Tom Hartsfield does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Picture a reclusive man, dripping with sweat all night in a dark lab, illuminated only by crackling sparks that periodically leap from enormous machines and cast a purple glow across his face. This was Nikola Tesla, the archetype of the mad scientist. His inventions fill the world around us; they are instrumental to our modern electrical grid. They are quiet, reliable, invisible machines.
Perhaps his most famous invention is the Tesla coil – a contraption that produces beautiful flying arcs of electrical energy. It was invented by Tesla in an attempt to transmit electricity wirelessly.
Transformer in action
The principles behind the Tesla coil are relatively simple. Just keep in mind that electrical current is the flow of electrons, while the difference in electric potential (voltage) between two places is what pushes that current. Current is like water, and voltage is like a hill. A large voltage is a steep hill, down which a stream of electrons can rapidly flow. A small voltage is like a near-flat plain with almost no water flow.
The power of the Tesla coil lies in a process called electromagnetic induction. This is where a changing magnetic field creates a voltage that compels current to flow. In turn, the flowing electric current generates a magnetic field. When electricity flows through a wound up coil of wire, it generates a magnetic field that fills the area around the coil in a particular pattern.
Similarly, if a magnetic field flows through the centre of a coiled wire, a voltage is generated in the wire, which causes an electrical current to flow.
The voltage (“hill”) generated in a coil of wire by a magnetic field through its centre increases with the number of turns of wire. A changing magnetic field within a coil of 50 turns will generate ten times the voltage of a coil of just five turns. (However, less current can actually flow through the higher potential, to conserve energy.)
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This is exactly how a common alternating current (AC) electrical transformer, found in every home, works. The constantly fluctuating electric current flowing in from the power grid is wound through a series of turns around an iron ring to generate a magnetic field. Iron is magnetically permeable, so the magnetic field is almost entirely contained in the iron. The ring guides the magnetic field (in green to the right) around and through the centre of the opposite coil of wire.
The ratio of coils on one side to the other determines the change in voltage. To go from 120V household wall voltage to, say, 20V for use in a laptop power adaptor, the output side of the coil will have six times fewer turns to cut the voltage to one sixth its original level.
How the coil rolls
Tesla coils do the same thing, but with a much more dramatic change in voltage. First, they employ a pre-made high voltage iron core transformer to go from 120V wall current to roughly 10,000V. The wire with 10,000 volts is wrapped into a large (primary) coil with only a handful of turns. The secondary coil contains thousands of turns of thin wire. This steps up the voltage to between 100,000 and 1,000,000 volts. This potential is so strong that the iron core of a normal transformer cannot contain it. Instead, there is only air between the coils.
The Tesla coil requires one more thing: a capacitor to store charge and fire it all in one huge spark. The circuit of the coil contains a capacitor and a small hole called a spark gap. When the coil is turned on, electricity flows through the circuit and fills the capacitor with electrons, like a battery. This charge creates its own electric potential in the circuit, which tries to bridge across the spark gap. This can only happen when a large amount of charge has built up in the capacitor.
Eventually so much charge has accumulated that it breaks down the electrical neutrality of the air in the middle of the spark gap. The circuit closes for a fleeting second and a huge amount of current blasts out of the capacitor and through the coils. This produces a very strong magnetic field in the primary coil.
The secondary wire coil uses electromagnetic induction to convert this magnetic field to an electric potential so high that it can easily break apart the air molecules at its ends and push their electrons in wild arcs, producing enormous purple sparks. The dome on the top of the device acts to make the secondary coil of wires receive energy more fully from the first coil. With some careful mathematical calculations, the amount of electrical energy transferred can be maximised.
Flying blue streamers of electrons flow off the coil and through the hot air searching for a conductive landing place. They heat the air and break it into a plasma of glowing ion filaments before dissipating into the air or surging into a nearby conductor.
A tremendous light show is generated, as well as a loud buzzing, crackling sound, which can be used to play music. The electrical theatrics are so stunning that Tesla was known to use his device to scare and mesmerise visitors to his lab.
Tesla might not have invented a source of unlimited power, which was one of his goals, but he did design a brilliant machine to demonstrate the sheer power and beauty of electricity.
Nikola Tesla was a unicorn person before “unicorn person” became a term.
He was a Serbian inventor who came up with the idea of wireless energy transfer among things like alternating current, induction motors and many others.
I would say that he built out his idea of global wireless energy transfer in three phases. The very first was the Tesla Coil, which I made a video about. You can check it out below.
The second phase of his scaling plan was when he built the Magnifying Transmitter. He built this at his laboratory in Colorado Springs.
This was essentially a larger version of the Tesla Coil. Using it as an analogy, the first tower represents the primary coil, and the second tower represents the secondary coil.
