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SGTC I. - Small Tesla Coil

     Tesla coil is a device producing a very high voltage with high frequency. It was invented in 1897 by American physicist Nikola Tesla with Croatian origin. (Hence its name). Description of its functioning can be read in detail on thousands pages, so I will try to be brief: the capacitor charges to the point when the spark gap discharge occurs. The capacitor is then connected to the PRIMARY and the resulting damped oscillations (Figure below) of high frequency many tens to hundreds of kHz. When the capacitor has is low, discharge ceases to exist and everything is repeated. Repetition rate ignition spark is tens of thousands of Hz. High frequency oscillations are induced in the secondary and there is a very high voltage. Primary and secondary should be tuned to same resonant frequency. This is done by changing the number of turns of the primary or by changing the capacity of the capacitor. Primary is formed by a few turns of very thick wire or copper tubes. Secondary is a cylindrical coil (solenoid) with several hundreds or thousands of threads. Tesla coil secondary must be grounded. Tesla coil is powered by a soft supply of voltage of about 5 - 20kV (may be less, but the tension is able jump only to a very small distance and thus there are problems with the construction of the spark gap). Voltage can be either AC (50/60Hz) or DC. Very good is a neon sign transformer, because it has the appropriate voltage and current and is soft (current limited). You can also use another type of transformer, such as a microwave (the MOT, 2.1 kV + doubler) but it is quite hard and you need to limit the current using a ballast. The second option is the dc voltage from the switching power supply. Small Tesla coil can also be powered by a power supply with CRT television set high voltage transformer, like this 20kV Switching power supply.
     My Tesla coil is also using this supply. Spark gap is about 1mm distance between the electrodes, the capacitor has a capacity of 10n, primary has 2 turns of tripple wire, and the secondary has 400 turns. Primary diameter is 11cm and secondary 6.5 cm. This is my first Tesla coil :).

     !!! WARNING !!! Tesla coil is an extremely dangerous device! Its supply voltage is deadly! Without knowledge of the principles of working with high voltage, you can not construct it. Tesla coil causes a broadband radio frequency interference. Electromagnetic radiation can damage electronic devices or storage media. The spark gap produces ozone (O 3), nitrogen oxides and other toxic gases, they have to be ventilated! Spark gap emits UV radiation. Current at ignition discharge of up to several kiloampers. Capacitor can remain charged even after shutdown. The device is very noisy and can damage hearing. Everything you do at your own risk! For any injury or damage I do not take any responsibility.

The schematic of the spark gap Tesla coil.

The Tesla coil primary waveform (simplified).

The entire device

The Tesla coil operating.

Spark gap at the right hand.

Three tips

Plasma ball...

...a fluorescent tube in 20cm distance

Heatsing as an additional secondary capacity

once more

Spark gap. The screws are not ideal for this, but it also works in small TCs.

Homemade capacitor 10n 30kV made of aluminium and plastic foil.

Primary and secondary on a spool.