The Wonderful Alternator: What It Does and Why It Matters

Here’s a scenario. You’re driving on a dark backroad somewhere on the outskirts of Tacoma trying to escape I-5 traffic. But you get lost. There are no street lights. There’s a chill in the air. Your headlights are flickering, but you’re more concerned with figuring out how to get home. You decide to pull over for a few minutes to map yourself. You briefly cut the engine but keep the lights on.

You finally get your destination plugged in and go to turn it back on, but nothing happens. You try a few more times, but still nothing.

Unbeknownst to you, your alternator has been failing for a while now and has finally given out. As you sat in your car the battery depleted itself and there was nothing to recharge it. In other works: you’re stuck.

This is just one situation that can happen to you if you’re caught unprepared.

What It Does

Your alternator is an important part of your car. It is what charges up your battery and what powers the electrical systems. Your headlights, dash board, overhead lights: all of it depends on your alternator being function and properly distributing electrical power.

Your battery’s primary function is starting the engine and to turn on lights while the engine isn’t on. But the power supply in your battery is limited and will eventually be eaten up/ Without your alternator your battery wouldn’t recharge and wouldn’t be able to start your engine.

How It Works

Your alternator is made up of several parts that work in tandem to bring power to your car. It includes alternator belt, the tensioner, rotor, stator, and the diode.

The rotor spins quickly around the alternator when pulled by the alternator belt. The rotor is situated in a coil of wires called the stator. The stator harnesses the electrical energy produced by the friction of the rotating belt. The electricity produced through this process is called AC, which stands for alternating current. Electricity in this form can be conducted in two directions. The electrical systems in cars utilize electricity that flows in one direction. The AC that is produced in converted to DC (direct current) through a diode (pronounced die-od). DC current flows in one direction, making it usable throughout the car.

How Long Does It Last?

The lifespan of the typical alternator ranges from 60,000 to 150,000 miles. Your car’s age can play a role in where you land on this spectrum. Newer cars typically have a longer lifespan, while older ones are on the shorter side. Make and model also play a role. Most manufacturers will have maintenance schedules in your owners manual. This should be your go-to when deciding when to go in for routine maintenance.

Signs of Wear

There are things you can watch for that are clues of impending failure.

  1. A dead battery can be a sign of a faulty alternator. Since the alternator is what recharges the battery, a dead battery could be a sign that the battery isn’t getting properly recharged. This is especially true if you have just installed a brand new battery and are already experiencing issues.
  2. If your engine is stalling or cutting, there could be an issue. The fuel injection process requires electricity. An issue with your alternator could impede this process.
  3. Issues with headlights or the lights on the dash can also be an indicator of problems. Since these fixtures use electricity as well, a problem with the alternator can effect the output of DC and thus cause lights to flicker, dim, or go out completely.
issues with your alternator can cause lights to dim

If you’re having issues but are still unsure if your alternator is the culprit, try this. On a long stretch of road, hit the gas and accelerate quickly. Make sure your lights are on. As you accelerate, take note of the RMP’s. If your lights brighten when RMP’s are up, that’s a sure sign of an issue.

If you’re having issues with your alternator come in to Courtesy Auto and Tire of Tacoma. We’re right next to the mall, and are ready to get your car back to tip-top shape.


For more information visit this How Stuff Works article for a great breakdown.