Permanent-magnet alternating generator used mainly to produce electrical current for the ignition system in various types of internal-combustion engines, such as aircraft, marine, tractor, and motorcycle engines. The main parts of a magneto are a permanent-magnet rotor, a primary winding of a small number of turns of coarse wire, a secondary winding with a large number of turns of fine wire, a cam-type circuit breaker, and a capacitor. As the rotor turns, it produces a current in the primary winding, charging the capacitor. The cam breaks the circuit, and the magnetic field around the primary winding collapses. The capacitor releases its stored current into the primary winding, causing a reversed magnetic field. The collapse and reversal of the magnetic field produce a current in the secondary winding that is sent to the spark plugs.
This entry comes from Encyclopædia Britannica Concise.
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