15.05.2024

What is a car alternator and how does it work?

When it comes to powering your car's stereo, headlights, heated seats, and many other electrical components, you might think that a battery does it all. And you'd only be partially right. A car alternator does it all.

What is a car alternator?

car alternator

Under the hood, an alternator looks like a small cylinder and it's usually attached to the engine. The car alternator, along with the battery and voltage regulator, is one of the three main parts of a car's electrical charging system. The function of the alternator is to supply electricity that is stored in the car battery. The alternator takes mechanical energy from the drive belt connected to the engine crankshaft pulley and then converts this mechanical energy into electricity.

Components of the alternator

Pulley

A pulley driven by the drive belt is on the outside of the alternator. The engine crankshaft pulley drives the belt, which rotates the generator pulley, providing the mechanical energy that it converts into electrical energy.

Overrunning Clutch Pulley

A pulley design with a freewheel clutch, also known as an overrunning clutch, is common. It is designed to prevent torque from being transferred to the drive shaft when the speed of the driven shaft becomes too high.

Rotor

The rotor is a cylindrical part attached to a metal shaft that is rotated by the generator's drive belt. It is an electromagnet that has six pairs of poles. 

Stator

The stator surrounds the rotating rotor of the generator. A series of three copper windings are attached to the inside of the stator. When the magnetized rotor rotates, alternating current is induced in the stator windings.

Voltage regulator

The voltage regulator closely “monitors” the supply of power from the alternator to the battery. If the engine speed is too high and the voltage rises, the voltage regulator reduces it.

Rectifier (diode bridge)

The alternator in a car produces alternating current, but the battery needs a direct current to charge. The role of the rectifier is to convert the alternating electrical charge into a DC charge that is compatible with the car battery. Rectifiers use a series of diodes to take the alternating current and redirect it in one direction. By restricting the flow of energy in one direction, the rectifier converts the AC charge into a DC charge that charges the battery.

How does a generator work?

The alternator powers most of your car's electronic components while you're driving:

and much more.

The alternator provides DC power to all of them. The alternator is also responsible for charging your car's battery while driving.

The alternator works by turning mechanical energy into electrical energy. When the engine is running, it drives a belt that rests on a pulley attached to the alternator. The pulley turns the rotor shaft of the generator, which rotates a set of magnets inside a coil. These rotating magnets generate alternating current in the stator, which is then sent to the generator's rectifier. The rectifier converts this AC energy into DC energy.

Alternators (ideally) should last for the life of your vehicle. But general wear and tear, overheating, exposure to water, faulty parts, or frayed wires can take your alternator out of service before your car goes to the junkyard.

Possible car alternator failures

Mechanical failures:

Drive belt breakage;

bearing wear;

damage to the alternator housing;

wear of collector rings;

stator corrosion;

wear of carbon brushes.

Electrical failures:

voltage regulator failure:

shorted or open diode bridge;

open or shorted stator or rotor windings.

Warning signs of a faulty alternator

Typical signs of a faulty alternator are often mistaken for battery problems. One of the following problems could be a sign of a broken car alternator:

Separately, we will mention the signs of breakage of the pulley with an overrunning clutch:

Increased noisiness of the generator and belt, especially at high speeds;