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The Six Pack Tesla Coil - Photo: Craig Newswanger

The inventions of Nikola Tesla are all around us: radio, AC power, fluorescent lighting, and remote control devices are just a few. Tesla was ahead of his time, in many ways, and his work with high-frequency alternating currents has inspired engineers, scientists, geeks, inventors, artists, dreamers, and (frankly) quacks for more than a century. The Tesla coil is particularly fascinating because of the elemental, visceral nature of the electrical arcs it produces. It’s like watching lightning strike. Tesla himself used these spectacular effects to wow audiences with the wonders of AC electricity.

Six-Pack Spark - Animation: Craig Newswanger

Since Tesla’s time, hobbyist “coilers” have made many discoveries and improvements to the basic design, achieving bigger sparks with less input current. With the advent of plastics, improved wire insulators, and a better understanding of theory, the modern Tesla coil looks very different from the original. The basic circuit and concepts are the same, but almost everything else is different.

One thing that is the same, in this project, is the capacitor design. Ours is made from glass beverage bottles, very similar to the champagne bottles that Tesla himself often used.

Safety

Along with the wonder and awe of a Tesla coil comes a significant level of danger. It is the responsibility of anyone who builds or operates a Tesla coil to ensure the safety of themselves and anyone who might come near, either during a demonstration or inadvertently. Whenever you approach the coil, unplug the power cord and hang on to the plug end as you work. If the location is not entirely secure, consider adding a safety key switch so you can pocket the key.

A Tesla coil’s high-frequency electrical field can damage or destroy cardiac pacemakers/defibrillators, hearing aids, and other biomedical devices. I’ve never seen this happen, but it’s imperative to warn audiences of the possibility before demonstrations.

Similarly, the Tesla coil can damage other sensitive electronics nearby. I have personally destroyed a stereo receiver, a garage door opener, a wireless phone system, and two PC network cards. It again falls to the maker to make sure that the coil is operated at a sufficient distance from any valuable electronics, flammable materials, pets, and of course small children.

There are many hazards to be aware of and in this single article we cannot cover them all. If in doubt, contact a nearby Tesla hobbyist or an engineer experienced in high-voltage devices and electrical safety. If you have any doubt about your abilities in this area, don’t attempt the build. Period!

DANGER!

  • Assume the capacitor is always charged. Capacitors can retain a charge for days. No matter what anyone else tells you, always safely discharge the six-pack capacitor yourself, and jumper it with a sturdy clip lead before touching any of the components. Keep the jumper in place when you’re not operating the coil.
  • Do not operate the coil around small children or animals.
  • Operate in clear spaces at least 20 feet from flammable materials. The electric field generated by a Tesla coil can create sparks within furniture and in the ceilings of structures. Sparks can ignite combustible solids, liquids, and especially vapors.
  • Do not touch the NST terminals. Both sides of the neon sign transformer are “hot.” Some NSTs have exposed primary terminals carrying line voltages. Current at the NST secondary terminals is usually low, but the voltages are high enough to cause painful shocks and secondary injuries from loss of motor coordination.
  • Do not stare at the sparks. Electrical arcs in air emit ultraviolet light that can damage eyes and skin on extended exposure. Clear polycarbonate sheet can be used to shield the spark gap and block most of the UV generated by the sparks.
  • Do not operate the coil without proper ventilation. Electrical arcs in air produce ozone, nitrogen pentoxide, and several other nitrogen oxides that are hazardous to health. Note that nitrous oxide is not produced.
  • Do not operate indoors without ear protection. This Tesla coil can produce hazardous levels of noise. It’s less of a problem outside, but indoors the sound is loud.

How It Works

Fundamentally, a Tesla coil is just a transformer, like the one that steps household electricity down to a voltage suitable for charging your cellphone. All transformers have two coils — a primary and a secondary — and most of those you encounter in daily life transform voltages based on the different numbers of turns in each coil. A Tesla coil works on a slightly different principle, creating the very high voltages needed to produce long arcs in open air mostly through the inductive difference between its primary and secondary coils.

