Vaz 21213, Руководство по ремонту, Страница: 144 / 222

Mount the alternator on the tester and connect as shown in
Fig.7-5. Start the tester motor, using rheostat 4, set the alternator
output voltage at 13 volts and raise the rotor speed to 5000 rpm.
Run the alternator at this speed for at least 10 minutes and then
measure the alternator output amperage. The reading for a sound
alternator should not be below 55 amperes.
When the measured amperage is much lower, this is an indi-
cation of some fault in the stator or rotor windings or damaged
diodes. If this is the case, very thorough diagnostics will have to
be carried out in order to locate the fault.
The output voltage should be measured at rotor speed of
5000 rpm. Set rheostat 4 to test amperage of 15 amps and take
the reading of the alternator output voltage to be within 14.1±0.5
volts at the ambient / alternator temperature of 25±10 ° ë.
If the voltage reading falls outside the range specified, replace
the complete voltage regulator with a new unit which is proved
good. Then repeat the test procedure. Normal voltage indicates
that the old regulator is faulty and must be renewed. If the fault per-
sists, check the alternator windings and diodes.
Alternator - oscilloscope test
The oscilloscope offers an accurate and quick way to check
the alternator and identify the fault through the output waveform.
To perform the check make the connections as shown in
Fig.7-6. Disconnect the output lead common for three supple-
mentary diodes from the voltage regulator terminal «Ç» and make
sure the lead end does not touch the alternator housing. Connect
the battery lead to the regulator terminal «Ç» via warning light 1.
Now the field winding is only battery powered.
Start the tester motor and increase the rotor speed up to
1500-2000 rpm. Using switch 6, cut off the battery from the alter-
nator terminal 30; while using rheostat 4, set the output current at
10 amperes.
Check the voltage across the alternator terminal 30. When
the diodes and stator winding are sound, the output waveform is
«saw-shaped» with uniform peaks (Refer to Fig.7-7, I). In case of
a broken stator winding or shorted diodes, the waveform is quite
different - the peaks are no longer uniform and there are very
deep troughs (Fig.7-7, II Ë III).
Check to see the output waveform across the alternator ter-
minal 30 is normal; next check voltage across the alternator ter-
minal 61 or at the end of the lead disconnected from the voltage
regulator terminal «B». These points are a common connection
for three supplementary diodes (Fig.7-4), supplying current to the
field winding during the alternator operation. The output wave-
form must have the same even saw-shaped pattern. An irregular
waveform is an indication of damaged supplementary diodes.
Rotor field winding - testing
The field winding can be tested with the alternator in the vehi-
cle. It is sufficient to remove the housing and voltage
regulator/brush holder assembly.
142
Fig.7-5. Wiring connections for diode plate test:
1 - warning light (12 v, 3 W); 2 - alternator; 3 - voltmeter; 4 - rheostat;
5 - amperemeter; 6 - switch; 7 - battery
Fig.7-6. Alternator wiring connections for oscilloscope test:
1 - warning light (12 v, 3 W); 2 - alternator; 3 - voltmeter; 4 - rheostat;
5 - amperemeter; 6 - switch; 7 - battery
Fig.7-7. Alternator rectified waveform:
I - sound alternator; II - blown diode; III - diode circuit broken (stator winding)