Editing Electric generator (section)

===Direct current generators===
{{Main|Dynamo}}
[[File:Wechselstromerzeuger Crop LevelAdj.jpg|thumb|upright=0.8|[[Hippolyte Pixii]]'s dynamo. The commutator is located on the shaft below the spinning magnet.]]
[[File:High-Current Copper-Brush Commutated Dynamo.jpg|thumb|upright=0.8|This large belt-driven high-current [[dynamo]] produced 310 amperes at 7 volts. Dynamos are no longer used due to the size and complexity of the [[commutator (electric)|commutator]] needed for high power applications.]]

A coil of wire rotating in a magnetic field produces a current which changes direction with each 180° rotation, an [[alternating current]] (AC). However many early uses of electricity required [[direct current]] (DC). In the first practical electric generators, called ''[[dynamo]]s'', the AC was converted into DC with a ''[[commutator (electric)|commutator]]'', a set of rotating switch contacts on the armature shaft. The commutator reversed the connection of the armature winding to the circuit every 180° rotation of the shaft, creating a pulsing DC current. One of the first dynamos was built by [[Hippolyte Pixii]] in 1832.

The [[dynamo]] was the first electrical generator capable of delivering power for industry. 
The [[Woolrich Electrical Generator]] of 1844, now in [[Thinktank, Birmingham|Thinktank, Birmingham Science Museum]], is the earliest electrical generator used in an industrial process.<ref>Birmingham Museums trust catalogue, accession number: 1889S00044</ref> It was used by the firm of [[Elkington Silver Electroplating Works|Elkingtons]] for commercial [[electroplating]].<ref name="thomas">{{cite book|last1=Thomas|first1=John Meurig|title=Michael Faraday and the Royal Institution: The Genius of Man and Place|date=1991|publisher=[[Hilger & Watts|Hilger]]|location=Bristol|isbn=978-0750301459|page=51}}</ref><ref>{{cite book|last1=Beauchamp|first1=K G|title=Exhibiting Electricity|date=1997|publisher=IET|isbn=9780852968956|page=90}}</ref><ref>{{cite journal|last1=Hunt|first1=L. B.|title=The early history of gold plating|journal=Gold Bulletin|date=March 1973|volume=6|issue=1|pages=16–27|doi=10.1007/BF03215178|doi-access=free}}</ref>

The modern dynamo, fit for use in industrial applications, was invented independently by [[Sir Charles Wheatstone]], [[Werner von Siemens]] and [[Samuel Alfred Varley]]. Varley took out a patent on 24 December 1866, while Siemens and Wheatstone both announced their discoveries on 17 January 1867 by delivering papers at the [[Royal Society]].<ref name=Siemens1867>{{cite journal |doi=10.1098/rspl.1866.0082 |title=II. On the conversion of dynamical into electrical force without the aid of permanent magnetism |journal=Proceedings of the Royal Society of London |last=Siemens |first=Charles William |date=1867 |volume=15 |pages=367–369 |url=https://zenodo.org/records/1432047/files/article.pdf}}</ref><ref name=Wheatstone1867>{{cite journal |doi=10.1098/rspl.1866.0083 |title=III. On the augmentation of the power of a magnet by the reaction thereon of currents induced by the magnet itself |last=Wheatstone |first=Charles |journal=Proceedings of the Royal Society of London |date=1867 |volume=15 |pages=369–372}}</ref>

The "dynamo-electric machine" employed self-powering electromagnetic field coils rather than permanent magnets to create the stator field.<ref>{{cite journal |journal=Berliner Berichte|date=January 1867}}</ref> Wheatstone's design was similar to Siemens', with the difference that in the Siemens design the stator electromagnets were in series with the rotor, but in Wheatstone's design they were in parallel.<ref name=Siemens1867/><ref name=Wheatstone1867/> The use of electromagnets rather than permanent magnets greatly increased the power output of a dynamo and enabled high power generation for the first time. This invention led directly to the first major industrial uses of electricity. For example, in the 1870s Siemens used electromagnetic dynamos to power [[electric arc furnace]]s for the production of metals and other materials.

The dynamo machine that was developed consisted of a stationary structure, which provides the magnetic field, and a set of rotating windings which turn within that field. On larger machines the constant magnetic field is provided by one or more electromagnets, which are usually called field coils.

Large power generation dynamos are now rarely seen due to the now nearly universal use of [[alternating current]] for power distribution. Before the adoption of AC, very large direct-current dynamos were the only means of power generation and distribution. AC has come to dominate due to the ability of AC to be easily [[transformer|transformed]] to and from very high voltages to permit low losses over large distances.