What is an Alternator and How Do They Work?

Alternators are important components of automotive engines that provide electrical power for spark plugs, recharge the battery, and run accessories like the stereo, windows, and climate control system.

Motor vehicles as we know them were not conceived and invented in one piece. Rather, the basic components of the engine, drivetrain, and construction have evolved to meet the needs of society, and safety concerns, and to use the best materials available.

The first engine was made in the 1600s and was powered by steam. Frenchman Nicholas-Joseph Cugnot imagined a new use for the contraption in 1769 when he attached a steam engine to a land-based vehicle that’s considered the first powered vehicle. The first use of the two technologies was for steam trains, as automobiles didn’t develop significantly for another 100 years. In the 1880s Carl Benz, a German engineer, produced the first gasoline-powered internal combustion engines that drove adapted wagons, or “horseless carriages.” In America, inventor Ransom Olds developed the prototype automobile in 1901 and conceived an assembly line to mass produce it for consumers.

As more vehicles were produced and possessed by average people, adaptations multiplied, and trucks were created, enclosed cabins made them more comfortable, and lights (electric, not gas-powered) were added for nighttime driving. Steering and breaking systems improved as well.

Why Did Cars Switch From Generators to Alternators?

In the mid-1800s, electric motors were being developed at the same time as internal combustion (liquid fuel) engines, and both could be found in automobiles. Batteries were not yet a common tool, so engines were cranked with a large handle (rather than starting with a key).

Electricity was being introduced for many purposes, including running the London subway, lighting warehouses, and adapting human-powered millwork like weaving to machine-powered. It wouldn’t be long before internal combustion engines adapted portions of electric engines. Batteries became common parts of automobiles in the 1920s.

Early vehicles had generators to keep their batteries charged using direct current (DC) which flows through wires in one direction. But inventor Nikola Tesla had experimented extensively with electricity and coils, leading to the development of the alternator, a lighter replacement for the generator that created alternating current (AC) which flows through wires in both directions.

What Does an Alternator Do?

An alternator converts the mechanical power of a running engine into electricity to recharge the vehicle’s battery. Alternators also send electricity to spark plugs, which enable the engine to continue running (spark plugs cause gasoline to ignite, propelling the car). The battery uses much of its power to run the starter motor, which cranks the engine into motion. The battery also powers the electric components of the vehicle, including the stereo, lights, windshield wipers, adjustable seats, security system, and door locks.

Once the engine has started, the alternator receives power from the crank pulley at the bottom of the engine, which it converts using a coil, and sends to the battery for recharging as well as to the electrical components that are in use.

Important Considerations:

1. If an alternator malfunctions the battery gets drained from powering the starter and all of the systems itself without being recharged. So if your headlights are dim you should have a mechanic check your alternator and your battery.
2. Alternators are sized for their intended uses. They produce different levels of amperes, or electrical output, to run vehicle components. Buying a large alternator won’t ruin those components as the stereo, windows, wipers, and other features draw the amount of power they need, but buying an alternator that’s smaller than what is needed may not provide ample power for both battery recharging and to power electrical systems.
3. An alternator is cylindrical, with a belt attached to one end and wiring attached to the opposite side. There are many different types of alternators but a basic one will have three electrical terminals: one for power going to the battery, one for a voltage sensor, and one for the ignition to provide power for starting. The moving parts are encased in a housing that ensures no foreign matter is introduced but allows air flow to cool the moving parts.
4. Alternators are grounded to the vehicle’s frame.
5. Alternators generate power in relation to the vehicle’s speed: a faster car generates more.
    

How Car Alternators Work

The shaft that runs through the center of an alternator is spun by a belt attached to the engine’s crank. Inside the outer housing of an alternator are two sets of copper wire coils that spin in opposite directions, separated by an “iron claw” shaped barrier that creates magnetic poles. The inner coil generates an electromagnetic field and the outer, stator coil, generates electricity. A set of three diodes connected to the alternator by wires converts the raw, three-phase alternating current to direct current. A regulator attached to the alternator manages the electrical output so that it’s consistent with the needs of the vehicle (rather than surging as the car speeds on a highway and slowing when it’s at idle).

Troubleshooting a Bad Alternator

Here are a few ways to diagnose a failing alternator. Ultimately if your alternator fails, your check engine or battery light on the dashboard should alert you to a problem, which can be further diagnosed by a mechanic, using an OBD tool (available online for home mechanics):

1. Headlights that are too bright or too dim.
2. If your car dies (engine stops running) soon after starting, or the engine just “clicks” when you turn the key.
3. If your battery is less than three years old but the car won’t start.
4. If some of your electrical system stops working, like the electric windows or stereo, this could be the onboard computer compensating for insufficient power from the alternator. The computer should cut power to nonessential accessories first so that most of the power continues to operate the engine.
5. Whining or whirring sounds coming from the engine.
6. A smell like burning rubber or burning wires coming from the engine.
    

Regular checks and prompt attention to these warning signs can save you time and money, ensuring your car remains reliable on the road. Remember, consulting with a professional mechanic for a definitive diagnosis and repair is always recommended for the best care of your vehicle's electrical system.