Westerbeke 12.5 BTDA - Checking the Service Battery; 12 Volt DC Control Circuit; Battery Specifications and Care

DC ELECTRICAL SYSTEM
7. Now check the voltage between the alternator output ter-
minal (B+) and ground. If the circuit is good, the voltage at
the alternator will be the same as the battery, or if an isola-
tor is in the circuit the alternator voltage will be zero. If
neither of the above is true, a problem exists· in the circuit
between the alternator and the battery. Check all the
connections - look for an opening in the charging circuit.
TESTING THE STARTING
BATTERY/ALTERNATOR
(ENGINE RUNNING)
MULTIMETER az5J
e
OM
ENGINE
-c:::=---' GROUND
8. Start the engine again. Check the voltage between the
alternator output and ground;
The voltage reading for a properly operating alternator
should
be between 13.5 and 14.5 volts. If your alternator
is over- or under-cha!ging, have it repaired at a reliable
service
facility.
NOTE: Before removing the alternator for repair, use a
voltmeter to ensure that 12 volts DC excitation is present
at the EX.C tenninal if the previous test showed only bat-
tery yoltage at the B output tenninal.
If 12 volts is not present at the EXC tenninal
1
trace the
wiring and look for breaks and po()r r;ont)et;tions.
12 VOLT DC CONTROL CIRCUIT
The engine has a 12 volt DC electrical control circuit that is
shown on the wiring diagrams that follow. Refer to these
diagrams
when troubleshooting or when servicing the DC
electrical system.
A CAUnON: To avoid damage to the battery charging
circuit, never shut oU the engine batte.ry switch. while
. the engine Is running. Shut oU the engine battery switch,
hOWBVIIr, to avoid electrical shorts when working on the
engine's electrical circuit.
BAnERY
The minimum recommended capacity of the battery used in
the engine's 12 volt DC control circuit is 600-900 Coid
Cranking
Amps (CCA).
Checking the Service Battery
Check the voltage of the service battery. This battery should
have a voltage between 13 and 14 volts when the engine i~
running. If not, there is a problem in the service battery
charging circuit.
Troubleshoot the service battery charging
circuit by checking the wiring and connections, the solenoid,
isolator, battery switch, and the battery itself.
MULTIMETER CKID
TESTING THE SERVICE
8A,rl~RY (ENGINE RUNNING)
A CAUTION: To avoid damaging .t/Je altematoi diodes,
do not use a high voltage test11r (I.e. a 111egger} when
. pertonning tests on the alternator charging circuit.
Battery Care
Review the manufacturer's recommendations and then
establish a systematic maintenance schedule for your
engine's starting
batteries and hou.se batteries.
0 Monitor your voltmeter for proper charg~ng during
.engine.operation.
0 Check the electrolyte level and specific gravity with a
hydrometer.
0 Use only distilled water to bring electrolytes to a proper
level. ·
0 Make certain that batter)' cable connections are clean and
tight to the battery posts (and to your engine).
0 Keep your batteries clean and free of corrosion.
A WARNING: Sulfuric acid In lead batteries can
cauu severe burns on skin and da~age clothing. Wear
protective gear.