Schumacher PST-1000 - Manual (Page 7)

7
ALTERNATOR SYSTEM TESTS
The following test procedures will determine if there is a problem
in the diode stator, voltage regulator, electrical load requirements,
or in the alternator amperage output. The tests can pinpoint prob-
lems to the wires and connection between the charging output
terminal, the regulator, the field, and the battery.
Always compare test results with manufacturer’s specifications
before coming to conclusions regarding the performance or effi-
ciency of charging systems and their components. Look up the
engine’s alternator rating in a service manual. Check the alterna-
tor case for the output amperage rating. Be aware that
remanufactured alternators might not be marked correctly.
An alternator may have output amps nearly to specification even
though it has an open circuit diode. An open diode can overload
the remaining good ones leading to their eventual failure. To avoid
the possibility of overlooking this type of defect, the Analyzer in-
cludes a Diode/Stator indicator which senses missing volt cycles
(called ripple) when at least 20 output amps are being measured.
The lamp will come on bright and steady when it senses exces-
sive ripple. Disregard momentary flashes and the normal faint
glow of the lamp.
TERMINAL CAUTION
Never put a wrench on a live battery wire terminal. Burns
may result. Disconnect the battery ground cable first.
DIAGNOSTIC TEST PROCEDURE
If a cause for charging failure is found, correct it, and then con-
tinue this sequence to confirm system performance.
A. IF BATTERY HAS LOW CHARGE:
(If okay skip to B.) Always perform battery tests with ignition
switch in “OFF” position.
Check battery post connections. Check alternator drive belt,
and wire connections.
Test battery: If OK, Perform AMPERAGE OUTPUT TEST.
If OK, Check for excess (ignition switch OFF) battery drain.
B. RUN ENGINE WITH ACCESSORIES OFF:
Measure battery volts and observe car’s Charge Indicator
lamp. First test with engine stopped and ignition in the “RUN”
position, then start engine and observe at 1500 to 2000 rpm.
C. BATTERY IS NEVER ABOVE 13V AND CHARGE LAMP IS
ALWAYS ON; (If not; skip to D.)
Disconnect charge lamp wire at regulator.
(This may be in a connector with several wires.), (on Chrysler
cars check the field winding continuity.)
Then with engine stopped and ignition switch in RUN” position
If lamp stays on; look for a short to ground on the
disconnected wire.
If lamp stays off; Check alternator field circuit for a short
circuit, and check regulator for defect.
D. BATTERY IS NEVER ABOVE 13V AND CHARGE LAMP
NEVER LIGHTS; (If not; skip to E.)
Check instrument panel fuse.
Check field winding resistance to be between 2 and 10 ohms.
Brushes or winding may be open. Turn rotor while measuring.
Consult wiring diagram for car’s instrument panel to verify
that charge lamp circuit is good.
E. BATTERY GOES ABOVE 16V.
Regulator not working; field current always on full. If external
regulator, look for a wiring harness short or a bad regulator
ground connection. See REGULATOR GROUND TEST
F. DO AN AMPERAGE OUTPUT TEST
G. DO A LOAD REQUIREMENT TEST
END PROCEDURE
AMPERAGE OUTPUT TEST
The key to this test is to run the engine at an adequate speed,
and then load the alternator output to just below the regulated
voltage level so that the regulator applies maximum field current.
1. Hook up the Analyzer as described in the general instructions.
This includes having the Load OFF, the Battery Clamps
connected to the battery and the Amp Meter zeroed. The
battery should also have been verified to be good.
BATTERY
CHASSIS
SOLENOID
RELAY
KEY SWITCH
ALTERNATOR
REGULATOR
OUT
FIELD
Figure 6
Connection For AMPERAGE OUTPUT TEST
1. Place the Amp Probe around the alternator output wire. Try
to position the probe away from strong magnetism near the
back (shaft) end of the alternator to avoid measurement error.
2. Display Battery Volts on the Analyzer.
3. Start and run the engine at about 2000 RPM.
4. Turn the Load ON and increase until the battery voltage
decreases to be between 12.5 to 13.5 volts while reading the
output amperage.
5. Turn Load OFF and reduce RPM.
6. Test Conclusion
a. If the Diode/Stator lamp stayed on during the output test,
replace the alternator.
b. If the amperage abruptly decreased during the test, check
for a loose belt.
c. If output was less than 90% of rating, go to the Output
Resistance Tests.
OUTPUT RESISTANCE TESTS
These tests are appropriate if the Charging Output Amperage is
too low.
Circuit voltage drop measurements are made to determine if high
resistance is limiting the system’s amperage. The connections to
test are:
a. Charging output terminal to the battery POS (+) post.
b. Alternator housing to the grounded battery NEG (-) post.