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Demonstration hand-cranked magneto made circa 1925, on display at the Musée d'histoire des sciences de la Ville de Genève. 2kW Société de l'Alliance magneto generator for arc lamps, of around 1870. A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current.
A permanent magnet synchronous generator is a generator where the excitation field is provided by a permanent magnet instead of a coil. The term synchronous refers here to the fact that the rotor and magnetic field rotate with the same speed, because the magnetic field is generated through a shaft-mounted permanent magnet mechanism, and current is induced into the stationary armature.
Diagram of a disk MHD generator showing current flows. The third and, currently, the most efficient design is the Hall effect disc generator. This design currently holds the efficiency and energy density records for MHD generation. A disc generator has fluid flowing between the center of a disc, and a duct wrapped around the edge.
Description: A self-excited shunt-wound DC generator is shown on the left, and a magneto DC generator with permanent field magnets is shown on the right. The shunt-wound generator output varies with the current draw, while the magneto output is steady regardless of load variations. Page 196 Main Wikipedia article: Excitation (magnetic)
A telephone magneto is a hand-cranked electrical generator that uses permanent magnets to produce alternating current from a rotating armature. In early telegraphy , magnetos were used to power instruments, while in telephony they were used to generate electrical current to drive electromechanical ringers in telephone sets and activate signals ...
"Dynamo Electric Machine" (end view, partly section, U.S. patent 284,110) A dynamo is an electrical generator that creates direct current using a commutator.Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current ...
Separately-excited generators like this are commonly used for large-scale power transmission plants. The smaller generator can be either a magneto with permanent field magnets or another self-excited generator. A field coil may be connected in shunt, in series, or in compound with the armature of a DC machine (motor or generator).
The DC generator generates a small amount of electricity, just enough to excite the field coils of the connected alternator to generate electricity. A variation of this system is a type of alternator that uses direct current from a battery for initial excitation upon start-up, after which the alternator becomes self-excited.