Tesla coil - Misplaced Pages

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US1119732
View in elevation
Free terminal and circuit of large surface with
supporting structure and generating apparatus
(Larger)

A Tesla coil is a high-voltage, air-core, self-regenerative resonant transformer that generates very high voltages at high frequency, named after its inventor Nikola Tesla. The coil achieves a great gain in voltage by means of a resonant circuit, unlike a conventional transformer whose gain is limited to the ratio of the numbers of turns in the windings. The Tesla coil's outer conducting surfaces, which are charged to a high potential, have large radii of curvature to minimise leakage of the oscillating charge.

Description

The intensity of the voltage gain of the circuit with a free, or elevated, toroid is proportional to the quantity of charge displaced, which is determined by the product of the capacitance of the circuit, the voltage (which Tesla called "pressure"), and the frequency of the currents employed.

The primary and secondary coils make up an air-core transformer. Tesla coils are composed of two coupled LC circuits: the tank circuit, which is a series LC circuit composed of the capacitor, spark gap, and primary coil; and the second LC circuit, a series resonant circuit, which is the secondary coil and the toroid. The toroid is one terminal of a capacitor, the other terminal being the ground.

The terminal consists of a metallic frame, sometimes a circular ring covered with smooth half spherical metal plates (constituting a very large conducting surface). The terminal has relatively small capacitance, charged to as high a voltage as practicable. The elevated conductor, its outer surface, is where the electrical charge chiefly accumulates. It has a large radius of curvature, or is composed of separate elements which, irrespective of their own radii of curvature, are arranged close to each other so that the outside ideal surface enveloping them has a large radius.

The frame is carried by a strong platform and rests on insulating supports. The circuit consists of a coil in close inductive relation with a primary, and one end of which is connected to a ground-plate, while its other end is led through a separate self-induction coil (whose connection should always be made at, or near, the center in order to secure a symmetrical distribution of the current) and a metallic cylinder to the terminal. The primary coil may be excited by any desired source, such as an alternator, capacitor, or condenser. The important requirement is that a resonant condition be established.

The conductor of the shaft to the terminal is in the form of a cylinder with smooth surface of a radius much larger than that of the spherical metal plates, and widens out at the bottom into a hood (which is slotted to avoid loss by eddy currents and for safety). The secondary coil is wound on a drum of insulating material, with its turns close together. When the effect of the small radius of curvature of the wire itself is overcome, the lower secondary coil behaves as a conductor of large radius of curvature, corresponding to that of the drum (this effect is applicable elsewhere). The lower end of the upper secondary coil, if desired, may be extended up to the terminal and should be somewhat below the uppermost turn of the primary coil. This lessens the tendency of the charge to break out from the wire connecting both and to pass along the support.

Utilization and production

File:TCOIL3.png
Typical Tesla Coil Schematic
This circuit is designed to be driven with alternating current.
(Larger)

A large Tesla coil can operate at very high power levels, up to many megawatts. It should therefore be adjusted and operated carefully, not only for efficiency, but also for safety. If, due to improper tuning, the maximum voltage point occurs below the terminal, along the coil, a discharge (spark), or possibly a ball of plasma, might break out and destroy the coil wire, supports, or anything else in the way. It is advisable to begin the tuning (i.e. setting the primary coil's resonant frequency to the same value of the secondary coil's) with low-power, increasing the power gradually, until the apparatus has been brought under perfect control. To increase the safety, one or more elements or plates of slightly smaller radius of curvature or protruding more or less beyond the others (in which case they may be of larger radius of curvature) so that, should the voltage rise beyond the design limit, energy will be safely discharged to the air (capacitively-coupled to ground).

The Tesla coil produces currents or discharges of very high frequency and voltage, useful for various purposes including weather research, classroom demonstration, theater and movie special-effects production, and product/technology safety testing. In operation, high-voltage sparks may strike out in all directions from the toroid into the air, producing a dangerous yet beautiful lightning-like display of electricity "in action".

This device was an early predecessor (along with the induction coil) to a more modern device called a flyback transformer, which provides the voltage needed to power the cathode ray tube used in televisions and computer monitors. ("CRT" displays are now beginning to become obsolete due to the technological advancement and proliferation of liquid crystal displays and related technologies.) A modern variant of the Tesla coil is also used to power plasma globe sculptures and similar devices.

Theoretically, a variation of the Tesla coil could utilize the phantom loop effect to form a circuit to induct energy from the earth's magnetic field. This concept is part of Tesla's wireless transmission of electric power distribution system (US1119732 - Apparatus for Transmitting Electrical Energy - 1902 January 18). This type of coil may have been used as the basis for the Wardenclyffe Tower project.

Instances

Tesla coil in operation
This is a small tesla coil in operation.

The Colorado Springs laboratory of Tesla possessed the largest Tesla Coil ever built, known as the "Magnifying Transmitter". The Magnifying Transmitter is not identical to the classic Tesla Coil, but is based in principle on this coil. The world's largest currently existing Tesla coil was made by Greg Leyh. It is a 130,000 watt Tesla coil, part of a 38 foot tall sculpture. It currently resides at a farm near Auckland, New Zealand.

Popularity

Tesla coils are very popular devices among certain electrical engineers and electronics enthusiasts. Someone who builds Tesla coils as a hobby is called a "Tesla coiler", or simply "coiler". There are even "coiling" conventions where people attend with their home made Tesla coils and other electrical devices of interest.

It should be noted that there are rather significant safety issues regarding coil assembly and operation by hobbyists (including professional engineers).

External links

Patent

Information

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