A homopolar generator, also known as a unipolar generator, acyclic generator, or disk dynamo, is an electrical generator in which the magnetic field has the same polarity at every point, so that the armature passes through the magnetic field lines of force continually in the same direction.^[1]. The device is electrically symmetrical^[2], and generates continuous current. Some of these devices also have "homopolar magnets", which have pole pieces arranged around a common centre. An electrical generator is a device that produces electrical energy from a mechanical energy source. ... It has been suggested that Magnetic field density be merged into this article or section. ... layers]] that separate organs or subcompartments in organisms. ... Magnetic field lines of a bar magnet shown by iron filings on paper A magnet is an object that has a magnetic field. ... Line of force Line of flux. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...

History and development

The homopolar generator was developed first by Michael Faraday during his memorable experiments in 1831. It is sometimes called the Faraday disc in his honor. It was the beginning of modern dynamos — that is, electrical generators which operate using a magnetic field. It was very inefficient and was not used as a practical power source, but it showed the possibility of generating electric power using magnetism, and led the way for commutated direct current dynamos and then alternating current dynamos. Michael Faraday Michael Faraday, FRS (September 22, 1791 – August 25, 1867) was a British physicist and chemist who contributed significantly to the fields of electromagnetism and electrochemistry. ... 1831 was a common year starting on Saturday (see link for calendar). ... Dynamo can refer to more than one item. ... An electrical generator is a device that produces electrical energy from a mechanical energy source. ... It has been suggested that Magnetic field density be merged into this article or section. ... Conventional continuous current flows from the battery. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... City lights viewed in a motion blurred exposure. ...

The remains of the ANU 500MJ generator

Long after the original Faraday disc had been abandoned as a practical generator, a modified version combining the magnet and disc in a single rotating part (the rotor) was developed. Sometimes the name homopolar generator is reserved for this configuration. One of the earliest patents on the general type of homopolar generators was attained by Charles E. Ball (US238631; March 1881). Other early patents for homopolar generators were awarded to S. Z. De Ferranti and C. Batchelor separately. Nikola Tesla was interested in the Faraday disc and conducted work with homopolar generators ^[3]. He eventuially patented an improved version of the device and his U.S. Patent 406968 ("Dynamo Electric Machine") describes an arrangement of two parallel discs on separate, parallel axles, and joined like pulleys by a metallic belt. This would have greatly reduced the frictional losses caused by sliding contacts. Later, patents were awarded to C. P. Steinmetz and E. Thomson for their work with homopolar generators. The Forbes dynamo, developed by the Scottish electrical engineer George Forbes, was in widespread use during the beginning of the 20th century. Much of the development done in homopolar generators was patented by J. E. Noeggerath and R. Eickemeyer. Image File history File links Download high resolution version (1600x1231, 595 KB) Summary The remains of the RSPhysSE, ANU Homopolar generator. ... Image File history File links Download high resolution version (1600x1231, 595 KB) Summary The remains of the RSPhysSE, ANU Homopolar generator. ... Sebastian Ziani de Ferranti (1864-1930) was an electrical engineer and inventor. ... Charles W. Batchelor, inventor, associate of Thomas A. Edison, early executive of General Electric Company Charles W. Batchelor (December 25, 1845-January 1, 1910) was an inventor and close associate of American inventor Thomas Alva Edison during much of Edison’s career. ... Nikola Tesla (July 10, 1856 - c. ... Pulleys on a ship. ... Charles Proteus Steinmetz (1865-1923) Marconi Wireless Station in Somerset, New Jersey in 1921 Charles Proteus Steinmetz (April 9, 1865 – October 26, 1923) was a mathematician and electrical engineer. ... Elihu Thomson (March 29, 1853 - March 13, 1937) was an engineer who was instrumental in the founding of major electrical companies in the United States, Britain and France. ...

