7
6
Fig. 9
−
DC Shunt
−
Tool No. 19468
new art
NOTE: Before testing the alternator’s output (volts, amps),
first use an accurate tachometer and temporarily adjust the
engine speed to 3600 RPM.
WARNING:
UPON COMPLETION
of the alterna-
tor output test, always readjust the engine rpm to
its correct top no load governed speed! Otherwise
engine may exceed safe operating speed which
could cause personal injury. Correct speed is
found in the Service Engine Sales Manual Micro-
fiche, MS-6225 or the Service Sales Manual,
MS-4052.
AC ONLY ALTERNATOR
The AC alternator provides current for headlights only.
Current for the lights is available as long as the engine is
running. The output depends upon engine speed. 12 volt
lights with a total rating of 60 to 100 watts may be used. With
lights rated at 70 watts, the voltage rises from 8 volts at 2400
RPM to 12 volts at 3600 RPM, so the brightness of the light
changes with the engine speed.
AC Output Test
1. Insert RED test lead into
receptacle in meter.
2. Insert BLACK test lead into
receptacle in meter.
3. Rotate selector to
(AC volts) position.
4. Attach RED test lead clip to AC output terminal, Fig. 10.
BLACK TEST LEAD TO A GOOD
GROUND SURFACE
RED TEST LEAD
TO OUTPUT
PIN TERMINAL
Fig. 10
−
Testing AC Output
WHITE
CONNECTOR
5. Attach BLACK test lead clip to engine ground.
6. With engine running at 3600 RPM, AC output should be
no less than 14 volts.
7. If no or low output is found, replace the stator.
DC ONLY ALTERNATOR
The DC alternator provides DC current for charging a 12
volt battery. The current from the alternator is unregulated
and is rated at 3 amps. The output rises from 2 amps at
2400 RPM, to 3 amps at 3600 RPM.
Recommended battery sizes range from 30 ampere hour for
warm temperature service to 50 ampere hour in coldest
service.
WHEN CHECKING ALTERNATOR COMPONENTS,
MAKE THE TEST IN THE FOLLOWING SEQUENCE:
Alternator Output Test
1. Insert RED test lead into 10 A receptacle in meter.
2. Insert BLACK test lead into
receptacle in meter.
3. Rotate selector to
(DC amps) position.
4. Attach RED test lead clip to DC output terminal, Fig. 11.
5. Attach BLACK test lead clip to positive (+) battery termi-
nal.
6. With engine running at 3600 RPM, output should be be-
tween 2-4 amps DC.
a. Output will vary with battery voltage. If battery volt-
age is at its maximum, output will be approximately
2 amps.
7. If no or low output is found, test diode.
RED TEST LEAD TO
OUTPUT PIN TERMINAL
Fig. 11
−
Testing DC Output
BLACK TEST LEAD
TO POSITIVE BATTERY
TERMINAL
THE BATTERY MUST BE IN
GOOD CONDITION FOR
THIS TEST
Diode Test
In the Diode Test position, the meter will display the forward
voltage drop across the diode(s). If the voltage drop is less
than 0.7 volts, the meter will “Beep” once as well as display
the voltage drop. A continuous tone indicates continuity
(shorted diode). An incomplete circuit (open diode) will be
displayed as “OL.”
1. Insert RED test lead into
receptacle in meter.
2. Insert BLACK test lead into
receptacle in meter.
3. Rotate selector to
(Diode Test) position.
4. Attach RED test lead clip to point “A” and BLACK test lead
clip to point “B,” Fig. 12. (It may be necessary to pierce
wire with a pin as shown.)
a. If meter “Beeps” once, diode is OK.
b. If meter makes a continuous tone, diode is defec-
tive (shorted). Replace diode.
c. If meter displays “OL,” proceed to step 5.
5. Reverse test leads.
TSM
Summary of Contents for 405777 Series
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