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Electrical System
i03635721
Alternator - Test
Inspect the alternator for any visible faults. The faults
could be the following items.
• Frayed wires or damaged wires
• Loose connections or damaged connections
• Loose alternator pulley
• Loose alternator or damaged alternator
1. Put the positive lead “+” of a suitable multimeter
on the “B+” terminal of the alternator. Put the
negative “-” lead on the ground terminal or on the
frame of the alternator. Put a suitable ammeter
around the positive output wire of the alternator.
a. Turn the keyswitch to the ON position but do
not start the engine.
b. The system voltage matches the specification.
Go to step 2.
c. The system voltage is less than the
specification. Check if the battery is in good
condition. Refer to Systems Operation, Testing
and Adjusting, “Battery - Test” for the correct
procedure. Go to step 5.a. if the battery is in
good condition.
2. Put the positive lead “+” of a suitable multimeter
on the “B+” terminal of the alternator. Put the
negative “-” lead on the ground terminal or on the
frame of the alternator.
a. Start the engine and run the engine at least
75% of full throttle. Record the voltage on the
multimeter.
b. The voltage should be higher than the voltage
in step 1.b.. The voltage is less than the
maximum voltage listed for the alternator. The
alternator is partially charging. Go to step 3.
The voltage is more than the maximum voltage
listed for the alternator. There is overcharging
of the alternator. Check the alternator wiring.
Refer to Systems Operation, Testing and
Adjusting, “Charging System - Test” for the
correct procedure.
c. The value of the voltage is less than the
voltage in step 1.b.. Go to step 6.
Note: Severely discharged batteries can cause low
system voltage. This can occur even while the
engine is running above idle, and the alternator is
working properly. Correct low engine idle is
important. All alternators that are installed on this
engine are self-excited. The alternators must
exceed the turn on speed before charging will
begin.
3. Ensure that the batteries are not fully charged.
a. Fully charged batteries have open circuit
voltage above 12.5 V on 12 V systems or 25 V
on 24 V systems.
b. If the batteries are fully charged then crank the
engine for 30 seconds. This reduces the
battery voltage.
c. Connect a current probe or an ammeter to a
digital multimeter. The multimeter must have a
peak hold feature. Ensure that the probe is
zeroed. Clamp the probe around the output
wire “B+” .
d. Set the multimeter to “peak hold” or “max
mode” .
e. Turn on all electrical accessories.
f. Start the engine and run the engine at least
75% of full throttle. The peak current will
appear on the multimeter.
g. The current is at least 90% of the peak output
of the alternator. Go to step 4 or step 5.
h. The current is less than 90% of the peak
alternator output. Go to step 6.
Note: This test procedure is for applications with
a main disconnect switch.
4. Turn off all accessories. Turn the keyswitch to the
OFF position.
a. Connect a current probe or an ammeter to a
digital multimeter. Ensure that the probe is
zeroed. Clamp the current probe or an
ammeter around the ground cable. Clamp the
tool with the positive side away from the
battery. Record the value of the electrical
current.
b. The current value is below 2 amperes. Go to
step 4.d..
c. The current value is above 2 amperes. Go to
step 7.
UENR0623 81
Electrical System
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