One of the larger homopolar generators that was produced by Parker Kinetic Designs via the collaboration of Richard Marshall, William Weldon, and Herb Woodson. Parker Kinetic Designs have produced devices which can produce five mega-amperes. Another large homopolar generator was built by Sir Mark Oliphant at the Research School of Physical Sciences and Engineering, Australian National University. It produced 500 mega-joules and was used as an extremely high-current source for experimentation from 1962. It was disassembled in 1986. Oliphant's construction was capable of supplying currents of up to 2 mega-amperes. The ampere (symbol: A) is the SI base unit of electric current equal to one coulomb per second. ... Mark Oliphant (left) Sir Marcus Mark Laurence Elwin Oliphant (October 8, 1901 - July 14, 2000) was an Australian physicist and humanitarian who played a fundamental role in the development of the Atom bomb. ... The Research School of Physical Sciences and Engineering (RSPhysSE) was established with the creation of the Australian National University (ANU) in 1947. ... The Australian National University (ANU), is a university located in Canberra, the national capital of Australia. ... The joule (symbol: J) is the SI unit of energy, or work with base units of kg·m²/s². // Definition The joule is a derived unit defined as the work done or energy required, to exert a force of one newton for a distance of one metre, so the same...

Description and operation

The device consists of a conducting flywheel rotating in a magnetic field with one electrical contact near the axis and the other near the periphery. It has been used for generating very high currents at low voltages in applications such as welding, electrolysis and railgun research. In pulsed energy applications, the angular momentum of the rotor is used to store energy over a long period and then release it in a short time. There is a uncertain nature of the torque reaction in homopolar machines, though it is known that centrifugal and coriolis forces are generated in circular homopolar generators. In the 1980s, there was investigation of the "back torque" in these machines. Electrical conductivity is a measure of a materials ability to conduct an electric current. ... Spoked flywheel A flywheel is a heavy rotating disk used as a repository for angular momentum. ... It has been suggested that Magnetic field density be merged into this article or section. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ... In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. ... A railgun is a form of gun that converts electrical energy—rather than the more conventional chemical energy from an explosive propellant—into projectile kinetic energy. ... In physics the angular momentum of an object with respect to a reference point is a measure for the extent to which, and the direction in which, the object rotates about the reference point. ... The expression centrifugal force is used to express that if an object is being swung around on a string the object seems to be pulling on the string. ... In physics, the Coriolis effect is an inertial force first described by Gaspard-Gustave Coriolis, a French scientist, in 1835. ... The 1980s decade refers to the years from 1980 to 1989, inclusive. ... Back Emf is an Electromotive force that occurs in Electric motors where there is relative motion between the armature of the motor and the external magnetic field. ...

In contrast to other types of generators, the output voltage never changes polarity. The charge separation results from the Lorentz force on the free charges in the disk. The motion is azimuthal and the field is axial, so the electromotive force is radial. The electrical contacts must be made through a "brush" or slip ring, which results in large losses at the low voltages generated. The table below shows the results of different relative motions of the parts of a circular homopolar generator ^[4]. In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ... Electromotive force (emf),[hammid the smelly fucking arab that cant hold his farts] often denoted by , is a measure of the strength of a source of electrical energy. ... In electrical engineering, brushes conduct current between stationary wires and moving parts, most commonly in a rotating shaft. ... One or more images would improve this articles quality. ...

If the magnetic field is provided by a permanent magnet, the generator works regardless of whether the magnet is fixed to the stator or rotates with the disc. Before the discovery of the electron and the Lorentz force law, the phenomenon was inexplicable and was known as the Faraday paradox. The voltage is "undetermined" when both the indicator and the disk are rotated, regardless of whether the magnet is moving. There is a EMF and a nonuniform charge density, but no reaction of the indicator^[5]. An electric field is generated, but no voltage is brought out for display. This differs from the different relative motions of the parts of a rectilinear homopolar generator (where the answer would be "No"). Magnetic field lines of a bar magnet shown by iron filings on paper A magnet is an object that has a magnetic field. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ... A phenomenon (plural: phenomena) is an observable event, especially something special (literally something that can be seen from the Greek word phainomenon = observable). ... In 1832 famous scientist Michael Faraday performed some very interesting experiments with magnets and conducting disks. ...

The current, once started, may be sufficient to maintain itself and even increase in strength and the device would be operated as a self-excited generator.

