9kV Tesla Coil
9kv static spark gap tesla coil video journal
This is my first attempt at making a tesla coil. The measurements are here thanks to Teslacoil CAD, and JavaTC, all amazing pieces of software. This will give you the basic “numbers” but you should still take a look at Teslamap as well to calcuate your MMC capacitor bank.
Helpful resources that I’ve found are:
There were four major expenses, besides time… which has been months for me between gaps in free time.
The 9kv Franceformer neon sign transformer (NST). 9000 V AC, 30 mA, 60hz – $25
50 feet of 1/4 inch copper tubing – $35 from ebay, or $50 at Home Depot
1500 feet of 26 gauge magnet wire – $30 from ebay
high voltage capacitors (I only used 11 of them. I ordered 50 because I plan on making 2 coils, but you may only need around 20 or 30 depending on the size of your coil).
The caps I ordered were around $2 each and they are: Cornell Dubilier 942C20P15K-F. 0.15MFD. 2000VDC
Terminal block – $5 from home depot
High voltage wire, red and black, 10 gauge, about 10 feet each. $10
3″ diameter x 24″ long PVC pipe, precision cut at home depot, they see these pre-cut. $4
3″ shower pipe connector, $6. this looks like a cap for pvc but it is flat with rings around it so that your pipe can stand vertically, and be mounted on wood.
50 total 10 Megaohm 1/4 watt resistors, around $10
YOU MUST SAND OFF THE BLACK WRITING ON YOUR SECONDARY TOWER AND SPRAY LACQUER BEFORE WINDING YOUR COIL…
Secondary Coil Design
Diameter of secondary coil : 90.00mm
Winding height of secondary coil : 450.00mm
Wire diameter for secondary coil : 0.405mm
Spacing between windings : 0.00mm
Secondary turns : 1111.00
Secondary wire length : 349.07m
1/4 inch copper fridge tubing
13 windings, tapped around 7 to 8 for the (+) side
(-) is the inner most end of the tube that was fed through a hole and pinched underneath the wood, an alligator clip is used to connect this to the lower part of the spark gap
insulated standoffs were made from a white plastic cutting board chopped into 4 pieces and holes drilled every 1/4 inch (see pics). I would recommend 5 or 6 supports though… I messed two of them up and used them for supports of a ground ring.
WINDING THE SECONDARY TOWER
In order to wind such a large piece of PVC, you’ve got to invest some time in making a winding apparatus. There are lots of videos on youtube about this, and you’ll see all of them being horizontal. Well I didn’t have that much space, so I chose to make a vertical one. I also chose to make a jig that could hold various diameters so when I make different size coils I won’t have to completely redesign my winder. I found a variable speed motor that was going into the trash at my college. It worked, but it was twitchy at high speed.. that’s was OK, I only need very low speed. I bought a 4 inch diameter PVC cap from home depot, drilled a hole in it for the motor axle. I drilled four thumbscrew holes so that I could tighten the set pins around the tower when it winds, I can also put it on and take it off with incredible ease even while I’m winding it. The spool of wire is attached nearby to a vertical piece of 1/2 PVC pipe sticking straight up, pushed into a cap that was nailed into wood. the spool fits loosely around the thin PVC pipe allowing easy draw of wire.
MAKING THE MMC CAPACITOR BANK
I used Teslamap to figure out that I needed 11 caps in series to give me 22000 Volts at the right transformer resonance. The number of caps you need is strictly determined by the voltage and current of your transformer. A little tranny (ha) like mine only needed a safe zone of 22000 volts, so not many. With a higher voltage tranny and higher current, like 12000 V, 60 mA, you’ll definitely need many more, perhaps 30-40. These caps are not cheap, they’re around $2 each. You’ll also need a single 10 Megaohm 1/4 Watt resister soldered across the legs of each of your caps BEFORE you wire this thing together, this way you don’t burn out your caps so quickly. There’s not much to the mmc, just find some good thick plastic like a bin or a cutting board, acrylic or lexan is cool. Drill a bunch of holes for the legs and solder it together. The only way to test it is when you test the spark gap.
