Alternators

A traditional alternator uses a coil that uses DC power from the battery to produce a magnetic field. This coil is wound on a spool and is sandwiched between two metal flywheels with fingers of metal that alternate from one side to the other.

When this coil is powered, it makes each finger have a magnetic field. These alternate with each finger between north and south pole. As this assembly spins, the alternating poles of magnetism energize the outer windings of the alternator to produce AC power.

The benefit to this type of system is that it can produce more power at lower engine speeds which is why most cars and trucks use this system.

The down-side to this system is that it requires a charged battery to work.