Tesla Coil

 

So here you will find pictures, videos and eventually music of/from my Tesla Coil. It has taken me nearly 3 years to get it to the stage it is at now and it is nowhere near finished yet! It works to some degree but but I need to spend some time tuning it up before I can upgrade it to a musical version.

I guess I should tell you a bit about what a Tesla Coil is and how it works for those of you who don't know. A Tesla Coils full name is an Air Cored Resonant Transformer, in laypersons terms this means a transformer that has an air core as opposed to an iron core like standard transformers that you get in things like laptop chargers. The resonant part of the name means that the circuits within the Tesla Coil resonate with each other to step up the voltage more than you would normally get from a transformers primary and secondary windings. This is what is called and L/C resonant circuit. The L denotes the inductance and the C represents the capacitance. The ratio between these two values gives you a Q value which is the resonant value of the L/C resonant circuit.

These values are set out in the design stage of the build and are mainly governed by the size of the secondary coil and topload. Once you have the value for the secondary resonant circuit you can work out the values of the primary resonant L/C circuit and design your capacitor bank and primary coil to suit these specifications. More values that affect the resonant circuit are the input and output voltages, current and mains frequency input of your neon sign transformer.

If this still makes no sense to you feel free to leave a comment in the box below or send me an email from the contact page and I will endeavor to help you understand it all a bit better.

So let me tell you the story of my Tesla coil and how it has been developed. I started in August of 2007 after finding a video of a cymatics display which uses a resonating plate to create patterns in sand and iron filings. I looked around to find ways of building this and stumbled upon a website that was showing people how to create various different electronic experiments including Tesla Coils! From that day on I was hooked as they say, if you are interested in the website I found you can find it here they are very helpfull and have various parts for sale too.

 

Mk1 Tesla Coil

My Mk1 Tesla Coil was a battery powered version running of two car ignition coils, however this seemed a bit small to me and I decided to scrap it before it was finished! I managed to get some very small sparks out of it and I had the very cool lighting in a lightbulb effect as well. I may get this one running again as I can feed in an audio signal very easily to have some form of musical sparks! I just need to make a smaller pimary and secondary coil with a new capacitor bank that will complete the L/C resonant circuit. However I don't have an easy way of measuring the high voltage output of the ignition coils at the moment so the resonant circuit is going to be hard to build! I think my best way is to use a voltage divider with a number of resistors in series. It has been a long time since I have done this though so I will have to go into my brainsarchives to try and remember how to do it!! Here are some pics of the circuitry though, as you can see it was very very amateur but that gives it it's own personality in my opinion. All tesla coils are different and somewhat personal as well depending on budget, available parts and how much is fabricated from scratch.

 

Mk2 Tesla Coil

On to Mk2, this is where it gets serious!! I managed to get hold of a Neon Sign Transformer from my local neon shop, this gives me an input voltage of around 8,500 Volts! Now thats more like it. Of course when you are dealing with these sorts of voltages you have some inherent safety issues, not least the fact that if you touch the wrong part at the wrong time YOU WILL DIE!!!

I had to rethink the whole design of the system to enable safe operation and avoid destroying everything that is plugged into the same circuit as the coil. The main component used for this is called a Terry Filter named after its inventor Terry Fritz

(German I believe but i could be wrong leave a comment if you know better). This circuit basically filters out and high frequency kickback from the output of the coil from destroying anything further back from the filter. I'm not 100% sure exactly how it works but I know it works so I'm happy! However this does not mean I can go in and touch every part of the Tesla Coil willy nilly, I still have to be extremely carefull and make sure everything is completely discharged before making any adjustments.

The next part I had to redesign was the main structure and housing for the coil. After browsing the web and different mailing lists I decided to go with a design that has been used by many others using round discs of wood separated by lengths of PVC tubing. This enabled me to have different layers for different parts of the circuitry, and it also meant I was able to have some separation between the high and low voltage sections of the coil.

On the bottom floor is the Neon Sign Transformer or NST and the PC power supply which generates 12V DC to power the fans for quenching the spark gap (I'll go into this in more detail lower down. The high voltage output from the NST goes up to the next level and into the Terry Filter, from here it passes through the spark gap and then up to the the high voltage capacitor bank.

The capacitor bank is then rapidly charged and discharged by the high speed switching of the spark gap into the primary coil that is made from 8mm copper tubing. The amount of turns on the primary coil and the size of the charge capacitor determine the primary resonant circuit frequency. This has to be matched to the designed resonant frequency of the secondary coil and topload.

Videos

Here are a couple of videos of my tesla coil running, I should have a few more coming soon but the second video shows you a good overview of my Tesla coil but there is a lot of waiting around while I diagnose some problems. It was the first firing though!! The first video is at UCL for a students University project. The two neon signs are being lit up wirelessly using the Tesla Coil.

This is a much higher quality video but the Tesla Coil isn't running as well as it does now, still a great video though, thanks to David Kenny for that.