Most automotive alternators use a rotor where a rotating magnet inside the conductor generates the electricity.

The conductors which are coils wound around an iron core also allow the voltage of the current generated to be controlled, thanks to a voltage regulator. The rotor is usually set in motion by mechanical means.

The efficiency of an alternator usually depends on its size and is very often affected because of problems in the bearings, not enough cooling by the fan or even copper and iron loss.

Most automotive alternators operate at around 55% efficiency. However, this conversion of mechanical energy in your car into electrical energy can be increased if you increase its range. Way back, the alternator only had to power the lights and a horn.

Today, you have heating, stereos and fancy headlights that need much more power. So today, you have high-output and high-amp alternators, most of them made with high-quality magnets, bearings and windings.

Though many parts of a car have become very high-tech, the alternator still remains a fairly simple piece of equipment and is relatively easy to replace. How do you know when it needs to be replaced? You would need to do it if you find that the battery does not retain its charge, even when you charge it from an external source. Or if you were to hear a loud grinding noise that seems to be coming from the region of the alternator.

To know for sure if your alternator needs replacing, you should invest in a voltmeter which you can get for a few dollars and use it to measure the voltage. Of course, if you were to take it to your automobile mechanic, he could test it and tell you whether you should replace it or not.