Finally, the third phase of his scaling was to take it global. He planned and built out the Wardenclyffe Tower in New York.
However, this version failed and was eventually taken down in 1917, but we’re getting ahead of ourselves. Let’s take a look at what needed to happen before Tesla came up with his very first demonstration; the Tesla Coil.
Historical Beginnings
To explain Tesla’s journey towards global wireless energy transfer, there are a few key points in history and inventions that we need to go over first.
The first key invention is that of the battery in the 1780s. Two physicists, Galvani and Volta, conducted an experiment. I talk about the entire process in my article about the physics behind wireless energy transfer. I’ve linked it below.
Following the battery, a Danish physicist named Hans Christian Ørsted learned that a moving electric current creates a magnetic field. His discovery was the first to find the link between electricity and magnetism. He demonstrated this in a lecture in 1820.
Perhaps the most important invention hereafter for the Tesla Coil is the electromagnet. In 1826, William Sturgeon, an English physicist, discovered that electric current running through a wire coiled around an iron bar caused the iron bar to behave like a magnet.
He fittingly named this the electromagnet.
A few years later in 1831, a man named Michael Faraday wondered if he could make electricity with magnets. So, he used electromagnets. Faraday is most well known for discovering electromagnetic induction.
He used two separate coils wrapped around one iron ring and noticed that when he attached/disconnected a battery to the first wire, the second wire would get a jolt of electricity. He called this inducing a current.
This phenomenon is explained using Faraday’s Law of Induction, which states that:
a changing magnetic field will induce an electromotive force (EMF) in a loop of wire, where EMF is what causes electrons to move and form a current
At this point, all of the components necessary to conceive of the Tesla Coil had been invented, but the background doesn’t end here.
What Was Innovated?
Following Faraday’s discovery of induction, Nicholas Callan, an Irish priest, wanted to improve Faraday’s device.
He decided to wind both the primary and secondary coils around the same iron bar while keeping them electrically separate. Doing this allowed him to feel electrical jolts from wire that had not been directly connected to a battery!
He also found that if the primary wire, the one connected to the battery, was thick and that the secondary wire was thin and had been coiled more, the jolt produced was more powerful.
If the secondary coil has fewer loops than the primary coil, the result is more current and less voltage. However, Callan’s made a secondary coil with more loops than the primary coil, so the result was more voltage and less current.
Callan’s device was named the Step-Up Transformer. When he connected the battery to a coil, it became an electromagnet with a magnetic field. When he disconnected the battery, it lost its magnetic field.
Using Faraday’s Law, every time Callan connected or disconnected, he created a new current in the second coil of wire. He also used a wheel to mechanically connect and disconnect the battery, acting as a kind of “repeater.”
Though this version was later improved by William Sturgeon, Callan’s device was used for electroshock therapy for many years.
The biggest advancement thereafter was using the coil itself to disconnect and connect to the battery instead of using the wheel. How did this work?
Well, the current running through the primary coil caused it to behave like a bar magnet. The wire carrying the current was then connected to a switch so that it could pull on it and activate a spring in the circuit.
The movement of the spring would turn off the current. However, once the connection was removed, the primary coil would no longer be magnetic. This causes the spring to disconnect, and the switch to turn back on.
An Electrical Interrupter
This process of the switch turning on and off would click about 20 to 40 times per second and was named an electrical interrupter.
There was still room for innovation.
The electrical interrupter would sometimes spark. So, in 1853 a man named Armand Fizau created the Leyden Jar to absorb the spark. It was the first version of a capacitor.
This is something made of two large conducting materials separated by insulating material.
By adding the capacitor and getting rid of the spark, Fizau created a new device — one that took DC from a battery and made bursts of AC in the 1850s.
Though not necessary to understanding the Tesla Coil, I’ll mention too that in 1886, Heinrich Hertz added an antenna to the induction coil and created the first man-made radio wave.
This is where Tesla comes in.
Tesla’s Take
Having heard of the radio waves created by Hertz, Tesla visited the World Fair in Paris, 1889. He began tinkering with the induction coil. Among other things, he removed the interrupter and DC battery and replaced it with an AC generator.
This makes sense — why use a battery and mechanical switch to turn the current on and off when a generator that automatically switches the current’s direction could be used instead?
Though this first adaptation didn’t actually work out at the end (due to overheating and melting of wire insulation) it did lead to Tesla’s use of a spark or air gap.
With a few other tweaks, we finally arrive at the original version of the Tesla Coil which looked something like this:
The Original Tesla Coil Circuit Uses Capacitors and Spark Gaps
The modern version, which is what I recreated in my video, is slightly simpler. It no longer uses capacitors or spark gaps and looks like this:
Modern Version of the Tesla Coil Circuit
P.S. for an explanation of how electromagnetic induction works in the modern circuitry, watch my video linked near the beginning of this article.
