Westerbeke 8.0KW-60Hz Service Manual page 51

WESTERBEKE 51 A MANDO ALTERNATOR
DISASSEMBLY AND TESTING
FAN
HOUSING
EXCITER
TERMINAL
SENSING
TERMINAL
GROUND
TERMINALE
TESTING THE OUTPUT CIRCUIT
REAR HOUSING
p
Y-j'iRMlliALB
1. Connect the positive voltmeter lead to the output
terminal B and connect the negative lead to the ground
terminal E on the alternator.
2. Wiggle the engine wiring harness while observing the
voltmeter. The meter should indicate the approximate
battery voltage, and should not vary. If no reading is
obtained, or if the reading varies, check the alternator
output circuit for loose or dirty connections or
damaged wiring.
NOTE:
Prior to any alterno.tor testing, illSpect the entire
alterno.tor system wiring for defects. Check all cont!ectiollS
for tightness and cleanliness, panicularly battery cable
clamps and battery terminals. IllSpectthe alternator drive
belt for excessive wear and replace
if
necessary. Also adjust
for proper belttellSion.
A
WARNING:
A failed alternator can become very
hot. Do not touch until the alternator has cooled down.
A
WARNING
Before starting the engine, make
certain that everyone is clear of moving parts! Keep
away from sheaves and belts during test procedures.
A
WARNING
Multimeters and DC Circuits
DC and AC circuits are otter mixed together in marine
applications. Always disconnect shore power cords,
isolate DC and AC converters and shut down generators
before performing DC testing. No AC
tests
should be
made without proper knowledge of AC circuits.
REFER TO THE
WIRING DIAGRAMS FOR THE ABOVE
WIRING HARNESS CONNECTIONS
TESTING THE EXCITATION CIRCUIT
1. Connect the positive (+)'voltmeter lead to the excitation
terminal R on the alternator and the negative (-) lead to
the ground terminal E on the alternator.
2. Turn the ignition switch to the on position and note the
voltmeter reading. The reading should be 1.3 to 2.5
volts (see illustration).
3. If the reading is
between .75 and
1.1
volts, the
rotor field circuit probably is shorted or grounded.
Disassemble the alternator and test the rotor as
described under CLEAN AND TEST ALTERNATOR
COMPONENTS in this section.
4. If the reading is between 6.0 and 7.0 volts, the rotor
field circuit probably is open. Remove the regulator
and inspect it for worn brushes or dirty slip rings.
Replace the brushes if they are less than I14in. (6 mm)
long. If the brushes and slip rings are in good condi-
tion, disassemble the alternator and test the rotor, as
outlined under CLEAN AND TEST ALTERNATOR
COMPONENTS in this section.
Engines & Generators
43