How do Alternators Work

Have you ever wondered how the alternator in your car works.  Your car has and electrical system that sends power the most important essentials, such as your headlights, interior lights dash lights and so on and other non-important things as the radio ( you may not agree there), air conditioning , and all of those other things that we couldn't imagine living without and really depend on. Have you ever thought about where that power comes from? Most people would think it comes from the battery, now that's partially true.

But that is just one of the sources, so if you think about it in all actuality the power comes from your gas tank. And the link from the gas tank to the battery is called an alternator. It starts with power from the crankshaft which turns the"fan" belt,  or the serpentine belt and turns the alternator. So, the main function of the alternator is to convert power from the gasoline engine that drives you along the road, to electrical energy to keep the battery in tip-top condition.

Although Alternators vary by manufacturer, there are two elements common to all alternators; the stationary stator and the rotating rotor. The stator consists of three sets of individual windings wound around a laminated circular iron stator frame. Each individual winding is made up of seven coils, which in turn are made up of several individual loops all connected in series. Each coil and each loop are connected so as to increase the total voltage output. Each group of windings has only two leads, one for current to flow in, and the other for current to flow out.

Although it may vary by manufacturer, most leads are wired in a Y-configuration, in which the three sets of windings each occupy 1/3 of the stator. This means that each group of windings produces energy during 1/3 of each revolution. Since each revolution is divided into three steps, each step can be thought of as a phase, each phase occupying 120 degrees of the 360-degree circle. Due to the nature of three-phase alternating current, the type of energy produced by the interaction of the stator and the rotor is continuously variable with respect to time. The rotor is typically composed of a drum-shaped coil of wire, a pair of iron interweaving cups, a shaft, and two slip rings to connect the coil of wire to the car's battery. Since vehicles need to see DC, Diodes become extremely necessary.

Since AC is continuously alternating between positive and negative, diodes can be used so that only one positive and one negative is output. Basically, as the rotor poles turn within one of the stator coils, current flows first within one direction, and then in another. (During the first 180 degrees, of rotation, the current direction is positive, and during the second 180 degrees the current direction is negative). Using diodes to convert current from AC to DC is also known as rectification, and in most alternators, six diodes (two for each phase) are used.

Once you have the current converted over to DC, the last component required is a voltage regulator to determine how much energy is needed to be output from the diode bridge. (The diode bridge is the combination of all six rectification diodes, also referred to as a rectifier bridge). The sensor for the regulator is usually connected to the positive post of the battery and when it senses a low voltage condition, allows more energy to flow in the rotor coil, creating more energy in the stator coils. It does this through a series of points, raising the points off of the contacts to allow less current to flow, or dropping points onto the contacts to increase current flow.

How can you tell when your alternator is going bad? Most of the time the alternator dies slowly. Each of the three sections of the alternator generates its voltage out of phase with the other two sections.  Each of the three phases has its own windings in the alternator and each of the windings has its own pair of diodes. Each of these windings and/or diodes can fail, one set at a time. If this happens the alternator can still charge the battery, but only with a limited current, approximately 2/3 of its original capacity if one system fails.

If two systems fail, then it puts out only 1/3 of its rated capacity. And all that means to you is that you can go a long time on a half alternator. Chances are if you don't need headlights or air conditioning or other high current accessories, you would never know that the alternator was dieing!