Homopolar Generator

A homopolar generator, also called a unipolar generator, acyclic generator, disk dynamo or Faraday disc, is a direct current electrical device in which an electrically conductive disc or cylinder rotates in a plane perpendicular to a uniform static magnetic field, producing a voltage between its center and its outer rim. Michael Faraday built the first working example during his experiments in 1831, a result considered the beginning of the modern dynamo and the first demonstration that magnetism could generate electricity. As the disc spins, the Lorentz force separates electric charge radially across it, and because the output never reverses polarity the device produces true direct current without needing the rectifiers or commutators that most rotating generators require; small demonstration models produce only a few volts, though large research versions can reach several hundred volts while carrying currents that can exceed one million amperes at very low internal resistance. Modern homopolar generators are used for welding, electrolysis, railgun research and pulsed energy storage for scientific experiments.