1. ALTERNATOR

2. An alternator is an electromechanical device that converts mechanical energy to AC (alternating current) electrical energy, converts the AC to DC by rectifying it, regulates the DC voltage output to 12 Volts, and supplies this 12V DC power to charge the vehicle's battery and power the electrical components.

3. The Laws of Electromagnetism
An electric current in a wire creates a magnetic field around the wire. The direction (orientation) of the magnetic field is dependant on the direction of the current through the wire.
An electric current is induced in a loop of wire when the wire is moved towards or away from a magnetic field, or a magnet is moved towards or away from the wire. The direction of the current in the wire is dependant on the direction of the movement.

5. The Major components:
Rotor assembly
Stator
Diodes

6. On the back side of the alternator you'll find several terminals (or connecting points in an electrical circuit). Let's take a look at those:
S terminal - Senses battery voltage
IG terminal - Ignition switch that turns the voltage regulator on
L terminal - Closes the circuit to the warning lamp
B terminal - Main alternator output terminal (connected to the battery)
F terminal - Full-field bypass for regulator

7. Opening the alternator reveals a large cylinder with triangular finger poles around the circumference. This is the rotor.
A basic alternator is made up of a series of alternating finger pole pieces placed around coil wires called field windings that wrap around an iron core on the rotor shaft.

8. The rotor assembly fits inside the stator with enough room or tolerance between the two, so the rotor can spin at high speeds without striking the stator wall. On each end of the shaft sits a brush and a slip ring.

9. As the engine rotates the alternator pulley, the rotor spins past three stationary stator windings, or wire coils, surrounding a fixed iron core that makes up the stator. This is referred to as a three-phase current. The coil windings are evenly spaced at intervals of 120 degrees around the iron shaft. The alternating magnetic field from the rotor produces a subsequent alternating current in the stator.

10. Stators
Supported between the two halves of the generator housing are three copper wire windings wound on a laminated metal core.

11. Stators As the rotor revolves, its moving magnetic field induces a current in the windings of the stator.

12. How A Generator Works
A rotor inside a generator is turned by a belt and drive pulley turned by the engine.
The magnetic field of the rotor generates a current in the windings of the stator by electromagnetic induction.

13. How A Generator Works
Field current flowing through the slip rings to the rotor creates an alternating north and south pole on the rotor, with a magnetic field between each finger of the rotor.
The induced current in the stator windings is an alternating current because of the alternating magnetic field of the rotor.
The induced current starts to increase as the magnetic field starts to induce current in each winding of the stator.

14. How A Generator Works
The current then peaks when the magnetic field is the strongest and starts to decrease as the magnetic field moves away from the stator winding.
Therefore, the current generated is described as being of a sine wave pattern.

15. How A Generator Works (continued)
As the rotor continues to rotate, this sine wave current is induced in each of the three windings of the stator.
Because each of the three windings generates a sine wave current, the resulting currents combine to form a three-phase voltage output.

16. This AC current is fed through stator leads into a connecting set of diodes. Two diodes connect to each stator lead to regulate the current. The diodes are used to essentially block and direct the current. Since batteries need DC current, the diodes become a one-way valve that will only allow current to pass in the same direction.

17. A diode is a "solid state" device that allows current to flow in one direction only - "solid state" means it does this without any mechanical or moving parts. It relies on the different electrical properties of the materials it is made of to act as a one-way valve for current.

18. Arranging diodes so that current from each of the three stator wires is only allowed to pass in one direction, and by connecting the three outputs together, you get a reasonably smooth and stable DC output without any moving parts. (This arrangement is typically manufactured as a single part and is referred to as the diode pack or diode trio.)