Mjöllnir I: steady progress

Construction on the coil has seen steady progress. The chassis has been completed, although the top has yet to be screwed down to allow easier access to some of the components. The primary coil is also nearly complete after a full day of work. 5/8ths inch Plexiglas was used to space the spiral primary. After some difficulty using the drill press(the bits tend to 'bite' the plexi as you exit the back, destroying the piece :/), I milled the Plexiglas in the student machine shop on campus. I then wrestled 60 feet of 3/8ths inch copper tubing through the holes, making 13 turns on the primary coil. This should give an adjustable inductance around 57.2 micro-Henrys. The spacing on the coil is not perfect, but I'm hoping that with a little more tweaking it will serve its purpose well.

I have ordered 2000 feet of 26 awg magnet wire for the secondary coil and am eagerly awaiting its arrival in the mail. Making the secondary coil will likely be the most challenging task yet, but it will also mean I am nearing completion of the coil. One issue I am currently facing however, is that I'm unable to find 4 inch PVC piping in Davis. I may have to make another trip out to Lowe's in Sacramento to find the right PVC for the secondary. Next, I'll be focusing on constructing the main spark gap for my coil. Stay tuned.

It started in a bar on a Friday night...

We were celebrating Rachel's 21st at Sophia's in downtown Davis when the texting service Chacha was brought up in conversation. (Text any question to chacha (242242) and they'll respond within minutes with an answer. Pretty amazing, right?) We decided to put Chacha to the test and were coming up with questions to ask. Wondering what kind of response we would get from a subjective question, we wondered, why not ask if we should dye our hair blue? Rachel and I entered our texts, but before we sent them, we pinky swore we would do as Chacha said. Unfortunately, we both received a text along the lines of "pursue what your heart says." Again we texted Chacha, "yes or no?" No more than a minute had gone by when Rachel received the resounding, "Yes, of course you should dye your hair blue!" While again I received the less definitive answer to do what my heart told me. We decided however that this was close enough to a positive response! Not wanting to have her hair permanently dyed, we agreed before hand that temporary dye would suffice for Rachel.

Sunday came and Nick decided he would join the dye fest... here Carissa is giving a bit of dyeing instruction as Nick and I start the bleaching process.

Bleached hair! I'm kind of shocked looking in the mirror for the first time. :O

Here comes the blue....

.... and shampoo and rinse, shampoo and rinse, shampoo and rinse...

I have blue hair now! woohoo! (and I look like a Nerf dart, haha)

Rachel, you're next!

Mjöllnir I: starting construction

I was excited to find the two sites I frequent most on the internet both have Tesla related logos:

Having received many of the parts I ordered in the mail, I've started construction of the coil. In the picture below you will see the NST in the upper left, with a line filter (this protects the house and neighborhood from the coil which can cause power surges back into the grid) next to it. The capacitors which will make up the capacitor bank are in the middle and a half assembled NST protection filter is below the NST on the left. I also have here the copper tubing from which the primary coil will be made and a bag of 1Mohm resistors. A few tools and wires can be seen on the right.

I'm still waiting for the high voltage wire to come in the mail, so in the mean time I'll be constructing a chassis to hold all these goodies and support the secondary and top load. More to come later!

Mjöllnir I: already over budget

The second post on my tesla coil project and I'm already over budget. This doesn't bode well. My goal was to stay under $300 for the initial project, but purchasing things online adds up, especially with shipping costs and minimum purchase limits. Right now I'm at $320 dollars. Luckily, the only major componet I have yet to purchase is a couple thousand feet of magnet wire.

Next step will be to work on construction of the NST protection filter. I'm using a design by Terry Fritz.  A filter is needed to protect the transformer from high voltage surges created in the primary that can make their way back to the the relatively delicate windings of the neon sign transformer. This filter protects the transformer in a couple of ways. It 'removes' the transformer from the primary coil circuit via the 1K Ohm resistors, the safety spark gaps ground high voltage spikes by allowing them to easily arc to ground, the varistors shunt high voltage to ground, and the capacitors also help absorb (and bleed off via the resistors) voltage spikes.

Mjöllnir I: the beginnings of a tesla coil

Mjöllnir was Thor's hammer. According to Norse mythology, Thor's hammer had the power to throw lightning bolts. As Thor was the god of thunder, this seems only appropriate. The most identifiable parts of a Tesla coil (the tall secondary coil and large top load) are also roughly hammer shaped. For this reason (and the fact that it will release bolts of lightning) I felt Mjöllnir was a suitable name for my Tesla coil. When further research revealed Mjöllnir meant 'crusher', I pretty much had to go with it.

My goal for this project is to successfully design and build a Tesla coil at relatively low cost. All in all I hope to spend less than $300 total (right now I'm just over $100 for the NST, toroid components and cords). I hope to achieve a spark length of about 30in. with the largest theoretical length being 36.6 inches for a 15000volt, 30ma transformer. After completion of the basic coil, I expect my tinkering and alterations/improvements will increase the cost, but $300 will give me a good goal for the initial project.

To test my neon sign transformer (and to have a little fun in the process), I threw together a simple Jacob's ladder using an old coat hanger I stole from my roommate (thanks Ian ^_^). Note the plasma created between the two electrodes as the spark travels up the ladder.

After staring at a coat hanger and being mesmerized for far too long, I decided that my transformer was working. On to the top load.

Here is the toroid I created using 4" aluminum dryer ducting and an 8" pie pan I bought from ACE hardware. The size and shape of this top load gives a theoretical capacitance of 17.4 pF. My goal (to tune the coil to it's 1/4 wavelength frequency) was 17.2pF. I'm guessing the theoretical capacitance will be a bit high anyway so this should do just fine.

The next major step in the design of my coil will be to determine the appropriate tank capacitor size given the power output of the transformer. This will require a few calculations and some time spent online hunting down suitable high voltage capacitors. More to come later!