Tesla Coil For Sale? Best 51 Answer

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Are Tesla coils dangerous?

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Tesla coils are potentially dangerous if proper care is not taken during use. The Tesla coil should never be touched when it is on as it can shock a person and that shock can be fatal. There is also the possibility of deep burns. All spectators should keep a safe distance of at least 6 meters to avoid arcing when the coil is switched on. A Tesla coil can also damage items with arcing or through shared outlets; Always use the Telsa Coil on a dedicated outlet and not one shared by other electrical devices.

Electrical resonant transformer circuit invented by Nikola Tesla

A Tesla coil is an electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891.[1] It is used to generate high-voltage, low-current, and high-frequency alternating current.[2] Tesla experimented with a number of different configurations consisting of two or sometimes three coupled resonant electrical circuits.

Tesla used these circuits to conduct innovative experiments in electric lighting, phosphorescence, X-ray generation, high-frequency AC phenomena, electrotherapy, and the transmission of electrical energy without wires. Tesla coil circuits were used commercially in spark gap radio transmitters for wireless telegraphy and in medical devices such as electrotherapy and violet ray devices up until the 1920s. Today they are primarily used for entertainment and educational displays, although small coils are still used as leak detectors for high vacuum systems.

Originally, Tesla coils used fixed spark gaps or rotating spark gaps to provide intermittent excitation of the resonant circuit; recently electronic devices are used to provide the required switching action.

operation [edit]

A Tesla coil is a high-frequency oscillator that drives a double-tuned air-core resonant transformer to produce high voltages at low currents.[3][6][7][8][9][10] Tesla’s original circuits, as well as most modern coils, use a simple spark gap to excite oscillations in the tuned transformer. More sophisticated designs use transistor or thyristor[6] switches or vacuum tube electronic oscillators to drive the resonant transformer.

Tesla coils can produce output voltages from 50 kilovolts to several million volts for large coils.[6][8][10] The AC output is in the low-frequency range, typically between 50 kHz and 1 MHz.[8][10] Although some oscillator-driven coils produce a continuous alternating current, most Tesla coils have a pulsed output;[6] the high voltage consists of a rapid series of pulses of high-frequency alternating current.

The common spark excited Tesla coil circuit shown below consists of these components: [7][11]

A high voltage supply transformer (T) to bring the AC line voltage up to a voltage high enough to jump the spark gap. Typical voltages are between 5 and 30 kilovolts (kV). [11]

to increase the AC line voltage to a voltage high enough to jump the spark gap. Typical voltages are between 5 and 30 kilovolts (kV). A capacitor (C1) that forms a tank circuit with the primary winding L1 of the Tesla transformer

which forms an oscillating circuit with the primary winding of the Tesla transformer A spark gap (SG) which acts as a switch in the primary circuit

which acts as a switch in the primary circuit The Tesla coil (L1,L2) , an air-core double-tuned resonant transformer that produces the high output voltage.

, a double-tuned air-core resonant transformer that produces the high output voltage. Optionally, a capacitive electrode (upper load) (E) in the form of a smooth metal ball or torus is attached to the secondary terminal of the coil. Its large surface area suppresses premature air breakdown and arcing, and increases Q-factor and output voltage.

Resonant transformer[ edit ]

The specialized transformer used in the Tesla coil circuit, called a resonant transformer, oscillation transformer, or radio frequency (HF) transformer, works differently than a common transformer used in AC circuits.[12][13][14] While an ordinary transformer is designed to efficiently transfer energy from the primary to the secondary winding, the resonant transformer is also designed to temporarily store electrical energy. Each winding has capacitance and acts as an LC circuit (resonant circuit, tuned circuit) that stores oscillating electrical energy, analogous to the way a tuning fork stores mechanical oscillating energy. The primary coil (L1), which consists of relatively few turns of thick copper wire or tubing, is connected to a capacitor (C1) via the spark gap (SG).[6][7] The secondary coil (L2) consists of many turns (hundreds to thousands) of fine wire on a hollow cylindrical shape inside the primary coil. The secondary is not connected to an actual capacitor but also acts as an LC circuit, the inductance of (L2) oscillates with the stray capacitance (C2), the sum of the parasitic stray capacitance between the windings of the coil, and the capacitance with the annular metal electrode , which is attached to the high-voltage connector. The primary and secondary circuits are tuned to have the same resonant frequency[5] so they exchange energy and act like a coupled oscillator; With each spark, the stored energy rapidly oscillates back and forth between the primary and secondary sides.

The particular coil design is driven by the need to achieve low ohmic energy losses (high Q factor) at high frequencies,[8] resulting in the largest secondary voltages:

Ordinary power transformers have an iron core to increase the magnetic coupling between the coils. However, at high frequencies, an iron core causes energy losses through eddy currents and hysteresis, which is why it is not used in the Tesla coil. [14]

Ordinary transformers are designed to be “tightly coupled”. Both the primary and secondary windings are tightly wound around the iron core. Due to the iron core and the proximity of the windings, they have a high mutual inductance (M), the coupling coefficient is close to 0.95 – 1.0, which means that almost the entire magnetic field of the primary winding goes through the secondary winding. [12][14] The Tesla transformer, on the other hand, is “loosely coupled”,[6][14] the primary winding is larger in diameter and spaced apart from the secondary winding,[7] therefore the mutual inductance is lower and the coupling coefficient is only 0 .05 to 0.2. [15] This means that only 5% to 20% of the primary coil’s magnetic field passes through the secondary coil when it is open. [6][11] The loose coupling slows the exchange of energy between the primary and secondary coils, allowing the oscillating energy to remain in the secondary circuit longer before returning to the primary circuit and dissipating in the spark.

the coupling coefficient is close to 0.95 – 1.0 unity, which means that almost all of the magnetic field of the primary winding goes through the secondary winding. The Tesla transformer, on the other hand, is “loosely coupled”, the primary winding is larger in diameter and spaced apart from the secondary winding, so the mutual inductance is lower and the coupling coefficient is only 0.05-0.2. This means that only 5% to 20% of the primary coil’s magnetic field passes through the secondary coil when it is open. The loose coupling slows the exchange of energy between the primary and secondary coils, allowing the oscillating energy to remain in the secondary circuit longer before returning to the primary circuit and beginning to dissipate in the spark. Each winding is also confined to a single layer of wire, reducing losses from proximity effects. The primary side carries very high currents. Because high-frequency current flows mainly on the surface of conductors due to the skin effect, it is often made of copper tubing or strip with a large surface area to reduce resistance, and its turns are spaced apart, reducing losses from proximity effects and arcing between the windings are reduced.[16][17]

Unipolar coil design widely used in modern coils. The primary is the flat red spiral winding below, the secondary is the vertical cylindrical coil wrapped with fine red wire. The high voltage connection is the aluminum torus at the top of the bipolar coil of the secondary coil used in the early 20th century. There are two high voltage output terminals, each connected to one end of the secondary, with a spark gap between them. The primary consists of 12 turns of thick wire placed in the middle of the secondary to prevent arcing between the coils

The output circuit can take two forms:

Unipolar: One end of the secondary winding is connected to a single high voltage terminal, the other end is grounded. This type is used in modern coils designed for entertainment. The primary winding is located near the low potential lower end of the secondary winding to minimize arcing between the windings. Because ground (earth) serves as the return path for the high voltage, streamer arcs from the connector tend to jump to a nearby grounded object.

: One end of the secondary winding is connected to a single high voltage terminal, the other end is grounded. This type is used in modern coils designed for entertainment. The primary winding is located near the low potential lower end of the secondary winding to minimize arcing between the windings. Because ground (earth) serves as the return path for the high voltage, streamer arcs from the connector tend to jump to a nearby grounded object. Bipolar: Neither end of the secondary winding is grounded, and both are brought out to high-voltage terminals. The primary winding is in the center of the secondary coil, equidistant between the two high voltage terminals to prevent arcing.

Duty cycle [ edit ]

The circuit operates on a rapid, repetitive cycle in which the supply transformer (T) charges the primary capacitor (C1), which then discharges in a spark through the spark gap, creating a short oscillating pulse of current in the primary circuit that excites a high oscillating voltage above the secondary: [9] [11] [14] [18]

Current from the supply transformer (T) charges the capacitor (C1) to a high voltage. When the voltage across the capacitor reaches the breakdown voltage of the spark gap (SG), a spark begins, reducing the resistance of the spark gap to a very low value. This closes the primary circuit and current from the capacitor flows through the primary coil (L1). The current rapidly flows back and forth between the plates of the capacitor through the coil, creating a high frequency oscillating current in the primary circuit at the circuit’s resonant frequency. The oscillating magnetic field of the primary winding induces an oscillating current in the secondary winding (L2) according to Faraday’s law of induction. The energy in the primary circuit is transferred to the secondary circuit over several cycles. The total energy in the tuned circuits is limited to the energy originally stored in capacitor C1, so as the oscillating voltage in the secondary increases in amplitude (“ringing”), the oscillations in the primary drop to zero. Although the ends of the secondary coil are open, it also acts as a resonant circuit due to the capacitance (C2), the sum of the parasitic capacitance between the turns of the coil plus the capacitance of the toroidal electrode E. Current quickly flows back and forth through the secondary coil between its ends. Due to the small capacitance, the oscillating voltage across the secondary coil appearing at the output terminal is much larger than the primary voltage. The secondary current creates a magnetic field that induces a voltage back in the primary coil, and over a number of additional cycles the energy is transferred back to the primary coil, causing the oscillating voltage in the secondary coil to decrease (“ring down”). This process repeats itself, rapidly shifting energy back and forth between the primary and secondary tank circuits. The oscillating currents in the primary and secondary gradually decay due to the energy dissipated as heat in the spark gap and the resistance of the coil. When the current through the spark gap is no longer sufficient to keep the air in the spark gap ionized, the spark stops (“extinguishes”) and terminates the current in the primary circuit. The oscillating current in the secondary side can last for some time. The current from the supply transformer starts charging the capacitor C1 again and the cycle repeats.

This entire cycle takes place very quickly, with the oscillations decaying in a time on the order of a millisecond. Each spark across the spark gap creates a pulse of damped sinusoidal high voltage at the output terminal of the coil. Each pulse dies out before the next spark occurs, so the coil produces a series of damped waves, not a continuous sinusoidal voltage.[9] The high voltage from the supply transformer that charges the capacitor is a 50 or 60 Hz sine wave. Depending on the setting of the spark gap, there are usually one or two sparks at the crest of each half cycle of the mains current, i.e. more than a hundred sparks per second. Thus the spark appears continuously at the spark gap, as do the high voltage currents from the top of the coil.

