Shoot foot-long bolts of lighting through the air, light fluorescent tubes without wires, and power your other high voltage experiments with the aid of this tabletop-sized Tesla coil! Once the parts have arrived, it comes together in about a weekend, and for less than $200 even for those without a big bin of spare parts. I built this coil for fun over a few weekends during 10th grade, juggling eigenvalue problems and European history for drilling and soldering high voltage components.

The key to this coil's performance on such a tight budget is that all of its components are designed to work well together. Using some basic concepts from AC circuit design, the components are matched to perform well without requiring massive amounts of power. Some "coilers" use microwave oven transformers to pump kilowatts of energy through poorly matched circuits, resulting in large losses and mediocre performance. This instructable will show you how to avoid making such mistakes and how to properly design a spark gap Tesla coil.

UPDATE: This Tesla coil is now on sale on eBay for a starting bid of $99.99, less than the cost of the materials! http://www.ebay.com/itm/250-000-Volt-TESLA-COIL-Assembled-2-Foot-Tall-8-12-Sparks-/180826521311?pt=LH_DefaultDomain_0&hash=item2a1a19bedf

For contest entry details on this instructable, see step 10.

UPDATE: New diagrams for primary capacitor, primary coil, and spark gap construction have been added. Click the top left information icon to view them in full size.

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(I named it the "Valentine's Day Tesla Coil" in this video because I finished it over Valentine's Day weekend 2011)

To read more about this project, visit my website: http://xellers.wordpress.com/tesla-coils/sgtc-ii/

Step 1: Theory and Warnings

Although I don't want to spend too much time talking about exactly how a Tesla Coil works, I think that a rudimentary description is worthwhile given the amount of misinformation that exists on Instructables and elsewhere on the web.

Essentially, a Tesla Coil is a type of alternating current transformer that operates almost like any other (transformers are found in many electrical and electronic devices and are used to step up or step down the voltage of an alternating current signal). However, it relies on the principle of electrical resonance in order to massively increase the voltage of the alternating current signal.

One comment misconception is that the primary circuit (capacitor and inductor) "amplify" the signal from the high voltage transformer and that the ratio of turns between the primary and secondary coil is then used to create a high voltage. However, this is not quite the case.

During each alternating current half-cycle, the transformer charges the primary capacitor until the voltage across it exceeds the breakdown voltage of the spark gap. At this point, the capacitor and primary coil are connected and momentarily form a series LC circuit. Because the capacitor has an initial charge from the transformer, the LC circuit will oscillate much like a stretched spring will move back and forth once it is released. In fact, the differential equation describing a stretched spring moving back and forth with friction is virtually identical to the one that describes an LC circuit with an initial charge on the capacitor oscillating with stray resistance in the wires of the circuit.

These oscillations can exhibit three different types of forms: overdamped, critically damped, and underdamped (second image). In the overdamped condition (high damping factor, ζ), the current decays without crossing zero, while in the underdamped condition (low damping factor), it crosses zero many times and oscillates before decaying. This last condition is the one we hope to achieve in our coil.

Once the circuit is oscillating, the rising and falling magnetic field around the primary coil will induce current into the secondary coil. The goal is to maximize energy transfer between the primary and secondary coil and minimize energy lost to heating as a result of stray resistance.

The secondary circuit also acts as an RLC network. Its impedance, or resistance to an alternating current, will change as a function of the frequency that the primary circuit oscillates at. The third picture shows this relationship. If the frequency of the primary circuit matches that of the secondary circuit, then the amplitude of the secondary voltage will increase dramatically because the secondary impedance will be very low. Once the oscillations in the primary circuit have decayed, the transformer will switch polarity and recharge the capacitor, causing the cycle to repeat. This is similar to what happens when you try to force a sping to move back and forth; if you're not at the correct frequency, then it resists your push, but if you do manage to hit the right frequency, then even a small application of force can quickly increase the amplitude of its oscillations.

If you want a more mathematically rigorous explanation, be sure to take a look at this paper: http://tayloredge.com/reference/Machines/TeslaCoil.pdf There's actually quite a bit more going on than I made it sound like, so consider taking a look even if you're going to skip the mathematics.


That said, I want to give a few warnings to anyone who is considering this project. Tesla coils and other high voltage devices are extremely dangerous in the wrong hands and can easily injure or kill anyone who does not practice proper high voltage safety. I am not responsible for any accidents that may occur as a result of these instructions.