Nikola Tesla wirelessly lit up a bulb in the year 1891 using his coil, but as I said earlier, his dream was to send wireless power over large distances by using the earth.
After the Tesla Coil worked, he built the larger version that I mentioned earlier called the Magnifying transmitter. It was able to light up three incandescent bulbs at 100ft or 30metres away.
Following his second success, he built the Wardenclyffe Tower in Long Island in 1901. He wanted to use the tower to harness the energy that he thought was inside Earth, in the hopes of turning our planet into a gigantic dynamo.
The tower would take energy from a coal-power generator and send it deep into the ground with a metal rod. He thought that the Earth’s crust would transport the energy.
The tower, however, was considered a failure, was taken down in 1917 and never finished. There are many speculations as to why it didn’t work, some more sound than others, of course.
The article I’ve linked below does a great job of explaining some of the flaws of the tower and how Tesla tried to address
There’s a lot left for us to develop when it comes to modern-day wireless energy transfer. We’ve only scratched the service, even with other methods like radio wave transmission and inductive coupling. To read more about how wireless energy transfer looks now, read this article I wrote.
TLDR;
Previous inventions including the battery, electromagnet, induction theory and capacitors were all necessary precursors to the Tesla Coil
Tesla’s ideation of the coil is based on the principles of electromagnetic induction — a form of wireless energy transfer that we continue to build on now with things like wireless phone charging plates etc.
He tried to scale the coil by building the Magnifying Transmitter then the Wardenclyffe Tower
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How Tesla coils generate high-voltage electrical fields.(Image credit: by Ross Toro, Infographics Artist)
Named for its inventor, Nikola Tesla, this machine transforms energy into extremely high-voltage charges, creating powerful electrical fields capable of producing spectacular electrical arcs. Besides the lightning-bolt shows they can put on, Tesla coils had very practical applications in wireless radio technology and some medical devices.
A Tesla coil is made of two parts: a primary coil and a secondary coil, each with its own capacitor. The two coils are connected by a spark gap, and the whole system is powered by a high-energy source and transformer. Basically, two circuits are connected by a spark gap.
HOW IT WORKS:
1. The transformer boosts the voltage.
2. The power source is hooked up to the primary coil. The primary coil’s capacitor acts like a sponge and soaks up the charge.
3. Electric current builds up in the capacitor until it reaches a tipping point. The current streams out of the capacitor into the coil. Once the first capacitor is com-pletely wrung out and has no energy left, the inductor reaches its maximum charge and sends the voltage into the spark gap (basically a gap of air between two electrodes).
4. The huge voltage current flows through the spark gap into the secondary coil. The energy sloshes back and forth between the two coils.
5. The secondary coil has a top-load capacitor that concentrates all the current and can eventually shoot out lightninglike bolts.
The idea is to achieve a phenomenon called resonance between the two coils. Resonance happens when the primary coil shoots the current into the secondary coil at the perfect time that maximizes the energy transferred into the secondary coil. Think of it as timing a push to a swing to make it go as high as possible.
Tesla coil, an electrical transformer that uses high-frequency alternating current (AC) to increase voltage. Because of its extremely high voltage, the electricity in a Tesla coil can travel through the air, powering—or damaging—nearby electronic devices, often with arcs of lightninglike electricity. Though the Tesla coil produces extremely high voltage, the high frequency of the current generally makes it possible for most people to approach the device and even be struck by the arcs without suffering injury. The spectacular effects created by the Tesla coil make the device popular for scientific exhibitions, but the principles underlying the coil were also important to the development of radio technology.
The Tesla coil was invented by Serbian American inventor Nikola Tesla in 1891. Tesla was primarily interested in its potential to wirelessly transmit electricity, particularly for lighting. He hoped to build large coils scattered across Earth, each of which would provide power to any device with a receiver coil. However, he had little success with this plan. In 1893 Tesla gave a lecture and demonstration on wireless transmission in which he proposed signal transmission in conjunction with power transmission. He also obtained a patent describing the same principles, which is considered the first radio patent.
A Tesla coil is an electrical transformer, or a device that raises or lowers voltage, which is a measure of electrical potential. A Tesla coil generates very high voltage, often in excess of one million volts. It uses AC electricity, meaning that the voltage of the circuit changes at a particular frequency. A modern Tesla coil usually consists of an initial transformer that boosts voltage from the power source and sends it to a capacitor attached to the primary coil, which absorbs the high-voltage power. When the capacitor reaches a sufficiently high voltage, electricity flows across a spark gap, or a space between two high-conducting terminals, at a high frequency, creating an AC current in the primary coil.
