3-inch Tesla Coil Page

My First Tesla Coil.

Here are pictures of my old 3-in tesla coil at early and later stages of development.

Specs:

Primary: 1/4 in copper tubing, shallow cone.
Secondary: 300 turns red 20 AWG magnet wire, 3-in PVC form.
Spark Gap: single static with blower
Tank Capacitor: 9 nf pickle jar capacitor array
Transformer: 10 kV OBIT stack (69 ma)
Top Load: 3*15 toroid
Input Voltage Control: None
Ballast: Current limited input transformers.
Power Factor Correction Capacitors: None.
Filters: None
Max arc length: 24 inches (est).

Schematic:

Click here for the technical details of my coil, if you are the type of person who likes numbers.
Tesla coil schematic

Tank Capacitors:
These are some pictures of my homemade leyden jar type capacitors which I made out of large glass jars, aluminum foil, duct tape, a copper pipe, and salt water. Currently they are wrapped in electrical tape and coated with polyurethane for insulation (insulation makes the capacitors more efficient) the tightly fit foil receives the charge more efficiently, and I added acetic acid, hydrochloric acid and magnesium sulfate conduct current better (although over time, they really corrode my electrodes, this may effect capacitance, I do not know). A layer of mineral oil floats on top to hold in the charge (more insulation, for the solution this time, not the glass), I use mineral oil because it doesn't burn real easily which is essential, no fumes which is preferred, non toxic so the environment is happy, and it is dirt cheap, which to be honest, is why I really love the stuff.

Transformers:

These are some of my transformers. They are called OBITs, for oil burner ignition transformers. To demonstrate their power I have put a video of a Jacobs ladder produced by four of them. I have acquired eight of these transformers, and if they all worked correctly, hooking them all together would yield a pretty massive Jacobs ladder. Being the adventure-some person I am, I have used the Jacobs ladder plasma stream to roast marshmallows (not really reccommended, see below)!

Jacobs Ladder

The specs of these transformers are 120V in, 10,000 volts out limited to .023 amps out. With two wired in parallel, the amperage is limited .046 which is twice as high. With four of them hooked together, they put out 10KV at .092 amps, which is a harmful if not lethal dose I assure you. With all eight of them you are looking at 184ma which will really mess you up good. A piece of wood in the "Jacob's ladder" from just 3 of these transformers, instantly catches fire! It is interesting to note, the color of the plasma stream changes from pale white-yellow to a brilliant fire orange, which is because matter from the wood enters the streamer as it passes through and burns, think about what would happen to your finger in there! As I said, I have used the Jacobs ladder plasma stream to roast marshmallows! This is not exactly safe, but I used a fiberglass rod (which is an insulator), so I was not harmed electrically, anyway the marshmallows instantly caught fire, and cooked through in about 2 seconds, that is how hot these things are. The other reason I do not make a habit of this is that tiny metal particals are liberated form the electrical connections from the plasma, so my marshmallow was laced with copper, this is not healthy.

Primary Coil:
This is my primary coil. It is 1/4-in refridgerator tubing. I did not use a coil form or support of any kind, it is just sitting there.

Secondary Coil:
This is the top of my secondary with no top load. It is 20 gage enameled copper wire on a 3 in. PVC form, the top is 12 gage house wire threaded through some ceramic insulators. I use a metal support beam for an RF ground.

Top Load:
     The largest Top load my coil is capable of driving is a 3-in by 15-in toroid, I need three pickle jars caps to drive it, but it produces maximum arcs in that configuration, up to 25-in long.

Wireing:
     I use 14 AWG wire rated at 15kV. Honestly it is probably to thin, but it works ok I guess.

Spark Gap:
     The spark gap is what allows unimpeded transfer of energy from the capacitors to the primary, this one is currently a bolt between two brackets, changing the distance between the terminals changes the breakdown voltage of the gap, which majorly effects performace.

I may enclose the SG in welders glass for view ability but no radiation exposure. I have added a quenching fan to my spark gap so the arc is distinguished quickly, this means that the spark gap stops at an earlier notch, leaving more energy trapped in the secondary!

Before I continue, and show the really cool pictures, I should mention that these are really fascinating devices, but they are indeed dangerous. See my Safety page for details. And with no further ado, I give you some cool pictures of my coil in action!

Pictures:

These are small sparks generated when the coil is turned on first with with no, and then small top loads.

Notice the larger top load makes a bigger spark, that is because it delays the time before secondary breakout, resulating in a higher voltage. Theoretically this is not true, as a larger top capacitance reduces peak voltage, see my equations page, But in reality, a bigger toroid is better, as long as the power level of the coil is strong enough to have breakout. Below my coil, seen in the background, is lighting a fluorescent light bulb in my hand by sheer magnetic field. It also affects the TV upstairs, lights up several of the LED's in the house, and disconnects the Internet, in my second story bedroom. I may build a "Faraday Cage" to shield the rest of my house from EM radiation, so we can peacefully use the Internet and the coil at the same time, or I may just run the thing when everybody is offline (my new coil is run outdoors anyway, so no worries mate!). Filters on the low voltage side help a lot as well, these will be installed when I start messing with the thing again.

Some medium size arcs (medium for this coil), that wisp is about 6 inches long.

When the arc is pulled to a grounded wire, it becomes much more intense, but a little shorter (again, mind the UV exposure).

Bigger top load, bigger sparks.

Here my coil is grounded to a ground wire, it appears my sister who operated the coil while I took the pictures is getting struck in the face, but rest assured she is a few feet away, the camera angle does that, but the picture gives you a good idea of the size of the arcs (the toroid is 15 inches in diameter), and gives you a respect for the danger involved here, I have moved the "on" switch farther away, because although my sister got lucky, I personally have been nipped more than a few times. The grounded intense arcs have now reached a length of 12-13 inches, with up to 15 with a breakout point, but the free flying arcs occasionally struck things exceeding 14 inches away (including my hand) and are estimated at over 25in. in length.

Videos:

Here are some videos of my first generation Tesla coil in action. The last ones are the most recent and therefore the largest output, but the others are still worth looking at. If you have any questions about this project (like how to build one yourself) e-mail me and I'll get you started, I can tell you where to get materials you need, and give you fine tuning pointers, and of course tell you how to keep yourself from getting killed (which is a very real threat even with a small coil). And remember, you are only "finished" when you can step back and truly fear what you have created.

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The coil making sparks.

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More Small sparks.

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The flourescent lightbulb trick.

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More respectable Sparks.

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Also, more respectable sparks.

Home, Hobbies, Tesla coil

Scott Bogard. 2007