# Electric Generator > Motion turned into current - Date: 1831 - Era: Industrial age - Domain: [Electricity & Electronics](https://lastcodex.org/en/domains/electricity/) - Rebuild stage: IV (Science & industry) - Difficulty: 4/5 - URL: https://lastcodex.org/en/inventions/generator/ An electric generator turns mechanical motion into electric current by moving a magnet and a coil of wire past each other. Michael Faraday found the principle in 1831, and almost all the electricity used today still comes from machines built on it. ![Electric Generator · Motion turned into current](https://lastcodex.org/_astro/plate.BskuCTY6_Z1cDXm3.webp) ## Legend 1. Hand crank 2. Bevel gears 3. Horseshoe magnet 4. Coils on iron cores 5. Commutator and brushes ## What it is A generator converts mechanical work, from a hand crank, a water wheel, a steam engine or a turbine, into electric current. It needs a magnet, a coil of copper wire, and some way to move one past the other. Batteries are costly and run down; generators made electricity in bulk from coal or falling water. Power stations, car alternators, bicycle dynamos and wind turbines all work this way. ## How it works ![An iron ring with two separate coils, one wired to a battery, the other to a compass needle](https://lastcodex.org/_astro/v1.AEQGxqkO_Z22UlBJ.webp) *Faraday's induction ring: the needle jumped only at the moment the battery was connected or disconnected.* The principle is electromagnetic induction. When the magnetic flux through a coil (the amount of field passing through it) changes, a voltage appears across the ends of the coil. If the flux stays constant, there is no voltage. The faster the flux changes and the more turns the coil has, the higher the voltage. In the machine on the plate, built by Hippolyte Pixii in 1832, a crank turns a vertical shaft through a pair of bevel gears. The shaft carries a horseshoe permanent magnet whose poles sweep just under two fixed coils wound on iron cores. As a north pole comes under a coil, the flux through it grows and current flows one way. As the pole moves away, the flux shrinks and the current reverses. The south pole then repeats the cycle with the field the other way round, so the bare machine makes alternating current. Pixii added a commutator, suggested by André-Marie Ampère: a switch on the shaft that swaps the two output connections every half turn, just as the current reverses. The output becomes a pulsing direct current that can charge batteries or split water. ![A copper disc spinning between the poles of a horseshoe magnet, with sliding contacts on the rim and axle](https://lastcodex.org/_astro/v2.C845vBxq_Pp1sp.webp) *Faraday's disc of 1831 gave a small, continuous direct current.* As soon as current flows, the coils become magnets themselves and push back against the motion, so the crank gets heavier when a lamp is connected. The electrical energy that comes out is the work put in by the hand or the engine, minus losses to friction and heat. Nineteenth-century permanent magnets were weak, so large machines used electromagnets. In a self-excited dynamo, part of the machine's own output feeds them. The faint magnetism left in the iron starts a small current, which strengthens the field, which raises the current, until the voltage settles at a level set by the speed and by the saturation of the iron. A modern power-station generator spins an electromagnet inside fixed windings; with two poles it turns at 3,000 revolutions per minute for 50 hertz, or 3,600 for 60 hertz. ## How to build it A small hand-cranked alternator can light an LED or a torch bulb. **Make the rotor.** Cut a disc of plywood or hardwood about 15 cm across. Glue eight flat disc magnets (ferrite or neodymium) on one face, evenly spaced near the rim, so that the faces turned outward alternate north, south, north, south. Bind them with cord, because a loose magnet flies off at speed. **Wind the coils.** Wind eight flat coils of enamelled copper wire 0.3 to 0.5 mm thick, a few hundred turns each, all in the same direction, on a former about the size of a magnet. **Mount the stator.** Fix the coils on a board parallel to the rotor, one facing each magnet, with a gap of a few millimetres. Neighbouring coils always face opposite poles, so connect them in series with every second coil reversed; then their voltages add. **Gear it up.** A belt from a large pulley on the crank to a small one on the rotor shaft multiplies the speed four or five times. **Rectify and test.