Tesla coil
claimed by Julia Denniss
Tesla Coil
Named for its inventor, Nikola Tesla, a Tesla coil is an electrical resonant transformer circuit capable of producing a potential of millions of volts. The coil is used to produce high-voltage, low-current, high frequency alternating-current electricity. The Tesla coil was initially created as a power supply for Tesla's "System of Electric Lighting" and were used in experiments in electrical lighting, wireless telegraphy, and X-rays. The Tesla coil first appeared in Tesla's patent No. 454,622 (1891) for use in electric lighting. Tesla coils can output anywhere from 50 kilovolts to several million volts for larger coils. The alternating current output is usually between 50 kHz and 1 MHz, in the low frequency radio range.
History
Around 1891, Tesla created the Tesla coil while expanding on and repeating the experiments of Heinrich Hertz, who had discovered electromagnetic radiation in 1888. He intended to go beyond the traditional iron-core transformer design to generate higher-frequency radio waves. As part of the design, Tesla initially utilized a high-speed alternator but found that the high frequency current melted the insulation and overheated the iron core. He then included a "sparkgap" into the system, which put a gap of insulating material between the primary and secondary windings, while also eliminating the iron core entirely. He also placed a capacitor between the alternator and the primary winding to avoid burning out the coil. The capacitor could connect through the short gap to the primary winding set to form a resonant circuit, once it was first charged to a high enough voltage to rupture the air in the gap. The current through the spark gap causes the primary resonant circuit to ring at its resonant frequency. It then magnetically couples energy into the secondary circuit over a series of radiofrequency cycles. Eventually the gap "quenches" or stops conducting, which traps all the energy in the secondary circuit. The gap can then reignite, and the secondary circuit can then transfer that energy back to the primary circuit. The coil may fire many times during an alternating current cycle. The secondary winding must be grounded to the surroundings in order to keep the balance of charge.
"Electric current, after passing into the earth travels to the diametrically opposite region of the same and rebounding from there, returns to its point of departure with virtually undiminished force. The outgoing and returning currents clash and form nodes and loops similar to those observable on a vibrating cord. To traverse the entire distance of about twenty-five thousand miles, equal to the circumference of the globe, the current requires a certain time interval, which I have approximately ascertained. In yielding this knowledge, nature has revealed one of its most precious secrets, of inestimable consequence to man. So astounding are the facts in this connection, that it would seem as though the Creator, himself, had electrically designed this planet just for the purpose of enabling us to achieve wonders which, before my discovery, could not have been conceived by the wildest imagination." -- Nikola Tesla
Tesla saw the Earth itself as a potential conductor of electrical energy. Between 1899 and 1900, he worked in a laboratory in Colorado Springs and researched possible methods of wireless power transmission. There, he built a large Tesla coil that he called a "magnifying transmitter", intended to transmit power through the ground to a receiver far away. The main coil was 53 feet in diameter and could produce potentials from 12-20 megavolts at a frequency of 150 kHz. When in use, the apparatus created massive 140-foot "bolts" of electricity. The magnifying transmitter included a third coil, which produced high voltage by resonance. With the magnifying transmitter, Tesla was able to light up a set of lamps 26 miles from the laboratory without using any wires between the two points. Though Guglielmo Marconi went down in history as the "father of the radio", much of his technology was based on discoveries made by Tesla using his invention, the Tesla coil.
Fundamental Principles
Tesla coils can produce massive electric fields due to the ability to create high voltages. It is comparable to a transformer, yet there are key differences between the two. The principle behind the Tesla coil is achieving resonance.
Resonance occurs when the primary coil transfers the current to the secondary coil at the exact time when the energy passed on will be at a maximum. An adjustable spark gap gives the user more control over the voltage of the current produced. The primary and secondary coils must be tuned to resonate with each other. With a significant amount of voltage, the internal spark plug gap will become ionized air, becoming a sort of circuit. Through a series of capacitors, the coil can produce the required voltage.
The equation to find the voltage is
V2 = V1\sqrt{C1 \ C2} = V1\sqrt{L2 \ L1}
where V is the voltage, C is the capacitance, and L is the inductance.
Usage
Until the 1920s, Tesla coils were used commercially as sparkgap radio transmitters for wireless telegraphy. Guglielmo Marconi eventually replaced Tesla's sparkgap with less expensive technology involving a metal powder coherer on the receiver side. The Tesla coil was also used in electrotherapy and other pseudomedical devices. Today, Tesla coils are mainly used in entertainment, educational displays, music, and (with some small coils) in leak detection in high vacuum systems. A hobby community of "coilers" has been built by those who build and design Tesla coils for personal use. Tesla coils can be used to produce music by modulating the system's "break rate", or the rate and duration of high power radio frequency bursts. These can be regulated with a control unit and MIDI music data to produce the effect of a "singing" coil. In high vacuum systems, it is imperative to ensure that there are no leaks, as even tiny ones could affect the system. Scientists test for the presence of leaks by using high-voltage discharges given off by a small Tesla coil. The high voltage electrode of the coil is placed over the outside surface of the apparatus being tested when it is evacuated. The discharge given off by the coil travels through any leak below it and illuminates the imperfection to indicate points that must be filled in before using the apparatus. Glassware is often tested in this way.
Future
Due to the large amounts of voltages that they can create, Tesla coils could potentially provide wireless transmission of power. This would allow the transition away from cables and instead to a more mobile form of electrical power. However, the technology is still difficult to implement due to cost and distance limitations. With more advancements in technology, this idea could potentially become reality.
See also
http://www.physicsbook.gatech.edu/Nikola_Tesla
Further reading
External links
References
http://scipp.ucsc.edu/edu/tesla/teslacoil/whatisateslacoil.html
http://www.richieburnett.co.uk/operation.html#operation
Dommermuth-Costa, Carol (1994). Nikola Tesla: A Spark of Genius. Twenty-First Century Books. p. 75. ISBN 0-8225-4920-4.
U.S. Patent No. 454,622, Nikola Tesla, SYSTEM OF ELECTRIC LIGHTING, filed 23 June 1891; granted 25 April 1891
Duckon 2007-Steve Ward's Singing Tesla Coil video Archived January 1, 1970, at the Wayback Machine.
Mazzotto, Domenico (1906). Wireless telegraphy and telephony. Whittaker and Co. p. 146.
W. Bernard Carlson, Tesla: Inventor of the Electrical Age, Princeton University Press - 2013, page 120