Build Your Own Tesla Coil

screenbert writes "Ever wanted to keep stray dogs or neighbors from trampling your backyard, but just couldn't find the system to really deter them? Well this site shows how they built a bi-polar Tesla Coil system. I've always loved the Tesla coils on C&C when they'd zap the units as they went by. "

Comments

Re:Correction on the concept of Tesla Coils

[Arethan]

Where did you ever hear that?
Seriously, Tesla coils really were always about arcing electricity. His original idea for Tesla coil usage was wireless transportation of electricity. Basically, if you crank the volts enough, you can arc across the atlantic ocean. At least that was the idea.

Yes, Tesla also did some studies on structural harmonics. And yes, he did the structural harmonics work long before he came up with the idea for Tesla coils, but aside from being the brainchild of the same man, the two were never linked in any other way.

Also, I must say that I more enjoyed his work on structural harmonics. Shaking bridges and collapsing condemned buildings was all well and good, but the nutball had the idea that he could crack the earth in half if he used enough dynamite and timed it correctly. Good thing he didn't have the resources to try that one out. Tesla was crazy enough try it, just to see if it would work.

Science Fair

[inonurmi]

Back when I was about 13, three of us entered our school science fair with a tesla coil we constructed.

My father found an old Popular Electronics (or something) magazine from his hobby days with some plans. We hand wound the voltage stepup coil, made condensors out of perspex plates and tinfoil, and borrowed a Ruhmkorff Induction Coil from school.

The unit was powered by a car battery and could spark about an inch and a half.

We put two bent copper rods for the spark to jump between. The spark would run up and down between these rods like old mad-scientist movies.

It felt pretty cool to put a finger in the spark and watch it jump straight through, with only a weird tingling sensation.

Aaah the electric shocks, the smell of ozone, the burns and blisters - God I miss science fairs.

The tree pics at the bottom of the page

[Xtraneous]

Did anyone else notice that if you click on one of the three pictures at the bottom of the pages, it brings up a new page with that image? Try clicking on segments of that image... Interesting way to have an online photo-album. Seriously, has anyone else determined what relevence the colors have to the pictures, and where you click versus what type of image you get?

Re:Just pretty lightning.. not effective, here's w

[Monkelectric]

and theres a damn good reason its 100ma,

(from Electrical Saftey Engineering 2nd Edition)

Physioligcial Reaction to Current
3-5 mA Barely Perceptible
35-50 mA Extreme Pain
50-70 mA Muscle Paralysis
500mA Heart Stoppage (books word not mine)

Besides, dialectric strength is like voltage*thickness right? So a high current would be a waste of electricity ... assuming you DONT want to kill stuff :)

Keep your credit cards a few km away.

[Christopher Thomas]

I've wanted to build a Tesla coil for years.

The reason I still haven't is that they're about as good for electronics and magnetically sensitive media as a lightning strike. The intermittent arc gives off *vast* amounts of RF crud, which will induce currents in just about anything electronic and degauss anything magnetic nearby.

Your computer case will not save you if your machine has drive bays. All connected wires (modem, network, power) will also act perfectly well as antennas penetrating the case's shielding.

Credit cards and bank cards generally aren't shielded at all :).

Set up those Faraday cages before building anything like this.

Here's an easy Tesla coil recipe

[MillionthMonkey]

You can easily make a Tesla coil if you have an old busted TV to rip apart. In general, the older and bigger the TV is, the better. And color TVs are better than black and white. This won't be a *great* Tesla coil, but it will throw a spark a few inches long and you can do all the standard Tesla coil tricks with it (St. Elmo's fire, etc.) without investing too much time or money.

Yank the flyback transformer out of the TV, and discard all its primary windings. Keep the big high voltage secondary winding (the one with the zillions of turns). It's usually encased in rubber and may look like a big rubber wheel. Its main lead has really thick insulation and connects to the side of the picture tube (where it looks like a stethoscope). The other lead (the ground) won't be as heavily insulated.

The only other parts you need are two NPN power transistors (2N3055), two 5W power resistors (20 ohm and 200 ohm), some wire, and a good supply of DC current (12-24 V). The circuit is a piece of cake. The first time I did it, I put the whole thing together with alligator clips.

This circuit has two primary windings around the flyback transformer core. The power winding is 8 turns, with a tap in the middle. The feedback winding is smaller (4 turns), also with a tap in the middle. The power winding leads connect to the collector leads on the transistors, with the center tap going to the +24 V DC power source. The feedback winding leads connect to the gate leads, with the center tap there going to +2-3 V DC (connect the resistors in series across the DC power to get the lower voltage in between). The emitter leads are grounded.
As current flows through one transistor, the changing field in the core induces a voltage in the feedback windings that turns that transistor off and the other one on. Then current flows the other way, and the same thing happens in reverse. So the circuit tunes itself to the proper frequency. But it also means that the first time you power it up you run a 50-50 chance of connecting the leads to the wrong transistor gates, in which case you get a stable DC circuit. So if it doesn't work the first time, try exchanging the gate leads.

This circuit is fairly well known, and doing a Google search for "flyback" and "Tesla" I found a schematic for it right away. The guy mentions on that page that the transistors get really hot and he is not kidding- they do. Don't leave it running for more than a minute without a heat sink. The RF noise generated by Tesla coils is incredible so expect to generate some interference. They make lots of smelly ozone. And if you let a spark go through paper, you can start a fire so be careful.

If you're lucky you can get 20-30 kV, which throws a purple spark a couple inches. (I only got about 4 kV out of mine- the spark was about a half inch long.) Pick up a neon bulb when you're at Radio Shack- these light up if they're around. The effect on a candle flame is interesting. Don't stick your bare finger near it because the spark does hurt if it hits unprotected skin. But if you hold a metal object and use that to touch it, you don't feel a thing (it's high frequency AC). Cool tricks include having sparks jump from the coil to a metal object in your hand, having sparks jump from a metal object in your other hand to ground (even a lousy ground), and having fluorescent tubes glow softly if you hold them in your other hand. If you touch one terminal of a fluorescent to ground then it will glow brightly between that end and the place you are holding it, like there are Orcs nearby.

An interesting picture of Tesla, under active coil

[afflatus_com]

If you are interested in the picture on the website, here is an additional photograph of Tesla himself in the same pose, only his coil is giant-sized, and the arcs fill a warehouse. He is sitting reading a book under the giant coil with the million-volt sparks fly overhead.

Note that for this photo to work, it had to be reexposed several times for all the lightning forks to be catptured (and he sat at the end).

Picture of Tesla under his giant active coil

The noise genereated from the coil in the photo could be heard 10 miles away.