A vehicle’s electrical system depends on a constant flow of power to keep its many devices running properly. The alternator serves as its primary source of electricity. Does the alternator also charge the battery? Yes, it does. How does it do this?
A car alternator relies on magnetism to create electricity. Moving a magnetic field past a wire coil creates an electrical current. An alternator has several magnets and coils of wire inside. When the engine spins the alternator, a magnetic field inside will move and pass through wire coils, creating alternating current (AC).
The alternator taps into the engine’s mechanical energy through the serpentine belt and transforms it into electrical energy. This charges the vehicle’s battery. The battery powers devices like the starter motor, headlights, powertrain control module, and other electronics.
To better understand how the alternator creates AC, let’s discuss its parts and their roles:
The pulley is the component outside the alternator that’s driven by the serpentine belt, which is connected to the engine. With this connection, the alternator draws mechanical energy from the engine.
The pulley spins the rotor, which is like a cylindrical spool of wire around a metal core. This spool of wire is the alternator’s electromagnet. Electromagnets produce more powerful magnetic fields than a regular magnet. The brushes slide on the rotor’s slip rings and feed current into the rotor coil.
Outside the spool of wire are triangular or claw-shaped poles that alter the magnetic field created by the rotor. It alternates the north and south poles in a shape that corresponds to the stator’s arrangement. The claw poles are only spinning at a distance of .040 inch from the stator core.
The stator is a stationary part located around the rotor. The stator consists of coil wires. Three total wires wind around the stator in a specific manner that corresponds to the magnetic field made by the rotor. When the rotor spins, these three wires generate AC.
Most electronics need direct current (DC). The rectifier transforms the alternator’s AC into DC using six diodes, three positive and three negative.
The flow of electricity in an alternating current switches direction at a certain frequency. A diode keeps electricity flowing in only one direction, albeit the flow of electricity fluctuates on and off. A pair of diodes keeps the voltage flow consistent.
Because the stator is composed of three wire coils, the rectifier needs six diodes. The diodes are configured in a way that rectifies both half cycles of the stator’s AC voltage, resulting in a direct current that fluctuates in voltage.
Vehicle electronics require a constant voltage, otherwise you risk damaging the battery and other electronics. A voltage regulator adjusts the rotor’s magnetic field and power output, ensuring they’re smooth and constant. It feeds current to the rotor slip rings through the brushes using a pulsed current that varies to maintain 14.5 volts at the battery.
An alternator is similar to a generator in that both produce electricity using a stator and rotor. That said, an alternator can only produce an alternating current, while a generator can produce either AC or DC, making it more versatile.
An alternator can last anywhere between 80,000 and 150,000 miles.
A faulty alternator typically causes electrical system symptoms like difficulty starting. The most common components that can cause an alternator to fail include the bearings. The carbon brushes that conduct electricity to the rotor can also wear out. These brushes allow the electricity to reach the rotor, activating the electromagnet.
Alternators are quite reliable and can often last the vehicle’s lifespan. That said, there are ways to maximize their lifespan.
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