I also do not guarantee that your coil will work or that you will be satisfied with the results. Only attempt this project if you are willing to face failure on your first attempt and don't cut corners - if that capacitor has to be rated to a certain voltage or that wire has to be enameled, don't try to get an inferior product for less. It's better to wait and save up for the higher quality part than to end up with a pile of cheap, burnt out components.

Be sure to read the entire instructable and completely understand what you will have to do before attempting this project!
<p>Very Cool!!</p>
<p>i am having problems finding this cap,i realize the build was a few years ago but the cap i am finding with same rating is $7 a pop not $35 for 50 any help would be appreceated .i have buit coils but all junk box home brew and it has been a while check them out_---- </p><p>https://www.youtube.com/playlist?list=PL4bg9_mWxgkDxiVmtz3Gvc9RVgDHn5YgX</p><p>ch</p>
<p>i am having problems finding this cap,i realize the build was a few years ago but the cap i am finding with same rating is $7 a pop not $35 for 50 any help would be appreceated .i have buit coils but all junk box home brew and it has been a while check them out_---- </p><p>https://www.youtube.com/playlist?list=PL4bg9_mWxgkDxiVmtz3Gvc9RVgDHn5YgX</p><p>ch</p>
<p>i am having problems finding this cap,i realize the build was a few years ago but the cap i am finding with same rating is $7 a pop not $35 for 50 any help would be appreceated .i have buit coils but all junk box home brew and it has been a while check them out_---- </p><p>https://www.youtube.com/playlist?list=PL4bg9_mWxgkDxiVmtz3Gvc9RVgDHn5YgX</p><p>ch</p>
<p>These are the pictures! And some videos! but i think it would be better if you give me your email adress or you`d write to mine( komaromigy40@gmail.com) or to my facebook, https://www.facebook.com/gyurika.komaromi !!! I hope you can help me ( the top load fell off but it works pretty much the same :/ ill glue it back )</p>
<p>in these videos i run the zvs on 12 v but i have a 24 v psu too. it works pretty much the same with that too!!!</p>
<p>These are the pictures! And some videos! but i think it would be better if you give me your email adress or you`d write to mine( komaromigy40@gmail.com) or to my facebook, https://www.facebook.com/gyurika.komaromi !!! I hope you can help me ( the top load fell off but it works pretty much the same :/ ill glue it back )</p>
<p>These are the pictures! And some videos! but i think it would be better if you give me your email adress or you`d write to mine( komaromigy40@gmail.com) or to my facebook, https://www.facebook.com/gyurika.komaromi !!! I hope you can help me ( the top load fell off but it works pretty much the same :/ ill glue it back )</p>
Hi, i plan on running my sgtc with a 40-50kV zvs driver but i dont know the current and frequency of the output :( what can i do tp calculate the primary capacitors capacitance needed to run my 40cm tall 720 turns secondary with 6 turn flat primary?
You need to either use a DC flyback transformer or add a rectifier to the output of your ZVS driver. You can't run a spark gap Tesla coil off of a high frequency AC source.
Wow dude, you know a LOT about tesla coils, thanks for the advice, i managed it to get it running it lights up cfl bulbs, a little bit...and neons but the sparks are like max 1cm from a wire, i am using leyden jars, cuz this is a school project and i want to prove i can make an inexpensive tesla coil, so far i have added 4 and it got better...tweaked it a little bit, in java tc it said i need 0.9cm turn spacing on the primary coil...but everybody uses theirs without turn spacing, so far have 7 turns, java tc &quot;said&quot; I need 6 with six it is way worse...maybe I should put some leyden jars in series too, to increase voltage of the caps... I plan on adding a 12 v motor and make a rotary spark gap...what do you think...i will make a whole bucket of vine bottle leyden jars like 10 and then work with that xD maybe that'll help :/ you said i need 1.5x or higher voltage rating of the caps as my psu, in a video the guy said these are rated for at least 30-40kV i think it was right...when i make arcs with them if i stretch the wires more than 5 cm the bottles break... Anyways thank you, you helped me a lot! (the specs of my TC : 40cm high 5cm diameter, 0.5mm enameled copper wire, aprox 730-750turns, primary adjustable i think ill make a 8-10turn on as it seems it works better with more turns..., 2mm copper wire, insulated, 12x12 aluminum globe(plastic ball wrapped in aluminum, you said i could use painted balls or glass globes, which would work better, if ill find a lightbulb pr smth rigid and big enough ill make it work! ) You are the real mvp, cheers!