The secondary winding of the feeder transformer (T) is connected across the primary tuned circuit. It might appear that the transformer would be a leakage path for the HF current that dampens the oscillations. However, its large inductance gives it a very high impedance at the resonant frequency, so it acts as an open circuit for the oscillating current. If the supply transformer has insufficient short circuit inductance, high frequency chokes are placed in its secondary lines to block the HF current.

Frequency of vibration [ edit ]

To produce the largest output voltage, the primary and secondary tank circuits are set to resonate with each other.[8][9][12] The resonant frequencies of the primary and secondary circuits, f 1 {\displaystyle \scriptstyle f_{1}} and f 2 {\displaystyle \scriptstyle f_{2}} , are determined by the inductance and capacitance in each circuit:[8] [9 ][12]

f 1 = 1 2 π L 1 C 1 f 2 = 1 2 π L 2 C 2 {\displaystyle f_{1}={1 \over {2\pi {\sqrt {L_{1}C_{1}}} }}\qquad \qquad f_{2}={1 \over {2\pi {\sqrt {L_{2}C_{2}}}}}\,}

In general, the secondary is not adjustable, so the primary circuit is tuned, usually by a moving tap on the primary coil L1, until it oscillates at the same frequency as the secondary:

f = 1 2 π L 1 C 1 = 1 2 π L 2 C 2 {\displaystyle f={1 \over {2\pi {\sqrt {L_{1}C_{1}}}}}={1 \ over {2\pi {\sqrt {L_{2}C_{2}}}}}\,}

So the resonance condition between primary and secondary is:

L 1 C 1 = L 2 C 2 {\displaystyle L_{1}C_{1}=L_{2}C_{2}\,}

The resonant frequency of Tesla coils is in the low radio frequency (RF) range, typically between 50 kHz and 1 MHz. However, due to the impulsive nature of the spark, they generate broadband radio noise and, without shielding, can be a significant source of RFI interfering with nearby radio and television reception.

Output voltage [ edit ]

Large coil producing 3.5 meter (10 foot) long streamer arcs indicating millions of volts potential

In a resonant transformer, the high voltage is generated by resonance; The output voltage is not proportional to the turns ratio like in an ordinary transformer.[14][19] It can be calculated approximately from the law of conservation of energy. At the beginning of the cycle, when the spark starts, all the energy in the primary circuit W 1 {\displaystyle W_{1}} is stored in the primary capacitor C 1 {\displaystyle C_{1}}. If V 1 {\displaystyle V_{1}} is the voltage at which the spark gap breaks down, which is usually close to the peak output voltage of the supply transformer T, this is energy

W 1 = 1 2 C 1 V 1 2 {\displaystyle W_{1}={1 \over 2}C_{1}V_{1}^{2}\,}

When “ringing” this energy is transferred to the secondary circuit. Although some is lost as heat in the spark and other resistances, in modern coils over 85% of the energy ends up in the secondary.[9] At the peak ( V 2 {\displaystyle V_{2}} ) of the secondary sinusoidal voltage waveform, all energy in the secondary W 2 {\displaystyle W_{2}} is contained in the capacitance C 2 {\displaystyle C_{ 2}} between the ends of the secondary coil

W 2 = 1 2 C 2 V 2 2 {\displaystyle W_{2}={1 \over 2}C_{2}V_{2}^{2}\,}

Assuming no energy losses, W 2 = W 1 {\displaystyle W_{2}\;=\;W_{1}} . Substituting into this equation and simplifying, the peak secondary voltage is [8][9][14]

V2 = V1C1C2 = V1L2L1 . {\displaystyle V_{2}=V_{1}{\sqrt {C_{1} \over C_{2}}}=V_{1}{\sqrt {L_{2} \over L_{1}}}. }

The second formula above is derived from the first using the resonance condition L 1 C 1 = L 2 C 2 {\displaystyle L_{1}C_{1}\;=\;L_{2}C_{2}} .[14 ] Since the capacitance of the secondary coil is very small compared to the primary capacitor, the primary voltage is stepped up to a high value.[9]

The above peak voltage is only reached in coils in which no air discharges occur; For coils that produce sparks, e.g. entertainment coils, the peak voltage at the connector is limited to the voltage at which the air collapses and becomes conductive. [9] [14] [16] As the output voltage increases with each voltage pulse, it reaches the point where the air next to the high voltage terminal ionizes, causing corona, brush discharges, and streamer arcs to break out of the terminal. This happens when the electric field strength exceeds the dielectric strength of air, about 30 kV per centimeter. Since the electric field is greatest at sharp points and edges, air discharges begin at these points on the high-voltage connection. The voltage at the high voltage terminal cannot rise above the air breakdown voltage because any additional electrical charge pumped into the terminal by the secondary winding will simply escape into the air. The output voltage of outdoor Tesla coils is limited to a few million volts by air breakdown, [5] but higher voltages can be achieved by coils immersed in pressurized tanks of insulating oil.

Top-load or “toroid” electrode [ edit ]

Solid state DRSSTC Tesla coil with pointed wire attached to toroid to create brush discharge

Most Tesla coil designs have a smooth spherical or toroidal metal electrode on the high voltage terminal. The electrode serves as one plate of a capacitor, the earth as the other plate and forms the resonant circuit with the secondary winding. Although the “toroid” increases the secondary capacitance, which tends to reduce the peak voltage, its main effect is that its large-diameter curved surface reduces the potential gradient (electric field) at the high-voltage terminal; It works similarly to a corona ring, raising the voltage threshold at which air discharges such as corona and brush discharges occur.[20] The suppression of premature air breakdown and energy loss allows the voltage to build to higher levels on the peaks of the waveform, creating longer, more spectacular streamers when air discharges eventually occur.[14]

If the top electrode is large enough and smooth enough, even at the peak voltage, the electric field at its surface may never become high enough to cause air breakdown, and air discharges will not occur. Some entertainment coils have a sharp “spark point” that protrudes from the torus to start discharges.

Types [ edit ]

The term “Tesla coil” is applied to a range of high voltage resonant transformer circuits.

excitement [ edit ]

Tesla coil circuits can be classified by the type of “excitation” they use, which type of circuit is used to apply current to the primary winding of the resonant transformer: [5][21][22]

Spark Excited or Spark Gap Tesla Coil (SGTC): This type uses a spark gap to complete the primary circuit, exciting oscillations in the resonant transformer. Spark gaps have disadvantages due to the high primary currents they must handle. They produce a very loud noise during operation, harmful ozone gas, and high temperatures that may require a cooling system. The energy dissipated in the spark also reduces the Q factor and the output voltage. Tesla’s coils were all spark-excited. Static Spark Gap: This is the most common type, detailed in the previous section. It is used in most entertainment coils. An AC voltage from a high voltage supply transformer charges a capacitor which discharges through the spark gap. The spark rate is not adjustable, but is determined by the mains frequency of 50 or 60 Hz. Multiple sparks may occur on each half-cycle, so the output voltage pulses may not be evenly spaced. Static Triggered Spark Gap: Commercial and industrial circuits often apply a DC voltage from a power supply to charge the capacitor and use high voltage pulses generated by an oscillator applied to a trigger electrode to initiate the spark. [6] [22] This allows control of firing rate and excitation voltage. Commercial spark gaps are often enclosed in an insulating gaseous atmosphere such as sulfur hexafluoride, reducing the length and therefore energy loss in the spark. Rotating Spark Gap: These use a spark gap consisting of electrodes on the circumference of a wheel that is turned at high speed by a motor, producing sparks as they pass a stationary electrode. [22] Tesla used this type for its large coils, and they are used today for large entertainment coils. The rapid separation speed of the electrodes quenches the spark quickly, allowing “first notch” quenching, allowing for higher voltages. The wheel is usually driven by a synchronous motor so the sparks are synchronized to the AC line frequency, with the spark occurring at the same point on the AC waveform in each cycle, so the primary pulses are repeatable.

or : This type uses a spark gap to close the primary circuit, exciting oscillations in the resonant transformer. Spark gaps have disadvantages due to the high primary currents they must handle. They produce a very loud noise during operation, harmful ozone gas, and high temperatures that may require a cooling system. The energy dissipated in the spark also reduces the Q factor and the output voltage. Tesla’s coils were all spark-excited. Switched or Solid State Tesla Coil (SSTC): These use power semiconductor devices, usually thyristors or transistors such as MOSFETs or IGBTs, [6] triggered by a solid state oscillator circuit to switch voltage pulses from a DC supply through the primary winding. [22] They offer pulsed excitation without the disadvantages of a spark gap: loud noise, high temperatures, and poor efficiency. The voltage, frequency and excitation waveform can be finely controlled. SSTCs are used in most commercial, industrial, and research applications[6] as well as higher end entertainment coils. Solid State Single Resonant Tesla Coil (SRSSTC): In this circuit, the primary winding has no resonant capacitor and is therefore not a double-tuned circuit; only the secondary is. The current to the primary from the switching transistors excites resonance in the secondary tuned circuit. Single-tuned SSTCs are simpler, but the resonant circuit has an overall Q-factor that depends only on the secondary-side resonance. Dual Resonant Solid State Tesla Coil (DRSSTC): The circuit is similar to the double-tuned spark-excited circuit except that instead of the AC supply transformer ( T ) in the primary circuit, a DC supply charges the capacitor and instead of the spark-gap solid-state switch complete the circuit between the capacitor and the primary coil. Singing Tesla Coil or Musical Tesla Coil: This is not a separate type of excitation but a modification of the solid state primary circuit to create a Tesla Coil that can be played like a musical instrument, with its high voltage discharges reproducing simple musical tones. The drive voltage pulses applied to the primary winding are modulated at an audio frequency by a solid state “interrupter” circuit, causing the arc discharge to emit noise from the high voltage terminal. So far only tones and simple chords have been produced; The coil cannot function as a speaker and reproduce complex music or speech sounds. The sound output is controlled by a keyboard or a MIDI file that is applied to the circuit via a MIDI interface. Two modulation techniques were used: AM (amplitude modulation of excitation voltage) and PFM (pulse frequency modulation). These are mainly built as novelties for entertainment.

