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Old 08-10-2009, 08:53 PM   #1
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alternator testing

I know a few ways to test your alternator. But does anyone know how to test the alternator while the engine is running with a voltage meter?
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Old 08-10-2009, 09:17 PM   #2
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Just test the voltage while the car is running. It should be between 13.5 and 14.5 volts if your alternator is running properly.
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Old 08-19-2009, 04:46 PM   #3
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Originally Posted by Jay2TheRescue View Post
Just test the voltage while the car is running. It should be between 13.5 and 14.5 volts if your alternator is running properly.
I think you mean test it at the battery terminals. That's what I've heard, anyway.
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Old 08-19-2009, 04:59 PM   #4
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You can just plug a voltmeter into your cigarette lighter (unless your car deactivates it during cranking, in which case just find another 12V source).

You should have about 12.5 - 12.6 volts with the engine off.

Your voltage should be above 10 when the engine is cranking.

Your voltage should be between 13.5 and 14.7 when driving under regular conditions.

At idle, with all electrical devices activated (engine fan, air conditioner, lights, interior blower, etc.) you should be above 13.2 volts.

It is normal for your voltage to be highest when your engine is cold, and lower when your engine is hot- most voltage regulators are not temperature-compensated so voltage will drop when they get hot.

If your car meets all of the above conditions, your alternator is essentially working fine (or, at least, not the cause of your electrical problems).

-Bob C.
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