the alternator

An automotive charging system is made up of three main components: the battery, the voltage regulator, and an alternator. The alternator works with the battery to generate power for a vehicle’s electrical components, such as the interior and exterior lights and the instrument panel. An alternator gets its name from the term alternating current (AC).

Alternators are usually located near the front of the engine and are driven by the crankshaft, which converts the up and down motion of the pistons into a circular motion. Some early model vehicles used a separate drive belt from the crankshaft pulley to the alternator pulley, but most cars today have a serpentine belt, or a belt that drives all of the components that depend on the drive. crankshaft power. Most alternators are mounted with brackets that bolt to a specific point on the engine. One of the mounts is usually a fixed point, while the other is adjustable to tension the drive belt.

Alternators produce AC power through electromagnetism formed through the stator and rotor relationship which we will cover later in this article. Electricity is channeled into the battery, providing voltage to run the various electrical systems. Before we learn more about the mechanics of the alternator and how it generates electricity, let’s look at the various parts of an alternator in the next section.

alternator components

For the most part, alternators are relatively small and lightweight. About the size of a coconut, the alternators found in most passenger cars and light trucks are constructed with an aluminum outer casing, since lightweight metal does not become magnetized. This is important as the aluminum dissipates the tremendous heat generated in producing electrical power and as the rotor assembly produces a magnetic field.

If you inspect an alternator closely, you’ll find that it has vents on both the front and rear. Again, this helps in heat dissipation. A drive pulley is attached to the rotor shaft at the front of the alternator. When the engine is running, the crankshaft turns the drive belt, which in turn turns the pulley on the rotor shaft. In essence, the alternator transfers mechanical energy from the engine to electrical energy for the car’s accessories.

On the back of the alternator you will find several terminals (or connection points in an electrical circuit). Let’s take a look at those:

S terminal: detects battery voltage

IG Terminal – Power switch that turns on the voltage regulator

Terminal L – Closes the circuit to the warning lamp

Terminal B – Main alternator output terminal (connected to battery)

Terminal F – Full field bypass for regulator

Cooling is essential to the efficiency of an alternator. It’s easy to spot an older unit by the external fan blades that sit on the rotor shaft behind the pulley. Modern alternators have cooling fans inside the aluminum casing. These fans work in the same way, using mechanical energy from the rotating rotor shaft.

When we started to disassemble the alternator, we found the diode rectifier (or bridge rectifier), the voltage regulator, the slip rings and the brushes. The regulator distributes the power that the alternator creates and controls the power output to the battery. The bridge rectifier converts power, as we’ll see in the next section, while the brushes and slip rings help conduct current to the rotor field winding, or field wire. Now let’s open the coconut.

Opening the alternator reveals a large cylinder with triangular poles around the circumference. This is the rotor. A basic alternator is made up of a series of alternating finger pole pieces placed around coil wires called field windings that wrap around an iron core on the rotor shaft. Since we know that the pulley is attached to the shaft, we can now visualize how the rotor rotates inside the stator. The rotor assembly fits inside the stator with enough clearance or clearance between the two so that the rotor can rotate at high speeds without hitting the stator wall. At each end of the shaft is a brush and slip ring.

As we briefly mentioned, alternators generate power through magnetism. The poles of the triangular fingers attached around the circumference of the rotor are staggered, so the north and south poles alternate as they encircle the wire rotor field windings. This alternating pattern creates the magnetic field which in turn induces voltage in the stator. Think of the stator as the receiver’s glove, as it harnesses all the power created by the spinning rotor.

All of these components work together to give us the power we need to run our vehicles. Tesla captured this electrical power and used it to light cities, but we only need enough volts to power our stereo, lights, windows, and locks. Let’s take a look at how the alternator produces that power in the next section.

Understanding Alternator Power Output

In the early days, cars used generators instead of alternators to power the vehicle’s electrical system and charge the battery. That is no longer the case. As automotive technology evolved, so did the need for more power. Generators produce direct current, which travels in one direction, unlike alternating current for electricity in our homes, which periodically reverses directions. As Tesla demonstrated in 1887, alternating current became more attractive by generating higher voltage more efficiently, something necessary in contemporary automobiles. But because batteries can’t use AC power as they produce DC power. As a result, the alternator’s power output is fed through diodes, which convert AC power to DC power.

The rotor and stator are the two components that generate power. As the engine rotates the alternator pulley, the rotor passes through three stationary stator windings, or coils of wire, that surround a fixed iron core that forms the stator. This is known as triphasic current. The coil windings are evenly spaced at 120 degree intervals around the iron axis. The alternating magnetic field of the rotor produces a subsequent alternating current in the stator. This AC current is fed through the stator leads to a set of connecting diodes. Two diodes are connected to each stator lead to regulate the current. Diodes are essentially used to block and direct current. Since batteries need direct current, the diodes become a one-way valve that will only allow current to pass in the same direction.

Three-phase alternators have three sets of windings; they are more efficient than a single phase alternator, which produces a single phase alternating current. When working properly, the three windings produce three currents that make up the three phases. The sum of all three produces the total AC output of the stator.

The two basic stator winding designs are delta wound and wye style. Delta wounds are easily identifiable by their shape, as they are triangular. These windings allow for high current flow at lower RPMs. Wye windings resemble the flux capacitor seen in “Back to the Future”. These windings are ideal for diesel engines as they produce a higher voltage than delta stators at even lower RPMs.

After the AC/DC conversion, the resulting voltage is ready for use in the battery. Too much or too little voltage can damage the battery as well as other electrical components. To ensure the correct amount, a voltage regulator determines when and how much voltage is needed on the battery. One of two types of regulators is found in most alternators: the grounded regulator works by controlling the amount of negative or battery ground entering the rotor winding, while a field type Grounded works the other way around, by controlling the amount of grounding on the battery. positive. Neither is an advantage over the other.

With so many components working to create the vital electricity for our vehicles, it’s safe to say that the alternator is a crucial component under the hood. But like many parts of our cars, they fail. The next section will give you an idea of ​​how to determine if you are about to be stranded and what you can do if you need to replace your alternator.