Bt Generator Troubleshooting - Westerbeke BTG 8.5 Operator's Manual

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
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
INFERNAL WIRING SCHEMATICS.
a. Exciter Rotor (B-1 a, b, & c) & (B-2);
b. Rotating Field (B-3);
c. Main Stator (C-1 & C-2); and
d. Compound Transformer (D-1 & D-2).
The fault lies in one or more of the following components
in the exciter circuit:
a.
Exciter Stator (A-1 & A-2)
b. Bridge
Rectifier (G)
c. Selector Switch
(F)
d. Main Stator Auxiliary Wmdings (C-3)
e. Compound 'Ii'ansformer Auxiliary Winding (D-3)
2.
Twelve (12) volt DC excitation of
the
exciter stator 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.
· . . ·· .. · ·· · · · · · ·· · ·
If the generator does not
produce
140 - 150 volts AC,
then include
a
and
c.
I
/'·../
BATIERY
:~.:
:f_
CONNECTION.~-;-~-
I
I
I
TESTING THE
BRIDGE RECTIFIER
I
I
NOTE:
Current BT Generators use a bridge rectifier
that
is
configured d«ferently, connections are the same.
3. The absence of at)y voltage from the generator indicates a
fault with the main stator windings C-1 and C-2 and/or
the compound transformer windings D-1 and D-2.
Apply
1~ vol~
DC excitation to the exciter stator windings
as explained m paragraph 2. A fault in the main stator
and/or 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
rotorf!ield !3-1, B-2 or B-3. Excitation of the generator as
explained m 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 (C-3) and the compound
transformer {D-3). The AC voltage measured across the AC
terminals of the rectifier during engine operation is as fol-
lows:
120Volts
N/LFIL
11 - 20 volts AC
120/240
NILFIL
11 - 20 volts AC
Diodes in the
rectifier convert this AC voltage to DC and
supply it to the 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 1201240
NIL FIL NIL F/L
8 - 15 :volts AC 8 - 15 volts AC
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
(Meter
used:
Simpson 260 at
70°F
(21
oq
. 1. Set the ohmmeter scale on RXl (
+
DC) and set the
needle to zero.
2. Connect the positive ( +) lead from the ohmmeter to point
#4.
Taking the ohmmeter's negative(-) lead, momentarily
con~t
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 ohm-
mete~'s
needle should deflect when each point is touched,
showmg a passage of meter voltage through the diodes in
the rectifier.
1..,.,-IWESTERBEKE
l
Engine$ & Generators ·
43