Joseph Soto
Mr. Eldon Conder
EN 1410
April 9, 2014

What is a tesla coil?
A tesla coil is a resonant air core transformer system invented by inventor Nikola Tesla in the 1890’s. Originally, tesla coils were designed to broadcast electricity and signals wirelessly, however, several engineering and monetary setbacks prevented the tesla coil from becoming the popular mode of energy transfer, and a power distribution method architecture relying on use of power grid lines (wires/cables) became the prevailing and accepted method. Now, tesla coils are primarily used for short-range wireless power transmission, for lighting up some types of lights, and for presentation/entertainment purposes.

The operating principle behind a tesla coil is somewhat simple. Energy is sent to charge up a capacitor or set of capacitors. At a certain point, the capacitors are forced to discharge into the primary coil. When the energy that is stored in the capacitors is sent through the primary coil, a large amount of energy is induced “sent” into the secondary coil alternating current is basically just electricity that changes voltage. When a capacitor is fires the voltage changes from essentially zero to something really large in a very short time. Since there are more turns in the secondary coil, the induced energy has a higher voltage, but a lower current than in the primary coil. The capacitors recharge and start this cycle again.

The capacitance of the capacitor and the inductance of the primary coil determine how quickly this cycle occurs per second and is measured in units of frequency called hertz. If a tuning fork vibrates at a certain frequency and another tuning fork that, if you hit it, would vibrate at the same frequency were put near each other, then simply striking one tuning fork would make the other start vibrating too, why is that well it because of resonance Tesla coils can be said to behave similarly; if the frequency of the primary circuit matches the resonant frequency of the secondary circuit, then the tesla coil is optimal, and like a tuning fork, energy will go from one part (the first “fork”/primary circuit) to the other (the second “fork”/secondary circuit).

In the olden days, capacitors would be charged up and a gap of metal would be put to each of the capacitor’s leads. When the capacitor was fully charged, a spark would arc in between the gap, thus forcing the energy into the primary coil. After the spark occurred, the air in between the gap would be ionized. Ionized air acts sort of like a wire; electricity can move freely through it. Until the ionized air dissipated, energy would oscillate (move back and forth) between the capacitor and inductor many times. Instead of using spark gaps, we will be using transistors which are like little switches, but are controlled electronically. Turning the switch on and off quickly at certain frequencies will make the “lightning” coming out of the tesla coil make audible tones.

Keep in mind that even though we are turning the tesla coil on and off at a certain frequency (a certain number of times per second), its primary circuit is still oscillating (energy moving back and forth between the capacitor and primary coil a certain number of times per second) at a different frequency that we will match with the secondary circuit.

I have attached a simplified diagram of the basic way that we will hookup the tesla coil. This instructable is designed to be very flexible and allows for you to be your own designer through giving you the tools and basic knowledge needed to build one yourself from scratch.
Step 2: Overview

Required Materials:
Oscilloscope (makes life easier)
Computer (makes life easier)
Assorted PVC Pipe
Aluminum Tape
Aluminum Ducting
Wood/plastic something non-conductive
Speaker Wire/Thin/Thinly Insulated Wire/”Magnetic Wire”
Thicker Wire
HV Capacitors
Toroid
Misc. Wire
Speaker
MSP430 Microcontroller
Soldering Iron + Solder
Operational Amplifier
Assorted Resistors
Assorted Potentiometers
Bread Board
Project Case
Switch
Breadboard
Screws
Male/Female Jacks
Bridge Rectifier
Power Transistors
Heat Sinks
Conductive Cooling Paste
Glue
Varnish
Saw/Something to Cut Wood or Plastic
Drill
Fuse/Fuse Holder

Breaking it into Parts
Building a tesla coil is easier once one breaks building it into a series of parts, and I will explain how things basically operate as necessary along the way. I have divided the task into the following parts: (TheHomebrewGuru, 2012)

Step1.) Designing Inductor/Capacitor Circuits and the Toroid
In this step, (to avoid mathematics that intimidate the average layman from participation) we will use computer programs to help us approximate the size and parameters of our parts so we can build them.