<p>As long as you're not arcing between the primary and secondary or creating racing sparks in the secondary, the exact geometry of the primary doesn't matter that much. I recommend designing for a coupling factor of roughly 0.2 and then tuning by hand. Given how little capacitance homemade leyden jars usually have, more capacitance should be helpful as it will increase the band energy. I don't think you should worry about a rotary spark gap; that won't help you unless you're having trouble quenching the primary gap, which is an issue you only start running into at much higher power levels on the order of 1kW. Also make sure the aspect ratio of your secondary is not too high, the biggest problem I see in many first coil designs is a secondary that is too thin and tall. I could give better suggestions if you posted some pictures.</p>
<p>*bang energy</p>
The zvs driver is DC, it is a zvs flyback driver, sorry for my misexpression, so could you please help me with the capacitance?
<p>With a DC source, the output impedance of the source will limit how fast you can charge the primary capacitor (it's an RC circuit) and therefore determine the firing rate of the spark gap as a function of how far apart the electrodes are spaced (it's a relaxation oscillator). You can estimate the output impedance of your flyback using the power draw when it's arcing and the maximum output voltage when it's open-circuited (this is called a Thevenin equivalent circuit). Then, you can pick a capacitance based on how fast you want the spark gap to fire and how far apart you want to space the gap (how high of a voltage you charge to). I would recommend designing for 120Hz break rate just as in a 60Hz line-driven SGTC. Also, I would recommend using a much lower voltage source on the order of 10kV because you'll want your capacitors' voltage rating to be 1.5x to 2x the peak voltage you expect from the source.</p>
I forgot to mention that the sparks are really thin... Maybe the wires I am using are too long, thus decreasing performance?
Hey man, i have a question i need to have a 1 to 5 aspect ratio for my secondary or not?
No, the recommended aspect ratios are just rules of thumb. I suggest you start with a design based on some rules of thumb and then put it in JavaTC to tweak it however you want. Remember to add extra primary turns to detune your primary to compensate for streamer loading.
But i tuned it in JavaTC but it doesnt work FTW i even tried to flip the primary and then try all over again and still doesnt work :/
<p>Can you post some pictures and a video of your coil?</p>
Where? Here on instructables? I am new here but ill try tomorrow ok?
<p>will u plz tell me about the function of air gap or spark gap and which capacitor i can use in my tesla coil???</p>
My primary capacitance stands to 6.3 nF. Can I use a 10nF MMC?
<p>thk for u knd info</p>
<p>thk for u knd info</p>
<p>could i use two coils to wind the secondary, if i can how would i connect it together</p>
<p>Looks cool, BUT, the use of spark gaps in unshielded projects will create a type pf broadband transmitter, of the same type used back in 1912 when the Marconi Company made literal Spark Gap transmitters for ships, like Titanic.<br><br>Spark Gap transmitters and devices that use Spark Gaps and inadvertently transmit, create havoc on RF frequencies over an extremely broad range of frequencies. They are outlawed by the FCC and International Law. I suggest you shield your project VERY heavily. The last guy I saw in the FCC enforcement bulletins that was cited by them paid out $10,000.00. The FCC does not play.</p>
<p>could i use 628 feet of wire? thats all i can find.</p>
Im planning on purchasing a machined aluminum toroid. Is there a way to figure out the best size for optimal performance? A ratio or maybe an equation?
<p>What is the function of the top load? </p>
<p>It adds capacitance to the secondary. That means it stores charge on its surface and changes the resonating frequency of the secondary.</p>
<p>Why didn't you use a RC filter (Terry filter)? isn't it necessary to protect your NST?</p>
I have never had an NST or other transformer fail in a Tesla coil, but I'm sure the overall mean time between failures would be somewhat lower if I used a Terry filter (mostly likely because of the safety gap and not the actual filter -- it's easy to get the main spark gap spacing wrong and accidentally ring up a near-resonant primary capacitor at 60Hz). I don't believe a filter is absolutely necessary because placing the spark gap in parallel with the primary transformer shorts any conducted noise that might otherwise do damage to the secondary windings, and NSTs are designed to operate continuously driving the low impedance of an ionized discharge tube.<br><br>I might be convinced otherwise if someone presented noise measurements or tried to figure out quantitatively what it actually takes to make an NST fail. As it stands, I've seen people build successful Tesla coils with anything ranging from no filtering to Terry filters that cost more than the NST they're trying to protect.
