Magneto (generator)

A magneto is an electrical generator that uses permanent magnets to produce alternating current. Unlike a dynamo, there is no commutator and so they cannot produce direct current. They are categorised as a form of alternator, although they are usually regarded as distinct from most other alternators, which use field coils rather than permanent magnets.

Magnetos date from the earliest days of electrical engineering. Despite this, they have never been widely applied for the purposes of bulk electricity generation, for the same purposes or to the same extent as either dynamos or alternators. Only in a few specialised cases, as described here, have they been used for power generation.

Magnetos have advantages of simplicity and reliability, but are inefficient owing to the weak magnetic flux available from their permanent magnets. This restricted their use for high-power applications.

Some did find use as telephone magnetos in early telephones, particularly for ringing.

The most common application for magnetos was as an ignition magneto, in spark-ignition petrol engines, ranging from early cars to aircraft (for reliability) and small engines such as chainsaws (for simplicity).

Early power generation systems adopted bipolar dynamos as their generators. These had a two-pole stator with a field winding. It could generate considerable flux, and thus power, for the time. They also required a commutator to produce a direct current (DC) output, which was complex to make and required regular maintenance. In contrast magnetos were not generally used, as they were inadequately powerful.

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