How To Test Your New Alternator

1957 Chevrolet Truck

Testing your new alternator is as simple as turning your ignition key on. Take a look at your voltmeter. It should be reading 12 to 12.5 volts. If not then your battery may be run down a little or a lot depending on your voltage reading. Lets assume battery voltage is at exactly 12 volts on your new panel meter. Start your engine. As you are turning it over, watch you volt meter. It’s normal for your voltage to drop as the starter is engaged. Lets also assume that your engine started and your battery is fully charged. Your voltmeter should now indicate 13.5 to 14.5 volts.

Turn on your lights. Voltage may drop slightly. Turn on your stereo and or AC. Each new load may lower your voltage slightly especially at idle speed. However your system voltage should always remain well above the battery voltage with the engine off. A system voltage, with engine on, equal to or less than battery voltage is an indication of poor alternator performance. Your alternator must provide more current than your car and it’s equipment demands.


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