Demonstration hand-cranked magneto

A magneto is an electrical generator that uses permanent magnets to produce alternating current.

Hand-cranked magneto generators were used to provide ringing current in early telephone systems.

Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-powered internal combustion engines to provide power to the spark plugs.[1] The magneto is now confined mainly to engines where there is no available electrical supply, for example in lawnmowers and chainsaws. It is also universally used in aviation piston engines even though an electrical supply is usually available. This is because a magneto ignition system is more reliable than a battery-coil system.

Magnetos were rarely used for power generation, although they were for a few specialised uses.



Production of electric current from a moving magnetic field was demonstrated by Faraday in 1831. The first machines to produce electric current from magnetism used permanent magnets; the dynamo machine, which used an electromagnet to produce the magnetic field, was developed later. The machine built by Hippolyte Pixii in 1832 used a rotating permanent magnet to induce alternating voltage in two fixed coils.[2]

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. Power generation magnetos were limited to narrow fields, such as powering arc lamps or lighthouses, where their particular features of output stability or simple reliability were most valued.


One popular and common use of magnetos of today is for powering lights on bicycles.

Most commonly a small magneto, termed a bottle dynamo, rubs against the tyre of the bicycle and generates power as the wheel turns.

More expensive and less common but more efficient is the hub dynamo.

Although commonly referred to as dynamos, both devices are in fact magnetos, producing alternating current as opposed to the direct current produced by a true dynamo.

Medical use

The magneto also had a medical use for treatment of mental illness in the beginnings of electromedicine. In 1850, Duchenne, a French doctor, developed and manufactured a magneto with a variable outer voltage and frequency, through varying revolutions by hand or varying the inductance of the two coils, putting out or putting in both ferromagnetic cores.

Ignition magnetos

Magnetos adapted to produce impulses of high voltage for spark plugs are used in the ignition systems of spark-ignition piston engines. Magnetos are used in piston aircraft engines for their reliability and simplicity. Motor sport vehicles such as motorcycles and snowmobiles use magnetos because they are lighter in weight than an ignition system relying on a battery. Small internal combustion engines used for lawn mowers, chain saws, portable pumps and similar applications use magnetos for economy and weight reduction. Magnetos are not used in highway motor vehicles which have a cranking battery and which may require more control over ignition timing than is possible with a magneto system.


1896 Telephone, hand crank for magneto on right (Sweden)

Many early manual telephones had a hand cranked "magneto" generator to produce a (relatively) high voltage alternating signal to ring the bells of other telephones on the same (party) line and to alert the operator. These were usually on long rural lines served by small manual exchanges, which were not "common battery". The telephone instrument was "local battery", containing two large "No. 6" zinc-carbon dry cells.

See also


  1. ^ Selimo Romeo Bottone (1907). Magnetos for Automobilists, how Made and how Used: A Handbook of Practical Instruction in the Manufacture and Adaptation of the Magneto to the Needs of the Motorist. C. Lockwood and son. 
  2. ^ Alfred Urbanitzky (Ritter von), Richard Wormell Electricity in the service of man: a popular and practical treatise on the applications of electricity in modern life, Cassell & Company, limited, 1886 page 227, preview on Google books

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  • magnéto- — ♦ Élément, du lat. magneticus (⇒ magnétique). magnéto élément, du gr. magnês, magnêtos, aimant . ⇒MAGNÉT(O) , (MAGNÉT , MAGNÉTO )élém. de compos. Élém. représentant l adj. magnétique ou le subst. magnétisme. I. Élém. entrant dans la constr. de… …   Encyclopédie Universelle

  • Magneto — Magnéto Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom …   Wikipédia en Français

  • magneto — Element prim de compunere savantă cu semnificaţia (referitor la) magnet , magnetism . [< fr. magnéto , it. magneto , cf. gr. magnetos – (piatră) de Magnezia]. Trimis de LauraGellner, 23.05.2005. Sursa: DN  MAGNETO elem. magnet, magnetic,… …   Dicționar Român

  • magneto — 1882, short for magneto electric machine (see MAGNETO (Cf. magneto )) …   Etymology dictionary

  • magneto — ‘Generador eléctrico que funciona gracias a un imán’. Surge por abreviación de la expresión máquina magnetoeléctrica, lo que explica su inicial uso en femenino, aún vigente: «Renqueaba la magneto; a la cuarta intentona, prendieron los cilindros»… …   Diccionario panhispánico de dudas

  • magneto — {{/stl 13}}{{stl 8}}rz. n I, Mc. magnetoecie, rzad. {{/stl 8}}{{stl 7}} to samo, co iskrownik <fr. skrót machine magnéto électrique – maszyna elektromagnetyczna> {{/stl 7}}{{stl 20}} {{/stl 20}} {{stl 20}} {{/stl 20}}magneto {{/stl… …   Langenscheidt Polski wyjaśnień

  • magneto — sustantivo masculino,f. 1. (preferentemente femenino) Área: mecánica Potente generador eléctrico de los motores de explosión: la magneto de la moto. He tenido que cambiar la magneto del coche. Sinónimo: dinamo …   Diccionario Salamanca de la Lengua Española

  • magneto- — comb. form meaning magnetic, magnetism, from Gk. magneto , combining form of magnes (see MAGNET (Cf. magnet)) …   Etymology dictionary

  • magneto — a shortened form of magneto electric machine, has the plural form magnetos …   Modern English usage

  • magneto — mag*ne to (m[a^]g*n[=e] t[ o]), n. A small electric generator with an armature rotating in a magnetic field, having a secondary winding that generates a high voltage, such as one used to generate a voltage sufficient to cause a spark to jump… …   The Collaborative International Dictionary of English

  • Magneto- — Mag net*o , pref. [See {Magnet}.] A prefix meaning pertaining to, produced by, or in some way connected with, magnetism. [1913 Webster] …   The Collaborative International Dictionary of English

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