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PowerPedia:Tesla coil

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This later coil type is the usual device built by modern enthusiasts. (View in elevation: Free terminal and circuit of large surface with supporting structure and generating apparatus)
This later coil type is the usual device built by modern enthusiasts.
(View in elevation: Free terminal and circuit of large surface with supporting structure and generating apparatus)

A Tesla coil is generally known as a category of disruptive discharge coils, named after their inventor, Nikola Tesla. Tesla actually experimented with a large variety of coils and configurations (for tansmissions and reception), so it is difficult to describe a specific mode of construction that will meet the wants of those who ask about "Tesla" coils. One common feature of Tesla coils is that they are all composed of coupled resonant electric circuits. Applications include the wireless transmission of electricity


Early "Tesla" coils

Following the initial research of voltage and frequency by William Crookes, Tesla developed a series of coils that produced high-voltage, high-frequency currents. In the majority of Tesla's experiments, he used machinery of his own design to produce the Tesla effect. These early coils would use the "disruptive" action of a spark gap in their operation. The setup can be duplicated by a Ruhmkorff coil, two condensers, and a second, specially constructed, disruptive coil. (Norrie, pg. 228)

The Ruhmkorff coil, being fed from a main source, is wired to condensers (now called capacitors) on both ends in series. A spark gap is placed in parallel to the Ruhmkorff coil before the condensers. The discharge tips were usually metal balls under one inch in diameter, though Tesla used various forms of dischargers. The condensers were of a special design, small with high insulation. These condensers consisted of plates in oil that were movable. The smaller the plates, the more frequent the discharge of this early coil apparatus. The plates also help nullify the high self inductance of the secondary coil by adding capacity to it. Mica plates were placed in the spark gap to establish an air current jet to go up through the gap. This made the discharge more abrupt. An air blast was also used for this objective. (Norrie, pg. 230-231)

Early Tesla coil circuit.
Early Tesla coil circuit.
Tesla's condensers.
Tesla's condensers.

The condensers are connected to a double primary (each coil in series with a condenser). These are part of the second specially constructed disruptive coil. The primaries each have twenty turns of No. 16 B & S rubber covered wire and are wound separately on rubber tubes not less than a 1/8th inch thick. The secondary has 300 turns of No. 30 B & S silk-covered magnet wire, wound on rubber tube or rod, and the ends encased in glass or rubber tubes. The primaries must be large enough to be loose when the secondary coil is place between the coils. The primaries must cover around two inches of the secondary. A hard rubber division must be placed between these primary coils. The ends of the primaries not connected with the condensers are lead to a spark gap. (Norrie, pg. 35-36)

Tesla's later coils were considerably larger and operated at much higher power levels. These later systems were powered from large high voltage transformers, used banks of glass bottle capacitors immersed in oil to reduce corona losses, and used rotating spark gaps to handle the higher power levels. Tesla also dispensed with using oil to insulate the transformer coils, relying instead on the insulating properties of air. Tesla coils achieve great gain in voltage by loosely coupling two resonant LC circuits together, using an air-core (ironless) transformer. Unlike a conventional transformer, whose gain is limited to the ratio of the numbers of turns in the windings, Tesla coils' voltage gain is proportional to the square root of the ratio of secondary and primary inductances.

Magnifying transmitter

In 1899, Tesla decided to move and construct the Magnifying transmitter in Colorado Springs, Colorado. He chose this location primarily because of the frequent thunderstorms, the high altitude (where the air, being at a lower pressure, had a lower dielectric breakdown strength, making it easier to ionize), and the dryness of the air (minimizing leakage of electric charge through insulators).

Tesla kept a diary of his experiments in the Colorado Springs lab where he spent nearly nine months. It consists of 500 pages of handwritten notes and nearly 200 drawings, recorded chronologically between June 1, 1899 and January 7, 1900, as the work occurred, containing explanations of his experiments. The magnifying transmitter, which is noted in the diary, is an alternate version of a Tesla Coil. It is a high power harmonic oscillator that Nikola Tesla proposed for the wireless transmission of electrical energy.[1] Tesla's apparatus is a high-voltage, air-core, multiple-resonant transformer that can generate very high voltages at high frequency. He originally termed it self-regenerative resonant transformer, a term that is no longer in general use.


