Spark Gap Tesla Coil

Overview

A fully functional spark gap Tesla coil (SGTC) built from scratch over a semester at Red Rocks Community College. The coil uses a 9kV neon sign transformer (NST) as its power source, feeding into a homemade multi-mini capacitor (MMC) bank and a static spark gap. A Terry filter protects the NST from destructive voltage spikes produced by the LC tank circuit. The primary coil is a flat spiral of heavy copper tubing, tightly coupled to a hand-wound secondary of roughly 1,000 turns of 24AWG magnet wire. A toroidal top load capacitively loads the secondary, suppressing racing arcs and shaping the streamer discharge. Resonant frequency of the secondary is tuned to match the primary tank circuit by adjusting primary tap position.

Why It Exists

Built as a semester-long hands-on electronics project. The goal was to understand high-voltage resonant circuits, electromagnetic induction, and RF behavior by actually building something that makes lightning.

Features

• ·9kV / 30mA neon sign transformer power supply with MOV and bypass capacitor protection
• ·Terry filter (RC + MOV network) preventing NST destruction from resonant voltage spikes
• ·Homemade MMC capacitor bank from series/parallel polypropylene film capacitors, rated for tank circuit discharge currents
• ·Static spark gap with adjustable electrode spacing for breakdown voltage tuning
• ·Flat spiral copper tubing primary coil, tapped at multiple turns for impedance matching
• ·Hand-wound secondary: ~1,000 turns of 24AWG magnet wire on PVC form, sealed with polyurethane
• ·Spun aluminum toroid top load to control streamer corona and suppress unwanted arc paths
• ·Produces 4-6 inch electrical streamers at resonance

Tech Stack

Lessons

High-voltage work punishes careless assumptions. The Terry filter wasn't in the original design and two NSTs blew before adding it. Every component failure was a lesson in why the safety margins exist.