Westerbeke 65A-FOUR - Page 102

EXCITER ROTOR TROUBLESHOOTING
LOW VOLTAGE· EXCITER ROTOR
AND ROTATING FIELD
Position the exciter rotor/rotating field so the transient
suppressor
is visible at the 12 O'Clock position.
TESTING THE ROTATING FIELD WINDINGS
Place the ohm meter probes on the two large red wires (+)
and (-). These are the connecting wires for the rotating field
windings.
These wires do not need to be lifted off their connections
unless, when testing, there is an ohm valve discrepancy or a
continuity to
ground (the rotor shaft).
If this occurs, lift these two /large field wires off the diode
plates, isolate them, and repeat the above test.
NOTE: When removing these wires, be careful notto drop the
screws or washers into the rotor.
(+)
(RED)
TESTING THE EXCITER ROTOR WINDINGS
These windings are tested in pairs: A to B, B to C, and C to A
as shown on the drawing.
c
EXCITER ROTOR WINDINGS
VIEW OF ROTOR
FROM THE
BEARING END
12 a-CLOCK POSITION
Disconnect these three wires from the diode bridge plates
taking care not to drop any screws or washers.
With the wires clear from the bridge plates, test each pair
with an ohm meter, A to B, B to C, and C to A.
No continuity should be found between the rotor and any of
these three winding pairs.
TESTING THE DIODES
Diodes can be checked with an ohmmeter. Disconnect the
wire of the particular diode and test its resistance in both
directions. A perfectly functioning diode will show a very
high resistance in one direction and a very low resistance in
the opposite direction. A faulty diode will show either a very
low resistance, or an infinite resistance in both directions.
Should the whole bridge be replaced, remember to tighten
the screws with a suitable wrench and strictly comply with
the polarities and internal wiring diagrams in manual.
~~~~f--DIDDE
~ WESTERBEKE
Engines & Generators
90