Exciter Rotor Field - Westerbeke 7.6 kw EDT Operator's Manual

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7.6KW BT GENERATOR SINGLE PHASE
EXCITER ROTOR/FIELD
Auxiliary windings group a, b and c. Locate the three ter-
minal points on the, exciter rotor for these auxiliary winding
groups. Position the exciter rotor as shown in the i11ustration
and count off the porcelain knobs from the 12 o'clock point
either left or right to locate terminal points a, b and c.
Measure the resistance value between the pairs of terminal
points A &
B, B
&
C,
and C &A. There is no need to unsol-
der these connections unless a faulty reading appears. If this
occurs, unsolder and verify the winding fault There should
be no continuiJy found between any of the three terminal
points and the rotor shaft/case ground.
Auxiliary
Windings
1.0 -1.2 Ohms
RED & WHITE
DIODE
EXCITER ROTOR
Rotating Fi£ld Wuuli:ngs. Refer 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 reading 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.
Diodes. Six diodes are mounted on the exciter rotor; they rec-
tify the
AC
voltage produced by the three groups of auxiliary
windings to DC voltages and supply this DC voltage to the
rotating field windings.
RESlSTAilCE VALUE
11 llHMS 'THROUGH THE DIODE
- - - - - 1 1 OHMS
INFINITE
--~1['8-+:l-~==}1----
BLOCKING • _ .
INFINITE----
'The diodes can be easily checked in place with the use of a
cornman 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.
NOTE:
Attempting to check diodes in place with an ohmmeter
will give erroneous readings on the diodes due to the aUJCil-
iary winding's connections.
When leads
are
put across the diode, as illustrated, voltage
passes through the diode allowing the headlight to glow brightly.
+
o
12 VOLT
BAmRY
HIGH BEAM
12 VOLT BULB
GLOWS BRIGHT
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.
HIGH BEAM 12 VOLT BULB
DOES NOT GLOWfiS VERY FAINT
a. Should the bulb not glow with leads connected in both
directions, the diode is open internally.
b. Should the bulb glow with leads connected in both
directions, the diode is shorted internally.
In both a and b above, the diode should be replaced.
Check the resistance values of the rotating field windings
and the integrity of the resistors connected between tl,e
field windings.
Rotating FieldWuulings 7.0-8.0
oTm. (Reading taken
between the two red
&
white wires connected
(0
the
(+)
and
(-) terminals. of the exciter rotor as shown in tlle illustration.)
. Posi-resistor. (Infinite readings between bOtll yellow leads
lifted from the (+) and (-) terminals on the exciter rotor.) A
shorted posi-resistor will destroy the rotating field and cause
the AC output voltage to drop to zero.
Engines & Generators "
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