or : These use power semiconductor devices, usually thyristors or transistors such as MOSFETs or IGBTs, triggered by a solid state oscillator circuit to switch voltage pulses from a DC supply through the primary winding. They offer pulsed excitation without the disadvantages of a spark gap: loud noise, high temperatures and poor efficiency. The voltage, frequency and excitation waveform can be finely controlled. SSTCs are used in most commercial, industrial, and research applications, as well as higher-end entertainment coils. Continuous Wave: In these, the transformer is driven by a feedback oscillator which applies a pulse of current to the primary winding on each cycle of the RF current, exciting a continuous oscillation. The primary tuned circuit serves as the oscillator’s tank circuit, and the circuitry is similar to a radio transmitter. Unlike the previous circuits that produce a pulsed output, they produce a continuous sine wave output. Power vacuum tubes are often used as active devices instead of transistors because they are more robust and tolerant of overloads. In general, continuous excitation produces lower output voltages for a given input power than pulsed excitation.[22]

Number of coils [ edit ]

Tesla circuits can also be classified according to how many resonant coils (inductors) they contain:[23][24]

Two-coil or double-resonant circuits: Almost all current Tesla coils use the two-coil resonant transformer invented by Tesla in 1891, which consists of a primary winding to which pulses of current are applied and a secondary winding that produces the high voltage “Tesla coil” usually referred to these circuits.

or circuits: Almost all of today’s Tesla coils use the resonant transformer invented by Tesla in 1891 with two coils, consisting of a primary winding to which current pulses are applied and a secondary winding that generates the high voltage. The term “Tesla coil” usually refers to these circuits. Three-coil, triple-resonant, or magnifying circuits: These are three-coil circuits based on Tesla’s “magnifying transmitter” circuit, which he began experimenting with sometime before 1898 and was installed in his Colorado Springs laboratory in 1899–1900 and patented in 1902 . [25][26][27] They consist of an air-core step-up transformer with two coils, similar to the Tesla transformer, with the secondary connected to a third coil that is not magnetically coupled to the others, the so-called “Extra” – or “resonator” coil fed in series and resonates with its own capacitance. The output is taken from the free end of this coil. The presence of three energy-storing tank circuits gives this circuit a more complicated resonance behavior.[28] It is the subject of research but has been used in few practical applications.

history [edit]

Electrical oscillations and resonant air-core transformer circuits were explored before Tesla.[36][35] Resonance circuits with Leiden vessels were invented from 1826 by Felix Savary, Joseph Henry, William Thomson and Oliver Lodge.[37] and Henry Rowland built a resonant transformer in 1889.[30] Elihu Thomson independently invented the Tesla coil circuit at the same time as Tesla.[38][39][40][29] Tesla patented his Tesla coil circuit on April 25, 1891.[41][42] and first demonstrated it publicly on May 20, 1891 in his lecture “Experiments with Alternate Currents of Very High Frequency and Their Application to Methods of Artificial Illumination” before the American Institute of Electrical Engineers at Columbia College, New York ][33] Although Tesla in dieser Zeit viele ähnliche Schaltungen patentieren ließ, war dies die erste, die alle Elemente der Tesla-Spule enthielt: Hochspannungs-Primärtransformator, Kondensator, Funkenstrecke und “Schwingungstransformator” mit Luftkern.

Moderne Tesla-Spulen [ bearbeiten ]

Teslaspule (Entladung)

Teslaspule im Terrarium (I)

Moderne Hochspannungs-Enthusiasten bauen normalerweise Tesla-Spulen, die einigen von Teslas “späteren” 2-Spulen-Luftkern-Designs ähneln. Diese bestehen typischerweise aus einem primären Schwingkreis, einem Reihen-LC-Kreis (Induktanz-Kapazitäts-Kreis), der aus einem Hochspannungskondensator, einer Funkenstrecke und einer Primärspule besteht, und dem sekundären LC-Kreis, einem Reihenresonanzkreis, der aus der Sekundärspule plus einem Anschlusskapazität oder “Top-Load”. In Teslas fortschrittlicherem (Lupen-)Design wird eine dritte Spule hinzugefügt. Der sekundäre LC-Kreis besteht aus einer eng gekoppelten Luftkerntransformator-Sekundärspule, die den Boden eines separaten Spiralresonators mit dritter Spule antreibt. Moderne 2-Spulen-Systeme verwenden eine einzige Sekundärspule. Die Oberseite der Sekundärseite wird dann mit einem Topload-Anschluss verbunden, der eine „Platte“ eines Kondensators bildet, wobei die andere „Platte“ die Erde (oder „Masse“) ist. Der primäre LC-Kreis ist so abgestimmt, dass er auf der gleichen Frequenz wie der sekundäre LC-Kreis schwingt. Die Primär- und Sekundärspulen sind magnetisch gekoppelt, wodurch ein doppelt abgestimmter resonanter Luftkerntransformator entsteht. Frühere ölisolierte Tesla-Spulen benötigten große und lange Isolatoren an ihren Hochspannungsanschlüssen, um eine Entladung in Luft zu verhindern. Spätere Tesla-Spulen verteilen ihre elektrischen Felder über größere Entfernungen, um hohe elektrische Belastungen von vornherein zu vermeiden und ermöglichen so den Betrieb in freier Luft. Die meisten modernen Tesla-Spulen verwenden auch ringförmige Ausgangsanschlüsse. Diese werden häufig aus gesponnenem Metall oder flexiblen Aluminiumrohren hergestellt. Die toroidale Form hilft, das hohe elektrische Feld in der Nähe der Oberseite der Sekundärwicklung zu kontrollieren, indem Funken nach außen und von den Primär- und Sekundärwicklungen weg geleitet werden.

Eine komplexere Version einer Tesla-Spule, die von Tesla als „Lupe“ bezeichnet wird, verwendet einen enger gekoppelten Luftkern-Resonanz-„Treiber“-Transformator (oder „Master-Oszillator“) und eine kleinere, entfernt angeordnete Ausgangsspule (genannt „Extra Spule” oder einfach der Resonator), der eine große Anzahl von Windungen auf einer relativ kleinen Spulenform hat. Die Unterseite der Sekundärwicklung des Treibers ist mit Masse verbunden. Das gegenüberliegende Ende ist über einen isolierten Leiter, der manchmal als Übertragungsleitung bezeichnet wird, mit der Unterseite der zusätzlichen Spule verbunden. Da die Übertragungsleitung mit relativ hohen HF-Spannungen arbeitet, besteht sie typischerweise aus Metallrohren mit einem Durchmesser von 1 Zoll, um Koronaverluste zu reduzieren. Da sich die dritte Spule in einiger Entfernung vom Treiber befindet, ist sie nicht magnetisch mit ihm gekoppelt. HF-Energie ist stattdessen direkt vom Ausgang des Treibers in die Unterseite der dritten Spule gekoppelt, wodurch diese bei sehr hohen Spannungen „aufklingelt”. Die Kombination aus dem Zweispulentreiber und dem dritten Spulenresonator fügt dem System einen weiteren Freiheitsgrad hinzu, was die Abstimmung erheblich komplexer macht als die eines 2-Spulen-Systems.Das Einschwingverhalten für mehrere Resonanznetzwerke (von denen die Tesla-Lupe eine Teilmenge ist) wurde erst kürzlich gelöst.45 Es ist jetzt bekannt, dass eine Vielzahl von Es sind nützliche “Tuning-Modi” verfügbar, und in den meisten Betriebsmodi klingelt die zusätzliche Spule mit einer anderen Frequenz als der Master-Oszillator.

Primärschaltung [ bearbeiten ]

Demonstration des Prototyps der Zwillings-Tesla-Spule des Nevada Lightning Laboratory im Maßstab 1:12 auf der Maker Faire 2008

Moderne Transistor- oder Vakuumröhren-Tesla-Spulen verwenden keine primäre Funkenstrecke. Instead, the transistor(s) or vacuum tube(s) provide the switching or amplifying function necessary to generate RF power for the primary circuit. Solid-state Tesla coils use the lowest primary operating voltage, typically between 155 and 800 volts, and drive the primary winding using either a single, half-bridge, or full-bridge arrangement of bipolar transistors, MOSFETs or IGBTs to switch the primary current. Vacuum tube coils typically operate with plate voltages between 1500 and 6000 volts, while most spark gap coils operate with primary voltages of 6,000 to 25,000 volts. The primary winding of a traditional transistor Tesla coil is wound around only the bottom portion of the secondary coil. This configuration illustrates operation of the secondary as a pumped resonator. The primary ‘induces’ alternating voltage into the bottom-most portion of the secondary, providing regular ‘pushes’ (similar to providing properly timed pushes to a playground swing). Additional energy is transferred from the primary to the secondary inductance and top-load capacitance during each “push”, and secondary output voltage builds (called ‘ring-up’). An electronic feedback circuit is usually used to adaptively synchronize the primary oscillator to the growing resonance in the secondary, and this is the only tuning consideration beyond the initial choice of a reasonable top-load.

In a dual resonant solid-state Tesla coil (DRSSTC), the electronic switching of the solid-state Tesla coil is combined with the resonant primary circuit of a spark-gap Tesla coil. The resonant primary circuit is formed by connecting a capacitor in series with the primary winding of the coil, so that the combination forms a series tank circuit with a resonant frequency near that of the secondary circuit. Because of the additional resonant circuit, one manual and one adaptive tuning adjustment are necessary. Also, an interrupter is usually used to reduce the duty cycle of the switching bridge, to improve peak power capabilities; similarly, IGBTs are more popular in this application than bipolar transistors or MOSFETs, due to their superior power handling characteristics. A current-limiting circuit is usually used to limit maximum primary tank current (which must be switched by the IGBT’s) to a safe level. Performance of a DRSSTC can be comparable to a medium-power spark-gap Tesla coil, and efficiency (as measured by spark length versus input power) can be significantly greater than a spark-gap Tesla coil operating at the same input power.

Practical aspects of design [ edit ]

High voltage production [ edit ]

Tesla coil schematics Typical circuit configuration. Here, the spark gap shorts the high frequency across the first transformer that is supplied by alternating current. An inductance, not shown, protects the transformer. This design is favoured when a relatively fragile neon sign transformer is used Alternative circuit configuration. With the capacitor in parallel to the first transformer and the spark gap in series to the Tesla-coil primary, the AC supply transformer must be capable of withstanding high voltages at high frequencies

A large Tesla coil of more modern design often operates at very high peak power levels, up to many megawatts (millions of watts, equivalent to thousands of horsepower). It is therefore 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) may break out and damage or destroy the coil wire, supports, or nearby objects.

