Chapter A: General Diagnosis
31
Check voltage drop test on the ground circuit of the
generator in similar fashion. Connect the DMM between
the generator frame and negative battery terminal, fig-
ure 1-38.
This test is performed when the generator has enough
output to charge the battery at a 20 amp rate. It is fairly
common to see a negative (-) voltage under these con-
ditions. If voltage drop is excessively high, install an ex-
ternal ground strap between the generator and the en-
gine. This ground strap is always required when the
generator is mounted in rubber bushings. The normal
limit of voltage drop on this circuit is 0.2 volt.
Current Output Test
There are two stages to an generator current output
test, and some manufacturers suggest doing only one
stage or the other. Obtain specifications and follow pro-
cedures in the Service Manual for the unit being tested.
First Stage
Use a CSB analyzer, or attach a carbon pile across the
battery. Connect a voltmeter between the positive bat-
tery terminal and ground, and connect an ammeter be-
tween the positive battery terminal and the battery ter-
minal at the generator. Start and run the engine at the
specified test speed, typically 1,200 RPM, and adjust
the carbon pile either to maintain a steady 15 volt level
or to get the greatest possible ammeter reading. Com-
pare the ammeter reading to specifications.
This test uses the carbon pile to drop the system volt-
age and force the voltage regulator to raise the amper-
age output. This tests the component parts of the exist-
ing system for proper operation.
Second Stage
Perform this stage if the ammeter reading does not meet
specifications during the first stage. Under the same
test conditions, full-field the generator by bypassing the
voltage regulator. This provides maximum current
through the field windings so that the generator devel-
ops maximum output amperage. With a remotely
mounted regulator, use a jumper wire to provide battery
voltage or ground the field wire.
There are two different methods of full-fielding, con-
necting to power and connecting to ground, and it is im-
portant that the right method be used. If the regulator is
controlling the ground side of the field windings, the cir-
cuit is grounded. If the regulator is controlling the power
side of the field then the circuit should be connected to
battery power.
With the generator full-fielded, it is possible for the sys-
tem voltage to go excessively high. This high voltage
can present problems with electronic components.
Therefore, full-fielding is often only recommended after
it has been determined that the voltage regulator is not
functioning properly. This test is used to see if there is
an additional problem with the generator.
VHz~
~
10A
RPM
+
COM
A
CF
RPM
V
%
OFF
VHz
AMPS
30
0
20
40
50
OFF
BATTERY
TESTER
GENERATOR
BATTERY
Fig. 1-37.
Equipment connections for checking voltage drop in the
insulated, or positive, generator circuit.
VHz~
~
10A
RPM
+
COM
A
CF
RPM
V
%
OFF
VHz
AMPS
30
0
20
40
50
OFF
BATTERY
TESTER
GENERATOR
BATTERY
Fig. 1-38.
Equipment connections for checking voltage drop in the
ground, or negative, generator circuit.
Summary of Contents for ASE-A8
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