how alternator works


Find Out How an Alternator Works and When to Replace It

Automobiles are complex machines made of thousands of parts, each critical to a car’s operation. Yet because there are so many different components, understanding their differences and how they work can be confusing. For instance, a common misconception about a car’s battery is that it powers the radio, cabin lights, or headlights. However, this is untrue as the alternator is what supplies power to those components while the battery provides the energy to start and operate the engine. But like many components of a vehicle, there is more to how an alternator works than you may realize.

How Does an Alternator Work?

The alternator is crucial to your car’s starting and charging system. When looking at the front of the vehicle, you can spot it near the engine. As a generator, it transforms mechanical energy into electricity to recharge the battery when operating your vehicle. This way, the battery has the power to start your car and lasts longer.

An alternator’s power forms when the serpentine or drive belts make it rotate. Electricity is created by producing an alternating current (AC) as the alternator spins. Parts called rectifier diodes are found inside the alternator, and they change the alternating current to a usable direct current (DC). As the DC current moves into the battery, it provides voltage to help power your car’s audio functions and interior lights, headlights, and taillights.

What Are the Signs of a Bad Alternator?

Alternators can last for the life of a vehicle; however, certain factors like heat, overuse, water exposure, and general wear and tear can cause deterioration. If you suspect your alternator is failing, there are signs you can look for to help confirm the problem. These include:

  • Noticing your headlights or interior lights dimming,
  • Detecting a burning rubber odor,
  • Seeing the battery warning light illuminate on your dashboard,
  • Experiencing slowing of your power windows and stereo,
  • Losing power to electrical components,
  • Having trouble starting your engine,
  • Frequent stalling when driving your car,
  • Failing to jumpstart the vehicle, and
  • Hearing weird noises like growling, grinding, or whining under the hood.


When Should I Replace My Alternator?

Although several warning signs indicate alternator issues, there are other factors you’ll want to rule out before scheduling repair services. For instance, do you see signs of corrosion at the terminals and battery cable ends? Are the alternator’s wires attached securely? Does the battery hold a charge? A failing alternator will likely not be able to supply enough power to the battery. Therefore, your car will die soon after you jumpstart it. However, a jump may keep your vehicle running if your battery is the problem, not the alternator.

One of the easiest ways to pinpoint whether the issue stems from the alternator or the battery is by taking it to an automotive retail store for further diagnosis. Autozone, for example, offers free alternator and battery testing so you can locate the issue before heading to your mechanic. If the test shows your alternator is failing, you will want to replace it as soon as possible. Although it may not die immediately, driving a car with the possibility of stalling at any moment is dangerous to you, your passengers, and other motorists. That said, use your judgment. A vehicle with a weak alternator may be drivable for a short time as long as it’s not stalling. However, you will have to get a tow if the alternator is dead.

What Does a New Alternator Cost?

Replacing a dead or dying alternator is not cheap. Depending on your car’s make and model, a new one could cost between $583 and $777, excluding taxes or other added fees. In addition, where you live, who replaces it, and whether you use aftermarket/remanufactured or OEM parts can influence the final price. But the most significant factor influencing price will be your car’s warranty status.

How to Save Money When Replacing Your Alternator

Getting a professional diagnosis is often the best way to identify the source of a mechanical failure. Again, automotive shops like Autozone, Pep Boys, or Advanced Auto Parts may be able to diagnose the issue for free to save you money. But once you know the source of the problem, request an itemized quote from your mechanic to ensure you’re getting the most reasonable rate possible. If necessary, get a second opinion to compare the breakdown.

That said, investing in a comprehensive extended car warranty is the best way to avoid paying out of pocket to repair or replace a broken or malfunctioning part. When you buy a plan that protects the alternator, and other electrical system components, you’ll only pay the deductible–if you have one–and not the entire expense. Which provider offers the most beneficial protection plan for you? Review our preferred vehicle warranty picks to start your search today.

*Estimates derived from

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