Tesla experimented with these, and many other, circuit configurations (see right). The Tesla coil primary winding, spark gap and tank capacitor are connected in series. In each circuit, the AC supply transformer charges the tank capacitor until its voltage is sufficient to break down the spark gap. The gap suddenly fires, allowing the charged tank capacitor to discharge into the primary winding. Once the gap fires, the electrical behavior of either circuit is identical. Experiments have shown that neither circuit offers any marked performance advantage over the other.

However, in the typical circuit, the spark gap’s short circuiting action prevents high-frequency oscillations from ‘backing up’ into the supply transformer. In the alternate circuit, high amplitude high frequency oscillations that appear across the capacitor also are applied to the supply transformer’s winding. This can induce corona discharges between turns that weaken and eventually destroy the transformer’s insulation. Experienced Tesla coil builders almost exclusively use the top circuit, often augmenting it with low pass filters (resistor and capacitor (RC) networks) between the supply transformer and spark gap to help protect the supply transformer. This is especially important when using transformers with fragile high-voltage windings, such as neon sign transformers (NSTs). Regardless of which configuration is used, the HV transformer must be of a type that self-limits its secondary current by means of internal Short-circuit inductance. A normal (low Short-circuit inductance) high-voltage transformer must use an external limiter (sometimes called a ballast) to limit current. NSTs are designed to have high Short-circuit inductance to limit their short circuit current to a safe level.

Tuning [ edit ]

The primary coil’s resonant frequency is tuned to that of the secondary, by using low-power oscillations, then increasing the power (and retuning if necessary) until the system operates properly at maximum power. While tuning, a small projection (called a “breakout bump”) is often added to the top terminal in order to stimulate corona and spark discharges (sometimes called streamers) into the surrounding air. Tuning can then be adjusted so as to achieve the longest streamers at a given power level, corresponding to a frequency match between the primary and secondary coil. Capacitive “loading” by the streamers tends to lower the resonant frequency of a Tesla coil operating under full power. A toroidal topload is often preferred to other shapes, such as a sphere. A toroid with a major diameter that is much larger than the secondary diameter provides improved shaping of the electrical field at the topload. This provides better protection of the secondary winding (from damaging streamer strikes) than a sphere of similar diameter. And, a toroid permits fairly independent control of topload capacitance versus spark breakout voltage. A toroid’s capacitance is mainly a function of its major diameter, while the spark breakout voltage is mainly a function of its minor diameter. A grid dip oscillator (GDO) is sometimes used to help facilitate initial tuning and aid in design. The resonant frequency of the secondary can be difficult to determine except by using a GDO or other experimental method, whereas the physical properties of the primary more closely represent lumped approximations of RF tank design. In this schema the secondary is built somewhat arbitrarily in imitation of other successful designs, or entirely so with supplies on hand, its resonant frequency is measured and the primary designed to suit.

Air discharges [ edit ]

10 000 V, 60 Hz A small, later-type Tesla coil in operation: The output is giving 43-centimetre (17 in) sparks. The diameter of the secondary is 8 cm (3.1 in). The power source is a current-limited supply

In coils that produce air discharges, such as those built for entertainment, electrical energy from the secondary and toroid is transferred to the surrounding air as electrical charge, heat, light, and sound. The process is similar to charging or discharging a capacitor, except that a Tesla coil uses AC instead of DC. The current that arises from shifting charges within a capacitor is called a displacement current. Tesla coil 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 Tesla coil 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 an oscillating 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 to ground. Energy transfer occurs over a number of cycles, until most of the energy that was originally in the primary side is transferred to 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 the toroid begins to undergo dielectric breakdown, forming a corona discharge.

As the secondary coil’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 electrically 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, its properties are similar to an electric arc. The leader tapers and branches into thousands of thinner, cooler, hair-like discharges (called streamers). The streamers look like a bluish ‘haze’ at the ends of the more luminous leaders. The streamers 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.

The primary break rate of sparking Tesla coils is slow compared to the resonant frequency of the resonator-topload assembly. When the switch closes, energy is transferred from the primary LC circuit to the resonator where the voltage rings up over a short period of time up culminating in the electrical discharge. In a spark gap Tesla coil, the primary-to-secondary energy transfer process happens repetitively at typical pulsing rates of 50–500 times per second, depending on the frequency of the input line voltage. At these rates, previously-formed leader channels do not 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 available from the Tesla coil 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 Tesla coil’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 be otherwise expected by output voltage considerations alone. High-voltage, low-energy discharges create filamentary multibranched discharges which are purplish-blue in colour. High-voltage, high-energy discharges create thicker discharges with fewer branches, are pale and luminous, almost white, and are much longer than low-energy discharges, because of increased ionisation. A strong smell of ozone and nitrogen oxides will occur in the area. The important factors for maximum discharge length appear to be voltage, energy, and still air of low to moderate humidity. There are comparatively few scientific studies about the initiation and growth of pulsed lower-frequency RF discharges, so some aspects of Tesla coil air discharges are not as well understood when compared to DC, power-frequency AC, HV impulse, and lightning discharges.

Applications[ edit ]

Today, although small Tesla coils are used as leak detectors in scientific high vacuum systems[4] and igniters in arc welders,[47] their main use is entertainment and educational displays.

Education and entertainment [ edit ]

Electrum sculpture, the world’s largest Tesla coil. Builder Eric Orr is visible sitting inside the hollow spherical high voltage electrode sculpture, the world’s largest Tesla coil. Builder Eric Orr is visible sitting inside the hollow spherical high voltage electrode

Tesla coils are displayed as attractions at science museums and electronics fairs, and are used to demonstrate principles of high frequency electricity in science classes in schools and colleges.

Since they are simple enough for an amateur to make, Tesla coils are a popular student science fair project, and are homemade by a large worldwide community of hobbyists. Builders of Tesla coils as a hobby are called “coilers”. They attend “coiling” conventions where they display their home-made Tesla coils and other high voltage devices. Low-power Tesla coils are also sometimes used as a high-voltage source for Kirlian photography.

The current world’s largest Tesla coil is a 130,000-watt unit built by Greg Leyh and Eric Orr, part of a 38-foot-tall (12 m) sculpture titled Electrum owned by Alan Gibbs and currently residing in a private sculpture park at Kakanui Point near Auckland, New Zealand.[48][49] Another very large Tesla coil, designed and built by Syd Klinge, is shown every year at the Coachella Valley Music and Arts Festival in Coachella, California.[citation needed]

Tesla coils can also be used to generate sounds, including music, by modulating the system’s effective “break rate” (i.e., the rate and duration of high power RF bursts) via MIDI data and a control unit. The actual MIDI data is interpreted by a microcontroller which converts the MIDI data into a PWM output which can be sent to the Tesla coil via a fiber optic interface.An extensive outdoor musical concert has demonstrated using Tesla coils during the Engineering Open House (EOH) at the University of Illinois at Urbana–Champaign. The Icelandic artist Björk used a Tesla coil in her song “Thunderbolt” as the main instrument in the song. The musical group ArcAttack uses modulated Tesla coils and a man in a chain-link suit to play music.

Vacuum system leak detectors [ edit ]

Scientists working with high vacuum systems test for the presence of tiny pin holes in the apparatus (especially a newly blown piece of glassware) using high-voltage discharges produced by a small handheld Tesla coil. When the system is evacuated the high voltage electrode of the coil is played over the outside of the apparatus. At low pressures, air is more easily ionized and thus conducts electricity better than atmospheric pressure air. Therefore, the discharge travels through any pin hole immediately below it, producing a corona discharge inside the evacuated space which illuminates the hole, indicating points that need to be annealed or reblown before they can be used in an experiment.

Teslaphoresis [ edit ]

In 2016, Rice University scientists used the field of a Tesla coil to remotely align tiny carbon nanotubes into a circuit, a process they dubbed “teslaphoresis”.[50][51]

Gesundheitliche Probleme [Bearbeiten]

The high voltage radio frequency (RF) discharges from the output terminal of a Tesla coil pose a unique hazard not found in other high voltage equipment: when passed through the body they often do not cause the painful sensation and muscle contraction of electric shock, as lower frequency AC or DC currents do.[52][8][53][54] The nervous system is insensitive to currents with frequencies over 10 – 20 kHz.[55] It is thought that the reason for this is that a certain minimum number of ions must be driven across a nerve cell’s membrane by the imposed voltage to trigger the nerve cell to depolarize and transmit an impulse. At radio frequencies, there is insufficient time during a half-cycle for enough ions to cross the membrane before the alternating voltage reverses.[55] The danger is that since no pain is felt, experimenters often assume the currents are harmless. Teachers and hobbyists demonstrating small Tesla coils often impress their audience by touching the high voltage terminal or allowing the streamer arcs to pass through their body.[56][57][8]

If the arcs from the high voltage terminal strike the bare skin, they can cause deep-seated burns called RF burns.[58][59] This is often avoided by allowing the arcs to strike a piece of metal held in the hand, or a thimble on a finger, instead. The current passes from the metal into the person’s hand through a wide enough surface area to avoid causing burns.[8] Often no sensation is felt, or just a warmth or tingling.

However this does not mean the current is harmless.[60] Even a small Tesla coil produces many times the electrical energy necessary to stop the heart, if the frequency happens to be low enough to cause ventricular fibrillation.[61][62] A minor misadjustment of the coil could result in electrocution. In addition, the RF current heats the tissues it passes through. Carefully controlled Tesla coil currents, applied directly to the skin by electrodes, were used in the early 20th century for deep body tissue heating in the medical field of longwave diathermy.[53] The amount of heating depends on the current density, which depends on the power output of the Tesla coil and the cross-sectional area of the path the current takes through the body to ground.[54] Particularly if it passes through narrow structures such as blood vessels or joints it may raise the local tissue temperature to hyperthermic levels, “cooking” internal organs or causing other injuries. International ICNIRP safety standards for RF current in the body in the Tesla coil frequency range of 0.1 – 1 MHz specify a maximum current density of 0.2 mA per square centimeter and a maximum power absorption rate (SAR) in tissue of 4 W/kg in limbs and 0.8 W/kg average over the body.[63] Even low power Tesla coils could exceed these limits, and it is generally impossible to determine the threshold current where bodily injury begins. Being struck by arcs from a high power (> 1000 watt) Tesla coil is likely to be fatal.

