What Is A Car Alternator And How Does It Work?

  • Aug 17,2023
Close up of a belt on an alternator Close up of a belt on an alternator

When it comes to powering your car's radio, headlights, and other electronic components, you may think it's the battery that's putting in all the work. In reality, it's your alternator that keeps things up and running. But what exactly does an alternator do, and how does it work? Read on to find out what makes your alternator so important and how to recognize car alternator problems before they become a major issue.

What Is A Car Alternator?

Under the hood, an alternator looks like a small cylindrical generator. You will typically find it bolted to the engine. A car alternator, along with the battery and voltage regulator, is one of three main parts of a vehicle’s electric charging system. What an alternator does is supply electricity to be stored in a vehicle’s battery. It is the alternator’s function to take in mechanical power from a drive belt or serpentine belt connected to the engine’s crankshaft pulley and then convert this mechanical energy into electricity.

Alternator Components


Along the exterior of the alternator is a pulley driven by a drive or serpentine belt. The engine’s crankshaft pulley powers the belt, which spins the alternator pulley. The movement from the alternator pulley allows the vehicle’s alternator to function by providing mechanical energy it can convert into electrical energy.


The rotor is a cylindrical part attached to a metal shaft that is spun by the alternator’s drive belt. The rotor has a triangle pattern (called triangle finger poles) all around the outer circumference. These triangles are magnetic and have alternating north and south orientations around the rotor.

As the alternator rotor is energized, it becomes an electromagnet at its core.


The stator encases the spinning alternator rotor.

Attached to the interior of the stator is a series of 3 copper wire windings. As the magnetized rotor spins, alternating current is induced in the stator windings.

Voltage Regulator

While you may think you can’t have too much of a good thing, too much voltage can actually damage your car’s battery and other electronics. This is where the voltage regulator comes into play. The voltage regulator is the part of an alternator used to control the electrical output. The voltage regulator moderates the electricity creating the electromagnet in the rotor into the desired alternator output.


An alternator’s stator creates an Alternating Charge (AC) charge, but car batteries are powered by a Direct Current (DC) charge. The role of a rectifier is to convert the alternating electric charge into direct power that’s compatible with the vehicle’s battery.

Rectifiers use a series of diodes, a semiconductor device, to take in the AC charge and redirect the current into one direction of flow. By restricting the flow of power to one direction, the rectifier converts the AC charge into a DC charge the car battery can accept.

How Does An Alternator Work?

While the battery is essential for starting your car when it's off, the alternator keeps your car alive when the engine is running. The alternator powers most of the car's electronic components while you're driving around or idling, including your headlights, electric steering, power windows, windshield wipers, heated seats, dashboard instruments, and radio. The alternator supplies all of them with direct current (DC) energy. Your alternator is also responsible for charging your car battery while driving.

The alternator works by turning mechanical energy into electrical energy. When your engine is on, it powers a drive belt that rests on a pulley attached to the alternator. The pulley turns the alternator's rotor shaft, which spins a set of magnets inside a coil. These spinning magnets generate alternating current (AC) in the stator, which is then channelled to the alternator's rectifier. The rectifier converts that AC energy into DC energy, which activates your car's electrical systems.

Alternators can typically last the lifetime of your vehicle, but that doesn't always happen. General wear and tear, heat damage, overuse, exposure to water, faulty parts, or frayed wires can put your alternator out of commission before your car heads to the scrap yard.

Warning Signs Of A Bad Alternator

Without a working alternator, your car won't start in the near future or stay on for more than a few minutes. Yet the typical signs of a bad alternator are often mistaken for problems with the battery or other car parts that display similar symptoms. In other words, if you're experiencing only one of the issues below, it may be a sign of a bad alternator:

  • Dim or overly bright lights
  • Your battery is dead
  • Slow or malfunctioning accessories
  • Trouble starting or frequent stalling
  • Growling or whining noises
  • Smelling burning rubber or wires
  • Lit up battery warning light on dash

While these can be helpful indicators, any of these warning signs can also point to potential issues overall with your vehicle’s electrical system. Bring your car to your local Firestone Complete Auto Care to have your electrical system inspected so we can get to the root of the issue.

Keep Your Car Charged Up

Difficulties when starting your vehicle or charging your battery could be due to a faulty alternator! For professional diagnostics and transparent service recommendations, schedule an electrical system inspection or an alternator service at your nearest Firestone Complete Auto Care.

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