Step2.) Building a Base
In this step, we will build a base/case/stand for our tesla coil from wood or other available materials.

Step3.) Building the Secondary Coil
In this step we will take some PVC pipe and wind a bunch of thin wire around it. The size of the PVC pipe, the number of windings and the size of wire all depend on what was determined in step 1

Step4.) Building the Toroid:
In this step we will need to make the metallic doughnut. There are several ways to build one that I will highlight, but the dimensions will depend on what was determined in step 1.

Step5.) Building the Primary Circuit
In this step we will do something similar to what we did in Step 3, but we will use thicker wire and there will be less turns. There are many possible designs for primary inductors that I will highlight. A high voltage capacitor will be in series with the primary inductor. The voltage of our capacitor and the design of the primary inductor will have been determined in step 1.

Step6.) Building the “Bridge” Switching Circuit
In this step we will build a circuit that can make the tesla coil when to switch “on and off” much like a switch, except solid-state.

Step9.) Tweaking, Persistence, and Troubleshooting
Tesla coils are very finicky RF devices, and thus do not expect huge streamers right away. In fact, most tesla coilers spend years and blow many parts before they develop a really solid design. Adhering close to models and getting good parts will minimize frustration.
Step 3: Step 1 - Designing Inductor/Capacitor Circuits and the Toroid
You will need to download WinTesla here: http://www.mediafire.com/?si016unn6lt2qb0 (or ScanTesla works too). This is a good tesla coil modeling program that I have personally used in the creation of some of my coils and seems to work pretty well. Depending on available supplies, how large you want to build your coil, personal preferences, and your budget, you will want to plug values into the program to come up with ideal sizes for your secondary coil (diameter, length, guage, turns, frequency, etc.), for your capacitor, and for your topload (toroid). Do not worry about other parameters such as transformer and spark gap-related inputs. There are three different types of primary coils; a flat Archimedes spiral coil (“pancake” coil), a vertical cylindrical helix coil, or an inverse conical saucer. Whatever you choose does not matter, but have an eye for design and keep in mind that you will most likely be doing tweaking along the way to optimize your coil. If this is your first tesla coil project, I highly recommend first designing a small (maybe even handheld) tesla coil. This will lessen the pain associated with potential first-time false starts and the cost of mistakes. The main idea behind this step is to determine an ideal size for your coil.

If parameters are mismatched and the tesla coil isn't built correctly, it will be "out of tune." I have attached 3 pictures of different toroid sizes. Notice that if the toroid is too small or too big, the streamers aren't as long.

Step 4: Step 2€“ Building a Base
Now that you have a basic set of measurements for the primary coil and secondary coil, you will want to construct a base. I have done many different base types. Typically, bases are made of either wood or plastic. Both wood and plastic sheets are typically available at a nearby home improvement store. Generally, a larger base is required when designing a coil with a “pancake” type primary coil, while a smaller base is required for helical/cylindrical primary coils. Make sure that there is enough space under the primary coil in the base to put components (the capacitor and the switching circuit). In one of my designs, I screwed a plastic toilet flange to the base of the coil so that I would be able to remove my secondary coil whenever I needed to (remember, you will most likely be doing tweaking throughout the project, so you want to make things as modular as possible); the PVC pipe-based secondary coil fit snugly inside of it.

You will want to add a connector to connect the bottom of the secondary coil to ground. I drilled a small hole near where I was to insert the secondary coil and slipped a wire with a connector through it and then glued the connector in place, then under the base I connected the other end of that wire to ground.

Step 5: Step 3€“ Building the Secondary Coil
Take some PVC pipe and tape the end of a string of wire to the end of the pipe (make sure the PVC pipe is cut to the length determined in step 1, but leave a little extra space just in case). Now it’s time to start coiling! You will need to wrap the thin wire that you have selected in step 1 around the PVC pipe (yes, you will need to count the turns). It will be a very tedious task, but don’t get lazy here, and be careful to not let wire kink. When you are done and the wire is wrapped tightly, you may wish to put a layer of varnish around the coil to protect it (though it is not necessary).