Another reported hazard of this practice is that arcs from the high voltage terminal often strike the primary winding of the coil.[52][60] This momentarily creates a conductive path for the lethal 50/60 Hz primary current from the supply transformer to reach the output terminal. If a person is connected to the output terminal at the time, either by touching it or allowing arcs from the terminal to strike the person’s body, then the high primary current could pass through the conductive ionized air path, through the body to ground, causing electrocution.

Skin effect myth [ edit ]

An erroneous explanation for the absence of electric shock that has persisted among Tesla coil hobbyists is that the high frequency currents travel through the body close to the surface, and thus do not penetrate to vital organs or nerves, due to an electromagnetic phenomenon called skin effect.[61][8][64][65]

This theory is false.[66][67][68][52][62][69] RF current does tend to flow on the surface of conductors due to skin effect, but the depth to which it penetrates, called skin depth, depends on the resistivity and permeability of the material as well as the frequency.[70][71] Although skin effect limits currents of Tesla coil frequencies to the outer fraction of a millimeter in metal conductors, the skin depth of the current in body tissue is much deeper due to its higher resistivity. The depth of penetration of currents of Tesla frequency (0.1 – 1 MHz) in human tissues is roughly 24 to 72 centimeters (9 to 28 inches).[71][70][52] Since even the deepest tissues are closer than this to the surface, skin effect has little influence on the path of the current through the body;[69] it tends to take the path of minimum electrical impedance to ground, and can easily pass through the core of the body.[72][52][71] In the medical therapy called longwave diathermy, carefully controlled RF current of Tesla frequencies was used for decades for deep tissue warming, including heating internal organs such as the lungs.[72][53] Modern shortwave diathermy machines use a higher frequency of 27 MHz, which would have a correspondingly smaller skin depth, yet these frequencies are still able to penetrate deep body tissues.[67]

Related patents [ edit ]

Tesla’s patents

” Electrical Transformer Or Induction Device “. US Patent No. 433,702, August 5, 1890 [73]

“. U.S. Patent No. 433,702, August 5, 1890 ” Means for Generating Electric Currents “, U.S. Patent No. 514,168, February 6, 1894

“, U.S. Patent No. 514,168, February 6, 1894 ” Electrical Transformer “, Patent No. 593,138, November 2, 1897

“, Patent No. 593,138, November 2, 1897 ” Method Of Utilizing Radiant Energy “, Patent No. 685,958 November 5, 1901

“, Patent No. 685,958 November 5, 1901 ” Method of Signaling “, U.S. Patent No. 723,188, March 17, 1903

“, U.S. Patent No. 723,188, March 17, 1903 ” System of Signaling “, U.S. Patent No. 725,605, April 14, 1903

“, U.S. Patent No. 725,605, April 14, 1903 “Apparatus for Transmitting Electrical Energy”, January 18, 1902, U.S. Patent 1,119,732

Others’ patents

See also[edit]

References[edit]

Further Reading[edit]

Operation and other information

Electrical World

” The Development of High Frequency Currents for Practical Application “., The Electrical World, Vol 32, No. 8th.

“., The Electrical World, Vol 32, No. 8. “Boundless Space: A Bus Bar”. The Electrical World, Vol 32, No. 19.

The easiest way for most homeowners to lower their utility bills is to reduce energy use through self-discipline and increased efficiency. But for those who can invest some time and money, installing one or more green energy systems can yield larger, longer-term savings while doing more to protect the environment.

Choosing and purchasing a residential green energy system can be a big project. Some systems may not be cost effective for your home and others may not be compatible at all. But once you’ve identified your options and the installers in your area, you might be surprised at what’s in your price range.

Find out about local regulations and incentives for green energy

Before you get carried away, there are a few important factors to consider. First, states and localities differ in the way they regulate some renewable energy systems, particularly solar panels and wind turbines. If your city turns out to be severely restricting one or both, it’s good to find out early in the process. Call your local town hall or contact a local wind and solar installer to find out what is allowed in your area.

Second, there may be tax credits and other incentives that make it more affordable for you to buy a green energy system. As of 2018, the government’s residential renewable energy tax credit has been extended through the end of 2021 and applies to systems such as solar panels, wind turbines, geothermal heat pumps, and solar water heaters. Your state may offer additional tax credits, and your local utilities may even have programs to make it easier for you to install renewable energy.

generate electricity at home

1. Residential solar panels

Every ray of sunshine that lands on your roof is free electricity to go. All you need is a solar panel to capture it. And thanks to the aforementioned tax credit, many homeowners are getting in on the action.

Solar panels should be installed by professionals, and many installers will give your home a no-obligation assessment to determine the best installation locations and offer an estimate. Some may even install solar shingles that offer a more streamlined look.

The energy generated by solar panels must be used immediately or stored. If your home is using more energy than your solar panels are producing, the energy from the sun will simply offset the amount of electricity you have to pull from the grid. But if you’re generating more than you’re using, you may be able to sell that excess energy back to the utility, lowering your bills even further. Another option is to purchase a household battery that can store that energy until you need it after dark.

2. Wind Turbines

You don’t need the kind of giant turbines you see in wind farms to generate green energy for your home. A propeller as small as a trash can lid can save a large chunk of your home energy bills, as long as it is installed in a sufficiently windy area.

Again, professional installation is crucial, both to ensure the safety of the turbine and to place it where the wind can reach it. And just like solar panels, when you generate energy from wind turbines, you must use it or lose it.

3. Solar and wind hybrid systems

If you have sunny days and windy nights, a hybrid solar and wind system might be perfect for your area. The combination makes your home more likely to generate electricity 24/7, so with an extra house battery you could theoretically go completely off the grid.

4. Micro hydropower systems

Do you have a running stream on your property? You may be able to divert the water flow through a small turbine and let the stream generate electricity 24 hours a day for free. A micro hydro system is often even better than a hybrid system because the flow of water is more continuous and reliable than wind and solar.

5. Solar water heater

If a full solar system is out of your price range but you still have some sunny lots on your roof, a solar water heater is a cheaper way to get some free energy. With most solar water heaters, the tank itself is stored on the roof as part of the installation, giving it a bulkier look. But it lets the sun do the work of one of the biggest energy hogs in your home.

6. Geothermal heat pumps

Temperatures underground are much more stable than temperatures inside our homes, and in winter a ground source heat pump can steal some of that heat underground. These systems use a closed circuit of pipes to pump fluid through an underground channel into your home and back underground. Inside the house, a heat exchanger uses the heat from the pipes to heat living spaces with minimal energy consumption.

Renewable energy is a smart way to lower your bills while helping the environment. And with so many different ways to bring it home, generating your own energy might be more possible than you expected.

Why don’t we have wireless power?

This question comes from many members of our audience: Wouldn’t it be great if we could do away with the vast network of wires, big and small, that connect the electronic devices that rule our world to the power plants that generate electricity?

In reality we have wireless power. But it’s limited. At least for now, it’s only commercially viable over short distances (think millimeters to meters). Before we get to that, let’s go back in time more than a hundred years to a man with a dream of transmitting electricity wirelessly around the world: Nikola Tesla.

There is a long list of technologies attributed to Tesla and his research: radio, X-rays, remote controls, electric motors, to name a few. But one of his greatest ambitions was never fulfilled: to transmit electricity wirelessly around the world.

His first experiments revolved around sending electricity through ether. But these experiments could only send electricity over a short distance. Then Tesla had an idea: Would the connection be stronger if he went through the ground instead of through the air?

Here was his basic theory: sending electricity deep into the ground and using the earth like a giant conductor. Electricity could travel continuously for hundreds of miles, and anyone with a receiver could access it, Tesla theorized.

“Electricity can and will be transmitted wirelessly for all commercial purposes, such as lighting homes and powering airplanes, for the foreseeable future. I have discovered the essential principles and it only remains to develop them commercially. When that’s done, you can go anywhere in the world – to the mountaintop overlooking your farm, to the arctic or to the desert – and set up a small rig that gives you heat for cooking and light to read by. This equipment is carried in a bag that is not as big as a regular suitcase. In years to come, cordless lights will be as commonplace on farms as ordinary electric lights are in our cities today.” (Nikola Tesla, The American Magazine, April 1921)

Tesla moved his experiments to Colorado Springs, Colorado in 1899. According to Tesla’s lab notes, he managed to send electricity from his lab to lightbulbs sitting on the ground hundreds of feet away.

But Tesla wanted to get bigger. He began building the Wardenclyffe Tower on Long Island in 1901. Wardenclyffe would be the center of a series of experiments in transmitting wireless radio and telegraph signals – and sending wireless electricity. Tesla planned that the 17-story tower would send electricity from a coal-fired generator through 300-foot-long metal poles into the ground, where the electricity would travel hundreds of miles.

To this day, no one is sure if Tesla’s plan would have worked, said Marc Seifer, author of Wizard: The Life and Times of Nikola Tesla. Tesla’s business partner J.P. Morgan has withdrawn from the Wardenclyffe project. Tesla eventually went bankrupt and Wardenclyffe was demolished in 1917. His idea of ​​using the ground to send electricity long distances hasn’t been thoroughly tested, and electrical engineers are skeptical it would work, Seifer added.

But Tesla’s research influenced the way we send electricity wirelessly today

We’ve known since Tesla that it’s possible to send electricity wirelessly using magnetic induction. Or more specifically, using a magnetic field to generate an electric current. You already use this type of charging if you own an electric toothbrush.

And Tesla’s dream of global wireless power is still alive. The Japanese space agency is developing a solar satellite that would radiate energy back to Earth using microwaves. Your goal for the completion of the first rotating solar power plant? 2031 – just in time for Tesla’s 175th birthday.

At the height of his career, pioneering electrical engineer Nikola Tesla was obsessed with an idea. He theorized that electricity could be transmitted wirelessly through the air over long distances – either bouncing via a series of strategically positioned towers or via a system of suspended balloons.

Things didn’t go according to plan, and Tesla’s ambitions for wireless global power never materialized. But the theory itself was not disproved: it would simply have required an extraordinary amount of energy, much of which would have been wasted.

Now, research suggests that the architects of the 5G network may have inadvertently built what Tesla designed at the turn of the 20’s – homes, jobs and factories.