The first 'Magnifier' was assembled in New York City in the period between 1895 - 1898.[1] In 1899 a larger magnifier was constructed in Colorado Springs, Colorado. This machine was used to conduct fundamental experiments in wireless telecommunications and electrical power transmission. Measuring fifty-one feet (15.5 m) in diameter, it developed a working potential estimated at 3.5 million to 4 million volts and was capable of producing electrical discharges exceeding one hundred feet (30 m) in length.[2]

Colorado arrival

Tesla's Colorado lab was located in a highly geomagnetic location.
Tesla's Colorado lab was located in a highly geomagnetic location.

In 1899, Tesla decided to move and began research in Colorado Springs. He chose this location primarily because of the frequent thunderstorms, the high altitude (where the air, being at a lower pressure, had a lower dielectric breakdown strength, making it easier to ionize), and the dryness of the air (minimizing leakage of electric charge through insulators). Tesla kept a handwritten diary of his experiments in the Colorado Springs lab where he spent nearly nine months. It consists of 500 pages of notes and nearly 200 drawings, recorded chronologically between June 1, 1899 and January 7, 1900, as the work occurred, containing explanations of his experiments.

Tuned electrical circuits

While in Colorado, Tesla constructed many smaller resonance transformers and conducted further research on concatenated tuned electrical circuits. Tesla also designed various sensitive devices for detecting received electrical energy, including rotating coherers. These used a clockwork mechanism of gears driven by a coiled spring-drive which rotated a small glass cylinder containing metal filings. These experiments were the final stage after years of work on synchronized tuned electrical circuits. These instruments were constructed to demonstrate how a wireless receiver could be "tuned" to respond to a specific complex signal while rejecting others. Tesla logged in his diary on January 2, 1900 that a separate resonance transformer tuned to the same high frequency as a larger high-voltage resonance transformer (which acted as a transmitter) received energy from the larger coil, one of many demonstrations of the wireless transmission of electrical energy. These experiments helped to confirm Tesla's priority in the invention of radio during later disputes in the courts. These air core high-frequency resonant coils were the predecessors of systems ranging from radio to medical nuclear magnetic resonance imaging.

Power transmission

On July 4, 1899, Tesla discovered terrestrial stationary waves within the earth. He demonstrated that the Earth behaves as a smooth polished conductor and possesses electrical vibrations. Tesla demonstrated that the Earth could respond at predescribed frequencies of electrical vibrations. Tesla conducted experiments contributing to the understanding of electromagnetic propagation and the Earth's resonance. He transmitted signals several kilometres and lit neon tubes conducting through the ground.

Tesla researched ways to transmit energy wirelessly over long distances (via transverse waves, to a lesser extent, and, more readily, longitudinal waves). He transmitted extremely low frequencies through the ground as well as between the earth's surface and the Kennelly-Heaviside layer. He received patents on wireless transceivers that developed standing waves by this method. In his experiments, he made mathematical calculations and computations based on his experiments and discovered that the resonant frequency of the Earth was approximately 8 herts (Hz). In the 1950s, researchers confirmed that the resonant frequency of the Earth's ionospheric cavity was in this range. See Schumann resonance

The magnifying transmitter was the basis for Tesla's Wardenclyffe Tower project. Although modern Tesla coils are designed to generate disruptive discharges, this system was designed for wireless communication and power transmission via longitudinal waves and telluric currents. In 1925, John B. Flowers advanced a proposal to test Tesla's system and to implement the system. H. L. Curtis, the chief of the Bureau of Standards Radio Laboratory in Washington D.C., and J. H. Dillinger, a physicist, reviewed the proposal but declined to implement the proposed plan. Flower's mechanical analogy test was successful, though. [7]

Electromechanical oscillator

Tesla developed a reciprocating electromechanical oscillator as a source of frequency stable or isochronous alternating electric current used in conjunction with both wireless transmitting and receiving apparatus. This circuit element was applied in much the same manner as quartz timer crystals are now. He also proposed the use of this device for geophysical exploration - seismology—a technique that he called telegeodynamics.

Transmitter details

Transmitter details
The electrical oscillator, cited by Dr. Tesla as his most important and greatest invention, consists of three inductors:
The magnifier operated as a base-driven quarter-wave helical resonator. It is reported that Tesla operated the magnifier at 100 kHz. The oscillator created earth currents of such magnitude that sparks an inch long could be drawn from a water main at a distance of 300 feet from the laboratory station.