Leave a good length of wire extending from both ends of the pipe so that you will be able to work with it. With my first coil, I attached a male spade connector to each end so that I could unplug the secondary whenever I needed to. You can take a lighter to burn off the coating on speaker wire or magnetic wire and then wash the ends to make good connections. A varnish coating is not necessary, but leaves a nice, shiny, protective coating.

NOTE: the secondary coil should have wire that has an insulative coating, otherwise the tesla coil will not work. Speaker wire and similar wire types should be fine.

Step 6: Step 4€“ Building a Toroid
There are many ways to build a toroid, but essentially what is desired is a metal donut. One method for producing this donut is to buy aluminum ducting of the desired width, then bend it and wrap it with aluminum tape. This will work, but might look a bit tacky (I did this for my first coil). Some tesla coilers have tried wrapping inner tubes with aluminum tape or using paper mache (or just buy one online). Of course, for that undeniable flashy clean look, you might have to fork over some cash and buy a premade one on ebay (but that’s cheating!).

Step 7: Step 5€“ Building the Primary Circuit
The primary circuit consists of high voltage capacitors in series/parallel to produce the desired voltage and capacitance. These have to be HIGH VOLTAGE capacitors (around 20,000v is good), and from my experience, CDE capacitors (specifically, model CDE 942C20P15K) work pretty well. Capacitors in parallel have an added capacitance, so for a higher desired capacitance, put multiple capacitors of the same type in parallel. Your tesla coil will only be as good as the capacitors you use, so I highly recommend purchasing them (they are pretty cheap, reliable, and worth buying).

In my first coil, I didn't need the switching circuits because I used a spark gap instead, so after I had the primary and secondary circuit hooked up, I just added a motor that touched the spark gap wires together at regular intervals and I was done! Doing this is a good way to make sure that your tesla coil is build correctly.

Step 8: Step 6€“ Building the “Bridge€ Switching Circuit
Perhaps the trickiest part in building a solid state tesla coil is the “bridge” or “switching” circuit. The bridge switching circuit is the heart of the modern day tesla coil and is responsible for taking in a signal and switching large amounts of power on and off very quickly based on that signal. The transistors (“switches”) that are most commonly used are called IGBTs or sometimes MOSFETs are used (Insulated Gate Bipolar Transistors). Ignoring all of that technical jargon, IGBTs are ideal because they are generally good at switching at speeds needed for good coil operation and can handle large currents. Before good transistors, there was no electronic switching circuit at all, but just a gap in the wire called a spark gap or a rotating wire that would fire once the capacitor was filled or when the wires got close enough (because the voltage built up and eventually could leap across the gap). This is very inefficient, but if this is your first tesla coiling project, I recommend first using spark gaps and using a high voltage neon sign transformer as an input to the primary circuit instead (however, this does not allow for audio modulation). Before electricity is sent into the bridge circuit, it needs to be rectified with a rectifier rated for the amps that your coil uses (pick something high).

TRANSISTORS
Since IGBTs switch such large amounts of energy and are so small, they have a high tendency to die or blow. For this reason, do make sure that IGBTs used are properly fastened to heat sinks of adequate size (though do not have the metal parts touch it). I have recently used IXYS SS1040 IGBTs.
4hv.org recommends these model IGBTs for use in tesla coils:
HGT1N40N60A4D
HGT1N40N60A4
FGA40N60UFD
FGH30N6S2
IRG4PC50UD.

