Westerbeke BCGB Service Manual page 73

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EXCITER CIRCUIT CAPACITOR{S) TESTS
Measuring Resistance
To measure the resistance of the exciter winding locate the
#9 and the #50 Hertz capacitor connections.
NOTE:
Three numbered capacitor connections exist: #7, #8,
and
#9;
and two Hem connections #50 and #60.
Unplug any other connections from the capacitor noting
their position on the capacitor. Place one probe of the mul-
timeter on plug connection #9 and the other probe on the
50 Hertz lead. Measure the resistance value of the exciter
windings and compare to the figures below.
NOTE:
Lower residual voltage along with a lower winding
resistance will confinn a faulty winding.
EXCITER WINDINGS RESISTANCE
SingllfCapacitor Dual Capacitor Dual Exciter BCA Model
1.9 ohms 2.2 ohms 1.3 ohms 1.5 ohms
CHECKING FOR
CONTINUITY BETWEEN
LEAD 50Hz & LEAD
19 TO CASE GROUND _
.,;:'"
...
,
...
-\...;,
...
~,
TESTING THE CAPACITORS
A
WARNING:
Capacitors must be discharged before
handling as they store electricity and can pack a poten-
tially lethal charge even when disconnected from their
power source.
Discharge the capacitor by a bridging the terminals with an
insulated screwdriver.
Connect a multitester (highest ohm scale) to the capacitor ter-
minals. The meter should go to zero ohms and slowly return
to high. Discharge the capacitor again and reverse the leads,
the same results should be obtained.
lithe meter goes down and stays at zero ohms, the capacitor
is faulty (shorted) .
,i~~'"''
..
-;~"
If the meter fails to go down to zero, the capacitor is faulty
(open circuited) .
Indications of a defective capacitor:
I ,
/
(
,
'
,
I '
CHECKING FOR
CONTINUITY BETWEEN
LEAD 50Hz AND LEAD 19
TO THE AC TERMINAL LEADS
Checking Continuity
Check to make sure there is no continuity to the
ground/generator case from either of the two leads. Also
check that no continuity exists between either the #50
Hertz plug or the #9 plug and any of the main stator
winding leads on the AC output. If continuity is found
here, a fault exists between these two winding groups.
An
AC voltage is induced in these windings by the
rotating field. Checking the residual voltage output from
this winding can determine the condition of the winding
when troubleshooting. Test between leads #50 and #9 with
leads lifted off the capacitor(s).
RESIDUAL VOLTAGE:
Single CapaCitor Model:
Dual Exciter Model:
Dual CapaCitor Model:
10 -14 Volts AC from each winding
7 - 9 Volts AC from each winding
14 -16 Volts AC from each winding
o
Infinite resistance, or no rise in resistance
(shorted capacitor)
o
Infinite resistance (open capacitor)
CAPACITOR RATINGS
Single Capacitor Models
Dual Capacitor Models
Dual Exciter Models
MEASURING
CAPACITOR
RESISTANCE
25.0 MFD Pn#035985
31.5 MFD Pn#035978
18.0 MFD Pn#039556
NOTE:
The older single capacitor models have 25.0 microfarad
capacitors. New models now have
31.5
microfarad capacitors.
Dual exciter models have a 18.0 MFD capacity.
The capacitor rating is marked on the housing of the capacitor.
Engines & Generators
66