The layout of the Wardenclyffe magnifying transmitter is well known, based upon Tesla's patents [4,5] and various photographs [3,6] in which the concept was implemented. The magnifying transmitter is not identical to the classic Tesla coil. It has the short thick primary and secondary inductor characteristic of the Tesla coil, although magnetic coupling between the two is tighter. Because of this, more aggressive measures have to be taken in terms of primary spark quenching and providing additional insulation between the primary and secondary. In addition to these two large-diameter coils that comprise the master oscillator, Tesla added a third inductor called the "extra coil." Tesla experimented with the magnifying transmitter using continuous wave and damped-wave resonance modes.

Construction and theory of operation

In a classic Tesla coil the primary drives the ground end of the secondary coil to form the driver transformer, which resonates the entire secondary coil. In the magnifying transmitter the driving and resonating parts of the secondary are separate coils. From a circuit analysis standpoint, there is little difference between the classic coil and the magnifier.

The extra coil or helical resonator can be physically separated from the two close-coupled coils which comprise the master oscillator or driver section. The power from the master oscillator is fed to the lower end of the extra coil resonator through a large diameter electrical conductor or pipe to minimize corona. The magnifying transmitter's base-driven extra coil behaves as a slow-wave helical resonator, the axial disturbance propagating at a velocity of less than 1% up to around 10% the speed of light in free space. The Magnifying Transmitter's axial velocity electromagnetic field is established by the coil pitch and electrical charge propagation speed through the circuit. It is interesting to note that rigorous mathematical descriptions of Tesla's Magnifier did not become available until 50-100 years after Tesla's pioneering work. Modern analyses have succeeded in applying distributed "transmission line" descriptions of the "extra coil" rather than the usual lumped-constant analysis. Upon validation, recently developed models of resonator behavior show that distributed analysis is more accurate for all excitation modes. Nevertheless, lumped analysis can be used to design Tesla coils and magnifiers.


Using low frequency harmonic Maxwellian oscillations, Tesla attempted to develop standing waves of extremely low frequency in the Earth's electro-magnetic circuit. Based upon observations made with the device, Tesla reported that a type of Earth resonance can be excited (An example of an earth resonance is the Schumann resonance). Tesla states that he discovered with the device that Earth's resonance can be excited. Tesla set up standing electomagnetic waves with the magnifying transmitter in the telluric potential energy.

It has been proposed by some that Tesla was utilizing Earth's magnetic fields' extremely low frequencies in a global resonator of power and information. Some posit that this variation of the Tesla coil was mainly intended for wireless transmissions of information. In normal operation the device is relatively silent, generating a high power electric field, but if the output voltage exceeds the design voltage of the elevated terminal, high-voltage sparks will strike out from the electrode into the air. Tesla became the first man to create electrical effects on the scale of lightning.

Cripple Creek residents could hear thunder coming from his lab produced by the Colorado Springs machine. It has been reported that Colorado Springs residents near the lab would observe animal reactions as sparks jumped to their horse's shoes. Tesla himself was able to draw sparks from the local water main that was used, at times, as a ground connection. The air around the laboratory would glow with corona (similar to the phenomena of St. Elmo's Fire). One of Tesla's experiments damaged a Colorado Springs Electric Company generator by backfeeding high power radio frequency electrical transient currents into the city's power distribution system.

Wardenclyffe Tower

After leaving colorado Spring, Tesla began planning the Wardenclyffe Tower facility, and in 1901, construction began on the land near Long Island Sound. Various theories exist on how Tesla intended to achieve the goals of the facility, from the use of radio (such as a 200 kW wireless system) to putting a charge on the Earth itself. According to Tesla's writings, the facility had a dual purpose. Tesla had planned more than what he initially revealed to his investors. His station could not only transceive communication signals, but also transmit electrical power. Tesla stated,

"It is intended to give practical demonstrations of these principles with the plant illustrated. As soon as completed, it will be possible for a business man in New York to dictate instructions, and have them instantly appear in type at his office in London or elsewhere. He will be able to call up, from his desk, and talk to any telephone subscriber on the globe, without any change whatever in the existing equipment. An inexpensive instrument, not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or song, the speech of a political leader, the address of an eminent man of science, or the sermon of an eloquent clergyman, delivered in some other place, however distant. In the same manner any picture, character, drawing, or print can be transferred from one to another place. Millions of such instruments can be operated from but one plant of this kind. More important than all of this, however, will be the transmission of power, without wires, which will be shown on a scale large enough to carry conviction." ["The Future of the Wireless Art," Wireless tTelegraphy and Telephony, Walter W. Massie & Charles R. Underhill, 1908, pp. 67-71]

In overall appearance, the system looks similar to a very large Tesla coil. Tesla's Magnifying Transmitter was the test of this facility (i.e., proof of concept). Tesla intended to use the facility to perform operations, "with the transmission of electrical energy for power and lighting purposes by wireless ...". A second plant was to be constructed on the southern coast of England.

