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Quick-Check
Starting/Charging Test Procedures
To quickly
check Alternator Diodes we recommend the following: |
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ALTERNATOR - Ripple Voltage Test
Using a DMM
The
Alternator produces AC voltage and current. The battery
requires DC voltage and current to charge properly. Diodes
located within the alternator change (rectify) the
AC to DC. However, a small amount of AC can still be present
and no harm is done. Problems can develop when alternator
diode faults permit unacceptable amounts of AC to pass into
the vehicle electrical system.
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Set the meter to read “AC” Volts
(lowest range) .
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Connect the black COM lead probe tip
to the battery negative post.
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Connect the red Volts lead probe tip
to the battery positive post.
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Run the engine at 1500 RPM.
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Turn ON the high blower and high beam
lights.
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Your meter reading should not exceed .09
volts (90mV) AC.
High ripple voltage readings imply faulty diode(s) which
can cause:
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Undercharged battery.
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Stalling.
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Rough idle.
NOTE: If your meter reading exceeds
90 mV AC, use an ADL7100 labscope or equivalent to verify
that ripple voltage spikes do not exceed one volt peak to
peak. |
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ALTERNATOR -
Ripple Voltage Test
Using the ADL7100/LS2000 Labscope
HOOKUP:
- Connect the Red lead probe tip to the
battery positive (+) terminal.
- Connect the Black (COM) lead tip to
the battery negative (-) terminal.
SCOPE SETTINGS:
| VOLTS/DIV |
50mV/div AC |
| TIME/DIV |
1mS/div |
| SLOPE |
Rising Edge |
| Trigger
Level |
30mV |
| Trigger Mode |
Auto |
Run engine at 1000 - 1200 RPM with
high-beam lights and blower ON.
Usual ripple waveform is about 50 mV-100 mV peak-to-peak
voltage.
- If spikes go off the screen, adjust
volts/div setting to 100 mV.
- If necessary, adjust volts/div
setting to 200 mV.
- Spikes of one volt or more can cause
driveability problems.
- Spikes less than one volt are
harmless.
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