What is An Alternator In a Car And How Does It Work?


As the engine provides only mechanical energy, it does not generate electricity. So, we need a power source which produces electricity to power all the electrical accessories in your car. And that’s where the alternator comes in. The vehicle’s charging system consists of a car battery, a voltage regulator, and an alternator.

Your alternator converts mechanical energy to electrical energy with an alternating current. The stator and rotor inside the alternator work as magnets and rotate to generate the alternating current. Then the alternating current (AC) is transformed into a direct current (DC) that charges the battery.

Both overcharging and undercharging your battery can be a serious issue. The voltage regulator sends the power from the alternator to the battery and controls the amount of energy to provide a steady flow of power to the battery.

The alternator is a critical component of a car’s charging system, so it’s helpful to understand how it operates in case you have to deal with your car not starting.

What is an alternator?

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.

Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually, the term refers to small rotating machines driven by automotive and other internal combustion engines.

An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators

What Does An Alternator Do?

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 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) power. 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 around a coil. These spinning magnets generate alternating current (AC) around the coil, which is then channeled to the alternator’s rectifier. The rectifier converts that AC power into DC power, which activates your car’s electrical systems.

Alternators 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.

Components of an alternator

The components of an alternator are geared toward providing the right type and right amount of power to the vehicle. Your car’s charging system contains many parts, but these are the main components and their functions:

 alternator in Car
  • Regulator: The voltage regulator is a part that controls the amount of power supply from the alternator to the battery. It controls the charging process as it’s designed with various functions and work depending on their applications.
  • Rectifier: The rectifier is used to convert alternating current (DC) produce to direct current (DC) during the charging process.
  • Rotor: The rotor is a part that spins inside the alternator and rotates the pulley and drives belt system along. It acts as a spinning electromagnet.
  • Slip Rings: The slip rings are a means of obtaining direct current and offering power to the rotor.
  • Slip Ring End Bearing: Alternator bearings are designed to support the rotation of the rotor shaft.
  • Stator: A stator is an iron ring that contains several coils of wire wound around it. the part of the stator serves as the body of the alternator, creating an electrical current when a magnetic field is made.
  • Drive End Bearing: The drive end bearings also help to support the rotation of the rotor shaft.
  • Pulley: The pulley is a part connected to the rotor shaft and the drive belt system. Though the rotation is obtained from the engine transferred by the drive belt to the pulley. The rotation causes the charging process.

How do Alternators work?

You may think that the battery powers the electrics in your car, but that’s not the case. The battery provides the electricity needed for the starter motor to start the car.

When the car is running, the alternator generates energy to feed the electrical system and charge the battery. The alternator used to be called a generator, and it works in a similar way. In this case, a car’s internal combustion engine spins pulleys under the bonnet, which turns the pulley on the alternator and creates energy.

An alternator works together with the battery to supply power for the electrical components of the vehicle. The output of an alternator is direct current (DC). When the alternator pulley is rotated, alternating current (AC) passes through a magnetic field and an electrical current is generated. This is then converted to DC via the rectifier.

Advancements in technology have meant that alternators have changed vastly in the last 50 years. Originally, alternators were only used to generate a current that was controlled by an external regulator.

The introduction of a built-in regulator, in the 1990s, used the warning light to excite the alternator and start the charging process. Many modern vehicles adopted a load request type charging system with the introduction of smart charge systems and CANBUS systems which are now widely being used.

These systems are controlled by the vehicle Engine Control Unit (ECU). As the vehicle demands more load the ECU sends a signal to the alternator requesting it to start charging. The alternator has to cope with varying electrical loads and adjust its charge rate accordingly.

These days it is easy for these types of alternators to be misdiagnosed faulty if a charging fault is experienced on the vehicle but more often than not, no fault is found with the alternator.

Wiring an alternator diagram

How does the alternator charge the battery?

Before the battery can use the power coming from the alternator, it needs to be converted to a format that the battery can use. That’s because electricity can flow in different currents or directions. Car batteries operate on one-way direct current (DC) electricity, while alternators output alternating current (AC) electricity, which occasionally flows in reverse.

So prior to going to the voltage regulator, a power intended for the battery goes through a diode rectifier to turn into DC. After the conversion, the battery can use the power to recharge.

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