One of the key principles of the Tesla coil is resonance—achieving the frequency at which the device’s primary coil induces maximum voltage in the secondary coil. This is achieved through magnetic coupling, also called inductive coupling. The two coils are not tied together with a conductor; rather, electricity is run through the primary coil, which creates a magnetic field. This magnetic field creates an electrical current in the secondary coil, at a much higher voltage. To achieve this increase in voltage, the secondary coil must have many more windings than the primary coil. Frequently, the primary coil has only one or two windings, while the secondary may have hundreds or thousands. The secondary coil also contains a capacitor, which builds up extremely high voltage.
The resulting high voltage results in a magnetic field so strong that arcs of electricity flow like lightning from the Tesla coil to nearby objects. These lightninglike discharges can even flow to people, but this is usually dangerous only if a nearby person has a pacemaker or other medical device that could be affected by the Tesla coil. Though the voltages are very high, the impedance of the coil is high enough that only a small current is produced in humans who interact with it, and the frequency of the current is such that it has little interaction with nerve cells. A popular demonstration of a Tesla coil is to have a person hold a metal rod in one hand and a lightbulb in the other. Holding the rod close to the coil produces an arc of electricity that travels through the person’s body and lights the bulb. Fluorescent lightbulbs and other devices can also be powered by proximity to the Tesla coil, even without drawing an arc. It was this ability to produce wireless power that Tesla found so compelling.
(or a 4th-order transformer-coupled multiple resonance network with distributed load capacitance)
After several experiments with variants of the Tesla coil circuit, as a transformerless circuit, a capacitively coupled circuit, and a 6th-order directly coupled circuit, I made this more usual version, using a transformer. My main intention was to test the modeling of inductances and mutual inductance, but I also wanted to see how this method improves the performance of these.systems, by allowing independence between the voltage gain and the energy transfer time. The schematic diagram of the system is shown below:
The circuit is a classical "Tesla coil", with the only nonusual feature being that tuning is achieved by varying the distributed capacitance of the top terminal, varying the length of the antenna above it. This is the same method that I used in my other systems.
The circuit worked very well, producing streamers and arcs to a grounded object that easily reach 25 cm (specially when the antenna is covered by a half sphere). Its performance is significantly better to what I obtain with a directly coupled system using the same elements, and more regular and insensitive to tuning, certainly due to the faster energy transfer.
C1 (5.07 nF) and L2 (28.2 mH) are the same elements used in my other systems. The neon sign transformer (5 kV, 30 mA) and the spark gap are also the same. L1 is a flat coil, made with insulated #18 solid wire, with 14.7 turns, minimum radius = 7 cm, and maximum radius = 12.5 cm. It was designed to have an inductance of 58.7 µH, and a coupling coefficient with L2 of 0.105. This results in operation in mode 9:10, as my first directly coupled system, but with 5 times bigger input energy.
Design:
This system was designed in the following way: First, the operating mode k:l was selected. This ratio of integers with odd difference (the usual is to have l = k+1) determines the ratio of the two resonance frequencies of the complete system (l/k), and the number of cycles required for complete energy transfer (l/2 cycles of the primary voltage). In this case the mode 9:10 was selected. The coupling coefficient and the element values are obtained from the equations [1]:
L1C1=L2C2=(k2+l2)/(2(w0kl)2) k12=(l2-k2)/(k2+l2)
From the parameters of L2 (L = 28.2 mH, self-capacitance = 5.55 pF) and C1 (C = 5.07 nF), and adding 5 pF, to account for the top terminal and antenna, to the total capacitance C2 (C = 10.55 pF), L1 is obtained as 58.7 µH, and w0/(2p), the base frequency that multiplies k and l to produce the two resonances, as 30.84 kHz. The two resonances are then ideally at 277.58 kHz and 308.43 kHz. The separate pairs L1-C1 and L2-C2 resonate at 291.79 kHz. The required coupling coefficient is k12 = 0.105.
The secondary coil has 32 cm of length, 4.4 cm of radius, and 1152 turns of #32 wire. The primary coil dimensions can be calculated from this version of Wheeler's formula for flat spirals:
L = 100/2.54 ((r1+r2)N)2/(60r2-28 r1) µH
where r1 is the internal radius, r2 the external radius, both in meters, and N is the number of turns. Choosing r1 = 0.07 m and r2 = 0.125 m, 14.7 turns are required. The coupling coefficient was calculated numerically by Neumann's formula, implemented in my Teslasim program. In this case the required coupling is obtained with L1 2.7 cm below L2. Since I mount L2 in a support that rises it by 3 cm, I mountedL1 over a plastic disk with a hole for the base of L2 at the center, "sewing" the wire coil over the disk with silicone string. In this way L1 would stay at approximately the correct distance, and it would be easy to adjust the distance by rising L1 or L2.
