Westerbeke 8.0KW-60Hz Service Manual page 80

BT GENERATOR TROUBLESHOOTING
Exciter Rotor/Field,
1. Auxiliary windings group a, b and c. Locate the three
terminal points on the exciter rotor for these auxiliary
winding groups. Position the exciter rotor as shown in the
illustration and count off the porcelain knobs ,from the 12
0'
clock point either left or right to locate terminal points
a, b and c. Measure the resistance value between the pairs
oftenninaIpointsA & B, B &C, and C &A. There is no
need to unsolder these connections unless a faulty reading
appears. If this occurs, unsolder and verify the winding
fault. There shouldbe,no continuity found between any
of the three terminal points and the rotor shaft/case
ground.,
"RED,wHIT~(REliI
DIODE'
2. Rotating Field Windings. R<)fer to the illustration above
of the exciter rotor. The field winding connections are
noted as the
(+)
and (-) connections of the red & white
striped wires. Measure the resistance value with your
ohmmeter between these two connection points. These
connections need not be unsoldered unless a faulty read-
ing appears. If this occurs unsolder the connection and
verify the resistance reading. With these connections
lifted, there should be no continuity to the rotor shaft.
This would indicate a short to ground with these field
windings.
3. Diodes. Six diodes are mounted on the exciter rotor; they
rectify the AC voltage produced by the three groups of
auxiliary windings to DC voltages and supply this DC
voltage to the rotating field windings.
The diodes can be easily checked in place with the use
of
a common automotive 12-volt high beam headlight bulb,
some jumper leads and the generator's 12 volt starting
battery.
A short or an open in a diode can easily be found with
the above without having to unsolder and isolate each
diode to' check it with an ohmmeter.
RESISTANCE VALUE
11 OHMS THROUGH THE DIODE .
, '-
_~;
oilMs ' "
INFINITE
rlllr::ki=·:-=:----~~'---:-.:..--
BLOCKING ,-'
- - I
-j::I- :
INFINITE--"
NOTE:
Attempti~g'
to check diodes in place with an ohm-
meter will give erroneous ,readings on the diodes due to
the auxiliary winding's connections.
4. When leads are put across the diode, as illustrated, volt-
age pas,8es through the diode 'allowing the headlight to
giow brightly. '
+
----~
o
1:iiJ BATtERY '.
~!9,Q,E
High beam 12V bulb
'flOWS bright
S. Reverse the leads across the diode. The diode should
block voltage passing through it, and the headlight should
not glow, or it may glow faintly.
a. ShoUld the bulb not glow with leads connected in botb
directions, tbe diode is open internally.
b. Should the bulb glow witb leads connected in both
directions, tbe diode is shorted internally.
In botb a and b above, tbe diode should be replaced.
Check tbe resistance values of tbe rotating field windings
and the integrity of tbe resistors connected between the
field windings.
BATTERy
6. Rotating Field
Wmdings
(Reading taken .
between
the
two red&\i>hite wiiesconnected to the
(+)
.,' IUld.(-) terminals of tbe exciter rotor as shown.
7;
S~ppressor. (Infinite reil<fugs between hoth yellow ieads
"lifted from tbe
(+)
and (-) terminals on tbe exciter rotor.)
A shorted suppressor will destroy the rotatiag field and cause
the AC output voltage to drop to zero.
~
WESTERBEKE
Engines & Generators
74
)