The magneto is the white block in the following photo (this is the magneto for a chain saw):
The idea behind a magneto is simple. It is basically an electrical generator that has been tuned to create a periodic high-voltage pulse rather than continuous current. An electrical generator (or a magneto) is the reverse of an electromagnet (see How Electromagnets Work for details). In an electromagnet there is a coil of wire around an iron bar (the armature). When you apply current to the electromagnet's coil (e.g. With a battery), the coil creates a magnetic field in the armature. In a generator, you reverse the process. You move a magnet past the armature to create electric current in the coil.
A magneto consists of five parts:
- An armature. In the above magneto, the armature is shaped like a capital "U". The two ends of the U point toward the flywheel.
- A primary coil of perhaps 200 turns of thick wire wrapped around one leg of the U
- A secondary coil of perhaps 20,000 turns of very thin wire wrapped around the primary coil
- A simple electronic control unit that commonly goes by the name "electronic ignition" (or a set of breaker points and a capacitor)
- A pair of strong permanent magnets embedded in the engine's flywheel.
With a magneto, a permanent magnet passes a coil of wire causing current to form in the wire which after some other steps, can power an ignition in an engine.
The engine spins a coil of wire amid the poles of a permanent magnet to supply a fundamental source of electrical energy. Seeing that the magneto is a self-contained incorporated ignition unit creating its own electrical power generation, an automobile which has additional electrical material also needs other means to generate electrical power for that equipment.