** The output is alternating current. Four diodes in a bridge turn it into pulsing direct current. Light an LED from the bridge through a one-kilohm, half-watt resistor, which keeps the current under about 20 milliamperes as long as the output stays below about 20 volts; check the voltage with a meter before cranking hard. Charging a battery needs a proper charge controller suited to its type, not diodes alone. Without bought magnets, steel bars can be magnetised inside a coil fed for a few seconds by a battery, with a car bulb in series to limit the current. A self-excited dynamo, once started from residual magnetism, needs no permanent magnet at all. > **Safety.** Rotating parts catch fingers, hair and loose clothing: guard the belt and rotor. Neodymium magnets snap together hard enough to pinch skin and shatter; keep them away from pacemakers. Voltage rises with speed, and larger machines reach dangerous levels. Never connect a home-made or portable generator to a building's wiring or to the mains: current fed back into the network can kill line workers, and only an electrician fitting a proper transfer switch should make such a connection. ## History and evolution In 1820 Hans Christian Ørsted showed that an electric current deflects a compass needle. Michael Faraday reasoned that magnetism should, in turn, be able to produce electricity. On 29 August 1831, at the Royal Institution in London, he wound two coils on an iron ring and saw a galvanometer needle jump each time he connected or disconnected a battery on the other coil. That autumn he spun a copper disc between the poles of a magnet and drew a continuous current from it. He presented the results to the Royal Society on 24 November 1831. ![A Gramme ring: an iron ring wound with many coils, each joined to a bar of the commutator](https://lastcodex.org/_astro/v3.D5EKnwL6_1zqeS2.webp) *The Gramme ring spread the winding all around the armature, so the current hardly pulsed.* Within a year Pixii, a Paris instrument maker, built the hand-cranked machine on the plate. In 1866 and 1867 Samuel Alfred Varley, Werner Siemens and Charles Wheatstone each announced the self-excited dynamo, and Siemens named the dynamo-electric principle. Around 1870 Zénobe Gramme built a ring armature that gave a smooth current. On 4 September 1882 Thomas Edison's Pearl Street Station in New York began supplying direct current at 110 volts from six steam-driven "Jumbo" dynamos. Alternating current later won for long distances because transformers can raise its voltage; in 1891 a three-phase line carried power 175 km from Lauffen am Neckar to Frankfurt. Charles Parsons coupled a dynamo to a steam turbine in 1884, and turbine-driven generators have powered most large stations since. In 1975 the first of three 600 MW units started at the Grand Coulee Dam, with a stator 22 metres across. ## Key figures - Induction discovered: 29 August 1831, by Michael Faraday - Pixii's magneto-electric machine: Paris, 1832 - Self-excited dynamo: 1866 to 1867 (Varley, Siemens, Wheatstone) - Pearl Street Station, 1882: Six dynamos of about 100 kW each, 110 V direct current ## Requires - [Battery](https://lastcodex.org/en/inventions/battery/): Chemistry that pushes a current (1800) - [Iron Smelting](https://lastcodex.org/en/inventions/iron-smelting/): Wider adoption around 1200 BCE; ore, charcoal and a bloomery (c. 1,200 BCE) ## Leads to - [Aluminium](https://lastcodex.org/en/inventions/aluminium/): Alumina turned into metal by electricity (1886) - [Lead-Acid Battery](https://lastcodex.org/en/inventions/lead-acid-battery/): Electricity kept in lead and acid (1859) - [Incandescent Light Bulb](https://lastcodex.org/en/inventions/light-bulb/): A glowing filament in a vacuum (1879) - [Radio](https://lastcodex.org/en/inventions/radio/): Messages without wires (c. 1895) - [Steam Turbine](https://lastcodex.org/en/inventions/steam-turbine/): Steam spinning the world's generators (1884) - [Transformer](https://lastcodex.org/en/inventions/transformer/): Raising and lowering the voltage (1885) - [Water Turbine](https://lastcodex.org/en/inventions/water-turbine/): Falling water turned into electricity (1827) - [Wind Turbine](https://lastcodex.org/en/inventions/wind-turbine/): Wind turned into electricity (1887) - [X-Ray Imaging](https://lastcodex.org/en/inventions/x-ray/): Seeing through the body (1895) ## Sources - [Michael Faraday](https://www.theiet.org/membership/library-archives/the-iet-archives/biographies/michael-faraday/), The Institution of Engineering and Technology (IET) Archives - [Magnetoelectric machine by Pixii](https://catalogue.museogalileo.it/object/MagnetoelectricMachineByPixii.html), Museo Galileo, Florence - [Chronik: Generatoren](https://www.vde.com/de/geschichte/chronik/generatoren), VDE Verband der Elektrotechnik - [Milestones: Pearl Street Station, 1882](https://ethw.org/Milestones:Pearl_Street_Station), IEEE Engineering and Technology History Wiki Fact-checked on 2026-10-11. --- The Last Codex · https://lastcodex.org/en/inventions/generator/ · © The Last Codex. 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