Saab SONETT III Service Manual page 58

Testing
Note the following before testing the alternator or its
component parts:
Only direct current with a maximum voltage of 24 V
may be used to test rectifiers.
A glow lamp (110 or 200 V) must not be used for insu-
lation and short circuit tests, as it may cause damage to
the rectifiers.
The rectifier diodes must be unsoldered before the stator
winding insulation is tested at 80 V/40 W.
The battery cables must not be disconnected while the
engine is running for the purpose of measuring the charg-
ing current.
If it is necessary to solder or unsolder diode connections,
the diode connecting wire must be held in a pair of flat
pliers to conduct away excess heat, on account of the
heat sensitivity of the semiconductors. (Solder and un-
solder the connections quickly with a hot soldering iron.)
Avoid mechanical stram n at the point where the connect-
ing wires issue from the heat sink assembly; the wire must
not be bent or subjected to bad at the point of attach-
ment.
During repairs to the alternator, whether in the car or on
a test bench, the battery must be discorinected.
Only instruments having not more than 8 V voltage may
be used for measuring resistances on the accembled
alternator.
Testing the alternator on a test bench
When on the test bench, the alternator must be driven by
its belt pulley only.
Connecting wires must be fitted with cable shoes or pin
connectors. I mprovised connectors must not be used on
the battery either.
During testing a 12 volt battery must be coupled in paral-
lel with the alternator. The battery serves as a buffer to
damp out the peak voltages that occur when the load is
switched on and off. If these peaks exceed the permitted
maximum voltage, the rectifier effect of the diodes will
be lost. The voltage limit for silicon diodes is about 50 V.
Magnetization
Unlike a DC generator, the alternator does not demagne-
tize spontaneously after a long period of disuse. A 12 V
indicator lamp with a power of at least 1.2-2 W must
therefore be connected between terminals D+ and B+
(see wiring diagram). Bias current is then supplied to the
exciter winding through the indicator light, alternator
terminal D+, regulator terminal D+, the closed regulator
contacts and terminal DF. It is important in this con-
nection that the lamp wattage is at least as high as that
stated above. Self-excitation begins as soon as the alter-
nator voltage opens the exciter diodes, which occurs at
1-2 V. The voltage then rises rapidly and the potential
difference across the indicator lamp gradually diminishes.
The lamp remains lit until battery voltage has been at-
tained.
Mounting the alternator
The alternator can be tested in most types of generator
test bench. In some cases it may be necessary to provide
suitable extra mounting and drive arrangements.
CAUTION
When mounted for testing the alternator must be
secured by screws in the normal manner and not
clamped in place or secured by other means.
Testing with the voltage regulator
Mount the alternator in the test bench and connect it to
the voltage regulator. Do not misconnect the terminals!
Connect the excitation ammeter to terminal DF on the
alternator. Connect the battery and indicator lamp. Con-
nect the voltmeter to terminal B+. For bias, increase the
speed from zero until an alternator voltage of about 14 V
is obtained, then reduce speed again.
Testing at 2/3 maximum current
Connect the battery and load the alternator. Adjust the
speed to exactly 2000 rev/min. The alternator must then
deliver two-thirds of the maximum current, i.e. 23 A.
Checking speed for maximum output
Connect the battery. Load the alternator and run it warm.
I ncrease speed. The maximum output of 35 A at 14 V
should be obtained within the speed range 2700-3700
rev/min.
Nov. 1972
SAAB
321-8