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An induction coil or "spark coil" (archaically known as a Ruhmkorff coil) is a type of disruptive discharge coil. It is a passive electrical device used to produce high-voltage pulses from a low-voltage DC supply.
Description
Induction coils consist of two coils of copper wire wound around a common iron core. One coil, called the primary, is made using tens or hundreds of turns of coarse wire. The other, called the secondary, typically consists of many thousands of turns of fine wire. Electrical current is passed through the primary, creating a magnetic field. The primary behaves as an inductor, storing energy in the associated magnetic field. When the primary current is suddenly interrupted, the magnetic field collapses. This causes a high voltage pulse to be developed across the secondary terminals. Often, the high secondary voltage is sufficient to cause an electrical discharge, or spark, to jump across an air gap.
The term "Induction coil" is also used for a coil carrying high-frequency AC and intended to induce eddy currents to heat objects placed in the interior of the coil, such as in induction heating or zone melting.
History
The induction coil was discovered during early experiments with electricity, probably by Nicholas Callan in 1836, and further developed by Heinrich Ruhmkorff. This type of disruptive discharge coil remains in common use as the "ignition coil" or "spark coil" in the ignition system of internal combustion engines. A smaller version is used to trigger the flash tubes used in cameras and strobe lights. They were used by Hertz to demonstrate electromagnetic waves existed, as predicted by James Maxwell, and by Marconi in early wireless telegraphy. They were supplanted in wireless or radio work by vacuum tubes by 1920.
See also
Further reading
- Norrie, H. S., "Induction Coils: How to Make, Use, and Repair Them". Norman H. Schneider, 1907, New York. 4th edition.
- Faraday M (1834): Experimental researches on electricity, 7th series. Phil. Trans. R. Soc. (Lond.) 124: 77-122.
External links
"Induction coil"