I have been involved with electronics for most of my life. Computers. Transistors. Integrated Circuits. Radios.
But the realm of high voltage has always been a different universe to me. Things that are well-behaved at battery power are chaotic at high tension. Construction techniques that are conservative at household voltages are brazenly sloppy when introduced to ten thousand volts. Everything needs to be rethought.
Why is this arcing? Where is that purple glow coming from? What was that green flash? Why is that steel thing melted? Will these burns heal themselves or should I go to the hospital? Speak louder, I can barely hear you after the explosion.
Unless you're working during a thunderstorm, you don't say these things. Metal doesn't melt when you're programming an Arduino microcontroller.
People who build Tesla coils say these things all the time.
I want to explain Tesla Coils to you. I want you to know why they are not magic and how they work. I want you to know why there are almost no female Tesla Coilers and why guys who spend a lot of time making lightning with Tesla coils have a very difficult time getting dates and maintaining relationships. I want to try to explain to you why in the 21st century anyone would go to the trouble of fabricating a device that can kill or otherwise seriously injure its creator and innocent bystanders, and which after over a century of effort has been proven to have no actual value other than to render the builder less attractive to others.
I want to explain to people what I have done and why I'm so interested in this weird, dangerous, useless device.
I'm not sure I can. It may take me several essays. I'll try my best, then, to tell you what it is.
First, I need to explain resonance.
As this is the internet, we don't need a history lesson. You can click on Nikola Tesla and find out all about him and the inventions that bear his name. But because I don't want you to stop loving me, I want to explain the coil to you in iceowl terms. I want you to know the concepts and pictures that are rolling around my brain. I hope it works.
Ok, darling. Let's think about frequency.
The natural frequency of an object is the way it vibrates when it is "pinged" by something. Think of a bell. You ping a bell and it rings at its natural frequency. The note or tone of a bell has to do with its size. Big heavy bells make low sounds. Tiny bells make high sounds. The size of something and what it's made of determine its natural frequency, and just about everything has a natural frequency.
If you go around pinging something at its natural frequency, you are said to be in resonance with it. When you ping something at its resonant frequency, you cause the vibrations to build up, and reinforce each other, exactly in the way you push someone who is on a swing in a park. You keep adding small pushes at exact the right time, and the person on the swing goes higher and higher.
In a Mythbusters episode they reproduced one of Tesla's experiments with resonance by determining the natural frequency of an unused truss bridge, and then created a device which would "ping" the bridge with a pneumatically actuated rod that struck the bridge at exactly that same frequency, thereby causing the bridge to resonate. The tiny vibrations caused by the air-powered pinger were timed at exactly the right frequency to cause the pings to add up. Eventually they got the whole bridge to shake just by hitting it with a tiny metal rod, over and over, at exactly the right time.
Electronic devices resonate too and are filled with all sorts of resonant circuits. Every radio transmitter, be it WiFi, or GPS, or 4G telephone, or AM radio, has a circuit to spit out electromagnetic waves that is "tuned" to a specific central frequency. Similarly, the receiver of such radio waves has an input which is "tuned" to a frequency. That thing that does "tuning" is a circuit which is resonant to the chosen frequency. It vibrates well at the frequency you desire, and not so well, or not at all, at other frequencies.
Think of a tiny bell. Could you get a tiny bell to sound like a gong? No way. No matter how hard you hit it, it's just going to make its tiny bell "ting". It vibrates at its natural frequency, and no matter how much you try to get it to resonate at a different frequency, you're going to fail. You're going to get nothing out of it, till you hit the frequency it's happy with. That's the bells "tuning", and there are electronic circuits that work exactly the same way.
There are lots of ways in electronics to tune something or to resonate at a particular frequency. But a common simple way is to use devices called capacitors and inductors and connect them together. Capacitors are devices that store energy in electric fields. Inductors are devices that store energy in magnetic fields. Magnetism and electricity are two aspects of the same thing (light, actually) and are related by all sorts of physics. Suffice to say that when you put these two items together in a circuit in your iPhone, they shuttle energy back and forth between each other at a certain frequency, converting magnetic fields to electric fields and back again. They do this reliably at a frequency determined by their size, and so they're said to be resonant at that frequency, just like a bell is when you strike it.