THE BRIDGE
Circuit schematics may look scary, but it really is just a way of graphically representing what goes where. Remember, you can use this link to help determine what symbol means what: http://library.thinkquest.org/10784/circuit_symbols.html
Half Bridge switching circuits use less IGBTs, but do not switch as much power as Full Bridge (H-Bridge) circuits. Similarly, Half Wave rectifiers do not convert as much AC power into DC power as Full Wave rectifiers. You will want a Full Wave rectifier, but do connect a fuse to the mains in order that your tesla coil does not draw too much current and then subsequently blow IGBTs as readily.
I have attached 2 simple schematics of how the two types of bridge circuits are wired in their most basic configuration, however, that is without important modifications to make your coil more failsafe.
There are several plans for bridge rectifier circuits online that have been tested and are reliable, and if this is your first time using switching circuits, I recommend first using them before trying to design one yourself, however, if you are adventurous and/or even know exactly what you are doing, expect hours of testing and work with an oscilloscope. I HIGHLY recommend starting out with a half-bridge circuit before moving on to a full-bridge. That is what I did with my first tesla coil, and it was difficult enough replacing 2 IGBTs when they blew, let alone 4!
Check http://www.richieburnett.co.uk/sstate.html http://stevehv.4hv.org/drsstcdesign/ISSTC_sch2.JPG for free plans from other tesla coilers. Notice that the big part in the middle of Steve Ward’s plan looks a lot like the full bridge diagram photo that I have posted. In fact, it is a full bridge, except with a few modifications to protect the circuitry. I’ll talk a little about that.

CIRCUIT PROTECTION
Diodes let electricity in one way, but block it in the other direction. This is very useful in protecting circuits from failure. TVS diodes (transient voltage suppressing diodes) are used frequently. Remember, IGBTs and transistors are very delicate, so it is best to have as much protecting them as possible. Notice in the schematic at the second link that diodes are placed between the transistors to ensure that voltage does not go where it is not supposed to. Use the schematic as a reference to design your own circuits and for good places to put your diodes. P6KE and SK07 (part number) diodes are pretty good for general protection. They should be rated around 440v and 600w. Keep in mind that since diodes let electricity go in one way and not the other, the way that they are oriented is very important. There is often a stripe on diodes that indicated polarity that corresponds to the little diode arrows in the schematic.

Capacitors can be used for making voltage graphs more clean or smooth and help absorb unexpected voltage changes. Like we did with the diodes, use the schematic as a reference for building your own circuit. Notice that two large capacitors are placed after the bridge rectifier (these are not high voltage).

You will need to install Code Composer studio for your MSP430 in order to load codes to it. Specify a folder that you want to work in, and start a new project called Muzak. Follow the instruction book that comes with your MSP430 to do this. Once you have Code Composer Studio, download these files and/or copy and paste their code (this will require opening the .rar file): http://www.mediafire.com/?oogn9t59vvk4p2b

What this code does is put a signal through pin P1.0. Once you load the code onto the board, you should see the red LED (light) blinking. This is because the music signal is sent through the LED and thus it blinks along with the song. To hear the song, remove the jumper across pin 1 hook up two wires from a speaker to P1.0 and Ground. You should here the song playing. Do you recognize it?

MODIFYING TO FIT YOUR COIL
Look at the signal through an oscilloscope.
The signal for “on” is when the voltage reaches past a threshold voltage (the top part of the square wave). Don’t worry about the threshold voltage yet, because we will be using op-amps to increase the amplitude of the signal. But basically the top part of the square wave is “on” and the long bottom part at near 0 volts is “off.” When the coil is “on” energy flows freely into the primary circuit. A good analogy is an everyday playground swingset; imagine that swinging one way represents energy going into the capacitor and swinging the other way represents energy going into the inductor (primary coil). When you swing, energy goes back and forth, but to go back and forth requires that you begin pushing the swing. When energy flows into the primary circuit (the “on” stage) is analogous to someone pushing.