Measurements in the assembled system, after proper tuning at low power, showed that L1 ended a bit larger than calculated, with 59.8 µH, and that the coupling was also increased, to ~0.12. The resonances were measured as 289 kHz for C1-L1, and 270 kHz - 305 kHz for the whole system. The observed waveforms put the operating mode between 7:8 and 8:9. The losses caused by the tuner in the primary circuit cause some distortion in the ideal waveform, explaining the apparent inconsistency between the number of cycles before the first notch and until the second notch. A simulation including 3 ohms of resistance in the primary circuit agrees well with the observation. The increased primary inductance can be atributed to wiring inductances in the setup (it would be enough the complete the 15th turn to exceed the measured inductance). The increased coupling may be due to wiring, due to capacitive coupling (note that my capacitive transformer system has a similar structure, but in this case the capacitance between L2 and L1 is very small), or, more probably, due to the nonuniform current distribution in L2, and even due to the presence of a shorted turn caused by the top terminal, not considered in the calculations. It was easy to adjust the system for correct operation in modes 7:8 or 9:10, by moving L1 by less than1 cm. Actually, the difference in efficiency between these modes or anywhere between them is insignificant.
An interesting observation is that the effective coupling can be substantially changed if L2 is connected to one side of L1, with the other side of L1 grounded. If I connect L2 to the center of L1 and ground its outer side, the mode decreases to close to mode 6:7, and there is a visible improvement in the performance. Reversing the connections of L1 is also possible, but it decreases the effective coupling. The observed decrease was to mode 12:13. This connection is knows as "Oudin coil", and was first described in 1892. In this case, it was made with two separate coils.
An Oudin coil with inductances L1 and L2, and coupling coefficient M, can be transformed into an equivalent Tesla coil by the aplication of the "T" equivalent of a transformer twice, as shown below:
In the example, using the observed k12 = 0.12, k12' = 0.16, corresponding closely to a bit less than the observed mode 6:7. The reverse connection corresponds to a negative M, what gives k12' = 0.075, corresponding to a bit more than the observed mode 12:13.
Programs that can design and simulate the behavior of this system, and others, can be found here. Extensive materials about Tesla coils can be found in the archives of the Tesla list.
A short video with a demonstration of the device in operation in March 2006.
[1] See the papers about "multiple resonance networks" here.
Nikola Tesla (Smiljan, July 10, 1856-New York, January 7, 1943) was a physicist, inventor and engineer Serbian U.S.. He is best known for his revolutionary work and his many contributions in the field of electromagnetism in the late nineteenth and early twentieth centuries. His patents and his work formed the basis of modern alternating current electric power (AC), including the polyphase power distribution and the AC motor, with which he has contributed to the birth of the second industrial revolution. His admirers go so far as to call it “the man who invented the twentieth century”. We know that this device operated by emitting electrons from the single electrode through a combination of field emission and thermionic emission. Once liberated, electrons are strongly repelled by the high electric field near the electrode during negative voltage peaks from the oscillating high voltage Tesla coil. Tesla experimented with a large variety of coils and configurations. He used to conduct innovative experiments on the electric light, the phenomena of alternating current and high frequency transmission of signals and power without wires.
Theoretical introduction
The Tesla coil is a device consisting of a transformer that uses electromagnetic induction to generate high frequency lightning very similar to those of atmospheric origin even if the amount is very small built for the first time by Nicola Tesla. It is a type of resonant transformer which consists of two coupled resonant circuits. A transformer Tesla coil operates in a manner different from a conventional transformer, in which the voltage gain is limited to the ratio of the numbers of turns of the coils. Otherwise, the voltage gain of a Tesla coil can be significantly larger. The coil transfers energy from an oscillating resonant circuit (the primary) to the other (the secondary). As soon as the primary transfers energy to the secondary, the voltage of the secondary production increases until all primary energy available was transferred to the secondary.
There are various types of coils tesla:
-Tesla Coil solid state: this type of coil is called “solid state” since it is controlled by an electric circuit without moving parts and without spark gap. The resonance frequency is generated directly by an electronic circuit. Tesla coils transistor using the operating voltage of the primary lower, typically between 175 to 800 volts and driving the primary coils using a bridge circuit to a half or a full bridge mosfet or bipolar transistor to switch the primary current.
-Tesla Coil Tube: for fans of the genre, these types of coils operate valves. To get exhausted really interesting and climb power, it is necessary to find huge military type valves such as GU81M in some specialized market or electronics fair. The particularity of the coils Tesla valve that is running at high frequency, make harmless discharges due to the skin effect, coils fed by thermionic valves typically operate with voltages between 1500 and 6000 volts, while most of coils spark gap operate with primary voltages of 6000 to 25 000 volts. The primary winding of a traditional transistor Tesla coil wraps only the lowest part of the secondary (sometimes called resonant).