I would tell you the equation of resonant frequency given the value of the capacitor in farads and the inductor in henrys, but they say you lose half your readers as soon as you introduce math. Therefore I'll just say that the number pi is involved, and whenever pi is involved the natural world is all tangled up in your invention.
Which is to say that nature is involved in resonance.
Tesla made his coil to transmit power without wires. He was going to do it by electrically vibrating the earth. The idea he had was that if you could knock down a building by tapping it gently at its resonant frequency (he nearly did that for real) perhaps you could tap the earth at its resonant frequency and build up enough "pressure" in the form of electricity that anyone anywhere could just hang a sort of antenna off of something and power would flow into that thing.
Forget about the fact that resonating the earth, if it was even possible, might have other serious consequences - perhaps shattering the earth into tiny fragments. And then, of course, we can worry - what about things that are sort of accidentally connected to wires of the right length and power flows into them? But nobody was concerned about that. They were too busy trying to fly.
And in fact, it is possible. It's just really expensive and hard to do. Tesla kept building bigger and bigger resonators, but he never got to the dream of global wireless power distribution. Nowadays Tesla coils are relegated to museums and people's garages. Some guys, like Greg Leyh, actually still aspire to a version of Tesla's original idea. Lightning on Demand is such an effort going on today in the Nevada desert. www.lod.org
By the way, all radio works, more or less, by vibrating the earth. So this is no kind of unusual magic nor has it been for nearly 100 years.
The Tesla Coil is a remarkably simple device as electronics go. And there are people who will still say, "Nobody knows how they work," but really, that's just to maintain the aura of mystery. If there's anything as of yet unknown about Tesla coils it's only because they have such little practical use that there has been no industrial or governmental effort of enough size to produce a detailed analysis. As such, it's left to enthusiasts to provide the data for the physics. Though detailed knowledge of the physics is not necessary to build a successful coil.
It doesn't make it any less amazing to see one running.
A Tesla coil is two magnetically linked resonant circuits. That's it.
Oh, woah. What the hell does that mean? We love you but we can't understand you. Do you want a cookie?
Yes, cookie, please. Here's an explanation:
A resonant circuit, as I mentioned above, is a connection of circuit elements that vibrate at a certain frequency when electrically "pinged". In this case, we're talking about an inductor and a capacitor, which shift energy back and forth between electric and magnetic fields. The sloshing of energy back and forth happens at the "resonant frequency". In fact, a Tesla coil has two such circuits. One is an input circuit, and one is (surprise) an output circuit. Each one has one inductor and one capacitor, and energy sloshes back and forth in each one of them at a particular resonant frequency.
So you have these two circuits, each of which has one inductor and one capacitor, and energy sloshes around in each of them at a certain frequency. Now, what is an inductor - actually - and what is a capacitor?
An inductor is a coil of wire. That's pretty much it. You take some wire, coil it up, voila, inductor. Another word for inductor is "electromagnet," and perhaps you have some intuition about that. Put electricity into a wire coil, and you can pick up nails with it. They use electromagnets to lift ferrous garbage at the junk yard. Another thing about wire coils is you can wave a magnet around them and they generate electric potential and current.
Inductors are just typically very weak electromagnets.
A capacitor is two flat plates of something that conducts electricity, like aluminum foil, for instance, that arranged to face each other with some kind of gap between them. Imagine a piece of aluminum foil. Now cover it with your teflon cutting board. Now put another piece of aluminum foil on top of the cutting board. Now connect a wire to the top foil piece and another wire to the bottom foil piece. Voila, capacitor. If you were to connect that to a battery, it would actually store a little (very little) electricity that would come out when you took the battery away and connected the wires to something like a meter.
In fact, the input circuit of a Tesla coil has a coil of wire and so does the output circuit, but they're made up of wire of different thicknesses and length - but they're still recognizable as wires. The capacitors are very different in structure between the input and output circuits, and it might be hard to tell what they even are by looking at them. The capacitors on the input circuit are frequently store-bought cylinders with wires coming from them. The output capacitor is a big metal donut that sits atop the tall coil of wire that is the output inductor.
Now there is another circuit element in electronics called a transformer. You have seen transformers. They're on the power poles near your house and in those little black power supply thingies you plug into the wall that charge your cell phone and run your laptop. Transformers all function by the same principle, and they're everywhere thanks to Tesla.
