STEP 4: BUILDING YOUR SECONDARY COIL
The secondary coil is in principle an inductor. An inductor is essentially something that resists changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic field in the coil.
Inductance(L) is described by Faraday’s law:
Where µ is the magnetic permeability and Inductance is in Henrys (H).
How do we use this?
An inductor uses changes in magnetic field to cause current to flow in wires. Current from our spark gap flows into the outer coil of our primary inductor and then spirals inwards following the coil until it reaches the end near our secondary coil. The secondary coil amplifies the electromagnetic pulses from the primary winding and outputs high voltages at low current (which is why it is safe to touch the arcs made by a small coil such as this). It is a thin copper wire wrapped tightly and closely around a PVC pipe. The secondary is coiled up into more turns than the primary- the primary can have 6 turns while the secondary can have hundreds. The current increases proportionally to the number of turns and so does the inductance. The primary and secondary coils must be in resonance (each impulse of energy must be properly timed) to maximize energy transfer. At resonance, the voltage from the secondary will peak and when completely out of resonance it will drop tremendously. We will investigate this more when building our primary coil.
Circuit diagram from
http://www.rmcybernetics.com/science/high_voltage/tesla.htm
How to build it
I started by first completing some calculations. Deepfriedneon is an excellent guide to follow when building and it has some very useful calculators that I utilized to figure out my parameters for building.
We know that a secondary coil is made up of a PVC pipe and thin copper wire. I chose a pipe of 2”diameter and a 24 gauge wire (approx. 0.02”). The secondary must have around a 6:1 aspect ratio. So for 2” diameter pipe, it must be at least 12” in length. I made mine around 18” to get a greater amplification of voltage but cut the pipe to be 24”(make sure to leave a couple inches on the bottom and a couple at the top). I then started at 2” inwards from the pipe and wound the copper wire around the pipe as closely as possible. It would help tape the wire every couple inches of winding so that it doesn’t come lose. When you’re done, you should have hundreds of turns (minimum that you need is probably around 900) but the exact number is unimportant. Now scrape the coating off a few inches of wire at the top and bottom of the coil, leaving it lose for connections to ground and the top load later. To set it up, I cut a circular hole in the middle of a larger circular piece of wood mounted on four pegs. I left the few inches of scraped wire on the bottom ungerneath the stage I created.
Finished product:
