Service manual
ALTERNATOR
TESTING
e. Now check the voltage between the alternator output
tenninal (B+) and ground.
If
the circuit is good, the
voltage at the alternator should be the same as the bat-
tery,
or
if
an isolator is in the circuit the alternator volt-
age will be zero.
If
not, a problem exists in the circuit
between the alternator and the battery. Check all the
connections
-look
for an opening in the charging cir-
cuit.
TESTING
THE
STARTING
BATTERY·
ALTERNATOR
(ENGINE
RUNNING)
MU
LTIMETER
WITCH
!~
!RID
G
. "
COM
/1\-
ENGIN
E
GROUND
f.
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 alterna-
tor is over-
or
under-charging, have it repaired at a reli-
able service shop.
NOTE:
Before removing the alternator for
repair,
use
a
voltmeter
to
ensure
that 12 volts DC excitation
is
pre-
sent at
the
EXC terminal if
the
previous test showed
only battery voltage at
the
B output
terminal.
If
12
volts
are
not present at
the
EXC
terminal,
trace
the
wiring looking for breaks and poor connections.
Jump
the
12
V
to
the
Exc.
terminal from a known 12V
source
and operate the
alternator.
If
the
voltage output
is
13-14
volts,
the
alternator
is
o.k.
Trace
the
cause
for
12
volts not present at
the
Exc.
terminal.
Alternator
is
Working
4. Check the voltage
of
the service battery. This battery
should have a voltage between
13
and 14 volts when the
engine is 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.
mID
.
MULTIMETER
G
COM
SERVICE
BATIERY
TESTING
THE
SERVICE
BATTERY
(ENGINE
RUNNING)
A
CAUTION:
When
perfonning
tests
on
the
alter-
nator
charging
circuit
do
not
use
a
high
voltage
tester
(i.e.
Megger).
You
can
damage
the
altemator
diodes.
ALTERNATOR
INSPECTION
When rebuilding the engine, the alternator should be cleaned
and inspected.
The
housing can be wiped off with a solvent
and the alternator tenninal studs should be cleaned with a
wire brush. Make certain the studs are tight and clean the
wiring connections that connect to the wiring harness.
Turn the rotor pulley by hand. It should
tum smoothly.
Depending on when the alternator was last serviced, the
brushes may need replacing.
If
the alternator is at all suspect,
send it to a service shop for testing and overhaul.
Engines
&
Generators
51