A transformer works on alternating current. A transformer is two coils of wire placed close together. When AC electricity is run through one of the coils, it sets up an alternating magnetic field. That magnetic field is "felt" by the second coil, which produces electricity (remember the electromagnet thing?) One coil is the input, and one coil acts as the output. If the size of the wire is exactly the same in both input and output, and if there are the same number of loops of wire in the input as the output - the voltage and current are the same in the output as the input (ok not exactly, but for the sake of argument...). But the output and input are not connected directly by wires, only by the magnetic field. So you get electricity from the output coil just because it's picking up the magnetism spit out by the input coil.
Now - what if the input coil has a different number of loops of wire than the output coil? Well, say the output coil has 10 times more loops than the input coil, you can get 10 times more voltage at the output as you put on the input. Similarly, if the output coil has 10 times less loops than the input, you get 10 times less voltage. Thus, when you plug in one of those black wall warts to charge your cell phone, and you present the input coil with 110V (if you live in the U.S. - 220V if you're in Europe) if the output coil has 10 times less loops than the input, so you only get 11V at the output. Thus you have transformed 110v into 11v, which makes it safe to plug in you cell phone.
There are other circuit thingies in the wall wart which change AC to DC - but let's not get wrapped up in that. And secondly, just because the voltage has gone from 110V to 11V doesn't mean you have necessarily thrown away all the other volts. And just because you can create higher voltages with more loops on the output doesn't mean you're getting something for nothing. It's not magic. It actually costs energy to make those extra volts.
The important thing to note is that transformers can make smaller voltages out of bigger voltages, but they can also make even bigger voltages out of smaller voltages by putting two coils of wire close together and allowing them to connect magnetically. Transformers that make small voltages from big voltages are called "step down" transformers, and transformers that make higher voltages from smaller ones are called "step up" transformers.
Tesla coils are step up transformers. They step up the voltage between their input and output by many times.
So now you have two resonant circuits, bouncing along at their natural frequency, and you connect them magnetically and you step up the input voltage by a whole lot.
The result is absolutely gorgeous and undeniably attractive to most males of the species.
This is called plasma. As much as boys love sex and sports and beer and rock and roll, boys love plasma fireballs.
More about Tesla coil structure: The input circuit of a Tesla coil, as with all transformers, is called the "primary". The output is called the "secondary". The primary circuit is driven by high voltage. We're not just going to give it 110V house current - oh no. That's wimpy stuff and wouldn't make lightning.
What we do is use a step-up device to increase house current to high voltage before we put it in the Tesla coil to get stepped up some more. There are various techniques to do this. I use one of the old styles in my Tesla coil. My primary is driven by a neon sign transformer. Neon signs are everywhere, and they require between 5000 volts and 15,000 volts to light up, depending on the size of the sign. Neon sign transformers take 110V house current (in US) and step it up to 5000 volts or more. My NST (neon sign transformer) has an output voltage of 15,000 volts and you only have to plug it into 110 volt house current to get the 15,000 volts. I connect the 15,000 volts of my NST to the input of my Tesla coil.
My Tesla coil primary has 17 loops (called "turns") of "wire". In my case the wire is copper refrigeration tubing, 1/4" in diameter. My secondary coil has a couple thousand turns of 30-gauge magnet wire. Thus my voltage step up is in the range of 50 times or maybe 100 times. (It's not a simple multiplication of 17:2000 because of something to do with the magnetic coupling - but it's a lot.)
My input is 15,000 volts, and I'm stepping that up by about 50 or 100 times. That means my secondary can have over a million volts on it when the coil is running.
Excuse me, but merely typing those numbers gives me orgasmic goose bumps of glee.
There's one other interesting piece of the Tesla coil. Simply presenting 15,000 volts of alternating current to the Tesla coil primary doesn't do very much for a couple reasons. Most interesting reason is that the frequency of the electricity coming out of your wall socket is 60hz (50hz in UK), which is very low indeed. That means the electricity sloshes back and forth out of your socket 60 times per second. Most radio transmission occurs above 1,000 hz. FM radio is in the realm of 100,000,000 hz. Satellites are in the realm of 2,000,000,000 hz. And your typical Tesla coil is tuned to somewhere between 90,000 hz and 250,000 hz.