Because 5G relies on a dense network of masts and a powerful array of antennas, it’s possible that the same infrastructure, with some tweaks, could beam power to small devices. But the gearbox will still suffer from the main drawback of Tesla’s towers: high energy wastage, which may be hard to justify given the urgency of the climate crisis.

5G networks

Decades ago it was discovered that a tightly focused radio beam could transmit energy relatively long distances without using a wire to carry the charge. The same technology is now used in the 5G network: the latest generation of technology to transmit the Internet connection to your phone via radio waves transmitted by a local antenna.

This 5G technology is said to offer a 1,000x increase in capacity over the last generation, 4G, to enable up to one million users per square kilometer to be connected – making those moments of searching for signals at music festivals or sporting events a thing of the past.

To support these upgrades, 5G uses some engineering magic, and that magic comes in three parts: very dense networks with many more masts, special antenna technology, and the incorporation of millimeter wave (mmWave) transmission alongside more traditional bands.

Read more: 5G: What will it offer and why is it important?

The latter, mmWave, opens up much more bandwidth at the expense of shorter transmission distances. For comparison: Most WLAN routers work in the 2 GHz band. If your router has a 5GHz option, you’ll have noticed that movies streamed more smoothly – but you’ll need to be closer to your router for it to work.

Keep increasing the frequency (like mmWave, which operates at 30GHz or more) and you’ll see even bigger improvements in bandwidth – but you’ll need to be closer to the base station to access it. For this reason, 5G towers are more densely clustered than 4G towers.

The final bit of magic is adding many more antennas – between 128 and 1,024 compared to a much smaller number (just two in some cases) for 4G. Multiple antennas allow the masts to form hundreds of pencil-like beams that target specific devices, giving your phone efficient and reliable internet on the go.

These happen to be the same raw materials needed to build a wireless power grid. The increased network density is particularly important as it opens up the possibility of using mmWave bands to transmit various radio waves that can carry both Internet connectivity and electrical energy.

Experimenting with 5G power

The experiments used new types of antennas to facilitate wireless charging. In the lab, the researchers were able to beam 5G power over a relatively short distance of just over 2 meters, but they expect a future version of their device to deliver 6 μW (6 millionths of a watt) over a distance of 0.5 to 1.5 meters can transmit 180 meters.

For comparison: Conventional Internet of Things (IoT) devices consume around 5 μW – but only in the deepest sleep mode. Of course, IoT devices will require less and less power to run as smarter algorithms and more efficient electronics are developed, but 6 μW is still a very small amount of power.

That means, at least for now, that 5G wireless power probably isn’t practical for charging your cellphone during the day. But it could charge or power IoT devices like sensors and alarms, which are expected to be widely used in the future.

Read more: Explainer: the Internet of Things

For example, factories are likely to use hundreds of IoT sensors to monitor conditions in warehouses, predict failures in machines, or track the movement of parts along a production line. The ability to beam power directly to these IoT devices will encourage a shift to far more efficient manufacturing processes.

teething

Until then, however, there are still challenges to overcome. To provide wireless power, 5G masts use about 31kW of energy — the equivalent of 10 kettles constantly boiling water.

Although concerns that 5G technology can cause cancer have been largely debunked by scientists, that amount of energy emanating from pylons could be unsafe. A rough calculation suggests that users must be at least 16 meters away from towers to comply with US Federal Communications Commission safety regulations.

Read more: Four Experts Explore How the 5G Coronavirus Conspiracy Theory Started

However, this technology is still in its infancy. It is certainly possible that future approaches, such as B. New antennas with narrower and more focused beams that could significantly reduce power required – and wasted – by each mast.

Currently, the proposed system is more reminiscent of the fictional “Wonkavision” in Roald Dahl’s Charlie and the Chocolate Factory, which accomplished the feat of beaming confectionery into TVs – but had to make a much smaller one out of a giant block of chocolate at the other end.

Because it consumes a lot of power compared to the power it delivers to devices, 5G wireless power is speculative at the moment. But if engineers find more efficient ways to beam electricity through the air, it could well be that Nikola Tesla’s dream of wireless power could be realized – more than 100 years since his attempts failed.

Electrical safety warning

The Tesla Coil produces extremely high voltage, high frequency sparks. NEVER TOUCH THE OUTPUT OF THE TESLA COIL. At best, you’ll get an uncomfortable burn; in the worst case, you get a potentially life-threatening shock.

The Tesla coil control board is also dangerous while the bus capacitors are being charged. NEVER SERVICE THE BOARD WHILE IT IS POWERED UP. ALWAYS WAIT AT LEAST FIVE MINUTES AFTER SWITCHING OFF THE CARD, SO THAT THE CAPACITORS ARE DISCHARGE BEFORE WAIT.

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I use wireless power every day.

In my toothbrush:

And in my cell phone:

The method used in my devices is called inductive charging. I talk a bit more about that in my answer to this question. This is currently the most common and practical form of wireless power transmission. But as many of the comments have noted, this is considered near field transmission. And with an effective range of just a few millimeters, it’s very close-range.

The amount of energy transferred and the efficiency of the transfer can be increased quite a bit (although still considered near-field) by adding a capacitor to each of the inductor coils and tuning the resulting RLC networks to have a high Q-factor equal ( resonance) frequency. A team from MIT researched the use of inductive resonance as a wireless power transmission system.

The researchers have since formed a company called WiTricity to further develop the technology. Although they haven’t brought any product to the commercial market yet, they have made some impressive demonstrations:

The term WiTricity was used for a project that took place at MIT in 2007, led by Marin Soljačić. The MIT researchers successfully demonstrated the ability to wirelessly power a 60-watt light bulb using two 5-turn copper coils of 60 cm (24 in) diameter that were 2 m (7 ft) apart, with an efficiency of about 45%. The coils were designed to resonate together at 9.9 MHz (≈ wavelength 30 m) and were oriented along the same axis. One was connected inductively to a power source, the other to a light bulb. The setup turned on the bulb even when the direct line of sight was blocked by a wooden panel. Researchers were able to operate a 60-watt light bulb at about 90% efficiency at a distance of 3 feet. The research project was spun off into a private company, also called WiTricity.

It is important to note that the distance between the transmitter and receiver plays a crucial role in how much energy can be reliably transmitted. As seen in this MIT project based article, the voltage drop is exponential with respect to the distance between the coils:

But there are many other methods such as microwaves and lasers that are capable of much greater distances. However, these methods are very directional and therefore applicable over a much smaller area than Tesla’s proposed Wardenclyffe Tower, which would be omnidirectional. There are also many other factors to consider when implementing any of these methods:

Microwave: Energy transfer via radio waves can be made more directional, allowing energy to be transmitted over greater distances using shorter wavelengths of electromagnetic radiation, typically in the microwave range. A rectenna can be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies in excess of 95% have been realized. Power beams using microwaves have been proposed for the transmission of energy from orbiting solar power satellites to Earth, and beaming of energy to deorbiting spacecraft has been considered.

…

For terrestrial applications, a large area 10km diameter receive array allows the use of large total power levels while operating at the low power density recommended for human electromagnetic exposure safety. A power density of 1 mW/cm2, which is harmless to humans, distributed over an area with a diameter of 10 km corresponds to a total output of 750 megawatts. This is the level of performance found in many modern power plants.

…

The wireless high-performance transmission with microwaves has proven itself. Experiments in the tens of kilowatts were conducted at Goldstone, California, in 1975 and more recently (1997) at Grand Bassin, Reunion Island. With these methods, distances of the order of one kilometer can be achieved. Laser Advantages of laser-based energy transfer compared to other wireless methods are: The collimated monochromatic wavefront propagation enables a narrow beam cross-sectional area for long-range energy transfer. Compact size of solid-state laser photovoltaic semiconductor diodes fit into small products. no high-frequency interference with existing radio communications such as WiFi and cell phones. access control; Only receivers illuminated by the laser receive power. Its disadvantages are: laser radiation is dangerous, even at low power it can blind people and animals, and at high power it can kill through localized heating. The conversion into light, e.g. B. with a laser, is inefficient. Converting it back to electricity is inefficient, with photovoltaic cells achieving efficiencies of 40% to 50%. (Note that the conversion efficiency with monochromatic light is slightly higher than with solar radiation from solar panels). Atmospheric absorption, as well as absorption and scattering from clouds, fog, rain, etc. cause losses that can be as high as 100%. As with microwave blasting, this method requires a direct line of sight with the target.

And of course there is the “perturbed charge of ground and air” method used by Tesla. As for the Tesla system, it was shut down because funding ran out and the stock market collapsed. The main reason why it hasn’t been attempted since then is that such a system could not be rigorously measured. Therefore, the energy suppliers could not bill per consumption and earn a lot of money. Without a way to monetize the technology, investments in R&D will never be made. At least that’s the (conspiracy) theory. Although there are many other reasons why this method is either not feasible or just wouldn’t work.

I couldn’t find an article with definitive figures on efficiency. But I suspect efficiency is the main reason you don’t see this technology in broader application. However, it exists, people like me (read: not rich) have access to it, and it works pretty well.

To edit:

I found a case study conducted by the Wireless Power Consortium, makers of Qi chargers for my phone, which states (emphasis mine):

In this section, we compare the total power consumption over a 5-year period. Case study: Average system efficiency of wireless charger N sys-wireless = 0.50 (50%) Average system efficiency of wired power supply N sys-wired = 0.72 (72%) Assume that the average charging power is 2W.

So the wired part of your system is 72% efficient and the wireless part is 50% efficient. An inductive method is used in which the coils are a few millimeters apart. Compare that to Joel’s WiTricity, which claims 40% efficiency over 2 meters.

Factor in the additional costs associated with the additional circuitry and components for a wireless system compared to the cost of a piece of copper wire, and you can see why long-distance wireless power transmission is still considered impractical for use in the field mass market is considered.

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The output of a Tesla coil is indeed AC, but much higher than 60Hz. Using a 50 or 60Hz supply is convenient as it has the power to create a decent charge on a capacitor connected across a spark gap connected to the primary winding. See this explanation to get started.

The primary coil (across the spark gap) resonates with the primary capacitance and this forms a parallel tuned circuit. In high Q parallel-tuned circuits, the current flowing between the primary coil and the capacitor is very high, typically in the tens to hundreds of kHz.

