@ l
3. Extract brush holderlregulator. U n -
solder wire connection linking it t o the
rectifier.
4. Remove 2 nuts and lower rear
mounting bracket. Unscrew 4 through
bolts.
5. Withdraw e n d plate together
with rectifier @ a n d stator @ .