One of the site's purpose was global wireless telecommunications and broadcasting. Wardenclyffe in operation may have allowed secure multichannel transceiving of information and may have allowed universal navigation, time synchronization, and a global location system. The plant was built for trans-Atlantic wireless telecommunications and radio broadcasting.

The site was to be used by Tesla as part of an installation in creating a distribution system for electricity that would allow power to be transmitted over any distance without wires. This is why Tesla designed Wardenclyffe in a different manner than modern (or as Tesla termed them, "Hertzian") broadcasting stations. Instead of supplying electricity through a current grid system, users would simply "receive" power through antennas on their roofs. At the time the power grid was quite limited in terms of who it reached and the Tower represented a potential way to significantly reduce the cost of "electrifying" the countryside.

The facility was meant to be the start of a national (and later global) system of towers broadcasting power to users as electromagnetic waves. There is some evidence that Wardenclyffe might have used extremely low frequency signals combined with a higher frequency signals. In practice, the transmitter electrically influences both the earth and the space above it. He made a point of describing the process as being essentially the same as passing electricity through a wire by conduction. Tesla believed that energy could be efficiently transmitted from the facility via longitudinal "non-Hertzian" (or maxwellian) waves (ed. see waves in plasmas for examples). Powered by an industrial alternator, the tower was apparently intended to inject large amounts of energy into a natural Earth circuit, using the Earth-Ionosphere network as the transmission circuit. Tesla called his wireless technique the "disturbed charge of ground and air method".

In various writings, Tesla explained that the Earth itself would behave as a resonant LC circuit that could be electrically excited at predescribed frequencies. However, Earth resonance would be of a very low frequency (about 7 Hz) which would utilize Schumann resonance. Alternatively, a surface or ground wave, similar to the Zenneck wave could have been utilized. Others believe that earth currents were to be utilized. According to Tesla, the planet's large cross-sectional area provides a low resistance path for the flow of earth currents. The greatest losses are apt to occur at the points where the transmitting and receiving stations are connected with the ground. This is why Tesla stated,

"You see the underground work is one of the most expensive parts of the tower. In this system that I have invented it is necessary for the machine to get a grip of the earth, otherwise it cannot shake the earth. It has to have a grip on the earth so that the whole of this globe can quiver, and to do that it is necessary to carry out a very expensive construction." [Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony and Transmission of Power, p. 203]

Later coils

The later coil type (and it's derivations) is the usual device built by modern enthusiasts and most often cited for Tesla intent to transmit large amounts of power to be used locally. The coil is an air-core, dual-tuned resonant transformer that generates very high voltages at radio frequencies. 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. When Tesla patented a later device (U.S. Patent 1,119,732 — Apparatus for Transmitting Electrical Energy), he called it a high-voltage, air-core, self-regenerative resonant transformer that generates very high voltages at high frequency. However, this phrase is no longer in conventional use.

Although modern Tesla Coils are designed to generate long sparks, Tesla's original system were designed for wireless communication and power transmission, so he used large radii of curvature to prevent corona and streamer losses. Tesla coils' outer conducting surfaces, which are charged to a high potential, have large radii of curvature to minimise leakage of the oscillating charges through corona discharges or sparks. 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.

Later coils consist of a primary tank circuit, which is a series LC circuit composed of a high voltage capacitor, spark gap, and primary coil; and the secondary LC circuit, a series resonant circuit consisting of the secondary coil and the toroid. In Tesla's original plans, the secondary LC circuit is composed of a loaded secondary coil which is then placed in series with a large helical coil. The helical coil is then connected to the toroid. The toroid actually forms one terminal of a capacitor, the other terminal being the Earth (or "ground"). The primary LC circuit is "tuned" so that it will resonate at the same frequency as the secondary LC circuit. The primary and secondary coils are magnetically coupled, creating a dual-tuned resonant air-core transformer. Most oil insulated transformers need large and long insulations at their connections to prevent discharge in air. Many later version Tesla coils spread their electric field over a large distance to prevent high field strength in the first place.

