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

If you’ve heard the term “alternator” before, you probably know that it’s an essential part of your vehicle. But what is an alternator? In reality, it’s the car alternator that produces the majority of your vehicle’s electricity, your battery is mainly just used to start your vehicle and provide power when the engine isn’t running.

The alternator is a critical component of a car’s charging system, so it’s helpful to understand 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 bigger problems.

What is an alternator?

An alternator is an electrical generator that converts mechanical energy to electrical energy so that you can charge and replenish the battery in your engine and other electrical components in a car.

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.

What Does An Alternator Do?

Since the engine only provides mechanical energy, it does not generate electricity. So, we need a power source that produces electricity to power all the electrical accessories in your car. And this is where the alternator comes into play. 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 serious problems. The voltage regulator sends the current from the alternator to the battery and controls the amount of energy to provide a constant current flow to the battery.

Components of an alternator

As you can imagine there are differences in alternator construction and therefore there are different numbers of components depending on the supplier.

Alternators consist of three main components: rotor, stator, and rectifier. There are more components and we will come back to them throughout our discussion.

 alternator in Car

1. Rotor And Stator

The rotor and stator are the electricity-producing components of an alternator. The rotor, a cylindrical piece surrounded in magnets, spins inside of the stator, which holds a fixed set of conductive copper wiring. The movement of the magnets over the wiring is what ultimately creates electricity.

2. Rectifier

The rectifier is the assembly in any alternator that converts the AC (alternating current) that the alternators produce into DC (direct current) that is used by the battery and vehicle’s electrical system.

The rectifier converts AC to DC using diodes, which are semiconductors that are one-way gates. Diodes only allow current to flow in one direction, so alternating current becomes a direct current.

3. Brushes And Slip Rings

The rectifier converts the power, while the brushes and slip rings help conduct current to the rotor field winding or wire field.

4. Diode Trio

Exactly like the rectifier, the diode trio input terminals are connected to each stator voltage output. The output terminal of each diode is connected together. The diode trio converts part of the stator output voltages to a DC voltage.

5. Voltage Regulator

The diode trio output is fed to the voltage regulator and becomes the energizing voltage for the rotor electromagnet once the engine is started and running. If you remember, the faster the rotor spins, the more voltage is induced in the stator.

The voltage regulator is an electronic device that acts like an alternator voltage monitor as it keeps an eye on the battery voltage. The purpose of the voltage regulator is to adjust the excitation voltage of the electromagnet so that the stator output voltages are kept relatively constant regardless of the rotational speed of the rotor.

6. Bearing

Needle bearings are alternator components that make it possible for the rotor to spin inside the stator. These components enable the alternator to generate electricity and sustain a battery charge.

Faulty bearings may not allow the rotor to spin, and the bearings may emit squeaking or grinding sounds. This can ultimately result in alternator failure and a drained battery.

6. Pulley

A drive pulley is attached to the rotor shaft on the front of the alternator. When the engine is running, the crankshaft turns the drive belt, which in turn spins the pulley on the rotor shaft.

In essence, the alternator transfers the mechanical energy from the engine into electrical power for the car’s accessories.

How do Alternators work?

You may think that the battery powers the electricity 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.

The alternator works by turning mechanical energy into electrical energy. As the alternator rotates, it creates a DC voltage primarily to charge the vehicle battery. The battery provides the huge current required to start the vehicle engine.

Once the vehicle is running, the alternator assists by providing power to run the vehicle’s electrical systems.

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 as 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 Produces Electricity?

The process of generating electricity begins with the engine. On most modern vehicles, alternators are driven from the engine’s crankshaft via a serpentine belt, although older vehicles may have a separate pulley leading from the crankshaft to the alternator.

The movement of the belt – the mechanical energy – spins the alternator rotor at high speed in the stator.

Electricity is generated when the rotor turns. The magnets surrounding the rotor are intentionally placed so that when they pass the copper wires in the stator, a magnetic field is created.

This magnetic field, in turn, produces a voltage that is captured by the stator. This power then reaches the voltage regulator, which distributes power to the vehicle and manages the amount of voltage the battery receives.

How Does The Alternator Charge The Battery?

Before the battery can use the energy coming from the alternator, it must be converted into 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), while alternators produce alternating current (AC), which occasionally flows in reverse.

Before the current for the battery goes to the voltage regulator, it goes through a diode rectifier to convert it to DC. After the conversion, the battery can use the electricity for recharge. You can’t recharge your battery with a faulty alternator, look at these 7 warning signs of a bad alternator.

How Long Does An Alternator Last?

You may also be wondering about the alternator lifespan. The average lifespan for most alternators ranges from 80,000 and 150,000 miles. Usually, an alternator lasts about seven years. There are a few factors that can affect your alternator lifespan on the roads of Blasdell.

  • Alternator quality
  • Driving conditions
  • Power drain on the alternator

How much does it cost to replace an alternator? Different alternators are required for different vehicles. So, the price depends on the make/year and model. But before replacing your alternator, you need to check if it is working or not. If you don’t know how to do this, read our guide How to test an alternator?