So how to do you get lots of hertz out of so few hertz coming from your wall? Even the NST with all its 15,000 volts is just vibrating at the same frequency of the wall - 60hz. Well, the input to the coil is a tuned circuit, so if you "ping" it electrically, it will ring like a bell at its resonant frequency. In the case of my Tesla coil, I make the "pings" by connecting the 15,000 volts to a spark gap.
A spark gap is simply two bare wires that are reasonably close together but not touching. There's nothing but air between them. If you raise the voltage between the wires high enough, the air between the wires ionizes, and an electric current flows through the ionic path between the wires making a great snapping sound and a bright flash of white light. It's pretty much the same as an electric arc welder, or a brilliant searchlight arc lamp.
The spark gap in a Tesla coil acts as a switch that opens and closes as the arc forms and then extinguishes several times per second, thereby making electric pulses that act like "pings" to a bell. The inductor and capacitor on the primary circuit slosh the energy from the neon sign transformer back and forth between electric fields and magnetic fields at the resonant frequency which is thousands of times per second. This sloshing creates a magnetic field which is "felt" by the secondary coil and sets up a voltage there, which in turn creates a sloshing between the inductor and capacitor on the secondary at many thousands of times per second.
Now you have very high voltage, very high frequency things happening in the secondary of your Tesla coil. And the way you wire up a Tesla coil secondary is you connect one end of the long coil of many loops to the ground - the earth itself. And you put a metal donut on top. That acts as the capacitor, but also becomes an electrode connected to the sky. So the Tesla secondary is connected to the ground, and the sky. It's not connected to the primary circuit by anything but air and magnetism.
The result is that you're actually vibrating the electric stuff of the planet with very high voltage at high frequencies, and the air surrounding the coil can't take it. It explodes into a plasma of purple lightning around the high intensity electric field.
Then you have your own private lightning storm.
Lightning is loud - and arcs of purple plasma are very loud. They shatter the air with resounding cracks many times per second, so it sounds like the buzzing of a billion unhappy bee ghosts. If you do this indoors, it will leave your ears ringing.
The arcs snake sinuously through the ether, reaching out and grabbing for reality itself, then disappearing just as quickly as if drawn back into the coil like a genie into a bottle.
At first you wonder: will it implode the neighborhood into a black hole? Will it destroy our way of life? Then you wonder if it will burn down your house. And then when the neighborhood is still intact and the house is still standing, you do the classic Tesla coil experiment, which is to hold out a fluorescent bulb and watch it burst to light in your hand as if it is plugged in.
Power is being transmitted through the space between you and the coil to light the bulb in your hand. It happens invisibly. The arcs of lightning never touch you - and you'd be very badly burned if they did. In fact, you are being caressed by the less powerful fingers of electricity that are invisible. All the while purple and white arcs of plasma writhe and roil near the toroid atop your secondary.
Then, if your mind is still clear, you wonder: "if power is shooting out and lighting this bulb in my hand, and lots of invisible electricity is going all over the place, I wonder if power is getting into all my household electronic devices - and I wonder if random shooting power will blow them up?"
If you are smart you now shut off your private lightning storm. You go and check your stuff.
If you are lucky - very very lucky, then everything still works.
More likely, something electronic that you own and love has been touched by the invisible fingers of lightning and is now officially junk.
"It's my creation.
Is it real?"
- Weird Science, Oingo Boingo
People have asked me, "Iceowl, why build a Tesla coil? What are they good for?"
The answer to those questions are: One - "Because I must." Two - "See answer number one."
Tesla coils are potentially lethal devices. Yet there are no recorded deaths via coil. Though it could be that when the morgue receives a steaming electrically fried human carcass, the cause of death is simply listed as electrocution.
So nobody knows exactly how many deaths have occurred due to exposure to coil arcs because the last thing the EMTs are going to suspect is that some enterprising household engineer has zapped himself to death trying to resonate the planet.
Building a Tesla coil takes some ingenuity. A coil project will take you anywhere from a couple weeks to a couple months. It's kind of like trying to build a bicycle from scratch - it's a simple electronic device, yet devilishly complex to tweak to get to function well. If you're used to fixing electronic things you're used to sticking your hands and probes into various circuits while they're running to perform tests. Try that with your coil and you fry.
