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DIY voltage test

Is your electrical system up to the task of feeding all of your boat’s electronic components and electric accessories? Here’s a do-it-yourself procedure from Ed Sherman of the American Boat and Yacht Council that’ll help you with that question.

Be sure to assess the electrical system after installing new electronics or other components.

“I call it the three-step voltage test. It’s simple and could save you a lot of headaches,” says Sherman, who has authored two books about marine electrical systems: “The Powerboater’s Guide to Electrical Systems” and “Advanced Marine Electrics and Electronics Troubleshooting.” If your boat fails the test, it’s time for a higher-output alternator.

1. Use a multimeter to accurately test the voltage in every battery. “Record the readings because tenths of a volt count here,” Sherman says.
2. Start the engine and rev it up to about 2,500 rpm — or half of its normal running rpm — with all of the electrical components turned off. “You should see about a 1- to 2.5-volt increase in the voltage reading, depending upon the battery state of charge and voltage regulator settings,” he says.
3. Turn on all DC components that are normally running. Intermittent loads, such as bow thrusters or anchor windlasses, do not need to be in operation. Read the voltage at the battery with those components running and while the engine is operating at the rpm cited in step two. The reading should increase by at least 0.5 volts over the static reading. “What that tells you is the alternator is able to supply enough current to run all your loads and still have some voltage left over to recharge the battery,” Sherman says. “With a DC system, whenever the engine is running the alternator is what’s really feeding all the loads on the boat.”

See related articles:

- Managing your boat's power consumption

- What's the best battery for you?

This article originally appeared in the December 2011 issue.