By Contributor Updated Mar 24, 2022

A Tesla coil, named after inventor Nikola Tesla, is a high‑voltage resonant transformer capable of producing spectacular electrical discharges. With readily available materials, you can construct a functional coil that delivers a stunning visual display. Follow this step‑by‑step guide for a reliable build, while keeping safety at the forefront.

Building the Components

Step 1 – Select a Transformer

Choose a transformer rated at 9 kV or higher with a current rating of at least 30 mA. Neon‑sign transformers are readily available and ideal for beginners. Oil‑furnace ignition transformers or automotive ignition coils are alternative options that produce more subtle displays.

Step 2 – Construct the Capacitor

Layer five sheets of 12 × 12 × 0.032 in. polystyrene with four thin metal plates (copper, aluminum foil, or lightweight aluminum). This stack forms the main capacitor for the circuit.

Step 3 – Create the Spark Gaps

Use four L‑brackets and bolts, attaching round end caps to the bolt ends. These will serve as the adjustable spark gaps.

Step 4 – Wire the Primary Coil

Wrap a heavy‑gauge bare wire six or seven times around a cylindrical form at least eight inches in diameter. Punch 1/8‑inch holes in four pieces of PVC pipe and thread the wire through to create the primary coil. The holes should be evenly spaced.

Step 5 – Wind the Secondary Coil

Wrap enameled wire tightly around a 3‑inch PVC form to produce about 500 turns. Varnish the coil with several heavy coats and allow it to dry evenly for durability.

Step 6 – Install Radio‑Frequency Chokes

Wind 20 turns of enameled wire on two separate 1½‑inch diameter PVC pipes. These act as radio‑frequency chokes (RFCs) to improve coil performance.

Assemble the Parts

Step 1 – Position the Discharge Terminal

Mount a brass doorknob on top of the secondary coil; this will serve as the top discharge terminal. Place the secondary coil inside the primary coil and secure both to the center of a wooden board.

Step 2 – Attach Supporting Components

Fasten the remaining PVC pipes to the underside of the board. Attach the spark gaps and RFCs to the top of the board. Slide the transformer underneath, then place the capacitor on top of it.

Step 3 – Grounding

Connect a ground rod to the wire leading from RFC 2 to the primary coil for proper safety grounding.

Materials Needed

• Transformer (≥9 kV, ≥30 mA)
• 5 sheets of 12 × 12 × 0.032 in. polystyrene
• 4 10‑inch square metal plates
• 4 L‑brackets
• 4 bolts with round end caps
• Heavy‑gauge wire (for primary coil)
• Enameled wire (for secondary coil & RFCs)
• 3‑inch diameter, 12‑inch PVC tube (for secondary coil)
• Two 1½‑inch diameter, 6‑inch PVC pipes (for RFCs)
• Brass doorknob (discharge terminal)
• 4 additional PVC pipes, slightly taller than transformer (for mounting)
• Glue (optional)
• Wooden board (mounting surface)

Safety Warning

Tesla coils can deliver lethal voltages. Never operate or assemble a coil without a thorough understanding of electrical safety. Follow all local regulations, use appropriate personal protective equipment, and test in a controlled environment.