-Tesla Coils-gap: this is the most common, which exploits the high frequency produced when the capacitor is discharged once loaded on the primary energy transferred to the secondary. The purpose in any case is to generate the primary winding a 3 frequence resonant with the secondary circuit, which must receive energy as a real antenna, transforming however to very high voltages, consequently decreasing the amperage. Even with a significant loss of electric shock well designed Tesla coil can transfer over 85% of the energy initially stored in the capacitor to the secondary circuit. The coils newer typically consist of a primary accumulation circuit that is a circuit composed of a high voltage capacitor, a spark gap, and a primary coil; And the secondary circuit, a series resonant circuit consisting of the secondary coil and the toroid .
The first reels
In the original design of Tesla for its largest coil, used a top terminal that consists of a metal frame in the shape of toroid, covered with smooth plates of metal in a semicircle (constituting a surface driver very large). In its largest complex Tesla employed this type of shaped element inside a dome. The upper terminal had a relatively small capacity, loaded with a voltage as high as possible. The outer surface of the upper terminal is where the electric charge accumulates. In the original plans of Tesla, the secondary LC circuit is composed of a coil loaded then placed in series with a large helical coil. The helical coil was then connected to the toroid. The majority of modern coils uses only a single secondary circuit. The toroid is in effect a terminal of a capacitor, the other terminal being grounded. The LC circuit is tuned to the primary so as to resonate at the same frequency of the LC circuit secondary. The primary and secondary coils are magnetically coupled, creating a resonant air-core transformer. The first Tesla coils needed large insulation to their connections to prevent discharges into the air. More recent versions of Tesla coils emit electric fields over large distances, thus allowing operations outdoors.
The coils modern
The most modern Tesla coils use simple toroids, typically constructed from metal wires or tubes bent aluminum, to control the high electric field near the top of the secondary target and discharges outside, away from the coils and primary secondarie. The Tesla coil is also famous for its ability to turn on the fluorescent tubes at a great distance without electrical connections. The modern Tesla coils, based on transistor or vacuum tubes, do not use a spark gap, but take advantage of the oscillations obtained directly from the transistor or vacuum tubes. The primary induces alternating voltage in the lower portion of the secondary, while offering “pushed” regular (similar to thrust properly calculated and provided in an oscillation of the field). Additional energy is transferred from the primary to secondary inductance and capacity of the upper terminal during each “push”, and secondary output voltage of production constitutes the upper ring of the apparatus. An electronic feedback circuit is usually used to synchronize the primary oscillator to the growing resonance in the secondary, and this is the only consideration tuning. The primary resonant circuit is formed by connecting a capacitor in series with the primary coil of the coil, so that the combination forms a series circuit with a resonant frequency close that of the secondary circuit. Because of the additional resonant circuit, are necessary manual adjustments and a tuning adaptive.
The Tesla Coil built by us
We used:
-A GENERATOR OF HIGH-VOLTAGE COIL A PRIMARY-SECONDARY COIL WITH TORUS-A CONDENSER FOR HIGH-VOLTAGE a spark gap
This is the circuit diagram:
High voltage generator
To build the generator I used a high voltage transformer for neon signs, it is a normal two-winding transformer with a laminated iron core. Features:-Primary circuit: 230V-secondary circuit: 3,500 V 35mA The transformer is a static electric machine (because it contains parts 6movimento) reversible, which serves to vary the voltage and current with constant power. The transformer is a machine able to operate only in alternating current, because it exploits the principles of electromagnetism variables related to the flows of the magnetic field. The voltage and amperage output depend on the ratio of the number of turns of the primary and secondary circuit, here’s an example: If the first coil consists of 100 turns were present in the second 1000 turns 10V and the voltage is 100V . So, the higher the ratio of the number of turns, the greater tension that it will have in the secondary coil.
For high voltage capacitor
We used a Leyden jar which typically consists of a glass container (for example a bottle) covered by a metal coating 7 on the outside and inside is a saline solution that will be the two armatures. In parallel to the high voltage generator we hooked a Leyden jar, that by having a very low capacity but high voltage electrical work is the most ancient form of capacitor. The Leyden jar was used to conduct many early experiments with electricity during the second half of the eighteenth century. The Leyden jars have an electrical capacity rather low, which combined with high dielectric strength and thickness of the glass, making them ideal as capacitors for high voltage.
Spark gap
It is simply two screws spaced rounded head supported by two angular platelets.
Primary coil
To build it took the power cable cross section 0.5 cm2 wound on the outer surface of a tube about 8 cm high (no. of turns: 11).
Secondary coil
Made up of enameled wire of 1mm wrapped too ‘it on a pipe, a terminal is connected to the toroid on top of the coil, the’ other is grounded.