Physics

Like all dynamos, the Faraday disc converts kinetic energy to electrical energy. However, unlike all other dynamos, this machine cannot be analysed using Faraday's own law of electromagnetic induction. This law (in its modern form) states that an electric current is induced in a closed electrical circuit when the magnetic flux enclosed by the circuit changes (in either magnitude or direction). However, the circuit in the Faraday disc is parallel to the magnetic flux vector and therefore encloses no magnetic flux. Therefore, Faraday's law does not apply to this machine. Kinetic energy (SI unit: the joule) is energy that a body possesses as a result of its motion. ... Electrical energy or electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. ... Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux. ...

Instead, the Lorentz force law is used to explain the machine's behaviour. This law, discovered thirty years after Faraday's death, states that the force on an electron is proportional to the cross product of its velocity and the magnetic flux vector. In geometrical terms, this means that the force is at right-angles to both the velocity (azimuthal) and the magnetic flux (axial), which is therefore in a radial direction. The radial movement of the electron then creates an electric current between the centre of the disc and its rim. In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ... In mathematics, the cross product is a binary operation on vectors in a three-dimensional Euclidean space. ... The velocity of an object is simply its speed in a particular direction. ... Magnetic flux, is a measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. ...

There is a subtle difficulty in this explanation, which often leads to a misunderstanding of how the machine works. The key word in the preceding paragraph is velocity, which prompts the question, "velocity relative to what?". If the velocity relative to the magnet is assumed as the cause of the Lorentz force, then the explanation contradicts special relativity, which states that it is impossible to tell whether a uniform magnetic field is moving or stationary. This assumption would also imply that rotating the magnet and not the disc would cause a current to flow, which is not what experimenters have found. Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. It replaced Newtonian notions of space and time and incorporated electromagnetism as represented by Maxwells equations. ...

The correct interpretation of the velocity of the electron is that it is relative to the static parts of the machine, which are the sliding contacts and the circuit to which they are connected. In the language of special relativity, these objects act as the 'observer'. It is the velocity of the electron relative to these components that causes it to experience the Lorentz force. Observation is an activity of an intelligent living being, to sense and assimiliate the knowledge of a phenomenon in its framework of previous knowledge and ideas. ...

Patents

The United States Patent Office uses the clasification class 310 (Electrical generator or motor structure) and subclass 178 (Dynamoelectric; Rotary; D.C.; Homopolar) for these devices. Many of the homopolar patents were obtained prior to 1975.

