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What Is an Alternator and What Does It Do?

The alternator works with the battery to generate power for the electrical components of the vehicle, such as the interior and exterior lights and the instrument panel. The alternator gets its name from the alternating current term (AC). Alternators are typically found near the front of the engine and are driven by a crankshaft, which converts the up-and-down movement of the pistons into 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 the components that rely on crankshaft power. Most of the alternators are mounted using brackets that bolt to a specific point on the engine. One of the brackets is usually a fixed point, while the other is adjustable to tighten the belt.

Alternators produce AC power through electromagnetism formed by the relationship between the stator and the rotor, which we will touch on later in the article. Electricity is channelled into the battery, providing the voltage needed to run the various electrical systems.

Most of the alternators are relatively small and lightweight. Approximately the size of the coconut, the alternators found in most passenger cars and light trucks are constructed using an aluminum exterior housing, as the light metal does not magnetize. This is important because aluminum dissipates the enormous heat generated by the generation of electrical power and because the rotor assembly produces a magnetic field. 

If you inspect the alternator closely, you will find that it has vents on both the front and back sides. Again this helps to dissipate the heat. The drive pulley is attached to the rotor shaft at the front of the alternator. When the engine is running, the crankshaft rotates the drive belt, which in turn rotates the pulley on the rotor shaft. In essence, the alternator transfers the mechanical energy from the engine to the electrical power of the vehicle's accessories.

Cooling is essential to the efficiency of the alternator. An older unit can be easily spotted by the external fan blades found on the rotor shaft behind the pulley. Modern generators have cooling fans inside the aluminum housing. These fans operate in the same way, using the mechanical power of the spinning rotor shaft.

Parts of an Alternator

  • Stator and Rotor: Magnets inside of the alternator that spin to create the alternating current to convert energy into electricity.
  • Diodes: Transforms the alternating current into a direct current for charging the battery and allowing for the current to travel in just one direction; from the alternator to the battery.
  • Voltage Regulator: Prevents power surges by ensuring voltage stays in the appropriate range. 
  • Cooling Fan: Located on the inside or outside of the alternator to protect internal components from overheating by dissipating heat that is generated from the formation of energy.

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