More specifically, a Tesla coil is an air-core, dual-resonant transformer. Air-core means that the coils are hollow, rather than wrapped around metal or ferrite cores as in common transformers. Dual-resonant means that the circuits containing both primary and secondary coils are tuned to “ring” at the same frequency.

coil-schematic_v2

The combination of the primary coil (an inductor) and the capacitor (the bottles, in this design) create a resonant LC circuit that “rings” at a particular frequency. This is called the tank circuit.

Since both tank circuit and secondary coil are tuned to the same frequency, they pass energy back and forth when “struck” with an electric impulse. Imagine striking a bell near a drumhead tuned to the same note.

Tesla Coil Anatomy Diagram v2

The electrode on the top of the coil is called the top-load. You can imagine the top-load as a capacitor with one side connected to the secondary coil, the other side connected to ground, and the air all around as the insulator between the two “plates.”

This Tesla coil is designed to be powered by plugging into a wall outlet, and uses a neon sign transformer (NST) to step 120V AC up to about 10kV at 25mA–30mA. Solid-state voltage converters are not appropriate for this application, nor are modern NSTs manufactured with ground fault protection circuitry. You’ll need a used or old-stock NST; fortunately these are not hard to find on eBay and, sometimes, Craigslist. Neon shops may have old units hanging around.

Designing the Six-Pack Coil

The math for designing a Tesla coil is not especially difficult, but it can get tedious. Fortunately, coil hobbyist Bart Anderson has paved the way for us with a wonderful JavaScript program called JavaTC. If you’re interested in the math, Bart’s site classictesla.com has resources and links that will lead you as deep as you want to go.

JavaTC was instrumental in designing the six-pack Tesla coil. The output text file describing the six-pack coil is available here.

Spend some time playing with JavaTC, tweaking the specs for the six-pack coil, and you’ll quickly develop a feel for how the various design parameters affect one another. If you have to use a different transformer, make a different top-load, use a different wire gauge or any other major changes, you can use JavaTC’s auto-tuning feature to understand how to modify the design.

Build Your Six-Pack Tesla Coil

First-time “coilers” should follow this build as closely as possible. Use a neon sign transformer rated for 9kV at 25mA, strive for a main tank capacitance as close to 0.005µF as possible, and do not substitute parts if it can be avoided.

Plan your build carefully before you start. Don’t just jump in and start building without reviewing every aspect of the design. High-frequency resonant circuits are very sensitive to small changes, and poor attention to planning can make the tuning process very frustrating.

Craftsmanship is also important. Take your time, particularly with the secondary coil, where a single crossed winding or a skimpy varnish job can easily result in a nonfunctional or very short-lived coil.

Good design, attention to detail, and patient craftsmanship will pay off with a long, noisy spark that draws oohs, aahs, applause, and admiration from everyone who sees it.

REQUIRED RESOURCES (ONLINE):

EXTRA RESOURCES (ONLINE):

Craig Newswanger

Craig Newswanger

Craig Newswanger is a behind-the-scenes member of ArcAttack, the musical Tesla coil crew. He has been an Army photographer, a Disney Imagineer, and a maker of laser light shows and holographs. He built his first computer from a kit in 1975; today he builds things at his Resonance Studio Workshop in Austin, Texas.


  • Jordan

    Wow, wonderful project and step by step instructions.

  • Jason

    For the NST, is “Not UL 2161″ at all similar to “non GFI”? From what I can tell the two look related.

    • https://www.facebook.com/craig.newswanger Craig Newswanger

      You basically want an NST without a ground fault detector.
      There are a few listed on ebay. Just look for an older transformer that does not have a reset button.

  • Mike C

    Looks like the schematic for the Terry Filter does not quite match what was built. The varistors are in series with each other and only connected with the RC ladder at the endpoints. The schematic shows that the each resistor, capacitor and variac are in parallel. See picture in step 28 for comparison. The following schematic seems to match what was built: http://www.twotowers.com/images/NSTFilt.jpg The magazine version has the same schematic as above.

    • https://www.facebook.com/craig.newswanger Craig Newswanger

      Thanks for the catch, Mike.
      I sent a note to the Make editor to fix the web version.
      Unfortunately its in the print version.
      Cheers
      Craig

      • Rich

        so what does the correct way look like?

