How Do Alternators Work?

The Importance of Your Truck's Alternator

Alternators are an integral part of your semi-truck's electrical system. With an alternator, all of the systems that power your commercial truck will work together to make sure your everything runs properly. Without an alternator, your battery won't charge, and your truck won't start.

To give you a little more knowledge on the subject of alternators, we've decided to do a series of articles on the subject. Read on to learn more about your commercial vehicle's alternator system!

A Brief History of the Alternator

Before the 1960's vehicles used DC dynamo generators that came with commutators. When silicone diodes became cheaper and more available, the alternator gradually replaced the dynamo style generator and made it possible to handle increased loads from larger headlamps, electric wipers, and other accessories.

In some early automobiles, an engine-driven magneto system was used to generate low voltage alternating current that was supplied to trembler coils. These coils provided the high voltage used to generate current.

Modern vehicle alternators were first used in military applications in World War II. These alternators were used to power radio equipment and specialized vehicles. Post war, taxis and emergency vehicles were able to be equipped with optional alternators that were decidedly more efficient than magneto systems.

What is an Alternator?

A type of electric generator, alternators are designed to charge the battery and power the electrical system when your semi-truck's engine is running. Simply put, an alternator is designed to turn mechanical energy into AC electrical energy.

The alternator generates power for your vehicle. As the alternator rotates, it creates a DC voltage that charges the truck's battery. The battery then lets off the large current required to start the engine. Once the vehicle is running, the alternator provides power to all of its electrical systems.

Alternators have three major components, a rotor, a stator, and a rectifier.

1. Rotor: A drive belt pulley system spins the rotor on a shaft while the engine is running. In the center of the rotor is an electromagnet that consists of a length of conductive wire wrapped around a piece of magnetic metal. Voltage is applied to the coil wire which creates a magnetic field around the coiled wire.


2. Stator: The rotor is housed inside of the stator unit. The rotor spins inside the stator without physically touching the sides. On the end of each shaft there is a slip ring. The stator has three separate coil windings with one end of each connected together. The rotor spinning inside the stator will induce voltage across the windings due to a rotating magnetic field.


3. Rectifier: The rectifier is how the alternator produces the DC voltage needed to start a vehicle. Consisting of several diodes that only allow current to flow in one direction, the rectifier converts part of the stator output voltages to a DC voltage.

How Does An Alternator Work?

Dynamos and alternators are designed to produce alternating current at the onset. In a DC generator, AC current is created in the rotating armature which then converts to DC by the commutator and a series of brushes. When a vehicle uses an alternator, the AC current is generated in the stationary stator, and is then converted to DC by the rectifiers or diodes.

The field current moves to the rotor windings by way of slip rings. The low current and slip rings ensure longer life and durability over energy gathered by a DC generator.

The field windings obtain power from the battery through the ignition switch and regulator. A parallel circuit supplies the charge. Once the engine is running and the alternator is generating power, a diode feeds the field current from the alternators main output.

Requiring a voltage regulator, automotive alternators work by modulating the small field current to produce constant voltage at the battery terminals. Modern designs do away with the voltage regulator and make it a function of the engine control unit (ECU).

What Are The Symptoms Of A Bad Alternator?

Here are a few signs your semi-truck's alternator may need to be replaced.

1. Dim or overly bright lights: When an alternator starts failing, the output is typically inconsistent. If your lights are too bright, too dim, or flickering, it's a sign that your alternator is about to fail.


2. Dead battery: A bad alternator won't charge the battery while your engine is running, causing the charge to deplete faster than usual. One way to test whether the issue is related to the battery, or the alternator is to jumpstart the car.


3. Slow or malfunctioning accessories: If your alternator is failing, it won't supply sufficient power to the truck's accessories. For instance, if your windows are moving slower than what is typical, it could be a sign of an alternator that's on its last leg.

Shop Alternators Today!

If you are looking for a replacement alternator for your commercial truck, then you've come to the right place. With a multitude of alternator parts for you to choose from, you won't have any issue finding the exact part you've been looking for. Shop alternators today!