Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

testing batteries, charging systems, and starter circuits 21

Turn off all electrical loads and rev the engine for 5 seconds.
The unit provides a screen view to ensure that engine rpm is
detected. It then advances to a horizontal tachometer-type
display. Bring the engine rpm to the level of the vertical line
and hold.

Now turn on electrical loads. Select critical, commonly used

DC loads that you may need or use simultaneously with the

engine running; for example, navigation lights, bilge pump

and blower circuits, all navigation and communications

equipment, and refrigeration systems. You want to be certain

that the system can supply all these circuits and have ade-

quate power left to recharge the batteries at the same time.

The rpm scale for the loaded running test. Rev the engine
to the vertical line and hold.

With loads on, idle the engine.

After idling, rev the engine again to the vertical line. This
screen shot shows the engine is just below the correct rpm.

The diode/ripple test measures AC voltage leakage past

the rectifier assembly in the alternator. This test can indi-

cate imminent charging system failure, or an electrically

“noisy” alternator that can affect the performance of some

onboard marine electronic equipment. This test is simply a

go, no-go test——pass/fail. It can be performed separately

with a digital multimeter set to the AC volts scale (anything

in excess of 0.4 VAC is considered excessive).

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