Examine individual changes

'{{About|a specific type of [[transformer]]|the more general electrical component|Inductor}} An '''induction coil''' or "spark coil" ([[archaism|archaically]] known as a '''Ruhmkorff coil''' after [[Heinrich Ruhmkorff]]) is a type of [[disruptive discharge]] [[coil]]. It is a type of electrical [[transformer]] used to produce high-voltage pulses from a low-voltage [[Direct current|DC]] supply. To create the flux changes necessary to induce voltage in the secondary, the DC current in the primary is repeatedly interrupted by a vibrating mechanical [[Switch|contact]] called an ''interrupter''. Developed beginning in 1836 by [[Nicholas Callan]] and others, the induction coil was the first type of transformer. The term 'induction coil' is also used for a coil carrying high-frequency [[Alternating current|AC]] producing eddy currents to heat objects placed in the interior of the coil, in [[induction heating]] or [[zone melting]] equipment. [[File:Induktionsapparat hg.jpg|thumb|270px|Antique induction coil used in schools, Bremerhaven, Germany]] ==How it works== [[File:Induction coil cutaway.png|thumb|270px|Induction coil showing construction, from 1920.]] An induction [[coil]] consists of two coils of insulated copper wire wound around a common [[magnetic core|iron core]]. One coil, called the ''[[primary winding]]'', is made from relatively few (tens or hundreds) turns of coarse wire. The other coil, the ''[[secondary winding]],'' typically consists of many (thousands) turns of fine wire. An [[electric current]] is passed through the primary, creating a [[magnetic field]]. Because of the common core, most of the primary's magnetic field couples with the secondary winding. The primary behaves as an [[inductor]], storing energy in the associated magnetic field. When the primary current is suddenly interrupted, the magnetic field rapidly collapses. This causes a [[high voltage]] pulse to be developed across the secondary terminals through [[electromagnetic induction]]. Because of the large number of turns in the secondary coil, the secondary voltage pulse is typically many thousands of [[volt]]s. This voltage is often sufficient to cause an [[electrical discharge]], or [[Electrostatic discharge|spark]], to jump across an air gap separating the secondary's output terminals. For this reason, induction coils were called spark coils. The size of induction coils was usually specified by the length of spark it could produce; an '8 inch' (20 cm) induction coil was one that could produce an 8 inch arc. ===Mercury and electrolytic interrupters=== The small 'hammer' interrupters described above were used on coils creating up to 8 inch (~120 kV) sparks. Larger coils used motor-driven interrupters.<ref>{{cite book|last=Collins|first=Archie F.|title=The Design and Construction of Induction Coils|date=1908|publisher=Munn & Co.|location=New York|url=http://books.google.com/?id=dJNPAAAAMAAJ&pg=PA98}} p.98</ref> The largest coils, used in radio transmitters, used either electrolytic or mercury turbine 'breaks'. ==Construction details== To prevent the high voltages generated in the coil from breaking down the thin [[Electrical insulation|insulation]] and [[Electrical arc|arcing]] between the secondary wires, the secondary coil uses special construction so as to avoid having wires carrying large voltage differences lying next to each other. The secondary coil is wound in many thin flat pancake-shaped sections (called "pies"), connected in [[Series circuit|series]]. The primary coil is first wound on the iron core, and insulated from the secondary with a thick paper or rubber coating. Then each secondary subcoil is coated with an insulating layer like [[paraffin]], connected to the coil next to it, and slid onto the iron core, insulated from adjoining coils with paper disks. The voltage developed in each subcoil isn't large enough to jump between the wires in the subcoil. Large voltages are only developed across many subcoils in series, which