Operation
The Leyden jar capacitor is perfect for building an oscillator: The capacitor is charged by high voltage, and accumulates electric charge until it is sufficient to overcome the dielectric strength of the air between the electrodes of the spark gap of about 3 KV / mm. The main function of the oscillator is to “excite” electrically the primary coil of high frequency pulses, the energy is transferred from the primary coil to the secondary coil, a voltage that is obtained depends on the number of turns of the secondary and the frequency, and if very high, due to the formation of lightning that depart from the toroid place on top of the coil. While generating discharges, electrical energy is transferred to the surrounding torus. The electric currents that flow through these discharges are actually caused by the rapid change of the amount of charge from one point (the top terminal) to other places (nearby regions of air). The process is similar to a charge or discharge of a capacitor. The current that is created by the flow of charges within a capacitor is called displacement current. The discharge of Tesla coils are formed by a result of displacement currents as soon as the pulse of electric charges are rapidly transferred between the high voltage toroid and nearby regions of air (called regions of space charge). Although the space charge regions around the toroid are invisible, they have a fundamental role in the appearance and location of Tesla coil discharges. When the spark gap generates sparks, the charged capacitor discharges into the primary coils, causing oscillations in the primary circuit. The oscillating primary current creates a magnetic field which is coupled to the coils of the secondary transferring energy in the second part of the transformer and causing it to oscillate with the ability of the toroid. The transfer of energy takes place in a number of cycles, and most of the energy that was originally in the primary is transferred to the secondary. The larger the magnetic coupling between the coils, the shorter the time required to complete the transfer of energy. As the energy is formed inside of the secondary oscillating circuit, and the air surrounding the toroid begins to undergo dielectric breakdown, forming discharges. The induced current in the secondary coil in turn generates an electromagnetic field with frequency coupled with the primary, and this can cause the ionization of the surrounding air: you can experience this phenomenon approaching a fluorescent tube torus is seen to turn on without any electrical connection. When the neon atom is “excited” by a high-frequency one or more 10 electrons pass on the outer orbits with higher energy level of the atom. At this point the electrons unstable tend to return to their original orbits releasing the same amount of energy that had previously absorbed in the form of light. If current Tesla coils are used primarily to produce spark discharges (artificial lightning, electric arcs), the purpose for which they were designed was to generate streams of wireless energy transmission. The Tesla Coil although spectacular, because the propagation of electromagnetic waves at high frequency which can be very dangerous in the event of a ‘prolonged exposure (many years) with these radiations can cause cardiac arrest and also tumors. For this reason it is discussed how to make our experiment more secure and planned to use a grounded Faraday cage which prevents the leakage of electromagnetic waves by making the tesla coil 100% secure.
Spark gap tesla coil or SGTC is a simple form of tesla coil that is capable of producing super high voltages in the output.
Big coils with high voltage input is very dangerous. So we are going to make a mini version of SGTC using bug zapper circuit. Once you are expert in handling high voltage then you can go for bigger design.
Components required for spark gap tesla coil
High Voltage transformer ( bug zapper circuit )
High voltage capacitor ( Approximately 5nf, > 2kv )
4v – 9v battery
Primary coil ( 1mm insulated copper wire )
Secondary coil ( 0.2mm magnet wire )
Spark gap arrangement
Alligator clips
Some 0.5mm insulated connecting wires
High voltage transformer
This tutorial is for mini version of spark gap tesla coil. Small high voltage transformer can be found inside bug zapper ( mosquito racket ).
Take out the circuit from bug zapper along with its battery.
High Voltage Capacitor
High voltage capacitor of value approximately 5nf ( low capacity ) and 1 to 10 kv is difficult to find in market, So I made my own capacitor of 5nf and 10kv using aluminium foil and plastic sheets.
Spark Gap
Spark gap is basically an air gap that acts as switch. It switches on when capacitor gets charged enough to jump across the air gap.
I made it using PVC pipe of 50mm outer diameter and two pieces of one inch screw. The tip of both screw point each other as shown. I have used screw so the gap can be adjusted.
Primary coil
The primary coil comprises of 3 turns made using 1mm insulated copper wire.
Use 50mm diameter PVC pipe as core for primary.
Secondary Coil
Make 300 to 1000 turns of 0.2mm magnet wire around 30mm diameter PVC pipe ( as core ). Make coils ( turns ) one after another such that no turn should overlap. The length of pipe should get covered.
Top load
Top load can be made using lite weight aluminium structure. It will be good if It has smooth surface and no sharp corners.
Generally people wrap plastic ball inside aluminium foil for this purpose.
Circuit diagram
This is a general circuit diagram for Spark gap tesla coils.
The bug zapper circuit is going to cover the bounded part of circuit diagram as shown.
Connections
The connections of circuit is quite simple as it has only few components.