TESTING THE SPARK GAP:
When you test the spark gap, you wire everything together in parallel. the NST (+), mmc (+) and spark gap (+) all together. This is only during the testing phase. Once you get your primary done, you’ll wire it to one side of the spark gap and then the other side to ground – this makes the spark gap “in series” with the primary coil.
I highly recommend doing this before wiring your primary together, make sure each of your individual components works on its own and then one by one it works together. This should be done in your garage!!! At least 5 feet away from anything, wear gloves and eyewear… ! And preferably have someone else in the room with you in case you get shocked and are near death — it can happen pretty easily with this device…
TUNING THE TESLA COIL
If you have available to you an oscilloscope, function (signal) generator and a frequency counter (sometimes found on pricey voltmeters), then you should go ahead and try to tune your coils using this method. Using the regular method of trial and error will certainly work, but I wanted to try to use these devices and see more detail of what’s going on in the coil at certain spots and with different toploads. I searched lots of sites and videos on the subject of tuning, but finally came down to this site as being the one that truly made sense and instantly worked first try. Most sites tell you to look for a peak in voltage at just the right frequency, however this site asks you to find the matching DIPS in voltage, which for my particular setup seemed to work like magic!!
GO HERE IF YOU WANT TO TUNE YOUR COIL:
My transformer was a 120V pluggable type that had a chain cord on it. I thought this was pretty dangerous so I put together a quick and cheap safety switch made of a normal light switch and an outlet. I had to find a 3 prong plug to attach things to. With this I can plug in two appliances, or an entire power strip.
MAKING THE PRIMARY
Winding this was a huuuuuuge pain in the ass… I would suggest using more supports to make it easier.
This is a close-up of how I mounted the insulated standoff rails to the wood board. The yellow zip tie goes into the wood, and then the vertical piece is for the ground ring, attached with a white zip tie.
Here you can see most of the entire ring from the inner most coil to the outermost. The innermost tube is fed through a hole underneath the wood. That is attached to the lower end of the spark gap with a thick wired alligator clip.
SECONDARY EARTH GROUND WIRE
The earth ground is ONLY used on the secondary bottom, and the ground ring located above the primary (if you decide to have one). I used metal socket leads that clip together, they can handle the voltage pretty well if you solder them to the wires themselves. The ground wire is a relatively thin maybe 20 guage solid copper insulated wire that I attached in a straight line to a copper spike I made from extra primary tubing. I hammered the spike as far as I could into the ground, it was about 6 inches or so.
MODULAR TOPLOAD SYSTEM
When I set out to make this beast, I wanted to be able to make it swappable and modular. I wanted to change out the secondary tower, as well as trying out various topload shapes. If this is your first coil, you’ve got to get a good large topload on it. I didn’t at first and learned after two weeks of trial and error that I didn’t have enough capacitance and my secondary res frequency was wayyyyy too high. Adding a simple, cheap and damn sexy toroid completely changed the dynamics of my system. I used a simple 4″ aluminum dryer vent (it had a built in connector on one end, you just squeeze it into shape), then put two pie pans together with a simple toilet bowl nylon screw I had laying around. The pie pans will squish a little bit, but that’s perfectly OK.
View from underneath the pie pan. The screw on cap is mounted into the pie pan, the wire leading to the pie pan is attached with a screw that goes through the bottom pie pan only.
The 3 inch female screw coupler with the male screw cap, extremely handy when you want to make swappable toploads
Drilled a hole in the male screw cap, put in a nylon screw from a toilet bowl mount. These are very easy to find at hardware stores on their own. I use one cap for each topload, caps are around $1 each.
The top of the secondary has the socket leads attached. In this pic the secondary is attached to an experimental topload made of a clip that I can use to attach various objects like CD’s and nails. I’ve heard that going through the center of the coil isn’t a good idea, and it’s probably not considering you could send arcs into your secondary’s interior.