TROUBLE SHOOTING
US / WHISPER 6/8/11 / July 2009 / Copyright © 2009 Mastervolt
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5.3
SPECIAL PROCEDURES ALTERNATOR
5.3.1
Residual voltage check / excitation
procedure
When residual magnetism disappears there is no residual
voltage. Residual magnetism can disappear after the
generating set being out of service for a long period or
suffered a short circuit. This can be solved by charging the
capacitor ("flashing") independently with a small 9 Volt
battery. This can be done while the engine is stationary
and the wiring is connected.
If the generating set battery is used for
flashing one must take care. A short circuit
can cause heavy sparking, fire and injuries
When flashing does not bring back voltage, the
capacitor(s) should be renewed. When this does not help,
the rotating rectifier diodes should be tested and a winding
resistant test should be executed.
5.3.2
Testing rotary rectifier diodes
The diodes in the rotor can be checked with a multimeter.
When the diode is faulty the alternator will not generate
any voltage.
The flexible lead connected to the diode should be
disconnected at the terminal end, and the forward and
reverse resistance checked. A healthy diode will indicate a
very high resistance (infinity) in the reverse direction, and
a low resistance in the forward direction. A faulty diode will
give a full deflection reading in both directions with the test
meter on the 10,000 ohms scale, or an infinity reading in
both directions. Replace the diode.
DIODE
Fig. 16.
Fig. 15.