  • Jason

    Is Green Foam somehow critical for the top load? The part number listed comes up as ”
    12″ Styrofoam Extruded Wreath, sku# 601211, Brand:STYROFOAM Brand Foam” at my local “BIG BOX” craft store.

    • Brian

      Hobby Lobby has some wreath forms in the floral dept. made of dense green foam that are close, but not truly toroidal–they’re like a cross section of a large hollow cylinder. In another part of the store you’ll find the white polystyrene toroids like the one Craig used. It’s their item no. 601211, bar code SKU 46501 00120. They cost four and a half bucks and work quite well.

  • Jason

    Anyone have any luck finding the Flat-top pipe caps specified above?
    My local LOWES stores have boxes of caps with the exact numbers on them – however the parts inside are totally different numbers and are round.

  • Eric Anderson

    I will play with the online design tool but a quick question before I start. My transformer is 12kV but 60 mA, not 25-30 mA. Is this a non starter for the basic design of this project? What will I need to modify?

  • http://how-to-build-a-tesla-generator.blogspot.co.nz/ Patrick

    Wonder guide here, I think its totally possible to buidl your own tesla coil and run it from your own home. Ppl are trying to find ways to save on electricity bills. check out this link and learn how to build your own tesla coil for your home! http://how-to-build-a-tesla-generator.blogspot.co.nz/

  • Doc

    I think you calculated the total capacitance based on a series of caps not a parallel wiring

  • dbell5

    A couple of questions/comments on the Terry Filter:
    The BOM calls out for 14 sets of components, but the schematic only shows 12. This could cause some confusion for folks.
    Also, if I read the build step (27) correctly, it does NOT connect the junctions between the MOVs to the RC pairs, but the schematic does show those connections.

    Dave

    • brandon

      You are correct, the wiring schematic for the terry filter is incorrect. The way it is built and the way the schematic shows do not match. However the build instructions are correct.Again the schematic is incorrect on the number of MOV’s. The BOM is good though. I know this because I just built and tested the filter today. The rest of the instructions are great! Makes it so a layman like me can build such a contraption

  • Russ Angel

    I know someone that has built a tesla coil in their front room,they take great pride in showing it off without a thought for safety or consideration for others.I will be sending them this informative article.

  • Kait

    Is this type of Tesla coil able to emit varied pitches and play music like a singing Tesla coil?

    • brandon

      No, a singing tesla coil is more involved than this. However i do believe some of these components made in this can be used for a singing tesla coil

  • azgolfrat

    what is meant by “2C” of salt? 2 cc’s?

  • azgolfrat

    ok, sorry, two cups of salt got it.
    my capacitors continue to read .4 nf instead of the expected .83. I had to use bid light lime bottles, which are 12 oz long neck bottles. Perhaps the glass is thicker, which would lower the capacitance. This might also move A in the wrong direction. Anyone else see this problem? I’ll check the multimeter calibration also.

  • brandon

    This thing was a blast to build! Thanks for the tutorial. Works pretty well too, I do however see pink streams instead of a blue or purple. Just out of curiosity why is this? I am strictly speaking on running it without a nearby ground for it to strike.
    Oh and I tried using a more of a cone shaped primary coil, still used these original combs, just dropped it down a 1/16th of an inch per wind

  • terre

    I would love to see how your shop is organized sometime. Looking over the parts list, I believe I do have most of these items, including some contraption that actually will wind wire at different speeds endlessly, but usually can’t put my hands on enough of them to start much less complete a project. My passion is to encourage others to find theirs’ by supporting and enabling- so far not too successfully. I feel that if I reach the right person in education, it may still come together, as I have a space I have offered for free to makers (declined!). There must be others who need a garage/yard/ house to experiment in in Tampa…..

  • Max

    What happend to the build instruction one could see on this site a few days ago?

    • ccouden

      Hi Max, sorry for the confusion. We moved to a new web hosting service this month and are still ironing out some bugs. We’ll have the project step back up as soon as possible!

      • Max

        Thank you for your respons, then we know. We have had a lot of help from this site while building our own prototype.

  • Andreas Wright

    go to – eco inplix – google it and learn more

  • xaasda

    Type in Google ‘ inplix eco ‘ and learn more

    • Eve Cobbler

      thx for advice