This creates an alternating magnetic field that hits the second coil. This second coil has a much higher Q than the first coil and is matched to ground by the capacitance of the large lead. It’s also a parallel resonant circuit and when tuned to the same frequency as the primary resonance it produces quite large voltages that most of us have seen in videos.

All of this occurs at much higher frequencies than AC power systems. Typically in Tesla coil demonstrations, a medium voltage DC power supply is used to charge C1 to the voltage required to break the spark gap.

As an aside, I’ve used low-voltage Tesla coils (matched primary and secondary) to couple useful amounts of energy across a 40mm gap to the power electronics of a rotating machine. OK, they don’t use the spark gap to initiate a spark, but they use the exact same principle. There is also a lot of talk about using this technique to wirelessly power lamps. However, I don’t think it will replace cables as the power transfer is quite inefficient.

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Electrical safety warning

The Tesla Coil produces extremely high voltage, high frequency sparks. NEVER TOUCH THE OUTPUT OF THE TESLA COIL. At best, you’ll get an uncomfortable burn; in the worst case, you get a potentially life-threatening shock.

The Tesla coil control board is also dangerous while the bus capacitors are being charged. NEVER SERVICE THE BOARD WHILE IT IS POWERED UP. ALWAYS WAIT AT LEAST FIVE MINUTES AFTER SWITCHING OFF THE CARD, SO THAT THE CAPACITORS ARE DISCHARGE BEFORE WAIT.

How to get Tesla Tower Mobile Legends (ML), of course, now we can do it easily. By using such a skin in competition, you simply change your tower to make it more attractive when it spawns in gameplay.

Because this is the latest skin for Tower in the Mobile Legends game that we can get under certain conditions.

Perhaps here we can find out the many latest updates where it only appears in the Mobile Legends game.

Then it will be easier to use the power of meta heroes for that push rank.

First of all, if you can find out firsthand, this is the coolest way to get Tesla Tower in Mobile Legends.

How to get Tesla Tower Mobile Legends

So the Tesla Tower that we can get is one of the latest Sacred Statue Skins.

Knowing the name of the Holy Statue yourself, you can change the look of the tower in-game.

Usually we have a tower related to the character, but now you can also get it through special skins.

The Tesla Tower included in the Skin Sacred Statue update this time is quite interesting so you really shouldn’t miss it.

The skin turns the tower into a building, but above it there is a powerful electric shock.

The enemy will look like they’ve been hit with an electric current when hit by a single attack from the turret.

If you’ve played Clash of Clans, you know what the Tesla Tower’s special shape will be.

How to get this skin is also very simple, it’s just that in this case you have to prepare a lot of diamonds.

How to get Tesla Tower Mobile Legends (ML)

Perhaps those of you who are interested in getting this Tesla Tower can actually try the method below.

First enter the Mobile Legends game and then select the shop section to proceed with shopping.

When you are in the shop, simply select the Recommendations section.

Here you need to look for the Lucky Sacred Statue to get the Tesla Tower skin.

After that, you can just open the event to get this Tesla Tower Statue.

With this you will later have to use the name Diamond to execute the spin.

Keep spinning until you get the new Tesla Tower Skin.

In this spin you only need to produce 30 diamonds, but up to 5000 more diamonds.

If you know how to get this you can just try to have the skin huh.

Although it can’t be fully confirmed that you have to use the diamonds, because in this game it’s random at times.

How to get Tesla Tower Mobile Legends (ML)

You might need 5000 more diamonds if you really want that cool skin.

After you get the Tesla Tower, just use it and make sure you build strong defenses as well.

The look this new statue gives you is really interesting, so don’t be surprised if you must have the skin.

This makes the game situation even more exciting due to the deadly electric shock from the tower.

Now that you know how to get Tesla Tower in Mobile Legends, just try to have one.

The appearance of the new skin is indeed quite unique and can be put to better use.

But you must always maintain your tower defense so that it doesn’t get destroyed and the alley is safe from enemies. Keep practicing, play wisely and don’t become a toxic player!

This week at Energy.gov, we take a look at the famous rivalry between two of the most important energy inventors and engineers in history: Thomas Edison and Nikola Tesla. Check back each day to learn more about their lives, their inventions and how their contributions are still influencing the way we use energy today. Support your favorite with the hashtags #teamedison and #teamtesla on social media or vote on our website. And don’t forget to submit questions about the inventors for our live Google+ Hangout with Tesla and Edison experts on Thursday, November 21 at 12:30 p.m. EUROPEAN DAYLIGHT TIME.

11. Tesla was born on July 10, 1856 in the Austrian Empire, now Croatia. He was the fourth of five children. After a checkered academic career in Europe, he worked as a telegrapher and electrician before moving to the United States in 1884 to work for Thomas Edison.

10. If you can’t imagine life without your TV remote, thank Nikola Tesla for making it possible. Tesla invented, predicted, or helped develop hundreds of technologies that play a huge role in our daily lives – such as the remote control, neon and fluorescent lighting, wireless transmission, computers, smartphones, laser beams, X-rays, robotics and much more, of course, alternating current, the basis of our current electrical system.

9. Innovation is in Tesla’s blood. Tesla once wrote: “My mother was an inventor of the first rank and I think she would have achieved great things had she not been so remote from modern life and its many possibilities. She invented and constructed all manner of tools and implements, and wove the finest designs from threads she spun.” He credited his parents’ influence for his success.

8. Tesla lived in New York City for 60 years and remnants of his time there still exist. The corner of 40th Street and 6th Avenue in downtown Manhattan was nicknamed “Nikola Tesla Corner” – with its own street sign – because of its proximity to Tesla’s laboratory at 8 West 40th Street, where he worked in 1900 while building his current one – infamous Tesla Tower on Long Island. A plaque at nearby Bryant Park Place commemorates the Engineer’s Club that awarded Tesla the Edison Medal on May 18, 1917. In his later years, Tesla would feed pigeons at nearby Bryant Park.

7. Tesla obtained his US citizenship in 1891, the same year he invented the Tesla coil. Tesla coils are a type of electrical circuit used to generate low-current, high-voltage electricity. Today they are widely used in radios, televisions and other electronic devices and can be used for wireless transmission. A coil at Tesla’s experimental station in Colorado Springs, Colorado, produced 30-foot sparks that could be seen 10 miles away.

6. During the War of Currents, Tesla’s favored alternating current (AC) battled Edison’s favored direct current (DC) for widespread acceptance. At stake was the foundation of the entire nation’s electrical system. Edison launched a campaign against AC, claiming it was dangerous and could kill people; Tesla countered by publicly subjecting himself to 250,000 volt shocks to demonstrate AC safety. In the end, AC won the battle.

5. Tesla designed the first hydroelectric power station in Niagara Falls, New York, harnessing the power of the falls, which he had admired since childhood. Construction took three years, and on November 16, 1896, electricity first flowed to houses in nearby Buffalo. A statue of Tesla on Goat Island today overlooks the falls.

4. “Teslas”, a unit used to measure the strength of magnetic fields, are named after Tesla. Another namesake is Tesla Motors, the electric car startup, in homage to Tesla’s role in inventing the electric motor.

3. In 1901 Tesla received financial support from J. Pierpont Morgan to build his Wardenclyffe laboratory in Shoreham, Long Island. The facility included the “Tesla Tower,” a 185-foot-tall structure with a 65-foot-tall copper dome transmitter at the top. Tesla’s vision was to use the tower to transmit signals and free, unlimited wireless power around the world. Today, thanks to Tesla’s early work, wireless power transfer is finally a reality – from wireless chargers for electric toothbrushes and smartphones to wireless charging of electric vehicles, a technology being researched at the Department of Energy’s National Labs.

2. Tesla was not a savvy businessman and suffered financially despite his successes. He lost financial support from Morgan, who felt he could not capitalize on Tesla’s wireless power concept, and sold his fortune to offset the double Wardenclyffe foreclosure. The property was later sold to a film processing company. In 1917, the US government tore down Tesla’s partially completed tower, fearing it would be used by German spies to eavesdrop on communications during World War I.

1. His long-abandoned Long Island lab will soon be a museum. Earlier this year, a nonprofit raised enough money to buy the long-abandoned Wardenclyffe. The group plans to restore the building and turn it into a Tesla Museum and science education center.

How a Tesla coil works

The Tesla coil is known to produce extremely high voltages. In this section we explain how the one tesla 10 inch coupled resonant coil can reach voltages in excess of a quarter million volts. We’re building on the basics to give you a thorough explanation of what’s going on.

Table of Contents:

Electricity, magnetic fields and induction

Let’s start with the basics of electromagnetism. One of Maxwell’s equations, Ampere’s Law, tells us that current flowing through a wire creates a magnetic field around it.

If we want to use this magnetic field to our advantage, like with an electromagnet, we wind up the wire. The magnetic fields of the individual windings add up in the center.

A constant current creates a static magnetic field. What happens if we pass an alternating current through the wire? Another of Maxwell’s equations, Faraday’s law of induction, tells us that a time-varying magnetic field induces a voltage across the wire that is proportional to the rate of change of the magnetic field:

If the current is cut off abruptly, Faraday’s law tells us there will be a sharp voltage spike. If an oscillating current flows through the coil, it induces an oscillating magnetic field in it. This in turn induces a voltage across the coil which tends to oppose the drive current. Intuitively, the magnetic field is “persistent” and induces a voltage that opposes any field change.

transformers

A transformer uses the law of induction to transform AC voltages up or down. It consists of two coils of wire around a core. The core is made of soft iron or ferrite, materials that are easily magnetized and demagnetized.

An oscillating current in the primary winding creates an oscillating magnetic field in the core. The core concentrates the field and ensures most of it goes through the secondary. When the magnetic field oscillates, it induces an oscillating current in the secondary coil. The voltage across each turn of wire is the same, so the total voltage across the coils is proportional to the number of turns:

Because energy is saved, the current on the higher voltage side of the transformer is reduced by the same proportion.

The Tesla Coil is a very souped-up transformer. Let’s briefly consider what would happen if it were a perfect transformer. The primary winding has six turns and the secondary winding has about 1800 turns. The primary runs at 340 volts, so the secondary is 340V x 300 = 102kV. That is a lot! But not quite a quarter of a million. In addition, because the Tesla coil has an air core and the coils are positioned relatively far apart, only a small fraction of the magnetic field generated by the primary winding is actually connected to the secondary winding. To better understand what is going on, we need to introduce resonant circuits.

resonant circuits

An oscillating circuit is like a tuning fork: it has a very strong amplitude response at a specific frequency called the resonant or natural frequency. The tines of the tuning fork vibrate severely when excited at a frequency determined by their dimensions and material properties. A resonant circuit achieves its highest voltages when operated at its natural frequency, which is determined by the value of its components.

