- This article is about magneto, the engine component. There are other articles about Magneto, the comicbook character and Magneto, the Mexican boy band. Magneto is also the codename for Microsoft Windows Mobile 2005.
A magneto provides pulses of electrical power to the spark plugs in some petrol-powered internal combustion engines, most commonly those in 2-stroke and 4-stroke engines used in small motorcycles, lawnmowers and chainsaws, as well as in most small aircraft, serving a similar function to the coil system found in automobiles. In aircraft, typically each cylinder has two spark plugs, each driven from a separate magneto. This arrangement provides redundancy in the event of a failure of one of the magnetos, and two sparks burn more efficiently than one.
Magnetos combine the functions of a dynamo, contact breaker points and coil into one unit. The engine turns a permanent magnet inside a coil of wire to provide a basic source of electrical energy. On each revolution, a cam opens the contact breaker one or more times, interrupting the current, causing the voltage in the secondary winding of the coil to reach a very high value, enough to arc across the electrodes of the spark plug. Because no battery or other source of energy is required, the magneto is a rugged, reliable and self-contained solution to providing ignition of the fuel. In some modern magneto designs, an electronic switch replaces the contact breaker.
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