are too widely separated to arc over. To prevent [[eddy current]]s, which flow perpendicular to the magnetic axis, and cause energy losses, the iron core is made of a bundle of parallel iron wires, individually coated with [[shellac]] to insulate them electrically. == History == [[File:Callans_1863_induction_coil_.jpg|thumb|250px|Callan's largest induction coil (Model of 1863), showing 'pancake' secondary construction. It was 42 inches (106 cm) long and could produce 15 inch (38 cm) sparks, corresponding to a potential of approximately 200,000 volts.]] [[Michael Faraday]] discovered the principle of induction, [[Faraday's induction law]], in 1831 and did the first experiments with induction between coils of wire.<ref>{{cite journal|last=Faraday|first=Michael|date=1834|title=Experimental researches on electricity, 7th series|journal=Phil. Trans. R. Soc. (London)|volume=124|pages=77–122|doi=10.1098/rstl.1834.0008}}</ref> The induction coil was invented by the Irish scientist and Roman Catholic priest [[Nicholas Callan]] in 1836 at the [[National University of Ireland, Maynooth|St. Patrick's College, Maynooth]]<ref>{{cite book|last=Fleming|first=John Ambrose|date=1896|title=The Alternate Current Transformer in Theory and Practice, Vol.2|publisher=The Electrician Publishing Co.|url=http://books.google.com/?id=17sKAAAAIAAJ&pg=PA16}} p.16-18</ref> <ref>http://www.nuim.ie/museum/ncallan.html</ref> and improved by [[William Sturgeon]] and [[Charles Grafton Page]]. The early coils had hand cranked interrupters, invented by Callan and [[Antoine Masson]]. The automatic 'hammer' interrupter was invented by C. E. Neeff, P. Wagner, and J. W. M'Gauley. [[Hippolyte Fizeau]] introduced the use of the quenching capacitor.<ref>{{cite web|last=Severns|first=Rudy|title=History of soft switching, Part 2|work=Design Resource Center|publisher=Switching Power Magazine|url=http://www.switchingpowermagazine.com/downloads/Oct%2001%20soft.pdf|accessdate=2008-05-16}}</ref> [[Heinrich Ruhmkorff]] generated higher voltages by greatly increasing the length of the secondary, in some coils using 5 or 6 miles (10 km) of wire. In the early 1850s, after examining an example of a Ruhmkorff coil, which produced a small spark of around ''2 inches'' (50 mm) when energized, American inventor [[Edward Samuel Ritchie]] perceived that it could be made more efficient and produce a stronger spark by redesigning and improving its secondary insulation. His own design divided the coil into sections, each properly insulated from each other. Ritchie's induction coil proved superior to other designs of the day, initially producing a spark of ''10 inches'' (25 cm) in length; later versions could produce an electrical bolt ''24 inches'' (60 cm) or longer in length.<ref>American Academy of Arts and Sciences, ''Proceedings of the American Academy of Arts and Sciences'', Vol. XXIII, May 1895 - May 1896, Boston: University Press, John Wilson and Son (1896), pp. 359-360</ref><ref>Page, Charles G., ''History of Induction: The American Claim to the Induction Coil and Its Electrostatic Developments'', Boston: Harvard University, Intelligencer Printing house (1867), pp. 104-106</ref> The full story of Page's invention of the induction coil in its modern guise is told in Robert Post, "Physics, Patents, and Politics: A Biography of [[Charles Grafton Page]]" (Science History Publications, 1976. In 1857, one of Ritchie's induction coils was exhibited in [[Dublin]], Ireland at a conference of the [[British Association]],<ref>Rogers, W. B. (Prof.), ''Brief Account of the Construction and Effects of a very Powerful Induction Apparatus, devised by Mr. E.S. Ritchie, of Boston, United States'', British Association for the Advancement of Science, Report of the Annual Meeting (1858), p. 15</ref> and later at the [[University of Edinburgh]] in Scotland.<ref>American Academy, pp. 359-360</ref> Ruhmkorff himself purchased a Ritchie induction coil, utilizing its improvements in his own work.