 At slow speeds, the output voltage increases with the square of the speed, but the magnetic circuit soon becomes saturated, resulting in much smaller increases as the speed increases.When used in circuits which include batteries charged from the output, a rectifier or reverse-current cut-out is normally required to prevent discharge of the batteries through the generator at very low speeds, or when the train stops.The Magnicon, developed by Macfarlane's in Scotland, is similar to the Metadyne, but whereas the latter has a two-pole armature winding, the Magnicon has a four-pole lap winding, and is sometimes referred to as a Metadyne with a short-pitched armature winding.