A portable magneto is a basic electrical generator, which is a form of motor with a hand crank that spins a wire winding inside several permanent magnets to generate electrical current. The magneto was a standard element in early, hand-cranked telephone systems, and they are still widely used in small gasoline engines that don't have electrical starters, such as lawnmowers and leaf blowers. Relatively simple yet durable devices, magnetos are built upon electromagnetism properties first defined by Michael Faraday in 1831.
Though technically a magneto uses permanent magnets, they can also be designed based on electromagnets that only exhibit magnetic properties when current is passing through them. Though a magneto generates alternating current (AC), dynamos are a variation that produce direct current (DC) by use of a rectifier to make the conversion. High-tension magneto designs are another variation that are often used in aircraft systems in place of batteries and alternators, as they are self-contained and tend to weigh less than the battery/alternator setup of typical automobiles.
Two basic designs exist for magnetos. A shuttle magneto operates by turning a coil of wire inside of the poles of a electromagnet, or set of permanent magnets, that are in stationary position, to generate electrical current. A inductor magneto, on the other hand, operates by turning the exterior magnets themselves around the interior wire coil to generate current. In ignition systems, both magneto designs incorporate capacitors, rectifiers, and ignition coils in the circuit to regulate the output voltage and boost it for effective spark generation at spark plugs.
One of the earliest large-scale applications for magnetos was in the design of power stations by Thomas Edison in the late 1800s using the flow of water or steam pressure to spin a generator or type of dynamo that produced direct current. It later proved impractical commercially as direct current is not easy to transmit reliably over long distances. Nikola Tesla's variation on the idea using AC took off, and his partnership with George Westinghouse led to widespread distribution of electrical power to US households.
Hydroelectric power stations built upon dams of large waterways are a form of, or series of, large magneto devices. They utilize the energy of the dammed water to power water turbines, which are a magneto-based electrical generator. One of the most widely used forms of renewable energy, hydroelectric power accounts for about 20-25% of world electricity production.