• G. D. Hathaway, "U.S. Patent 5587618, Direct current homopolar machine".
• W. F. Weldon, "U.S. Patent 5530309 Homopolar machine ".
• Antonios Challita, "U.S. Patent 5049771 Electrical machine".
• W. F. Weldon, "U.S. Patent 4858304, Method of constructing a rotor assembly for homopolar generator".
• W. F. Weldon, "U.S. Patent 4800311 Rotor assembly for homopolar generator".
• W. F. Weldon, "U.S. Patent 4544874 Homopolar generator power supply system".
• W. F. Weldon, "U.S. Patent 4246507 Removable brush mechanism for a homopolar generator ".
• Esko Ensio hubta-Koivisto, "U.S. Patent 3469137 Electric unipolar motor".
• E. C. Ketchum and D. H. Andrews, "U.S. Patent 1082579 Dynamo electric machine".
• A. Kingsbury, "U.S. Patent 992965 Dynamo electric machine".
• W. A. Dick, "U.S. Patent 992943 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 988377 Dynamo electric machine".
• H. Hertz, "U.S. Patent 988340 Unipolar exciter for turbo-generators".
• D. W. Troy, "U.S. Patent 979603 Dynamo electric machine".
• A. S. Hubbard, "U.S. Patent 970827 Dynamo electric machine".
• B. Von Ugrimoff, "U.S. Patent 970407 Cooling device for electrical sliding contacts".
• E. C. Ketchum, "U.S. Patent 966839 Brush holders for dynamos".
• J. E. Noeggerath, "U.S. Patent 960383 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 959959 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 937462 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 920626 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 900771 Armature for unipolar machines".
• J. E. Noeggerath, "U.S. Patent 895888 Unipolar dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 895887 Acyclic machine".
• J. E. Noeggerath, "U.S. Patent 890697 Protective device for unipolar machine".
• A. C. Eastwood, "U.S. Patent 881387 System of control for electric motors".
• J. E. Noeggerath, "U.S. Patent 873072 Dynamo electric machine".
• W. Mathiesen, "U.S. Patent 861192 Unipolar dynamo".
• E. Thomson, "U.S. Patent 859350 Unipolar generator".
• J. E. Noeggerath, "U.S. Patent 854756 Dynamo electric machine".
• C. Macmillan, "U.S. Patent 854749 Power transmission mechanism".
• C. Macmillan, "U.S. Patent 850664 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 832742 Unipolar alternating current machine".
• E. C. Ketchum, "U.S. Patent 826668 Dynamo".
• H. H. Wait, "U.S. Patent 806217 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 805315 Unipolar machine".
• C. P. Steinmetz, "U.S. Patent 804440 Dynamo electric machine".
• J. E. Noeggerath, "U.S. Patent 789444 Electric motor".
• E. R. Cox, Jr., "U.S. Patent 742600 Dynamo electric machine or motor".
• B. Bjarnason, "U.S. Patent 678157 Dynamo electric machine".
• F. W. Throop, "U.S. Patent 662042 Dynamo electric machine".
• G. Dalen and A Hultovist, "U.S. Patent 645943 Dynamo electric machine".
• F. G. Mayer, "U.S. Patent 561803 Dynamo electric machine".
• E. Thomson and M. J. Wightman, "U.S. Patent 550464 Dynamo electric machine".
• G. Rennerfelt, "U.S. Patent 523998 Dynamo electric machine".
• H. E. Dikeman, "U.S. Patent 518444 Dynamo electric machine".
• J. E. Maynadier, "U.S. Patent 515882 Dynamo electric machine".
• T. L. Willson, "U.S. Patent 495538 Dynamo electric machine".
• N. Tesla, "U.S. Patent 406968 Dynamo electric machine".
• J. B. Entz, "U.S. Patent 400838 Dynamo electric machine".
• R. Eickemeyer, "U.S. Patent 396149 Unipolar dynamo electric machine".
• E. A. Sperry, "U.S. Patent 354946 Dynamo electric machine".
• R. Eickemeyer, "U.S. Patent 352234 Electro magnetic and megneto electric machine".
• R. Eickemeyer, "U.S. Patent 351907 Device for taking electric currents from or to moving surfaces".
• R. Eickemeyer, "U.S. Patent 351904 Magneto electric and electro magnetic machine".
• R. Eickemeyer, "U.S. Patent 351903 Magneto electric and electro magnetic machine".
• R. Eickemeyer, "U.S. Patent 351902 Magneto electric and electro magnetic machine".
• R. Eickemeyer, "U.S. Patent 342589 Dynamo electric and electro magnetic machine".
• R. Eickemeyer, "U.S. Patent 342588 Dynamo electric and electro magnetic machine".
• R. Eickemeyer, "U.S. Patent 342587 Dynamo electric and electro magnetic machine".
• R. Eickemeyer, "U.S. Patent 342504 Magneto electric and electro magnetic machine".
• S. Z. De Ferranti, "U.S. Patent 341097 Unipolar dynamo electric machine".
• C. Batchelor and H. E. Walter"U.S. Patent 339839 Dynamo electric machine".
• C. Hering, "U.S. Patent 339772 Unipolar dynamo electric machine".
• G. Forbes, "U.S. Patent 338169 Dynamo electric machine".
• A. E. G. Lubke, "U.S. Patent 293758 Dynamo electric machine".
• A. F. Delafield, "U.S. Patent 278516 Dynamo electric machine".
• C. E. Ball, "U.S. Patent 238631 Dynamo or magneto-electric machine".

