Tesla coil

Tesla Coil


While studying about electromagnetism, I was fascinated by Electric and Magnetic fields. The concept of force-fields was new to me and when I read about Tesla Coils I had to try it out for myself.020

A tesla coil is a form of a resonant transformer. It creates a powerful electric field in its vicinity that produces large sparks and can be used to wirelessly power several simple electrical devices.

A resonant transformer is different from an ordinary transformer in the following ways:

  • 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 due to eddy currents and hysteresis, so it is not used in the Tesla coil.
  • Ordinary transformers are designed to be “tightly coupled” and have a high mutual inductance(M). The coupling coefficient is close to unity (0.9 – 1.0), which means almost all the magnetic field of the primary winding passes through the secondary. The Tesla transformer in contrast is “loosely coupled”, the primary winding is larger in diameter and spaced apart from the secondary, so the mutual inductance is lower and the coupling coefficient is only 0.05 to 0.2; meaning only 5% to 20% of the magnetic field of each coil passes through the other. This slows the exchange of energy between the coils, so that the energy alternates between primary and secondary slower. This allows the oscillating energy to stay in the secondary circuit longer before it returns back to the primary and begins dissipating in the spark.

A tesla coil can be used to light up fluorescent bulbs, tube lights and LEDs. The tesla coil generates such a powerful electric field around itself, that it wirelessly excites the gas atoms inside fluorescent tubes causing them to glow.



Following an online instructable, I made a 12V DC slayer-exciter (Tesla coil).  It was a simple design for a ‘single resonant solid state Tesla coil’. In this circuit the primary coil does not have a capacitor and so is not a tuned circuit; only the secondary is. The pulses of current to the primary from the switching transistors excite resonance in the secondary tuned circuit.


I am currently working on a more powerful version of the tesla coil (slayer exciter) that uses dual resonant coils.

Working on this project was a fun and informative experience. I discovered that a Tesla coil is indeed an electrifying example of the uses of electromagnetic fields. It was indeed enjoyable to see first-hand the effects and results of theories being taught to us in school.