Building a Tesla transformer at home

The essence of Tesla’s invention is simple. If you power the transformer with a current with a frequency equal to the resonance for its secondary winding, the output voltage increases by tens or even hundreds of times. In fact, it is limited by the electric strength of the surrounding air (or other medium) and the transformer itself, as well as by the loss of radiation of radio waves. The most famous reel in the field of show business: it is capable of throwing lightning!

Form and content

The transformer looks very unusual - it seems to be specially designed for show business. Instead of the usual massive iron core with thick windings - a long hollow dielectric pipe, on which the wire is wound in only one layer. This strange appearance is caused by the need to ensure maximum electrical strength of the structure.

In addition to its unusual appearance, the Tesla transformer has another feature: it necessarily has a certain system that creates current in the primary winding precisely at the secondary resonant frequency. Tesla himself used the so-called spark circuit (SGTC, Spark Gap Tesla Coil). Its principle is to charge a capacitor from a power source, followed by connecting it to the primary winding. Together they create an oscillating circuit.

The capacitance of the capacitor and the inductance of the winding are selected so that the oscillation frequency in this circuit coincides with the necessary one. Switching is carried out using the spark gap: as soon as the voltage across the capacitor reaches a certain value, a spark appears in the gap, closing the circuit. Often you can see the allegations that "the spark contains a full spectrum of frequencies, so there is always a resonant one, due to which the transformer works." But this is not so - without the correct selection of capacitance and inductance, a really high voltage cannot be obtained at the output.

Having decided to make our Tesla transformer, we settled on a more progressive circuit - a transistor one. Transistor generators potentially allow you to get any shape and frequency of the signal in the primary winding.

The circuit we have chosen consists of a driver transistor driver microcircuit, a small transformer for decoupling this driver from a supply voltage of 220 V, and a half bridge of two power transistors and two film capacitors. The transformer is wound on a ring of ferrite with an operating frequency of at least 500 kHz, three windings of 10-15 turns of wire are made on it. It is very important to connect transistors to the transformer windings so that they work in antiphase: when one is open, the other is closed.

The desired frequency arises due to feedback from the secondary winding (the circuit is based on self-oscillations). Feedback can be carried out in two ways: using either a current transformer from 50−80 turns of wire on the same ferrite ring as an isolation transformer through which the ground wire of the lower part of the secondary winding passes, or ... just a piece of wire that acts as an antenna, trapping emitted by the secondary winding of the radio wave.

Shake on the mustache

As the primary winding frame, we took a PVC sewer pipe with a diameter of 9 cm and a length of 50 cm. For winding we use an enameled copper wire with a diameter of 0.45 mm. The frame and coil of the winding wire are placed on two parallel axes. A piece of a PVC pipe of a smaller diameter acted as the axis of the frame, and the arrow from the bow, which was lying in the editorial office, played the role of the axis of the coil with the wire.

The winding should be very tight, turn to turn. The turns should not overlap each other. Only adhering to these rules, you can get a high-quality secondary winding, in which there will be no breakdowns between turns and parasitic corona discharges. The length of the actual winding is 45 cm, and the number of turns is 810. The manufactured winding must be coated with varnish, epoxy resin or something like that.

There are three primary winding options: a flat spiral, a short helical and a conical winding. The first provides maximum electrical strength, but to the detriment of the strength of the inductive coupling. The second, on the contrary, creates the best connection, but the higher it is, the more likely it is that a breakdown will occur between it and the secondary winding. Conical winding is an intermediate option that allows you to get the best balance between inductive coupling and electrical strength. We did not expect to get record voltages, so the choice fell on the screw winding: it allows you to achieve maximum efficiency and is easy to manufacture.

As a conductor, we took a power cable of audio equipment with a cross section of 6 mm², eight turns of which were wound on a segment of a PVC pipe of a larger diameter than that of the secondary winding frame, and secured with an ordinary electrical tape. This option cannot be considered ideal, because the high-frequency current flows only along the surface of the conductors (skin effect), so it is more correct to make the primary winding from a copper pipe. But our method is simple to manufacture and with not too large capacities it works quite well.

Control

For feedback, we originally planned to use a current transformer. But it turned out to be ineffective at low coil powers. And in the case of an antenna, it is more difficult to provide an initial impulse that will start oscillating (in the case of a transformer, another wire can be passed through its ring, on which a normal battery can be closed for a split second). As a result, we got a mixed system: one transformer output was connected to the input of the microcircuit, and the second wire was not connected to anything and served as an antenna.

Short circuits, transistor breakdowns and other troubles were initially supposed to be very possible, so an additional control panel was made with an alternating current ammeter 10 A, a 10 A automatic fuse and a couple of “neonoks”: one shows whether there is voltage at the input to the panel, and the other is whether the current goes to the coil. Such a remote control allows you to conveniently turn the coil on and off, monitor the main parameters, and also makes it possible to repeatedly reduce the frequency of trips to the shield to enable "knocked out" machines.

The last optional part of the transformer is an additional capacity in the form of a conducting ball or torus at the high-voltage output of the secondary winding. In many articles, you can read that it can significantly extend the discharge (by the way, this is a wide field for experiments). We made such a capacitance at 7 pF, putting together two steel cups-hemispheres (from the IKEA store).

Assembly

When all components are manufactured, the final assembly of the transformer is no problem. The only subtlety is grounding the lower end of the secondary winding. Alas, not all domestic houses have sockets with separate ground contacts. And where they are, these contacts are not always really connected (this can be checked with a multimeter: there should be about 220 V between the contact and the phase wire, and almost zero between it and the neutral wire).

If you have such sockets (we found them in the editorial office), then you need to ground them using them, using the appropriate plug to connect the coil. It is often advised to ground on a central heating battery, but this is categorically not recommended, since in some cases it can lead to the fact that the batteries in the house will be shocked by unsuspecting neighbors.

But here comes the crucial moment of switching on ... And immediately the first victim of lightning appears - the transistor of the power circuit. After the replacement, it turns out that the circuit is, in principle, quite operational, although at low power (200–500 W). When reaching the design power (about 1−2 kW), the transistors explode with a spectacular flash. And although these explosions are not dangerous, the “second of operation - 15 minutes of transistor replacement” mode is not satisfactory. Nevertheless, with the help of this transformer it is quite possible to feel yourself in the role of Zeus the Thunderer.

Noble goals

Although in our time, the Tesla transformer, at least in its original form, is most often used in a variety of shows, Nikola Tesla himself created it for much more important purposes. The transformer is a powerful source of radio waves with a frequency of hundreds of kilohertz to several megahertz. On the basis of Tesla's powerful transformers, it was planned to create a broadcasting system, a wireless telegraph and wireless telephony.

But Tesla’s most ambitious project related to the use of its transformer is the creation of a global wireless power supply system. He believed that a sufficiently powerful transformer or system of transformers could globally change the charge of the Earth and the upper atmosphere.

In such a situation, a transformer installed anywhere in the world that has the same resonant frequency as the transmitting frequency will be a current source, and power lines will no longer be needed.

It was the desire to create a wireless power transmission system that destroyed the famous Wardenclyff project. Investors were interested in the appearance of only a payback communication system. And the transmitter of energy, which anyone could take uncontrollably around the world, on the contrary, threatened losses to electric companies and wire manufacturers. And one of the main investors was a shareholder of the Niagara Hydroelectric Power Station and copper plants ...

The article “Lightning Throwers” ​​was published in the journal Popular Mechanics (No. 2, February 2013).

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