Optimizing a Spark Gap Tesla Coil

For my MYP Personal Project I set out to optimize a spark-gap Tesla coil — a resonant, high-voltage device associated with Nikola Tesla. My product goal was a working, improved setup, judged against criteria for function, accessibility and finish, estimated efficiency, safety considerations, and budget.

My learning goals were to understand high-voltage and resonant circuits better, to develop research and information-literacy skills by comparing approaches and judging advice, and to practise creative problem-solving by taking a design from theory into experiment. The project sits in the MYP global context of Scientific and Technical Innovation.

It was an investigation into the device and its design — not an attempt to prove that Tesla coils are a practical way to transmit power wirelessly.

I compared driver and oscillator circuits, and researched spark-gap design, capacitor arrangements, wiring, insulation, and cooling and safety considerations, using several online sources.

I also discussed the design with two of my school physics teachers, Mr Kassis and Mr Lykkas. Rather than treating every suggestion as equally reliable, I weighed advice against what I could test and the components I actually had.

Ideas I put into practice included a multiple-mini-capacitor (MMC) arrangement, a bleed resistor, and shorter primary wiring. I used circuit simulation to explore a self-oscillating driver before building it.

1. 01

   Testing an initial driver

   My first approach, a modified Colpitts oscillator, did not suit the characteristics of the salvaged high-voltage transformer I was using.

2. 02

   Learning from failure

   An astable multivibrator driver proved inefficient and led to transistors overheating and failing. A MOSFET-based attempt then did not switch as intended with the drive available.

3. 03

   A feedback-based driver

   I simulated a self-oscillating driver concept and then tested it in practice, revising components — including an IRF540 MOSFET and an added current-limiting resistor.

4. 04

   Diagnosing and revising

   When the coil later stopped working, I suspected a short in the secondary coil, but traced the fault to a damaged MOSFET. A DIY high-voltage component also proved ineffective, so I looked for parts with more suitable voltage ratings.

5. 05

   Addressing arcing

   Arcing between the primary and secondary coils led me to change their spacing and coupling and to add improvised insulating material. Adding a ferrite core raised the measured secondary inductance from 6.28 mH to 13.5 mH.

The final build is a physical, tested prototype assembled on an open, accessible base, with the coil, driver circuit, capacitor arrangement, and an adjustable spark gap I built.

According to my observations it produced visible arcs of roughly 3 cm and stronger electromagnetic effects than my first prototype. Better tuning may have contributed to that improvement as much as the ferrite core did. Its appearance stayed prototype-like, but it was easy to observe and maintain.

Function

Achieved — visible discharge and an electromagnetic effect

Build & appearance

Partial — accessible, but still prototype-like

Budget

About €74.32 in total, under the €200 ceiling

Efficiency

Estimated at about 60%, using assumptions about arc length, capacitor energy and spark rate

Compared with the first prototype

Longer arcs and stronger electromagnetic effects

These are my own assessments and estimates from the project report, not independently verified measurements. Voltage figures were inferred from arc length. High-voltage equipment is dangerous — this page is a record of a supervised school project, not a guide to building one.

• How oscillator circuits and impedance behave in practice, and how real component limits shape a high-voltage design.
• Soldering, and salvaging usable parts from old electronics.
• Evaluating sources and weighing advice instead of following the first suggestion.
• Using testing and failure analysis to decide what to change next — and adapting with the materials I had when arcing and insulation problems appeared.
• Other designs, such as a Slayer exciter or a solid-state Tesla coil, could have given different results; I chose the spark-gap design because it seemed easier to identify and test improvements.

This school project gave me a hands-on way to explore circuits, resonance, high voltage, component choice, testing, and iterative design — the topics that make me want to study electrical engineering. It was a learning experience rather than professional engineering work, and it showed me how much there still is to learn.