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What is an alternator and how it works

  • 2020-05-15 10:30:14
What is an alternator?

 

You can spot the alternator (with the tag hanging off it) in the foreground of this shot of a stock car engine. You can also see the serpentine belt looped around it.

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

Alternators are typically found near the front of the engine and are driven by the crankshaft, which converts the pistons' up-and-down movement into circular movement. (To learn more about the basic parts of car engines, read How Car Engines Work.) 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 one belt that drives all components that rely on crankshaft power. Most 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 drive belt.

Alternators produce AC power through electromagnetism formed through the stator and rotor relationship that we'll touch on later in the article. The 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, how it works, symptoms, testing, problems, replacement

An alternator is a generator of electric power in a car and is a major component of the vehicle's charging system. All cars with an internal combustion engine except for some hybrids have an alternator. When an engine is running, the alternator charges the battery and supplies additional electric power for the vehicle electrical systems.


Symptoms of alternator problemsAn alternator is bolted to the engine and is driven by a serpentine belt (drive belt).
An alternator is a maintenance-free unit. In some cars, it can last for up to 10-15 years without any repairs. If an alternator fails, the car may still run for a short time on battery power. However, the engine will stall as soon as the battery charge is depleted. Replacing an alternator with a new OEM part is expensive, but there are alternatives. Read more below.

The most common symptom of a problem with your vehicle's charging system is a battery-shaped warning light (in the photo) or the "CHARGE" icon that comes on while driving. Normally this warning light should come on when you turn the ignition, but should disappears as soon as the engine is started. If it stays on, there is a problem with your charging system.


The charging system warning light doesn't point directly to a failed alternator, although alternator problems are very common. Your mechanic will need to do further testing to pinpoint the defective part.
Another symptom of a weak charging system is when the dash lights and headlights dim at idle, but become brighter when the engine is revved. This problem could be caused not only by a weak alternator, but also by a failing battery, poor connection at the battery terminals or a loose serpentine belt. A whining/buzzing noise coming from the alternator is another symptom of alternator troubles. In some cars, it could be caused by a noisy alternator bearing. In some Jeep/Chrysler vehicles a bad alternator decoupler pulley could cause the same noise.


Cut-away of an alternator, showing the claw-pole construction; two of the wedge-shaped field poles, alternating N and S, are visible in the centre and the stationary armature winding is visible at the top and bottom of the opening. The belt and pulley at the right hand end drives the alternator.

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