The alternators work on the principle of electromagnetism to produce current. Here is how it works; If you take a strong magnet and pass it across a wire, that wire will generate a small voltage. Loop that same wire many more times, then if you pass the same magnet across the bundle of loops, a more sizable voltage is created =] in that wire.
There are two main components that sum up an alternator. These are the rotor and the stator. The rotor is wired directly to the alternator pulley. The drive belt turns the pulley, which in turn spins the rotor. The stator is placed on the body of the alternator and remains immovable. There is just enough room in the center of the stator for the rotor to fit and be able to spin without having any contact.
The stator has 3 sets of wires that have many loops each and are evenly distributed to form a three phase system. On some cases, the wires are connected to each other at one end and are connected to a rectifier assembly on the other side. On yet others, the wires are connected to each other end to end, and at each of the three connection points, there is then a connection to the rectifier.
##2The rotor has the most powerful magnet that passes close to the many wire loops that sums up the stator. The magnets in the rotor are actually electro magnets, not really a permanent magnet. This is done so that there is control of how much voltage the alternator produces by regulating the amount of current that produces the magnetic field in the rotor. In this way, there is control of the output of the alternator to the required need, this helps protect the circuits in the automobile from excessive voltage.
Now at this point the rotor has two interlocking sections of electro magnets that are prepared so that there are fingers of alternating north and south poles. that are evenly given on the outside of the rotor.
When the is a spinning of the rotor inside the stator and an application of current to the rotor through a pair of brushes that make constant contact with two slip rings on the rotor shaft. This makes the rotor to become magnetized. The alternating north and south pole magnets spin past the three sets of wire loops in the stator and produce a constantly reversing voltage in the three wires. That is to say that there is a production of alternating current in the stator.
At this point alternating current has been converted to direct current. This is done by using a series of 6 diodes that are positioned in a rectifier assembly. A diode aids current to flow only in one direction. If voltage tries to flow in the other direction, it is blocked. The six diodes are arranged so that all the voltage coming from the alternator is aligned in one direction thereby converting AC current into DC current.
There are 2 diodes for each of the three sets of windings in the stator. The two diodes are kept in opposite directions, one with its north pole facing the windings and the other with its south pole facing the windings. This arrangement makes the AC current coming out of the windings to be converted to DC current before it leaves the alternator through the B terminal. Connected to the B terminal of the alternator is a fairly heavy wire that goes straight to the battery.
Current to produce the magnetic field in the rotor issues from the ignition switch and passes through the voltage regulator. Since the rotor is spinning, there is a need to connect this current from the regulator to the spinning rotor. This is accomplished by wires connected to two spring loaded brushes that rub against two slip rings on the rotor’s shaft. The voltage regulator checks the voltage coming out of the alternator and, when it reaches a threshold of about 14.5 volts, the regulator reduces the current in the rotor to weaken the magnetic field. When the voltage drops below this level, the current to the rotor is increased.
Additionally, there is another circuit in the alternator to control the charging system warning lamp that is on the dashboard. Part of that circuit is another set of diodes placed inside the alternator called the diode trio. The diode trio takes current coming from the three stator windings and passes a small amount through three diodes so that only the positive voltage comes through. After the diodes, the wires are joined into one wire and sent out of the alternator at the L connection. It then heads to one side of the dash warning lamp that is used to tell you when there is a problem with the charging system. The other side of the lamp is connected to the run side of the ignition switch. If both sides of the warning lamp have equal positive voltage, the lamp will not light. Remove voltage from one side and the lamp comes on to let you know there is a problem.
This system however is not very efficient. There are many types of demerits of the charging system that it cannot detect, so just because the lamp is not lit does not mean everything is ok. A volt meter is probably the best method of determining whether the charging system is working properly