Resonant circuits use capacitors and inductors and are therefore also known as LC circuits. Because of the existing energy storage elements, they are also referred to as “tank circuits”.

Capacitors store energy in the form of an electric field between two plates separated by an insulator called a dielectric. The size of the capacitor depends on the size of the plates, the distance between them and the properties of the dielectric. Interestingly, the top load on the Tesla coil acts like a single plate capacitor, with the ground plane surrounding the coil acting as the opposite plate. Topload capacity is determined by its dimensions and proximity to other objects.

Inductors store energy in the form of a magnetic field around a wire or in the middle of a loop of wire. The primary inductance in the one Tesla 10-inch coil is six turns of AWG14 wire, and the secondary coil is approximately 1800 turns of AWG36 wire.

An LC circuit can have an inductor and a capacitor in series or in parallel. Here we use series LC circuits like this:

Consider what happens if you don’t drive the circuit (assume the AC source is replaced by a wire in the figure above) but start with the capacitor charged. The capacitor wants to discharge, so charge flows around the circuit through the inductor to the other plate. A magnetic field builds up inside the inductor. When the charge on each plate of the capacitor is zero, the current stops flowing. But at this point the inductor has stored energy in a magnetic field – which tends to resist changes. The magnetic field collapses and induces a continuous current in the same direction, recharging the capacitor and restarting the cycle in the opposite direction.

The resonant frequency of an LC circuit, or the frequency at which energy switches between the capacitor and inductor as described above, is:

Driving the circuit at its resonant frequency adds energy during each cycle. By providing a series of well-timed jabs, we can build extremely high tension! A spark breaks out in the Tesla coil and discharges the circuit as soon as the voltage is high enough.

DRSSTC

The One Tesla 10 inch coil uses a double resonant topology, hence the name Double Resonant Solid State Tesla Coil or DRSSTC. In a DRSSTC, the circuit driving the secondary LC circuit is another LC circuit tuned to the same resonant frequency. In the diagram below, L pri and L sec are the primary and secondary inductances, respectively. They are weakly coupled, connecting about a tenth of their magnetic fields.

There are several reasons why Tesla coils do not use a magnetic core. First, the voltages in the Tesla coil are so high that the core would quickly become saturated, i.e. beyond a certain point it would no longer be magnetizable. Also, most materials are resistive and will heat up in a magnetic field that switches rapidly, as is the case in the coil. The high voltage generated by the coil can also flash over to the core. Most importantly, the primary and secondary coils are loosely coupled – so the secondary coil is not loaded by the primary coil.

half bridge

How do we go about exciting the primary? We use a DC voltage source and apply the voltage in alternating directions across the primary winding.

The switches we use to apply a DC voltage in alternating directions across the primary side are IGBTs, short for Insulated Gate Bipolar Transistors. An IGBT is a transistor that can control very high voltages and currents. This is its schematic symbol:

Its terminals are labeled collector, gate, and emitter as holdovers from pre-transistor era vacuum tubes. A simplified model of an IGBT is a normally open switch that closes when a positive gate voltage (VGE) is applied. In the following half-bridge diagram, S1 and S2 represent the IGBTs. They switch on and off alternately, which switches the polarity of V bus /2 through L primary and C primary , the primary inductor and capacitor. The One Tesla 10-inch coil operates on a 340 VDC bus voltage, which we get from rectified and doubled mains voltage.

On the control board we get the bus voltage from rectified and doubled mains voltage. We’ll go into more detail about this part of the circuit later.

zero-current switching

When the IGBTs are fully on (switches closed) they are near perfect conductors. When they are fully off (switches fully open) they are near perfect insulators. However, when transitioning from fully open to fully closed or vice versa, they behave like resistors. Recall that the amount of power dissipated in a circuit is P = VI. If we try to switch the IGBT while the current through the circuit is large, it will heat up a lot! We need to time the switching of the IGBTs to the natural zero crossings of the primary LC circuit. On the One Tesla board, we achieve zero current switching by measuring the primary current and using control logic to ensure the transistors are switching at the correct times.

gate driving

IGBTs are anything but ideal switches. We want them to switch fast to minimize the time they are resistive and dissipating power. The problem with fast switching gates is that they have significant internal capacitance and it takes a lot of charge to fill up that capacitance and get the turn on voltage across the gate (a capacitor’s voltage is given by V = Q/C). ).

In order to charge CGE in the shortest possible time, we want to use a short, high-current pulse. Gate driver ICs are designed to do just that. We use UCC3732x ICs which can deliver up to 9A for short pulses. The logic circuitry in front of the gate drivers is nowhere near capable of supplying enough current to turn the gates on quickly, so the gate drivers are essential components. Finally, we need to isolate the gate drivers from the IGBTs using a gate driver transformer (GDT). Every IGBT requires a gate voltage applied between its gate and emitter in order to turn on. This is easy for the low-side IGBT (below) – its emitter is always grounded, which means its gate only needs to be pulled to +15V. For the high-side IGBT (above), things are not so simple, since its emitter is referenced to the collector of the low-side IGBT, a node that oscillates between 0 and V bus /2 (170 V in our case). That means we need to get the gate of the high side IGBT to V bus /2 + 15V to turn it on.

Luckily, there’s an easy way to get around this! We can drive the primary winding of a 1:1:1 transformer with the (bipolar) drive signal derived from a push-pull pair of UCCs. More specifically, we are driving the primary winding of the transformer with the difference in the outputs of an inverting and a non-inverting gate driver. This ensures that this signal is positive half the time and negative half the time. Because of transformer action, the voltage on each secondary of the GDT is guaranteed to replicate the voltage on the primary no matter where we connect the ends. This means that we can simply connect a secondary side between the gate and emitter of any IGBT and guarantee that V ge will always swing between 0 and 15 V (regardless of the potential of the emitter).

rectifier and doubler

The half bridge in a Tesla is driven by a doubler rectifier as shown in the diagram above. This rectifier alternately charges each capacitor on alternate half cycles of the AC input, resulting in a doubling of the source voltage across the load. In the positive part of the cycle, the top diode conducts and charges the top capacitor.

In the negative part of the cycle, the bottom diode conducts and charges the bottom capacitor. The voltage across the load is the sum of the voltages across each capacitor.

logic

As previously mentioned, control logic is required to sense the primary current and prevent the IGBTs from turning on and off while current is flowing through them. Let’s go through the above scheme from left to right. (Note that the part numbers in the schematic do not correspond to those on the board, but we use them here for explanation purposes only. Refer to the Eagle files available at http://onetesla.com/downloads for the complete parts schematic.)

The current transformer drops the primary current to a safe level for use in the logic area of ​​the board. R1 is a 5W resistor that will load down the transformer and limit the current. D1 starts conducting when the signal exceeds 5.7V, which is the rail voltage plus the forward voltage drop of the diode, effectively preventing the signal from exceeding 5.7V. D2 starts conducting when the signal is -0.7V. Together, D1 and D2 are protection diodes that limit the signal and prevent damage to the logic ICs when the signal from the current transformer is too high. Next, G1 and G2 are inverters that square the signal for subsequent ICs.

The optical receiver outputs 5V or 0V depending on the signal from the breaker. R1, R2 and R3 form a resistive network that ensures that the coil can only be ‘tickled’ by the breaker signal when it is switched on, with no feedback waveform present. When the coil is just ramping up there is no feedback signal but the interrupt signal goes to the UCCs. When the coil is operating, the feedback signal dominates the upper part of the signal path.

The inverted interrupt signal and the square wave from the squared primary current signal are then fed into a D-type flip-flop that performs logic that determines when the gate drivers receive a signal. They only turn on when there is a zero crossing as well as a signal from the breaker. The D flip-flop behaves according to the following truth table:

In our circuit, \PRE and D are pulled high. The inverted breaker signal fed into \CLR pulls \Q high when the breaker is on. When the breaker turns off, \Q remains high until the next falling edge of CLK (which is synchronized with the primary current zero crossings), at which point it switches low.

The inverting gate driver turns on when IN is high and EN is low. The non-inverting gate driver turns on when IN is high and EN is high.

interrupter

The oneTesla interrupter is a microcontroller based device that converts an incoming stream of MIDI commands into a stream of pulses for the Tesla coil. These pulses turn the entire coil on or off, thereby controlling both power throughput and music playback.

The MIDI commands are received via the MIDI input socket. Per MIDI specifications, the 4N25 optoisolator provides the necessary isolation to eliminate ground loops. When the microcontroller receives a note-on command, it begins outputting a pulse stream at the frequency of the note. The lengths of these pulses are specified by a lookup table in the firmware. The breaker uses separate MIDI channels to play multiple notes simultaneously – to play back two channels, the software simply generates impulse trains that correspond to each channel, and then performs the OR logic function on the impulse trains before outputting them. Limiting the maximum pulse width ensures that the resulting stream does not have excessively long pulses.

The power control scales the pulse widths linearly based on the position of the potentiometer. While this does not yield a linear spark length, it has the advantage of predictably scaling coil power consumption, a feature that would be lost if the scaling curves were optimized for linear spark growth.

So how does it make music?

Sound is a pressure wave. Its pitch is determined by the frequency of the wave. We can create sound in a number of ways: traditional speakers vibrate a membrane, and Tesla coils use the expansion and contraction of air as it is heated by plasma.

The resonant frequency of the secondary is around 230 kHz, well above the audio range. We can use bursts of sparks shooting off at 230kHz to create pressure waves at the audio frequency. A spark burst is triggered with each peak of the audio signal. The rapid firing of the sparks is faster than your eye can tell so it looks continuous, but in reality the spark forms and goes out at audio frequency intervals. This modulation technique is known as pulse density modulation (PDM) or pulse repetition modulation (PRM).

The current in the primary winding continues to increase while the bridge is being driven. It is important to make the bursts short enough so that the IGBTs don’t overheat. Within a single cycle, the current on the primary side can briefly reach hundreds of amperes. For thermal reasons, the maximum duty cycle of the bridge is about 10%. The breaker’s firmware has a look-up table of frequencies and turn-on times that are empirically determined by varying the pulse width and observing the spark power.