alternator broThough less often discussed than the car battery, the alternator is just as essential for creating and storing electrical power to start your engine and maintain function among all your car’s interior and exterior electrical components.

Alternators are small, lightweight devices usually installed near your car’s engine. They are roughly the size of a coconut and constructed out of aluminum because it’s a lightweight metal that doesn’t magnetize and allows for the easy dissipation of heat. These aspects of aluminum are crucial to the functionality of the alternator because it must endure tremendous heat generated by the electrical power that it produces. Alternators also have vents on their front and back sides and interior cooling fans to further aid with heat dissipation.

On the front of every alternator is a rotor shaft that is in turn connected to a drive pulley. When the engine is running, the crankshaft turns the drive belt, spinning the pulley on the rotor shaft. The alternator then transfers this kinetic movement or mechanical energy into electrical power for the car’s lights and whatnot.

On the back side of the alternator are several terminals that act as connecting points in a larger electrical circuit. There’s an S terminal that senses the voltage of the battery, the IG terminal that is basically an ignition switch for turning the voltage regulator on, the L terminal that closes the circuit to the warning lamp that comes on when the battery is running out of juice, the B terminal that connects to the battery and acts as the main alternator output terminal, and the F terminal that acts as a full-field bypass terminal for the purposes of the regulator.

Voltage RegulatorWithin the alternator lies a variety of electrical components including the voltage regulator, which distributes the power the alternator creates and controls the output of power to the battery. Alongside the voltage regulator can be found the rectifier bridge, which converts the power, while the brushes and slip rings help to conduct current to the rotor field winding.

If you really get to the center of the alternator you’ll find a large cylinder with a series of triangular finger poles lining its circumference. This makes up the rotor. The finger pole pieces are situated around coil wires called field windings that are repeatedly wrapped around an iron core on the rotor shaft.

Because the triangular finger poles are staggered around the cylinder’s circumference, the north and south magnetic poles alternate as they surround the wire rotor field windings. This creates a magnetic field that in turn induces voltage into the stator that encompasses the entire outside of the rotor without directly touching it. The stator harnesses all the electricity created by the spinning rotor’s magnetic field.

Alternators are so-named because they generate alternating current (AC) as opposed to direct current (DC). AC power generates higher voltage more efficiently, but because car batteries produce DC power, it’s necessary to use diodes to convert the alternator’s electrical power into useful energy for the battery.

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