Homopolar generator

A Unipolarmaschine (also called Unipolargenerator, homopolar machine or Faraday generator ) is an electrical machine in a special embodiment for producing a high direct current at low voltage. The peculiarity of the Unipolarmaschine is that they directly generated using unipolar induction DC. In contrast, DC generators typically produce only with the help of commutators (mechanical rectifier ) a ( pulsating ) DC.

The Unipolargeneratoren today have only a small practical importance as powerful rectifiers are available and the efficiency of the AC voltage supplied generators such as the synchronous generator or asynchronous generator is significantly higher. Unipolargeneratoren were in the early days of electrical engineering, especially in the first half of the 20th century, an easy way low, pulse- free DC voltage gain at low generator internal resistance. At that time, the only technical alternative to generate pulse -free DC voltage in the use of batteries or accumulators.


Main component of the Unipolarmaschine is a rotatably mounted spindle on which a disc is preferably made ​​of a highly electrically conductive material such as copper. Two sliding contacts, one at each edge of the disc and a rotational axis of the lead, the electrical connections to the outside. The arrangement is housed in a constant magnetic field which passes through the disk perpendicular to its surface, e.g. by a permanent magnet, horseshoe-shaped. It functions like a Barlow so cal wheel in " reverse mode ". In classical approach, the induction appears (see also Faraday's paradox) to be contradictory and performs particularly when - at the N- machine - co-rotating magnetic field generator also today still disagreement on the exact mechanism. Only with the aid of the theory of relativity and its application to the correct transformation of the electromagnetic fields to solve this contradiction.

The voltage can then be produced in accordance with the principles of the unipolar induction calculated as follows:

Ri, Ra and the outer and inner radius of the disk, the angular frequency of the disk, ω, and B the magnetic flux density.

The application of Unipolarmaschine now extends only to specialties of the art, for example, full round Rohrverschweißung, energy storage ( up to 500 MJ) for high current applications ( militär. railgun ) as the removable voltage ( up to 500 V) and low handling the high currents ( up to 300 kA) is difficult. One benefit is that a direct voltage can be removed, thus no rectification is necessary. One application is the use as a tachometer.

For the first time such a device by Michael Faraday in 1832, was built and described the " Unipolar Inductor".


Unipolar experienced in the 1950s, a renaissance as a source of high -power pulses. These machines use a solid metal plate, which serves as a flywheel to store rotational energy to short-term leave due to the very low-impedance conductor arrangement with little internal resistance very high electrical current pulses. Such a system was built by Marcus Laurence Elwin Oliphant at the Australian National University. The disk could store a rotational energy of 500 MJ and deliver pulsed currents up to 2 MA, which were used from 1962 to 1986 in experiments with synchrotron particle accelerators.

N- machine

A form of Unipolarmaschine is conceived by Bruce de Palma and denoted by N- engine arrangement of two axially polarized, cylindrical permanent magnet, between which a disc of metal is possible with low resistivity. During rotation of the assembly can be a DC voltage between said axis and the disc between the two magnets detected. Since these co-rotate, the field lines are not " cut " in the classic idea why the machine was assumed by some non-interaction, so supposedly no mechanical energy would be recorded. Seemingly contrary to this observation that is the law of induction, which finds expression in the Faraday paradox and is dissolved. The induced voltage can be explained by the relative motion of the rotating wafer and thus the B- field to the stationary collector contact. Attached to that is the measuring arrangement at the wafer and can also rotate this, no voltage can be detected. Consequently, the conservation of energy is not violated and these are just about an apparent perpetual motion.