Elihu Thomson (March 29, 1853 - March 13, 1937) was an engineer who was instrumental in the founding of major electrical companies in the United States, Britain and France. ... Charles Proteus Steinmetz (1865-1923) Marconi Wireless Station in Somerset, New Jersey in 1921 Charles Proteus Steinmetz (April 9, 1865 – October 26, 1923) was a mathematician and electrical engineer. ... Nikola Tesla (July 10, 1856 - c. ... Elmer Ambrose Sperry (October 12, 1860 - June 16, 1930) was an inventor and entrepreneur. ... Sebastian Ziani de Ferranti (1864-1930) was an electrical engineer and inventor. ... Charles W. Batchelor, inventor, associate of Thomas A. Edison, early executive of General Electric Company Charles W. Batchelor (December 25, 1845-January 1, 1910) was an inventor and close associate of American inventor Thomas Alva Edison during much of Edison’s career. ... There have been the following people named George Forbes. ...

See also

• Homopolar motor
• Bruce De Palma
• Faraday paradox

To meet Wikipedias quality standards, this article or section may require cleanup. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... In 1832 famous scientist Michael Faraday performed some very interesting experiments with magnets and conducting disks. ...

References and further reading

General references

• Don Lancaster, "Shattering the homopolar myths". Tech Musings, October, 1997. (PDF)
• Don Lancaster, "Understanding Faraday's Disk". Tech Musings, October, 1997. (PDF)
• John David Jackson, Classical Electrodynamics, Wiley, 3rd ed. 1998, ISBN 047130932X
• Olivier Darrigol, Electrodynamics from Ampere to Einstein, Oxford University Press, 2000, ISBN 0198505949
• Thomas Valone, The Homopolar Handbook : A Definitive Guide to Faraday Disk and N-Machine Technologies. Washington, DC, U.S.A.: Integrity Research Institute, 2001. ISBN 0964107015
• Trevor Ophel and John Jenkin, (1996) Fire in the belly : the first 50 years of the pioneer school at the ANU Canberra : Research School of Physical Sciences and Engineering, Australian National University. ISBN 0-85-800048-2. (PDF)

Citations

• ↑  Rudolf F. Graf, "Dictionary of Electronics; Radio Shack, 1974-75". Fort Worth, Texas.
  • ↑  Ibid.
• ↑  Thomas Valone, "Harnessing the Wheelwork of Nature : Tesla's Science of Energy", The Homopolar Generator: Tesla's Contribution. ISBN 1-931882-04-5 (ed. originally presented in the Proceedings of International Tesla Symposium, 1986, p. 6-29)
  • ↑  Ibid.
• ↑  Nikola Tesla, "Notes on a Unipolar Dynamo". The Electrical Engineer, N.Y., Sept. 2, 1891. (Also available at tesla.hu, Article 18910902)

Further readings

• Richard A. Marshall and William F. Weldon, "Parameter Selection for Homopolar Generators Used as Pulsed Energy Stores", Center for Electromechanics, University of Texas, Austin, Jul. 1980. (also published in: Electrical Machines and Electromechanics, 6:109-127, 1981.)

Thomas Valone is an engineering physicist with 25 years of experience in emerging energy sciences. ...

External links and other articles

• Robert Hebner, "Homopolar Generator". Homopolar Welding, UT-CEM.
• "K2-64: Unipolar generator". physics.umd.edu.
• Richard E. Berg and Carroll O. Alley, "The Unipolar Generator: A Demonstration of Special Relativity", Department of Physics, University of Maryland, 2005. (PDF)
• Richard Fitzpatrick, "Magnetohydrodynamic theory ", The homopolar generator. farside.ph.utexas.edu, 2006-02-16.
• "5K10.80 Homopolar Generator; Lecture Demonstrations.". physics.brown.edu
• Jean-Louis Naudin, "The Faraday Homopolar Generator Experiment". 13 April 1997.
• William J. Beaty, "Untried Homopolar Generator Experiments". 1996.
• Mike Galloway, "N-1 Homopolar Generator".
• Bruce E. DePalma, "The Trombly-Kahn Homopolar Generator; Critique of the N-Machine Constructed by Trombly & Kahn". 11 October 1985.
• Bruce E. DePalma, "A review of: "The Homopolar Handbook", by Thomas Valone". 2 February 1995.
• "The Faraday Disk Dynamo as the original over-unity device". Archer Energy Systems, Inc., 2006.