A Tesla Coil is a electrical resonant transformer invented by Nikola Tesla. It is used to produce high-voltage, low-current, high frequency alternating-current electricity. It is used to conduct experiments in electrical lighting, phosphorescence, X-ray generation, high frequency alternating current phenomena, electrotherapy, and the transmission of electrical energy without wires. But nowadays it is mostly used for entertainment purposes.

Step 1: Resonance

In physics, resonance is a phenomenon in which a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency.

Frequencies at which the response amplitude is a relative maximum are known as the system's resonant frequencies or resonance frequencies. At resonant frequencies, small periodic driving forces have the ability to produce large amplitude oscillations. This is because the system stores vibrational energy. Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes (such as kinetic energy and potential energy in the case of a pendulum). However, there are some losses from cycle to cycle, called damping.

Resonance occurs in an electric circuit at a particular resonant frequency when the impedance of the circuit is at a minimum in a series circuit or at maximum in a parallel circuit or when the transfer function is at a maximum.

Step 2: Types of Tesla Coils

Mainly there are two types of Tesla Coil's :

1. Spark Gap Tesla Coil (SGTC) - This type uses a spark gap to switch pulses of current through the primary, exciting oscillation in the transformer. This pulsed drive creates a pulsed high voltage output. Spark gaps have disadvantages due to the high primary currents they must handle. They produce a very loud noise while operating, noxious ozone gas, and high temperatures which often require a cooling system.

There are 3 types of SGTC's -

1. Static Spark Gap

2. Static triggered Spark Gap

3. Rotary Spark Gap

2. Solid State Tesla Coil (SSTC) - These use power semiconductor devices, usually thyristors or transistors such as MOSFETs, IGBTs or BJTs, to switch pulses of current from a DC power supply through the primary winding. They provide pulsed excitation without the disadvantages of a spark gap: the loud noise and high temperatures. They allow fine control of the voltage, pulse rate and exciting waveform.

Step 3: Materials Required

Enclosure - I used a old SMPS case and painted it

Secondary Coil -

1. Enameled Copper Wire - Above 30 AWG is recommended and around 180 meters for beginners

2. PVC or Acrylic pipe - Around 20 cm in length and 6.5 cm of outer diameter width

3. Epoxy or Varnish - To coat the secondary coil to protect it (Not necessary)

4. Plastic Disk - To cover one end of the pipe

Primary Coil -

1. 14 awg wire

2. Quick drying glue

Top Load -

1. Sponge Ball - The structure for the top load

2. Aluminium Foil - To cover the ball, to make it conductive

3. Glue

Circuit -

1. A power transistor - To switch the primary coil on and off, TIP31C recommended. (BJT ONLY)

2. Transistor heatsink - If exceeding 12v input

3. 40k resistor - To switch on the base of the transistor and so that it easily be overridden by secondary feedback

4. UF4007 diodes - To protect the transistor from voltage spikes.(1n4007 can also be used)

5. Two switches - To turn on and off the Tesla Coil and the fan

6. Wires

7. Perfboard - To solder on

Power Supply -

1. Transformer - I used 22v 2 amp transformer

2. Bridge Rectifier - To convert DC in to AC

3. Capacitors - To smooth down the voltage spikes. Around 10000uf 30v is recommended, if you can't find a 10000uf capacitor just use multiple capacitors in parallel to add up their capacity.

4. Voltage Regulator - For the fan. Not required if you are running it on 12v

5. Indicator LEDs and Resistors - Not necessary

Tools Required

1. Soldering Iron

2. Glue Gun

3. Screwdriver

4. Hacksaw or a sharp knife

Step 4: Secondary Coil

First, take the wire and stick it at one edge of the pipe and stick it or tape it and leave some extra wire hanging for connecting. Use your nail to keep the wire in position and keep rotating the pipe. When coating it with epoxy or varnish keep turning the coil for an even finish. The coil should have around 800 turns. But if you can, try to do around 1000.

Step 5: Primary Coil

Take your wire and wind it on something that is a little wider than secondary coil (less than 1 cm). Without leaving any spacing between the turns, glue it together. Leave some extra wire on the coil for connecting it to the circuit.

Use 4 or 5 turns, but if your transistor keeps dieing than use a higher number of turns. The key rule is that if you have a lower voltage and curent rating transistor than use more turns and if you higher rated transistor then use less turns.

Step 6: Top Load

Just take a knife and heat it over a flame and cut the sponge ball in half. You must take sponge ball that is wider than the secondary coil. Then take aluminium foil and cover both the halves and stick both the halves back together using glue and there you have your top load.

Drill a hole in the center of the plastic disk and insert a screw and connect the top secondary coil wire to the screw. Take a screw long enough that leaves some space between the disk and top load and also reaches the center of the top load. Now insert the sponge ball into the screw and you are done

Step 7: Circuit

The circuit is pretty easy....... And there's not much to explain, but here are some points to remember :

1. The transformer should at least be able to output 2 amps. (If you are using the same supply voltage as mine)

2. Don't forget to attach the transistor to a heatsink. And use thermal paste or thermal pads.

3. If you are using some other transistor, make sure that its collector to emitter voltage is at least 3 times the input voltage and that it can handle enough current.

4. If you transistor keeps burning out, then add more turns to the primary.

5. If your transistor has high current and voltage ratings and it doesn't get too hot, then you can improve the performance by using less turns in the primary.

6. The 40k resistor should be 1 watt or higher. If you don't it, then you can connect two 1/2 watt 80k resistors in parallel.

7. Make sure that the top secondary wire has a good connection with the top load.

8. It is not necessary but I have added switches to switch it on and off and for the fan.