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How Does a Car Charging System Work?

Car Charging System

Your car has a battery, but if it were solely responsible for powering the ignition along with all the accessories, it would go dead in a matter of minutes. To help with electrical duties, your car is also equipped with a charging system that not only increases power for everything that’s needed, but also helps recharge the battery. So what are the basic parts of this system, and how do they work? Let’s take a look at these vital power parts under your hood.


At the root of it all is the vehicle’s battery. Twelve-volt electricity is needed not only to get the car started, but also keep it running and to power things like the headlights. In modern cars, where the ignition is electronically produced, the battery is also the primary source of the electricity that starts the ignition process. The ignition spark starts its journey from the battery and runs through the coil(s), where it’s then sent to each spark plug to ignite the fuel and make the engine run.

Alternative StateCars alternator installed

AC power is created when magnets inside the alternator move past a coil of wire. As each pole of the magnet passes by, it moves electrons within the wire in one direction and then the opposite way, creating a flow of electrical current that moves back and forth. This is important in originating electricity, because the amperage is high enough to produce an ignition spark and still have enough power left over for everything else, such as your radio, fan, headlights and much more. In your vehicle’s engine, the alternator is propelled by a serpentine belt attached to the crank of the engine. As the engine spins, it turns the alternator, generating AC current. Before electricity leaves the alternator, however, it’s converted to DC via a circuit of diodes known as a “rectifier.” The rectifier converts AC current into DC by allowing electricity to flow in only one direction.

Voltage Regulator

Once DC current leaves the alternator assembly, it’s distributed and kept in check by a component called a “voltage regulator.” The regulator ensures the proper distribution of current between the car’s electrical needs and recharging the battery. When the current drops below 13.5 volts, the regulator applies current to the battery to charge it. When voltage rises above 14.5 volts, the regulator moves the current to the engine and accessories. This not only ensures the car operates properly, but also that the battery stays charged and is able to power the vehicle.

With just a few basic parts, a car’s ignition and charging system seems very simple, but its role is vital to your car’s functioning. Simple 12-volt DC current is converted to high-power AC, and then back to DC to be used for everything from ignition to headlights and much more.

Check out all the electrical system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on your car charging system, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.

Erich Reichert View All

Erich Reichert has been an editor and on-air personality in the radio control car hobby for 12 years. A certified car nut since birth, he has written for internationally published titles such as RC Car Action, RC Driver and Xtreme RC Cars, as well as Stuff Magazine, Road and Track and Super Street. He's covered everything from product reviews and tech articles to high-profile lifestyle pieces and celebrity interviews. Erich found his passion for writing after a successful career as an art director, working with brands such as Pepsico, NASCAR, MTV, Nintendo, WWE, Cannondale Bicycles and HBO. He's also a father, an avid hockey fan and an FIA race license holder who enjoys hiking, playing drums and movies.

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