The terminal consists of a metallic frame, sometimes a toroid 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 outer surface of the elevated conductor 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. The important requirement is that a resonant condition be established. A high frequency alternator or a capacitor discharge can be used to excite the primary coil.

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 for transmisson

A large transmitting Tesla coil of more modern design can operate at very high peak power levels, up to many megawatts (a million watts; hundreds of thousands of horsepower). Transmitters should therefore be adjusted and operated carefully, not only for efficiency and economy, but also for safety. If, due to improper tuning, the maximum voltage point occurs below the terminal, along the secondary coil, a discharge (spark), or possibly a ball of plasma, may break out and damage or destroy the coil wire, supports, nearby objects, or anything else in the way.

Please note that there are many experts strongly suggesting to switching the places of the spark gap and capacitor from the above circuit. In the original transmitting system the spark gap resided after the resonant tank. Resonant power tapping is cleverly switched over the spark gap where the capacitor charge is maximum. It is not the ordinary EE logic that current flow charges the capacitor, in this case we have the phenomenon that the charge is transferred to the output (it may be a charge collector, resulting in energy gains). Putting the spark gap in the ordinary place is a disinformation that according to experts is to degrate the phenomenas of the radiant energy where the Tesla was pointing.

Regardless of which configuration is used, the HV transformer must be of a type that self-limits its secondary current by means of leakage inductance. Neon-sign transformers have this property.

It is advisable to begin the transmitter tuning, in which the primary coil's resonant frequency is set to the same value of the secondary coil's, using low-power oscillations, then increasing the power until the apparatus has been brought under control. While tuning, a small projection (called a "breakout bump") may be added to the top terminal in order to stimulate corona and spark discharges (sometimes called streamers) into the surrounding air. One or more elements or plates of somewhat 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 too high, the powerful discharge may escape to the air. Tuning can then be adjusted so as to get the longest streamers at a given power level, corresponding to a frequency match between the primary and secondary coil. For a variety of technical reasons, toroids provide the best overall shape for top terminals of modern transmitting Tesla coils.

Since transmitting Tesla coils can produce currents or discharges of very high frequency and voltage, they are useful for various purposes including classroom demonstration, theater and movie special-effects, and product/technology safety testing. In typical operation, long, branching high-voltage sparks may strike out in all directions from the toroid into the air, producing a dangerous, yet strangely beautiful, lightning-like display of electricity "in action".

While generating transmission discharges, electrical energy from the secondary and toroid is transferred to the surrounding air as electrical charge, heat, light, and sound. The electric currents that flow through these discharges are actually due to the rapid shifting of quantities of charge from one place (the top terminal) to other places (nearby regions of air). The process is similar to charging or discharging a capacitor. The current that arises from shifting charges within a capacitor is called a displacement current. Transmitting Tesla Coils discharges are formed as a result of displacement currents as pulses of electrical charge are rapidly transferred between the high voltage toroid and nearby regions within the air (called space charge regions). Although the space charge regions around the toroid are invisible, they play a profound role in the appearance and location of discharges.

When the spark gap fires, the charged capacitor discharges into the primary winding, causing the primary circuit to oscillate. The oscillating primary current creates a magnetic field that couples to the secondary winding, transferring energy into the secondary side of the transformer and causing it to oscillate with the toroid capacitance. The energy transfer occurs over a number of cycles, and most of the energy that was originally in the primary side is transferred into the secondary side. The greater the magnetic coupling between windings, the shorter the time required to complete the energy transfer. As energy builds within the oscillating secondary circuit, the amplitude of the toroid's RF voltage rapidly increases, and the air surrounding toroid begins to undergo dielectric breakdown, forming a corona discharge.

As the secondary's energy (and output voltage) continue to increase, larger pulses of displacement current further ionize and heat the air at the point of initial breakdown. This forms a very conductive "root" of hotter plasma, called a leader, that projects outward from the toroid. The plasma within the leader is considerably hotter than a corona discharge, and is considerably more conductive. In fact, it has properties that are similar to an electric arc. The leader tapers and branches into thousands of thinner, cooler, hairlike discharges (called streamers). The streamers look like a bluish "haze" at the ends of the more luminous leaders, and it's the streamers that actually transfer charge between the leaders and toroid to nearby space charge regions. The displacement currents from countless streamers all feed into the leader, helping to keep it hot and electrically conductive.

