The battery is an electrical storage device whose primary purpose is to provide power to start your car’s engine.
It also enables you to run accessories with the engine off and provides reserve electrical power should your charging system be weak. Every time you start your engine the battery sends power to the starter motor which turns your engine over until the spark plugs spark and the fuel begins to combust. This process depletes your battery’s energy and continuing to attempt to start your car will eventually result in a dead battery.
Enter the alternator, whose purpose is to generate electricity to recharge your battery.
So why call it an alternator when it really is a generator? Because it generates alternating current. Up until the early 1960’s most cars used a direct current generator. It was found that an alternator, which generates alternating current (which is converted to direct current) was far more efficient, reliable and used fewer parts.
Your car contains many electricity hungry components such as lights, ignition system, fuel injection, windshield wipers, heater fans and on and on. All of these require feeding which is done with the alternator; otherwise your battery would go dead.
Let’s look at the inner workings of the battery and the alternator. As mentioned, the battery stores electricity and how it does this is quite remarkable. Car batteries are of the lead-acid type which use lead plates and sulfuric acid. The chemical reaction between these two components creates electricity.
As the battery discharges, the sulfuric acid breaks up with the sulfur attaching to the lead plates, leaving water behind. As the battery is recharged the sulfur leaves the plates and becomes reunited with the water to once again form sulfuric acid. This dance goes on until the battery becomes old and weak.
While batteries store electricity, alternators create it by spinning a large magnet past a coil of wires. The alternator operates as soon as your engine starts. Inside the alternator are components to convert the alternating current into direct current which is compatible with your car’s electrical system. The voltage output of the alternator would soon overload the electrical system if it wasn’t for the voltage regulator which keeps the output down to about 14 volts.
What maintenance do these two items require? The alternator and most batteries require no maintenance, however some batteries can be topped up with water if the level runs low. The alternator is belt driven so the belt needs to be inspected occasionally and replaced if worn. Battery terminals may become corroded and these should be inspected and cleaned if dirty. Otherwise it is a trouble free system.