Westerbeke 8.0KW-60Hz Service Manual page 79

BT GENERATOR TROUBLESHOOTING
Testing Residual Voltage
1. The amount of no·load voltage produced by the
generator can be an indicator of where in the generator
the problem/fault may lie.
Residual Voltage 10·14 volts AC (6
~tud)"
18,22 volts AC (12stuif)
This voltage is the AC voltage produced by the generator
from magnetism in the exciter stator field. This. voltage is
measured between the AC Neutral and Hot leg(s) with
no·load on the generator running at 60 hertz.
The presence of residual voltage is an indication that the
following generator components are
OK.
Refer to
INTERNAL WIRING SCHEMATICS.
a. Exciter Rotor (B·l
a,
b, & c) & (B·2);
b. Rotating Field (B·3);
c.
Main Stator (C·I &C·2); and
d. Compound Thansformer (D-I & D·2).
The fault lies in one or more of the following components
in the exciter circuit:
a. Exciter Stator (A·l & A·2)
b. Bridge Rectifier (G)
c. Selector Switch
(F)
d. Main Stator Auxiliary Wmdings (C·3) .
e. Compound 'Il:arisformer Auxiliary Wmding
(D·3)
2. '!\velve (12) volt DC excitation of the exciter statoi wind·
ings should cause the generator to produce between 140 •
150 volts AC between each hot lead and the neutral (12
volts DC is applied between the lifted
(+)
and (.) leads of
the bridge rectifier,
+
to
+
and . to . ).
Correct voltage produced with twelve volts DC excitation
indicates the fault is in one or more of the above listed .
. components b, d or e.
, ,lithe generator does·not produce 140 • 150 volli!
Ac
then include a and c. ' . ,
3. The absence of any voltage from the generator indicates a
fault with the main stator windings
C~1
and C·2 andlor .
the compound transformer windings D·I and D·2.
Apply
1~ vol~
DC excitation to the e:,citer stator windings
as explained m paragraph 2. A fault m the main'stator
andlor compound transformer windings such as a short
will cause the generator engine to load down and the
shorted windings to eventually produce smoke as the
excitation is continued.
4.
Voltage output greater than residual and less than rated
output (25 •
100
volts) indicates a fault in the exciter
rotor/field B·I, B·2 or B·3. Excitation of the generator
as
explained in paragraph 2 should produce a partial rise in
voltage output and, when removed, the voltage will return
to the original low output.
BRIDGE RECTIFIER
The
bridge rectifier is supplied AC voltage from the auxiliary
windings in the generator stator
(C3)
and the compound
transformer
(D·3). The
AC voltage measured across the AC
terminals of the rectifier during engine operation is as fol·
lows: .
120Volli!
NILFIL
17·55 volli!AC
120/240
, NILFIL
, 17· 55 'volts AC
Diodes in therectill.er'convyit !Iris AC voltage to DC and
supply it
to
tl:je 'Windings of the exciter stator to induce a field
through which the exciter
rotor
revolveS. The DC voltage
measured across the
(+)
and (-) terminals of the bridge recti·
fier during engine operation is as follows:
120
Volts 120/240
NILFIL NILFIL
g·17volli!DC g·17voltsDC
Failure of the bridge rectifier will result in a weak field being
produced by the exciter stator windings. A weak field is pre·
sent, due to the magnetism in the exciter stator, which will
cause the generator to produce residual voltage.,
Testing the Bridge Rectifier
~~~~~~ ,for Faults, with an Ohmmeter
, BRIDGE
RECTIFIER~~~;~~
, TESTING THE
BRIDGE RECTIFIER
(Meter used: Simpson 260 at 70 D F (21 DC)
: 1. Set the ohmmeter scale on RXI
(+
DC) and set the
needle to zero.
2. Connect the positive
(+)
lead from the ohmmeter to point
#4. Thking the ohmmeter's negative (.) lead, momentarily
contact points #1, #2, #3, and #5. The ohmmeter should
register no deflection for any of the points touched.
3. Remove the positive
(+)
lead from point
#4
and connect
the negative (.) lead
to
point #4 and, with the positive
(+)
lead, momentarily touch points #1, #2, and #3. The oinn·
meter's needle should deflect when each point is touched,
showing a passage of meter voltage through the diodes in
the rectifier.
NOTE: Currimt BT Generators'use a bridge rectijier that is
conjigured differently, connectiQns are the same.
r.' =~I
~ WESTERBEKE
Engines
&
Generators
73