In a transmitter's spark gap, the primary-to-secondary energy transfer process happens repetitively at typical pulsing rates of 50–500 times/second, and previously formed leader channels don't get a chance to fully cool down between pulses. So, on successive pulses, newer discharges can build upon the hot pathways left by their predecessors. This causes incremental growth of the leader from one pulse to the next, lengthening the entire discharge on each successive pulse. Repetitive pulsing causes the discharges to grow until the average energy that's available from the transmitter during each pulse balances the average energy being lost in the discharges (mostly as heat). At this point, dynamic equilibrium is reached, and the discharges have reached their maximum length for the transmitter's output power level. The unique combination of a rising high voltage Radio Frequency envelope and repetitive pulsing seem to be ideally suited to creating long, branching discharges that are considerably longer than would otherwise be expected by output voltage considerations alone. However, even 100 years later, there are many aspects of Tesla Coil discharges and the energy transfer process that are still not completely understood.

Utilization for reception

The later coil type, as with a great deal of his other inventions, can be used according to the "Tesla principle". The later coil system could be reversed and operated in a complementary manner. The primary coil and its capacitor can be used in receive mode to utilize atmospheric electricity and, if a transmitter is available, broadcasted power (thus becoming the secondary coil). Generally, though, many Tesla coils are not used for these purposes (including, but not limited to, such factors that they are not built with the double coil "primary" and the tube coil "secondary" as designated in the US1119732). This type of variation of the Tesla coil could utilize the phantom loop effect to form a circuit to induct energy from the earth's magnetic field and other radiant energy. This concept is part of Tesla's wireless transmission of electric power distribution system (which Tesla sought patent protection for in the patent US1119732, Apparatus for Transmitting Electrical Energy [1902 January 18]).

Theoretically, a way the Tesla coil can be treated when ultilized in this fashion is as a long conducting wire which can operate on the well known electromagnetic principles of a generator (via converting its velocity to electric energy). Electric potential is generated across a conductive coil by its motion through the Earth's magnetic field. The choice of the metal conductor to be used in a Tesla coil is determined by a variety of factors. Primary factors include low resistivity, high conductivity, and low density (pending the exact applicaiton).

When a large Tesla coil's primary cuts the planet's magnetic field, it generates a current. The conductive coil moving across said magnetic field lines of said external magnetic field at an angle to the local vertical to produce an electric current in said conducting coil and a resulting electrodynamic force acting on the coil. The anode makes electrical contact with the ionosphere via the "phantom loop". Functionally, electrons flow from the atmospheric plasma into coil, are tansformed for utlilization, and are emitted into the ground.

When an the coil rotates through a magnetic field (B), an electric field is generated in the coil's frame of reference. This can be stated as:

E = v * B = vB

where the magnetic field of the environment (B), being tangent to the Earth's surface in the north-south direction, is at right angles to the velocity of the Tesla coil (v), moving in a west-east direction. The electric field (E) will be at right angles to both the coil's velocity (v) and magnetic field (B), or along the local vertical. It should be noted that this electric field exists in the moving frame of reference because it is the resonating magnetic field which creates an electric field. It is assumed that the Earth's magnetic field (and any additional power broadcasts from a transmitter) is in the form of a standing wave (or any longitudinal waves in plasma that are an interconnected set of quasineutral, electrically conductive fluid composed of particles and fields which propagates in a periodically repeating fashion) and is at a different velocity than the Earth's body.

With a Tesla coil (L), a electric field (E) is generated in the coil. It produces a voltage (V) between the opposite ends of the coil. This can be expressed as:

V= E * L = EL cos tau = vBL cos tau

where the angle (tau) is between the coils vector (L) and the electric field vector (E), assumed to be in the vertical direction at right angles to the velocity vector (v) in plane, and the magnetic field vector (B) is out of the plane.