I know you really want to, but you can’t just simply plug the music board into the tesla coil. You have to adjust the signal’s PULSE WIDTH, FREQUENCY, and DUTY CYCLE. If pulse width is too high, then too much power will go through the IGBTs at once and they will blow. Similarly, if pulses go through the IGBTs one after the other too quickly, they will also blow. Finally, if the IGBTs are on for too high a percentage of the time (duty cycle) then they will overheat and/or blow. The key is to keep pulse width, frequencies, and duty cycle low, then to gradually increase them to see what they can handle or cannot handle. In my coil, I limited (absolute maximum) my pulse width to 200uS (microseconds), the frequency to around 150Hz (200 pulses per second), and around a 2.5% duty cycle (it can be on 2.5% of the time). Don’t expect anything much higher for your coil! Digital oscilloscopes (if you do not have one like me, see if you can use someone elses at a computer lab, college, or at a friendly engineer’s house) have the advantage that they measure all of these for you.

After you have adjusted the code, check the output waveform using the oscilloscope and continue modifying until you get a desired output that you feel good will work well with your coil (start low first!). Years ago the first time I experimented with audio boards my frequency was way too high, and so my tesla coil blew (plus the audio quality wasn’t that great because at
Step 10: Step 8€“ Amplifying the Microcontroller Signal

Now that you have basically everything put together, we can’t usually just hook the tesla coil’s bridge circuit up to the audio board and go. It’s not that easy, see, you have to make the amplitude of the signal above the IGBTs’ threshold voltage. In simple terms, you have to make the signal bigger so that it is strong enough to trigger the IGBTs. To do this, we can use something called operational amplifiers (“op-amps.”).
An operational amplifier is a little chip that we can hook up to a power source like a battery and use the power to make the input signal bigger. We use resistors connected in a certain way to control how much the signal is amplified (called “gain”). We learned earlier that potentiometers can be used just like resistors, except that they have a little knob that allows you to control their resistance without having to put in a new resistor each time you want to change the gain. Using a potentiometer you can simply turn the knob until the IGBTs are triggered (if everything is working correctly!). Some operational amplifier chips that I have used are the LM741 or the MC1458CP. These helped me step up the voltage of the signal from around 3 volts to around 9 volts (300% gain).

For beginners, op-amps can be a bit daunting because of the way that they are represented in diagrams (weird arrows…what’s going on?). However, all you have to do is know which part of the diagrams means what. I have included some pictures that help alleviate the confusion.
Remember, you will need to look up which pin is what on the specific op-amp model you will use. You will need to locate which pin is V+, V-, IN-, IN+, and 1OUT, then use the pictures to build the circuit. I used a 9 volt battery for my op-amp, and connected the minus terminal to ground.
The ratio of the resistor that is connected to the input with the resistors connected to the output determines the gain, so using a potentiometer instead of a resistor of constant value is useful. For my op-amp, I connected a 10k resistor to the input and two 1k resistors to the output.
Along the way you might want to check the oscilloscope to make sure that your op amp is correctly amplifying the signal.

Step 11: Step 9 €“ Tweaking, Persistence, and Troubleshooting

If you thought that the last step was the final step, think again. After hooking everything up, you WILL run into problems. Even for professional and experienced engineers, things usually do not work the first time around. In fact, this project took me a couple years to perfect. If your tesla coil is not operating correctly:

Check to make sure things are connected in the correct way

Make sure that you have circuit protection

Check to see if diodes are working correctly or if the IGBT/MOSFETs have broken

Make sure that IGBT/MOSFETs are fastened to a heat sink and aren’t getting too hot

Lower the pulse width, frequency, and/or duty cycle

Use a variance to slowly give power to your tesla coil

Contact other tesla coilers on 4hv.org with a specific question or seek outside help or research

Use an oscilloscope to tweak circuits until you get the desired waveform

Make sure that the frequency of the primary circuit is resonating with the secondary circuit. To do this, use a clamp to move the connection on the primary coil

Try using a breakout point on the toroid (connect a sharp metal point to the toroid such as a bent paper clip)

Make sure the fuse hasn’t blown

Use a speaker to see if the music is coming from the audio board

Make sure your connections are solid and not flimsy

Works Cited
TheHomebrewGuru. (2012, March 23). Build and code a Moster singing tesla coil. Retrieved Jam 25, 2014, from Instructable: http://www.instructables.com/id/Build-a-Musical-Tesla-Coil-like-a-Pro/