Take bug zapper circuit and connect its output point 1 & 2 ( shown in diagram ) to the terminals of high voltage capacitor. Here the bounded area of circuit is bug zapper circuit.
Now connect first end of capacitor to one end of spark gap ( use alligator clips ).
Connect the other end of spark gap to primary coil.
Connect the other end of primary coil to point 2.
Ground the lower end of secondary coil.
Attach top load to Upper end of secondary coil.
The secondary coil is placed inside of primary coil, such that primary coil surrounds secondary coil.
Safety Tip
Spark gap tesla coil produce super high voltage in the output that is very dangerous. Even a small design with low voltage input can cause harm.
Don’t touch the coil, circuit or sparks at top load with bare hands. Even after you turn off the circuit, there can be charges stored in capacitor that can shock you.
You can discharge the capacitor by shorting the spark gap.
The term ‘mad scientist’ could apply to Nikola Tesla. Perhaps he is the very source of it. He barley slept, sat down for dinner at exactly 8:10PM every night, and once spent a small fortune nursing his beloved pigeon back to health. All the while, Tesla’s contributions to science and engineering are matched by few. He patented hundreds of weird and wonderful inventions, some of which being very commercially fruitful – the AC induction motor to name one. There is good reason a certain modern car maker chose to be Tesla’s namesake.
The Tesla Coil is another iconic invention by Tesla. It may not have much practical use today, but has remained noteworthy because of the dazzling electric show it creates. It’s also a great exhibit for electrical engineering theory.
The Tesla Coil is a resonant transformer that outputs power at ultra-high voltage – as much as several million volts! With this comes the vivid ionizations of air, otherwise known as sparks. The sparks of the Tesla Coil can arc amazing distances and with a hyperactive intensity.
How The Tesla Coil Works - Key Principles
Transformers
Transformers use Faraday’s law of induction to step up or step down voltage. They consist of two coils near each other. When power is applied to one, a magnetic field is made and induces power in the opposing coil. The number of coil turns of each determines the output voltage.
An ideal transformer will step up or step down voltage according to the following formula:
VSC = VPC x (NSC / NPC)
Where:
VPC is the voltage in the primary coil
VSC is the voltage in the secondary coil
NPC is the number of coil turns in the primary coil
NSC is the number of coil turns in the secondary coil
For example, let’s calculate the output voltage in the scenario:
Input voltage = 240V
Primary coil turns = 4
Secondary coil turns = 8
VSC = 240 x (8 / 4)
VSC = 480 Volts
As you can see, voltage increases greatly depending on the number of coil turns used. Because power remains constant through the process, the current lowers as voltage is stepped up and vice versa (power = voltage x current).
Electrical Resonance
Imagine pushing someone on a swing. If you push too early or too late at each return interval, it’s hard to get the swing going. But if you push the swing exactly at its peak, it’s easy to reach higher heights with each push. This perfect timing of pushes is an example of resonant frequency.
Just like the swing, resonant frequency applies to electricity. Achieving resonance during a transfer of power allows the process to be efficient.
An example are LC circuits – L denoting ‘inductor’ and C denoting ‘capacitor’. Inductors are coils that make magnetic fields and capacitors are devices that store and discharge electrical charges. If an inductor and capacitor are arranged in a circuit and are perfectly tuned, the following happens:
Power flowing through the circuit charges the capacitor. When the capacitor is fully charged, it discharges and supplys power to the coil.
The power flows through the coil until all the charge from the capacitor is used. During which, the coil produces a magnetic field.
The magnetic field induces a voltage back through the coil but in the opposite direction. The voltage charges the capacitor back up and the magnetic field fades out just as the capacitor is about to discharge again.
As the capacitor and coil are resonantly tuned (like the person pushing the swing), the cycle continues over and over. In an ideal scenario, the cycle would continue forever. In reality, other resistive forces eventually bring the cycle to an end.
How The Tesla Coil Works - Animated Schematic Steps
Alternating Current (AC) power is supplied to the transformer. The transformer steps up the power to the primary circuit to high voltage and low current.
The power flowing through the primary coil creates a magnetic field. This induces even higher voltage power in the secondary coil, as it has many more coil turns than the primary. Secondary coils often have hundreds of turns, but less are shown in this schematic for clarity.
The capacitor and spark gap resonantly tune the circuits. The capacitor charges fully and then discharges with the spark gap breakdown voltage. The spark forms an LC circuit and allows power to seesaw resonantly between the primary and secondary circuits with a compounding effect. This amplifies the voltage in the secondary coil to ultra high levels.
The ultra high voltage in the secondary coil makes the air around the torus ionize. This creates the visual sparks and cracking sounds.
Assunto anterior
After several experiments with variants of the Tesla coil circuit, as a 
Measurements in the assembled system, after proper 
An interesting observation is that the effective coupling can be substantially changed if 
