A magneto is an electric generator that uses permanent magnets tae produce periodic pulses o alternatin current. Unlik a dynamo, a magneto daes nae contain a commutator tae produce direct current. It is categorized as a form o alternator, awtho it is uisually considered distinct frae maist ither alternators, which uise field coils rather than permanent magnets.
Haund-cranked magneto generators war uised tae provide ringing current in telephone seestems. Magnetos war an aa adapted tae produce pulses o heich voltage in the ignition seestems o some petrol ingines tae provide power tae the spark plugs. Uise o sic ignition magnetos for ignition is nou leemitit mainly tae the follaein kinds o engines:
- Engines wioot a law-voltage electrical seestem, sic as lawnmowers an chainsaws.
- Aircraft engines, in which keepin the ignition independent o the rest o the electrical seestem ensures that the ingine continues running in the event o alternator or battery failure. For redundancy, virtually aw piston ingine aircraft are fitted wi twa magneto seestems, each supplying power tae ane o twa spark plugs in each cylinder.