How does an Alternator Work | How an Alternator Works in a Car | Course Materials

What is an alternator?
First of all, let’s discuss what an alternator is and its purpose. By definition, an alternator is a device that converts mechanical energy into AC electrical energy.

In a vehicle, the engine turns a drive belt that rotates a pulley attached to the alternator. But wait a minute… Doesn’t a vehicle require DC voltage? Indeed, it does… but we’ll get to that later.

The alternator actually generates power for the vehicle. 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.

Alternator major components
As you can imagine, there are differences in alternator construction and as such, there are a different number of components depending on the vendor.

Alternators have three major components and they are the Rotor, stator, and rectifier. There are more components and we’ll get to those as we progress through our discussion

1. Alternator rotor
Let’s start with the rotor. A drive belt pulley system spins the rotor on a shaft while the vehicle engine is running.

At the heart of the rotor is an electromagnet often referred to as field windings. So, what’s an electromagnet? An electromagnet consists of a length of conductive wire wrapped around a piece of magnetic metal.

Voltage is applied to the coiled wire creating a current in it. This creates a magnetic field around the coiled wire. Much like a permanent magnet, there is a North and a South pole.

2. Alternator stator
The rotor fits inside the Stator. The stator is a stationary part of the alternator. The rotor spins inside the stator without physically touching it. On each end of the shaft sits a brush and a slip ring. We’ll talk about those later.

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 current which 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.