Coils take a lot of tuning. The primary and secondary have to be tuned to transfer magnetic energy. This requires tweaking of various wires and clips. Touch those clips while the coil is running and you fry. Turn your coil off and approach it before the capacitors discharge and you fry. Approach the toroid thinking - "all the sparks are coming from the front I'll go to the other side."
You get what you get. A bolt hits you - and you burn from the inside out. Skin unbroken and fair, burned mass inside. Just like getting hit by lightning.
And you have no one to blame but yourself.
There are numerous resources for the budding coiler. www.pupman.com is the TCML, or the Tesla Coil Mailing List. Lots of info and experience there. www.4hv.org has a lot of hard-core coilers.
Coilers are a helpful lot. But coilers are not like the rest of civilization. Think of the Society of Creative Anachronism where the jousters use sharpened magnesium-tipped lances. Think of Civil War reenactments with real cannonballs. Coilers exhibit a form of geekyness beyond that suffered peacefully by most geeks. www.geekgroup.com will give you an idea that the mania extends beyond just coiling. I wish it were not - but it's true.
In nearly a year of coiling I've run into exactly zero woman coilers. I can only guess that it's too much *much* for women. We coilers must be so instinctually foul we repel mates. Speaking in evolutionary terms - nature is pissed we weren't eradicated in the 19th century and prevents us from generating spawn.
Coilers may be ostracized and repellent but we are a helpful lot when it comes to assisting our bretheren.
Coilers have offered to come to my home to assist in coating my secondary with polyurethane. They have offered to teach me how to tap bars of steel. They have given me e-mail explanations running into tens of pages on subjects like: asynchronous spark gaps versus synchronous spark gaps. The correct MOVs for your Terry filter. The virtues of DRSSTCs (Dual Resonant Solid State Tesla Coils). How to spin aluminum to make topload toroids. Where to get your own pole pig. (A pole pig is the kind of transformer you see mounted on the sides of power poles. They're owned by the power company. If you can get your hands on one, it's a coiler's Valhalla. With a pole pig you can make a mightily powerful coil with lightning bolts that span entire backyards.)
It took me about two months to get my coil from concept to first light - that is, my first purple sparks.
Coiling is an obsession that links us to the guy who first conceived the earth could be resonated by human kind. It's strange and off-putting to the family and friends of the coiler. I show my coil to everyone. I've had reactions ranging from revulsion and fear, to sheer ecstasy from friends.
In the twenty-first century the Tesla coil does nothing. Serves no purpose. Tesla himself kept building bigger ones, sure that sooner or later he'd break through. But break through to what? What the hell was he really thinking when he felt his dead mother was being channeled through white doves with radiant red eyes?
We don't know. But we're with him. There's a zen electrical engineering spirit connection across the decades.
We keep coiling, and not one of us quite knows why.
One day, when I was well into tuning my first big coil I asked the pupman mailing list - "Ok, so tell me. Once you've got your coil tweaked and power maxed, and the purple lightning is 10' long and dangerous to all your neighbors, what do you do with the thing?"
Came the reply: "Put it in the corner of your garage and get a pole pig and build a bigger one."
Latest video of my coil is at http://yfrog.com/2opropellerrunz
It's a lot more threatening in real life.
He who created me filled me with sparks and lightning.
And therein lies my dialog with God.
Update: Upon conference with experts and doing the math, it turns out the max voltage in my secondary is actually closer to 630kV, than a megavolt, as I postulated in the text above. Still pretty high voltage, but not quite the million volts I thought. Well, back to the drawing board for more power.
Also, if you want to get really technical about it, my poetic statement about radio vibrating the earth is not as true as Tesla would have liked it to be. If one NEEDED to vibrate the earth (or any other planet, for that matter) to make radio work, there would be no such thing as radio astronomy or satellite communication. However, as a young man building my own radios, and as a ham today who still transmits over wires, I am still amazed how we simply neglect the fact that we (nearly) always include an earth ground in our antenna system to make it work well. Yes yes yes. We include the ground because it provides a zero-volt reference and stable point. But durn. It still makes earth part of the antenna system. Gee wiz, guys.