This is going to be my first proper tesla coil; I started building a coil several years ago from plans i found on the internet; from what I can remember it was going to have a 5" wide primary about 4 feet long, it was going to use salt water capacitors and a static spark gap, based on the size of the primary it was going to be huge. The only bit I constructed was what I believe to be the power supply (it was a long time ago!), it consisted of several components mounted on a small circuit board connected to a small transformer (probably 10-20 VA), how on earth this was going to power a 5 foot high tesla coil I don't know.
In these past few years I have gained in knowledge and wisdom and can now see that starting off small is definitely the way to go, that is why I have decided on a small 1 foot high coil that will run from a neon sign transformer, the design is based up on a dual system that I found on Sam Barrows's Site
Top Load: Toroidal shape made from aluminium ducting covered by metal tape.
Secondary: A piece of 4cm waste water pipe
Primary: Still to be decided
Capacitor Bank: MMC (multi mini capacitor) design, value still to be calculated
Spark Gap: Static gap made from lengths of copper pipe
Power Supply: NST (Neon sign transformer)
Like most of my projects I like to see something immediate that is why I built this bit first, it is simple and one of the most characteristic parts of a tesla coil.
I started by wrapping the ducting around and temporarily holding it together with some metal tape, I then dropped the perspex center in so it was carefully wedged in the middle, using a hot melt glue gun I glued the ducting to the perspex. Once the glue was dry I started wrapping tape around, I got through 2 roles to get to the state you can see below, i think it will take another 1 or 2 to smooth it off.
After reading how it took people hours to wind there secondaries I decided I need some kind of automatic winding jig, I am not one for building big complicated devices just to make something I quickly put together what you can see below. The plastic tube is taped to the end of the drill using masking tape, it is supported by a screwdriver held to the movable plate of the drill stand by a clamp (this way I can adjust it to get the correct height). The spool of wire was then set up on a piece of steel which rested on 2 gel batteries (I put a piece of tape over one of the terminals on each to stop them shorting out), for added stability I taped the steel rod to the batteries with a piece of marking tape. This was an incredibly simple setup taking a couple of minutes but allowed me to neatly wind a coil in 15 minutes that would have probably taken several hours by hand.
As you can see on the picture I put several turns of wire at each end for connecting up. When finished I removed most of the masking tape leaving a piece at either end, then using a can of "Polyurethane Coating" I gave the coil about 5 coats leaving it to dry in between; this helps keep the coils from moving and improves the insulation.
The Secondary Continued
I decided on a 15cm length of winding because I had read software that you should have a 1:3 ratio between the width and the height of the winding, I felt this would be a bit mean so I made it slight longer 15cm 1:3.75, after looking at several other designs the average ratio seems to be somewhere between 5 and 6 which would mean my secondary would be very small, because of this I put my jig back together and wound a second coil with 24cm of wire, this gave me a 1:6 ratio.
This way I can test the difference between the 2 coils and see what difference the length makes.
My initial plan was to use some small flexible copper pipe I saw at B&Q while I was buying the secondary pipe and top load ducting, I now think this copper pipe will be a little over sized for the col so I might have to go for some heavy gauge wire instead.
The Spark Gap
As this is my first coil I am not going to build a rotary spark gap but a static gap made from lengths of copper pipe, it will be made from a piece of 5 inch plastic pipe (probably the plastic pipe I bought for the secondary for my first attempt) with about 6 lengths of copper pipe bolted down the middle, by selecting different pieces of pipe to connect to a variable length gap can be created. I may attach a fan at one end to draw air through.
The Capacitor Bank
In my opinion this is the hardest part, this value determines the operating frequency of the system and in turn makes it work. I am going to go for a MMC design because it is the easiest method, it probably isn't the most reliable but the parts will be easy to replace if something goes wrong. Imagine spending days rolling your own capacitor and setting it in oil just to have the dielectric fail; the entire thing will be useless.
I am going to use a MMC system broken down into several different values, this way I can add or remove sections in order to tune the coil.
Thankfully as this is a small coil I can use an NST and I don't have to use some elaborate setup involving multiple transformers and ballast's.
I will let you know in a couple of weeks (probably months) when I finish it.