DIAGNOSIS AND TESTING -
Before performing charging system tests on the engine, note
the complaint such as slow cranking, battery dead or using an
excessive amount of water, top of battery wet, ammeter shows
charge at all times. This information will aid In isolating the
part ot the system causing the problem. The battery must be in
the proper state of charge (at least 1.200 specific gravity).
The following tests are made with the alternator in the
engine with output and regulator connections maintained to
the alternator except as noted in Steps 3 and 5 The field lead
FIG. 3. Ignition On - Engine Not Running
and voltage regulator are disconnected for these tests.
TEST 2-- IGNITION ON -
--DO NOT disconnect alternator output lead while
ENGINE NOT RUNNING
alternator is operating
(Refer to Figure 4)
--DO NOT disconnect voltage regulator while alternator is
The voltage regulator may he by passed with a short
jumper between the regulator and field terminals. Jumper
--DO NOT ground field terminal.
provides approximate correct voltage, fault is in the regulator
--Check battery condition. Use a fully charged battery
No change from high voltage indicates that the defect is in the
when testing alternator
brush or rotor circuit
--Disconnect ground cable of battery when removing and
installing the installing and alternator.
All readings indicated are for correct operation.
TEST 1 - IGNITION ON -
ENGINE NOT RUNNING
(Refer to Figure 3)
Correct voltage at regulator terminal is approximately 1.5 to
2.5 volts. This test evaluates excitation circuit. If voltage at
regulator terminal is
5.0 to 7.0 volts = open rotor (field circuit
FIG. 4. Ignition On - Engine Not Running
.75 to 1.1 volts = grounded rotor circuit
TEST 3 - FIELD DRAW TEST - IGNITION OFF
8 5 to 10.0 volts = open in regulator's load circuit
(Refer to Figure 5)
0 volts = open ignition switch or excitation resistor
This test evaluates complete field circuit, independent
If test results are uncertain, make Test 2.
of voltage regulator. Circuit is through brushes, slip rings, field
coil to ground Current should be 2 to 2 5 amps.. If less than
this, check brushes and slip rings. It Is desirable to use a field
rheostat in series with meter for protection of the meter.