The genesis of generators (part 2)

Drawing of Faraday disk, the first electromagnetic generator, invented by British scientist Michael Faraday in 1831.
Image: Émile Alglave

The foundation for building electric motors was laid with the invention of the battery by Allessandro Volta in 1800, the generation of a magnetic field from an electric current by Hans Christian Oersted in 1820, and the invention of the electromagnet by William Sturgeon in 1825.

Alessandro Volta's electric battery (Tempio Voltiano in Como, Italy).
Image: GuidoB

Nearly 200 years after Guericke created the first electrostatic generator, British scientist Michael Faraday built the first electric generator, comprising a tube of neutral material wound with a cotton-insulated coil of wire and a bar magnet. Connecting his apparatus to an instrument that detects electrical current, Faraday discovered that on passing the magnet back and forth through the stationary coil of wire, the instrument registered a current flowing.

Michael Faraday's electrical generator.
Images: Paul Wilkinson

Faraday was responsible for building the first electromagnetic generator, the Faraday disc (homopolar generator): a copper disc rotating between the poles of a horseshoe magnet and which produced a small DC voltage. This same method is used today, with the movement of a copper disc, or wire loop, between the poles of a magnet generating electricity. Long after the original Faraday disc had been abandoned as a practical generator, a modified version combining the magnet and disc in a single rotating part, or rotor, was developed.

The first generator built for public use was the dynamo, invented by Frenchman Hippolyte Pixii in 1833, based on Faraday’s concepts of electromagnetic currents. The dynamo cranked electricity by hand, creating alternating currents by using a magnet with revolving coils. Because many early uses of electricity required direct current, Pixii included a commutator to convert the alternating currents into direct currents.

Hippolyte Pixii's dynamo. The commutator is located on the shaft below the spinning magnet.
Image: DMahalko

The dynamo was the first electrical generator capable of delivering power for industry. The modern dynamo was invented independently by Sir Charles Wheatstone, Werner von Siemens and Samuel Alfred Varley in the late 1860s and used self-powering electromagnetic field coils to create the stator field instead of permanent magnets.


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The genesis of generators (part 1)
The genesis of generators (part 3)

14 Sep 2017

By Robyn Grimsley
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