My Car Alternator Won't Charge

Test your car's alternator to make sure it's charging the battery properly.

Your car's alternator is an electrical generator that supplies the power required to charge the battery and keep the car running. When the car is not running the alternator is not running. If your car frequently needs to be jump-started or there are periods of time where the engine is sluggish, you may need to replace the alternator. You can test your alternator to save you a few dollars at the mechanic's shop.

Things You'll Need

• Multimeter (volt meter)

Instructions

1. Turn on the car and rev the engine to 2,000-2,500 rpm. Make sure all headlights and other accessories are turned off.

2. Test your battery with a multimeter. Set the multimeter to "DC" and clip the red lead to the "+" terminal of the battery and the black lead to the "-" terminal of the battery. The multimeter should read between 13.5 and 14.4 volts with the engine still revved. You may need a helper for this step.

3. If the DC current coming out of the battery is less than 12 volts, you may need to have your alternator replaced. For a 12 volt system to stay properly charged the alternator must provide more voltage to accommodate the large power draw to the system while driving.

References

• Car Basics: How to Test Your Alternator