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Alternator
The development of solid state rectifiers (diodes) allowed the posibility to rectify the electrical energy outside the windings. That fact simplified the conformation of the generators allowing the use of the alternator instead of the dynamo.
The alternator uses the principle of electromagnetism to produce current. The way this works is simple. If you take a strong magnet and pass it across a wire, that wire will generate a small voltage. Take that same wire and loop it many times, than if you pass the same magnet across the bundle of loops, you create a more sizable voltage in that wire. There are two main components that make up an alternator. They are the rotating magnetic field and the stator. There is just enough room in the center of the stator for the rotor to fit and be able to spin without making any contact. In motorcycles the rotating magnetic field could be a permanent magnet instead of a windings.
Multipolar Flywheel
Are permanent magnet alternators in which the stator has a star configuration. That allows the use of a greater number of coils in the same space, that increases the current output. They have two coils one for generating electricity for accessories (horn, lights, etc.) and one for the CDI ignition (usually encapsulated). The coils are placed in the stator and the flywheel with permanent magnets are placed in that way that their poles are diametrically opposed to each other. They are used in scooters that has a high energy requirement.
Volante magnético tetrapolar
Tetrapolar single-phase alternators are the simplest alternators, provided with two coils to generate electricity, one for accessories (horn, lights, etc. thick wire coil) and one for the ignition (fine wire coil). The ignition coil can supply a transference ignition (point ignition) or an electronic ignition like CDI. The coils are placed in a fixed area, and the permanent magnets in the flywheel so that their poles are diametrically opposed to each other. It contains four poles, so the frequency of current generated is twice the engine speed. Usually if there is no electricity consumption on the bike, the lightening coil is deactivated and thus turning rotor resistance is lower.
They are widely used in mopeds and low cylinder motorcycle, are inexpensive but provide low power generalemnte. However it is possible to use this flywheels in a classic motorcycle like Gilera 150, with good results if the coils are reinforced.
Rotor Interno
Early alternators used an internal rotor and an external stator. In recent years were replaced in most of the models by external rotor, but still are used in high power and racing motorcycles.
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Last Edited: 17/08/2010