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How-To Test the Charging System

Old 09-19-2006, 06:05 PM
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How-To Test the Charging System

Tips and Tricks
~ Authored by Car Craft

“Having a robust charging system is an important part of a daily driven car. We spoke with Mark Hamilton, the automotive electrical mastermind behind M.A.D. Enterprises, about a couple of easy tests you can perform to verify whether your alternator, regulator, and wiring are up to the task. Make sure your battery is fully charged before performing either of these tests.

With the engine running (idling), grab a voltmeter and measure the voltage at the battery terminals. Ideally, you should see 14.2 volts, but Hamilton says you’re probably OK as long as the voltage is between 14 and 14.5 volts. This test ensures the alternator is providing sufficient charging at its least efficient low-speed operation.

Next, turn on all your power-draining accessories (i.e., headlights, air conditioning, stereo, wipers, blower motor, and so on) and hold the engine at cruise rpm; 2,500 rpm should be sufficient. Using your voltmeter, measure the voltage at the battery. Again, you’re looking for 14-14.5 volts to confirm that the electrical system is doing its job when there’s a full load placed on it. If the voltage regulator isn’t doing its job, you might see greater than 14.5 volts. If even one of the six diodes in the alternator is bad, however, expect to lose nearly half of the alternator’s output—in this case, you’d see below-normal voltage at the battery when all the accessories are turned on.”
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