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What Is the Output Voltage of GM Alternators?

by Elle Dunkle

An alternator is a must for all modern GM vehicles to operate. It is responsible for keeping the battery charged in the car, which in turn, keeps all the electrical systems functioning properly. The alternator creates direct current, measured in volts, to achieve this. If it creates too little or too much voltage, this can indicate a problem with the alternator, and it may need attention.

Ideal Voltage Output

Ideally, the GM alternator should be putting out anywhere between 13.5 and 14.5 volts. A voltage regulator helps regulate the voltage that an alternator provides. If the voltage dips below the optimal range, then the regulator kicks in to get the alternator to make more voltage. The opposite happens when voltage levels read too high. The regulator backs off and allows for the voltage to wind down until it is back within its normal range.

Higher than Usual Voltage

A high voltage reading, typically above 15 volts, indicates a problem. Though the regulator is designed to protect electrical components of the vehicle, sometimes it does fail. When the voltage output of an alternator reaches a higher-than-recommended threshold, it will destroy the battery and ruin the electrical system of the vehicle. A GM alternator that is producing too much voltage must be replaced.

Lower than Usual Voltage

When a car does not start or the lights are dim, it may be because the voltage output has dropped lower than 13.5 volts. When this happens, the battery is not being charged, and the electrical systems of the vehicle will fail. Low output can be caused by extreme drops in temperature and rainy conditions, but this quickly fixes itself once the car heats up.

If there is a real issue with the alternator, you may not know until you use several of your car's electrical components all at once. The alternator becomes overloaded and these systems stop working. This results in a car that stops and does not start. When the alternator doesn't work, the energy to power these things comes from the battery, soon worn down from lack of charging.

How to Measure Voltage Output

It is pretty simple to measure the output of a GM alternator. All you need is a voltmeter, also known as a multimeter. One of these can be purchased at a parts store or even an electronics store. Let the car idle for ten minutes before testing. Place the black stick of the meter on the negative terminal of the battery, while placing the red stick on the positive terminal. The voltage output will be displayed on the screen in the meter.

About the Author

Elle Dunkle began freelance writing in 2007 for various websites. Dunkle graduated from Pennsylvania State University with Bachelor of Science degrees in criminology and forensic science.

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