Lester Allan Pelton (1829 - March 14, 1908), was an American inventor who created the impulse water turbine. He was born in Vermillion, Ohio in 1850 and immigrated to California during the gold rush. Pelton made his living as a carpenter and a millwright.

The Pelton wheel introduced an entirely new physical concept to water turbine design (impulse as opposed to reaction), and revolutionized turbines adapted for high head sites. Up until this time, all water turbines were reaction machines that operated off of water's weight or pressure. Pelton's invention operated off the kinetic energy of a high velocity water jet.

According to a 1939 article by W. F. Durand of Stanford University in Mechanical Engineering:- "Pelton´s invention started from an accidental observation, some time in the 1870s. Pelton was watching a spinning water turbine when the key holding its wheel onto its shaft slipped, causing it to become misaligned. Instead of the jet hitting the cups in their middle, the slippage made it hit near the edge; rather than the water flow being stopped, it was now deflected into a half-circle, coming out again with reversed direction. Surprisingly, the turbine now moved faster. That was Pelton´s great discovery. In other turbines the jet hit the middle of the cup and the splash of the impacting water wasted energy."

From this observation, Pelton produced the Pelton wheel (water turbine). It was first used at the Mayflower Mine in Nevada City, California in 1878. By 1879 he had tested a prototype Pelton wheel at the University of California. In 1887 a miner attached Pelton's wheel to a dynamo and produced the first hydroelectric power in the Sierra Nevada Mountains.

A patent was granted in 1889 to Pelton, and he later sold the rights to the Pelton Water Wheel Company of San Francisco.

Later evolutions of the pelton turbine were the Turgo_turbine, first patended by in 1919 by Gilkes (http://www.gilkes.com/home.htm) and the Banki turbine .