<ref>American Academy, pp. 359-360</ref><ref>Page, pp. 104-106</ref> Induction coils were used to provide high voltage for early [[gas discharge]] and [[Crookes tube]]s and for [[X-ray]] research. They were also used to provide entertainment (lighting [[Geissler tube]]s, for example) and to drive small "shocking coils", [[Tesla coil]]s and [[violet ray]] devices used in [[quack medicine]]. They were used by [[Heinrich Rudolf Hertz|Hertz]] to demonstrate the existence of electromagnetic waves, as predicted by [[James Clerk Maxwell|James Maxwell]] and by [[Nikola Tesla|Tesla]] and [[Guglielmo Marconi|Marconi]] in the first research into radio waves. Their largest industrial use was probably in early [[wireless telegraphy]] [[Spark-gap transmitter|spark-gap radio transmitters]] and to power [[cold cathode]] [[x-ray tube]]s. By about 1920 they were supplanted in both these applications by [[vacuum tube]]s. However their largest use was as the [[ignition coil]] or spark coil in the [[ignition system]] of [[internal combustion engine]]s, where they are still used, although the interrupter contacts are now replaced by [[Solid state (electronics)|solid state]] switches. A smaller version is used to trigger the [[xenon flash lamp|flash tube]]s used in cameras and [[strobe]] lights. [[Image:Igncoil.jpg|thumb|left|Automobile [[ignition coil]], the largest remaining use for induction coils]] == Wireless charging == [[Toyota]]'s heavy duty division, [[Hino Motors]], is testing a new kind of [[hybrid electric vehicle]] without a plug (hybrid outboard chargeable vehicle). The energy in the batteries doesn't come from a plug and a charging point, but it comes from a wireless charging system built into the road. A series of induction coils built into the road resonate energy at certain frequency, like radio waves. The bus is able to capture those waves and store the energy in its batteries<ref>http://www.ecogeek.org/content/view/1431/</ref>. == Early patents == * {{US patent|52054}} The induction-coil, instead of being made movable upon the magnet * {{US patent|72616}} This compound coil is made like any ordinary induction-coil * {{US patent|74905}} The inner end of the induction-coil are surrounded by the prime coil * {{US patent|76654}} The induction-coil consists of a metallic conductor, copper is generally preferred * {{US patent|78495}} Energizing the primary wire of the induction-coil, the iron core becomes magnetized * {{US patent|90626}} Making use of an induction-coil * {{US patent|734197}} a split-coil improvement (1903). * {{US patent|1092417}} Induction coil comprising a soft iron core (Mar 5, 1913) == See also == * [[Charging station]] * [[Ignition coil]] * [[Spark gap transmitter]] * [[Transformer]] * [[Tesla coil]] * [[Electromagnetism]] * [[Faraday's law of induction]] * [[Ignition system]] * [[Inductor]] * [[Magnetic field]] == Footnotes == {{reflist}} == Further reading == * Norrie, H. S., "''Induction Coils: How to Make, Use, and Repair Them''". Norman H. Schneider, 1907, New York. 4th edition. * {{cite book|last=Collins|first=Archie F.|title=The Design and Construction of Induction Coils|date=1908|publisher=Munn & Co.|location=New York|url=http://books.google.com/?id=dJNPAAAAMAAJ&pg=PA98}} * {{cite book|last=Fleming|first=John Ambrose|date=1896|title=The Alternate Current Transformer in Theory and Practice, Vol.2|publisher=The Electrician Publishing Co.|url=http://books.google.com/?id=17sKAAAAIAAJ&pg=PA16}} Has detailed history of invention of induction coil * == External links == * [http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm Battery powered Driver circuit for Induction Coils] * [http://members.chello.nl/~h.dijkstra19/page8.html The Cathode Ray Tube site] [[Category:Transformers (electrical)|Induction coil]] [[Category:Electrical breakdown]] [[de:Funkeninduktor]] [[es:Bobina de Ruhmkorff]] [[fr:Bobine de Ruhmkorff]] [[it:Rocchetto di Ruhmkorff]] [[nl:Vonkinductor]] [[pl:Cewka Ruhmkorffa]] [[ru:Катушка Румкорфа]] [[tk:Induktiwlik tegegi]]'