Although a voltage can be build up between the ends of the Tesla coil, current will not flow unless an open circuit exists. Fortunately, atmospheric electricity is abundant in the vicinity of the Earth's atmosphere, there exists highly electrically conductive plasmas (which are kept partially ionized by solar sources of radiant energy). The electron and ion density varies pending various factors, such as the location, altitude, season, sunspot cycle, and contamination levels. It is known that a properly constructed anode will readily pull electrons out of the atmospheric plasma. Thus, to complete the citrcuit at the anode a sufficiently large area of uninsulated conductor need to be made.

The Tesla coil ejects electrons from the ground element or other suitable means. It is plausable that very large areas at one end of the Tesla coil could collect enough ions to complete the circuit. Upon having both ends of the Tesla coil open to allow the flow of electrons out of one Tesla coil end and into the other end, there will be enough conductivity in relation to the surrounding plasma to allow current to flow through the Tesla coil.

The amount of current (I) flowing through a Tesla coil depends on various factors. One of these is the circuit's total resistance (R). The circuit's resistance consist of the following components:

  • the effective resistance of the atmospheric plasma, and
  • the resistance of the Tesla coil.

Inaddition, a parasitic load is needed. The load on the current may take the form of a battery of capacitors, electrostatic motors/generators, or alternators (which inturn charges reserve power sources such as batteries). The recieved energy can be used to control power and communication circuit activation, as well as drive the any seconday function at the negative end of the Tesla coil.

The load can be viewed as a resistor which absorbs power, but stores this for later use (instead of being immediately dissipated). It is included as part of the "resistance". The charging load is not treated as a "base resistance" though, as the charging circuit can be turned off at anytime. When off, the operations can be continued without interruption using the power stored.

The preceding is not intended to be a comprehensive theory of the Tesla coil reception / generation process, but one of the first useful physical theory of the process. This is primarily because a general lumped-element model of the physical operation of a Tesla coil can only be approximately correct. Additional considerations and a distributed analysis can account for the operation of the Tesla coil generator in different manners. It has been suggested that the Tesla coil has been considered to behave more closely to that of a cavity resonator probe rather than a simple inductor (Corum, 1988).

Further reading and other references

Magnifying Transmitter citations
[1] - My Inventions : The Autobiography of Nikola Tesla, Hart Brothers, 1982, Ch. 5, ISBN 0-910077-00-2
[2] - Nikola Tesla : Guided Weapons & Computer Technology, Leland I. Anderson, Twenty First Century Books, 1998, pp. 12-13, ISBN 0-9636012-9-6.
[3] - Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power, Leland I. Anderson, Twenty First Century Books, 2002, pp. 74, 89-90, 107, 111, ISBN 1-893817-01-6.
[4] - Apparatus for Transmission of Electrical Energy, U.S. Patent No. 649,621, 15 May 1900
[5] - Apparatus for Transmitting Electrical Energy, Jan. 18, 1902, U.S. Patent 1,119,732, Dec. 1, 1914
[6] - Nikola Tesla Colorado Springs Notes, 1899-1900, Nikola Tesla Museum, Beograd, 1978.
[7] - Valone, Thomas, Harnessing the Wheelwork of Nature. ISBN 1-931882-04-5
Electrical World
  • "The Development of High Frequency Currents for Practical Application"., The Electrical World, Vol 32, No. 8.
  • "Boundless Space: A Bus Bar". The Electrical World, Vol 32, No. 19.
Nikola Tesla
  • "The True Wireless". Electrical Experimenter, May 1919.
  • "My Inventions", Electrical Experimenter magazine, Feb, June, and Oct, 1919. ISBN 0910077002
  • "The Problem of Increasing Human Energy", Century Illustrated Magazine, June 1900.
Corum and Corum
  • Corum, K. L., J. F. Corum, "Class Notes: Tesla Coils and the Failure of Lumped-Element Circuit Theory". 1999.
  • Corum, K. L., J. F. Corum, and A. H. Aidinejad, "Atmospheric Fields, Tesla's Receivers and Regenerative Detectors". 1994.
  • Corum, K. L., J. F. Corum, "Nikola Tesla, Lightning Observations, and Stationary Waves". 1994.
  • Corum, J. F., and K. L. Corum, "RF Coils, Helical Resonators and Voltage Magnification by Coherent Spatial Modes". IEEE, 2001.
  • Corum, K. L., J. F. Corum, "TCTUTOR", 1988, pp. 56-58.

Tesla's publications

  • Tesla, Nikola, "On the Transmission of Electricity Without Wires". Electrical World and Engineer, 5 March 1904.

