How Alternators Work

By: Josh Briggs & Kristen Hall-Geisler  | 
broken down car
The next time your car dies and leaves you stranded on the side of the road, don't blame just the battery; it could be the alternator, too. Flat vectors/Shutterstock

It's 11:45 p.m. and you just finished working a double shift. It's late, you're tired and you have class in the morning. As you fumble for your car keys, you can't help but shiver. It's about to snow.

You hop in your car and crank it up. The engine turns over grudgingly but eventually starts. After warming up the engine for a minute, you begin your journey home. Just as the heater begins to remove the frosty conditions inside the car, the radio begins to cut out. Soon after, the dash lights start to dim ever so slightly, but you keep driving.


Eventually, the radio and the heater quit altogether, and the comfortable warmth is slowly replaced by the outside chill. Your headlights are the next thing to start flickering. Now you're getting worried. Only 15 more minutes and you're home.

But the headlights dim to the point of being dangerous and the unthinkable happens: the engine starts to miss. Less than 5 miles (8 kilometers) from home, your engine dies, along with everything else in the car. You coast to a stop on the side of the road and pull out your cellphone. It's dead, so you plug it in to call for help. Guess what? No power. It's past midnight, and you're stranded on the side of the road.

This is an example of an alternator breathing its last breath. Your first thought might have been that the battery was dying. In a sense, you would be right because the battery and the alternator are related.