How Does An Alternator Work?

For all the electrical components in your car to function, they need a charge.This charge is produced, ultimately, by a device known as an alternator – which translates the motion of your car into electrical energy.

What is electromagnetic induction?

Some time ago, it was realised that passing a magnet beside a length of magnetically-conductive material will induce a current in that material.The strength of the current being generated, moreover, will vary according to the strength of the magnetic field, and the extent to which the wire in question is coiled.

This principle has since found enormous application in the world of motoring, in the form not only of entirely-electrical engines, but also of the starter motor whose role it is to get a modern internal-combustion engine turning to begin with.

But to function, the starter motor in your car will need a source of energy.This is the role of the car’s battery.But in order to maintain a charge, the battery will rely in turn on another crucial component:the car’s generator.In modern vehicles, this generator comes in the form of an alternator.

What is an alternator?

In an alternator, it’s the magnet that moves, rather than the coiled wires.The former is a collection of magnets that sit within a nest of copper wires.The former structure is known as the rotor, and the latter the stator.As the engine turns, so too does the rotor, which builds a charge on the stator.Since the amount of electricity drawn by the components of the car won’t even approach the amount that can be produced by the car’s engine (even accounting for the inefficiencies of translating the action of the engine into the rotor), the result is a self-contained system where an effectively infinite amount of electricity can be drawn (provided, of course that you’re driving the car as you listen to the radio, or operate the windscreen wipers.

What about regulating the current?

Of course, simply pumping whatever current the engine can generate straight into the battery is not going to be productive.For one thing, the current coming out of the alternator will be alternating, while the current required by the battery will be direct.In order to transform one into the other, two things are required.

First, the bottom half of the signal must be lopped off.This is done using a device called a diode.These allow the current to flow only in one direction, thus removing half of the current.In order to smooth the current out into a nice, even signal, capacitors are used.These fill up when current is available, and release their charge when there isn’t any.This fills out the gaps between the peaks.Capacitors vary in capacity and the speed at which they’re able to charge, but by employing a selection of different ones, it’s possible to easily smooth the signal into something flat, even, consistent, and battery-friendly.

Of course, this is only necessary in the case of alternators, which output an AC signal.In older cars, you’ll find another device called a dynamo which outputs a DC signal.This dispenses with the need to convert the signal, but since dynamos are far heavier and cumbersome than alternators, and the circuitry needed to change an AC signal into a DC one is so small and negligible in cost, dynamos have largely gone the way of the dodo.

In order to ensure that the battery receives a steady, healthy voltage, a component called a voltage regulator is required.This will help to protect the battery against spikes that might reduce its lifespan.There’s no point, after all, in providing a 12volt input to a nine-volt battery; the result will simply be damage.

How do I know when the alternator needs replacing?

The symptoms of a faulty alternator are broadly similar to those of a faulty battery.As the battery is drained without being topped up by the alternator, the components of your car will begin to fail, one-by-one.If the battery itself is faulty, these effects will tend to be more sudden.You might find that your headlights begin to dim, and then eventually the starter motor will cease to function.As you might imagine, this state of affairs is highly undesirable.If you’re in need of a replacement, you’ll find cheap starter motors online to suit a range of makes and models.There are Audi, Ford and BMW alternators, as well as those that’ll fit a range of other vehicles.