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Car Alternator: What Does an Alternator Do in a Car?

  • Author :
  • TATA AIG Team
  • Published on :
  • 07/05/2024

Have you ever thought about how your car's headlight functions? Have you ever searched the internet to check the mechanism of electronic components? Well, if you have searched a bit, you must have come across a term called the charging alternator.

But what is the use of an alternator in a car, its key components, and related aspects? This article will discuss all of them.

What is Alternator?

A car alternator is a crucial component of your vehicle’s electrical system. It serves as a generator of electric power to ensure that your car’s battery remains charged and supplies additional electricity to various electrical systems.

The alternator is a part attached to the engine and is turned by a belt called a serpentine belt. It's usually found at the front of the engine, near the radiator.

When your vehicle engine is running, the car alternator function kicks in. It converts mechanical energy (generated by the engine’s rotation) into electrical energy. This energy helps to charge the battery and power all the electrical components in your vehicle.

Car Alternators — How Does it Work?

To understand how the alternator in an engine works, you must understand its components and mechanism.

1. Pulley

The pulley is a small wheel that connects to the alternator via a drive belt. This belt also links to the engine's crankshaft. When the engine runs, it turns the crankshaft and the belt, which rotates the pulley.

As the pulley spins, it activates the alternator, which converts the engine's mechanical energy into electrical energy. This electricity is used to power the vehicle's electrical systems and to charge the car battery.

Modern vehicles often use an overrunning alternator pulley (OAP). OAP includes a clutch mechanism that allows the alternator to spin freely when the engine RPM drops. This design helps reduce wear on the drive belt and can improve fuel efficiency by minimising the energy required to drive the alternator under certain conditions.

2. Rotor

The rotor's core is iron. Copper wire is wound around it to form the field windings. When the ignition is on, these windings are energised, magnetising the iron core.

The rotor's shaft is supported by bearings that allow it to spin smoothly at high speeds. At each end of the rotor shaft, slip rings are connected to the field windings. Brushes, which are stationary electrical contacts, rub against these slip rings to supply current to the field windings.

3. Stator

The stator produces the initial DC voltage required to charge the vehicle battery. It consists of three stationary coils wound around an iron core. These coils remain fixed within the alternator casing and do not rotate. As the engine runs, the alternator pulley drives the rotor, which spins within the stator windings.

As the rotor rotates, this magnetic field sweeps through the stator windings. This movement induces an electrical current in the stator windings through electromagnetic induction.

The stator windings are spaced 120 degrees apart, creating three separate sets or ‘phases’ of output voltages.

4. Voltage Regulator

A voltage regulator ensures the electrical system receives a consistent and safe voltage level. It monitors and adjusts the alternator's output to prevent overcharging or undercharging the battery and safeguard the vehicle's electrical components.

These regulators use semiconductor devices to manage the alternator's output. They function by comparing the alternator's output voltage to a set reference value, typically around 14 volts. If the output exceeds this reference, the regulator reduces the alternator's field current, thus lowering the voltage. Conversely, if the voltage falls below the reference, the field current increases to boost the voltage to the desired level.

5. Rectifier

The rectifier has a series of diodes, which are semiconductor instruments that allow current to flow in only one direction. These diodes are arranged in a bridge configuration to convert the AC produced by the alternator's stator efficiently.

The rectifier not only converts this AC into DC but also works in conjunction with a voltage regulator to ensure that the output remains within a safe range for the car's electrical system.

Warning Signs of Bad Alternator

  • A modern car has a dashboard warning light that often resembles a battery symbol or reads "ALT" or "GEN," indicating issues with the alternator or charging system.

  • The alternator provides power to the headlights. If it fails, you may notice the headlights dimming or flickering, especially when the engine's RPM changes.

  • Although various reasons can cause a weak or dead battery, a failing alternator is a common culprit. The car alternator's purpose is to recharge the battery while the engine runs.

  • Slow-operating or malfunctioning electrical accessories, such as power windows or seat heaters, can be signs that an alternator is working poorly and not supplying enough power.

  • A malfunctioning alternator can produce unusual noises, such as whining or grinding due to bearing failure or other internal issues.

  • Overheating alternator components or drive belts can emit a burning smell, indicating a potential alternator failure.

  • The alternator ignites the spark plugs that flare up the fuel in your engine. If it fails, you might experience engine stalling or trouble starting the car.

  • If you find yourself replacing the battery more often than usual, it could be a sign that the alternator is not charging it.


  • Check for loose or worn drive belts that might affect the alternator's performance. Also, look for any physical damage to the alternator itself.

  • You can check the alternator's voltage output using a voltmeter. A healthy alternator should produce 13.5 to 14.5 volts.

What Causes Alternator Failure

  • Alternators typically last 5 to 8 years. Over time, the internal units can wear out, leading to failure.

  • Frequent and heavy use can strain the alternator, causing it to fail prematurely.

  • Excessive heat can damage the alternator's internal parts, reducing its efficiency and leading to failure.

  • A bad battery can overwork the alternator as it tries to compensate for the lack of charge, which can cause the alternator to fail.

  • A belt drives the alternator. If this belt is loose, worn, or breaks, the alternator won't function.

  • Using too many electrical accessories simultaneously can overload the alternator, leading to failure.

  • Neglecting regular maintenance can lead to alternator failure. This includes not checking belts and electrical connections.

  • Oil can leak into the alternator, causing its components to malfunction or fail.

  • Damaged or corroded wires can prevent the alternator from charging correctly.

  • Diodes within the alternator can fail, preventing the alternator from charging the battery.

  • Modern vehicles rely on computers to control the alternator working. A computer malfunction can affect the alternator's performance.

  • Fuses protect the alternator's circuits. If a fuse blows, the alternator may stop charging.

  • Physical damage from accidents or debris can cause immediate alternator failure.

  • Sometimes, alternators fail due to defects in the manufacturing process.

  • Incorrectly jump-starting the vehicle can damage the alternator.

  • Alternators can fail due to exposure to water, dirt, and other environmental contaminants.


The alternator is a key component in a car. It is responsible for the smooth functioning of your four-wheeler.

Just like an alternator, your car also needs four-wheeler insurance with zero dep insurance. Car insurance protects you financially from any mishap on the road. A zero depreciation cover from Tata AIG helps cover the depreciation cost of your vehicle and its components during claim settlement.

If you already have this plan, then be attentive to the car insurance renewal online date, as this coverage is not only important but also mandatory by law.


What is a car alternator?

An alternator is a component of the car’s charging system that generates electrical power for the battery and other electrical systems.

How does an alternator work?

It converts mechanical energy from the engine into electrical energy, supplying power to the battery and the car’s electrical components.

What happens when an alternator fails?

If an alternator fails, the car may run on battery power temporarily but will stall once the battery is depleted.

How do I know if my alternator is failing?

Some of the common symptoms of failing alternators include dimming lights, a dead battery, or a battery warning light on the dashboard.

How long does an alternator last?

Alternators typically last 5-8 years, but this can vary based on driving conditions and vehicle maintenance.

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