Electrical World

  • "The Development of High Frequency Currents for Practical Application"., The Electrical World, Vol 32, No. 8.
  • "Boundless Space: A Bus Bar". The Electrical World, Vol 32, No. 19.
  • "Mr. Tesla's Application of the Hertz-Wave Transmission". The Electrical World, Vol 32, No. 8.

Other publications

  • Bass, Robert W., "Self-Sustained Non-Hertzian Longitudinal Wave Oscillations as a Rigorous Solution of Maxwell's Equations for Electromagnetic Radiation". Inventek Enterprises, Inc., Las Vegas, Nevada.
  • Bieniosek, F. M., "Triple Resonance Pulse Transformer Circuit". Review of Scientific Instruments, 61 (6).
  • Corum, J. F., and K. L. Corum, "Disclosure Concerning the Operation of an ELF Oscillator". CPG Communications, Inc., Newbury, Ohio.
  • Corum, J. F., and K. L. Corum, "A Physical Interpretation of the Colorado Springs Data". CPG Communications, Inc., Newbury, Ohio.
  • Corum, J. F., and K. L. Corum, "Tesla's Colorado Spring Receivers (A Short Introduction)". 2003.
  • Corum, J. F., and K. L. Corum, "RF Coils, Helical Resonators and Voltage Magnification by Coherent Spatial Modes". IEEE, 2001.
  • de Queiroz, Antonio Carlos M., "Synthesis of Multiple Resonance Networks". Universidade Federal do Rio de Janeiro, Brazil. EE/COPE.
  • de Queiroz, Antonio Carlos M., "Designing a Tesla Magnifier". Universidade Federal do Rio de Janeiro, Brazil. EE/COPE.
  • Grotz, Toby, "Wireless Transmission of Power: An Attempt to Verify Nikola Tesla's 1899 Colorado Springs Experiment, Results of Research and Experimentation". TESLA, Inc., Craig Colorado.
  • Hartley, R. V. L., "Oscillations with Non-linear Reactances". Bell Systems Technical Journal, Sun Publishing. 1992.
  • Wait, James, R., "Electromagnetic Waves in Stratified Media". Pergammon Press, 1972. (2nd edition)
  • Ratzlaff, John T., "Dr. Nikola Tesla - Select Patent Wrappers From National Archives" (ed. this multi-volume set contains the various papers pertaining to the of the Tesla coil patent application process and it's revisions; Inaddition, it includes the different anodes that were not allowed by the USPTO.)
  • Valone, Thomas, "Harnessing the Wheelwork of Nature: Tesla's Science of Energy". Adventures Unlimited Press, October 2002. ISBN 1931882045
  • Bieniosek, F. M., "Triple Resonance Pulse Transformer Circuit". Review of Scientific Instruments, 61 (6).
  • de Queiroz, Antonio Carlos M., "Synthesis of Multiple Resonance Networks". Universidade Federal do Rio de Janeiro, Brazil. EE/COPE.
  • Haller, George Francis, and Elmer Tiling Cunningham, "The Tesla high frequency coil, its construction and uses". New York, D. Van Nostrand company, 1910.
  • Hartley, R. V. L., "Oscillations with Non-linear Reactances". Bell Systems Technical Journal, Sun Publishing. 1992.
  • Norrie, H. S., "Induction Coils: How to make, use, and repair them". Norman H. Schneider, 1907, New York. 4th edition.
  • Grotz, Toby, "The Influence of Vedic Philosophy on Nikola Tesla's Understanding of Free Energy".
  • Cheney, Margaret & Uth, Robert, "Tesla, Master of Lightning", published by Barnes & Noble, 1999 ISBN 0-7607-1005-8
  • Nichelson, Oliver, "Nikola Tesla's Energy Generation Designs", Eyring, Inc., Provo, Utah.
  • Nichelson, Oliver, "The Thermodynamics of Tesla's Fuelless Electrical generator". American Fork, Utah. (American Chemical Society, 1993. 2722-5/93/0028-63)
  • "Tesla: Master of Lightning". 1999. ISBN 0793635497 (PBS Video; Tesla )
  • Wikipedia contributors, Wikipedia: The Free Encyclopedia. Wikimedia Foundation.


Related Tesla patents

See also: List of Tesla patents


See also

- PowerPedia main index
- PESWiki home page

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