<p>So just to be clear before I start ordering parts, you <strong>can not </strong>have a NST power supply that complies with UL 2161, or contains any form of ground fault interruption, secondary or other wise. In other words, every single power source I've looked at on eBay. (for ex. <a href="http://www.ebay.com/itm/ALLANSON-NEON-TRASFORMER-930CP120-9-000-VOLT-FIX-YOUR-SIGN-/151533504018?pt=BI_Circuit_Breakers_Transformers&hash=item234819c612" rel="nofollow">this</a> and <a href="http://www.ebay.com/itm/9-000-volts-9kV-6-5kV-RMS-NEON-SIGN-TRANSFORMER-POWER-SUPPLY-/351268831090?pt=LH_DefaultDomain_0&hash=item51c940ff72" rel="nofollow">this</a>) If you could make a note next to or on the product list, it may help other juvenile coilers such as myself. Thanks again for this well written Instructable! </p>
<p>What length of cable should I look for in the primary coil?</p>
<p>that depends on the size of the coil you are building and the number ot turns you will need. generally it is at least 10 turns so that you have room to tune the coil. i used a 50 foot 1/4 inch copper tubing from lowes, did my ten turns and cut it off there and i had just enough left over for the strike rod. </p>
found these capacitors on ebay, they're from a supplier so they should be around for a while. <br> <br>http://www.ebay.com/itm/380266725123?ssPageName=STRK:MEWNX:IT&amp;_trksid=p3984.m1439.l2649#ht_1854wt_811 <br> <br>all the info you would need isn't there, but with a bit of research done after i recieved my order, they appear to be the crimped version of these <br> <br>http://www.panasonic.com/industrial/includes/pdf/ECW-H_C_New_Product_Introduction_Sheet.pdf <br> <br>which should(probably) be suited for coil use, though the specs are slightly different from the instructable, so you would need to change your MMC configuration. i will probably go with a 12x8 setup(12 per string, 8 strings in paralell) which yields a capacitance of 0.01uF and a voltage rating of 19200v(19.2kV). i will let you know how it goes when i finish my coil.
Hi. I am just wondering whether <a href="http://www.ebay.com.au/itm/100pcs-CBB-Metallized-Film-Capacitor-0-022uF-223J-2KV-/290562041937?pt=AU_B_I_Electrical_Test_Equipment&hash=item43a6d8e851#ht_762wt_1163" rel="nofollow">these capacitors</a> would also work?<br> <br> Cheers
<p>here is a great cap to use <a href="http://www.rmcybernetics.com/shop/high-voltage/hv-pulse-capacitor" rel="nofollow">http://www.rmcybernetics.com/shop/high-voltage/hv-...</a></p>
could you give a link for the resistors you used. Thanks.
yep :) here you go! happy coiling! <br> <br>http://www.ebay.com/itm/10-Meg-Ohm-Bleed-Resistors-Tesla-Coil-Capacitors-/360313237049?pt=LH_DefaultDomain_0&amp;hash=item53e457ae39
ok, just finished my tesla coil and ran it, these capacitors work great! highly reccomend them for their price, amount, and continuous availability.
<p>have you tried downloading a free long exposure iphone app like i did to get better pictures! here are some of my tesla , 2.5&quot; by 10&quot; secondary, and 12000v 30mA NST power supply and a SINGLE .01 uf 20kv pulse cap and a 12inch by 3 inch dryer duct top load. by the way this was my own tesla i built not off this instructable...</p>
I need 17 0.15 uf capacitors, and these appear to be perfect for my Tesla Coil <br> <br>http://www.digikey.com/product-detail/en/B32023A3154M/495-3802-ND/1648119 <br> <br>Can a MMC use polypropylene metallized film capacitors?
Yes - those are precisely the kind of cap you'd want to use (unless you can afford CDEs). <br> <br>Good luck!
All these capacitors are DC rated, but I see them in a configure which the voltage across them will be AC, due to ringing between the caps and the primary coil. a 2000VDC capacitor will have a rating like 400VAC, so I would think the AC rating is what I avoid exceeding, however it appears everywhere I look where they build an capacitor back, this is overlooked. What rating should I be concerned with?
Thanks for the speedy reply!
where would you recommend getting the transformer <br>
How can I build a quiet spark gap <br>Always it was loud

About This Instructable




Bio: My name is Daniel Kramnik - I like building Tesla coils, quadrotors, and robots!
More by Xellers:Build a Robotic Arm for the Science Olympiad DIY Electron Accelerator: A Cathode Ray Tube in a Wine Bottle How To Build A Spark Gap Tesla Coil (SGTC) 
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