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>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
Build a solid state or vacuum tube coil :P
Would a circuit board like a pcb or breadboard work to hold the capacitor bank?
i doubt it, as a breadboard would not provide enough insulation to contain such high voltages unless you modified it by removing un-needed rows, and then it may heat up, a pcb could work if it was custom for your bank, a pre punched prototyping board might arc, but i dont know
&Auml;&deg; will be running my tesla coil in a science competition indoors ( in a basketball court) where there is no access to a place to put a large metal spike in the ground so i was wondering if it would be ok to ground it to the ground in an outlet. &Auml;&deg;t is exactly the same as yours execpt my secondary is 4 inchs wide and i am using 30awg wire. Thanks.
well, provided the electrical system is properly grounded, you CAN, i did... but be sure to filter everything well with a specialized RF filter, as by grounding it to the outlet you can create potentially damaging RF interference that can damage sensitive things like flat screen tvs and computers and such if left unfiltered.
my transformer is the same as yours but 60ma. what will i need to change in the cappacitor bank? THanks <br>
See the step on building the capacitor - I discuss how a value is selected there. You'll need to run the calculations yourself. Good luck!
built a working Tesla Coil from this instructable :D made a few modifications due to necessity/improvement/budget/availability, but it works great! (still a bit out of tune though since I have been crazy busy) here is a video of it running <br> <br>,<iframe frameborder="0" height="315" src="http://www.youtube.com/embed/LU5a_YYZlOg?rel=0" width="420"></iframe> <br> <br>and pictures below.
Other quick note: in the video I used a PVC pipe with GTO high voltage insulated wire taped to the end, and the other end of the wire connected to the main ground, as a grounding rod to attract the arcs. while this is all well and good in this particular spark gap coil, i have read several places that other varieties of coils such as vaccum tube tesla coils can be damaged or destroyed by ground strikes such as this. <br> <br> Also, while this grounding rod worked safely, as a general rule you shouldn't really be attracting the sparks to you, as this can be dangerous or deadly. an improperly constructed, or improperly used grounding rod could cause electrocution, so DO NOT ATTEMPT! I AM NOT RESPONSIBLE FOR INJURY OR DEATH RELATED TO THIS METHOD!
also a quick note on the capacitor bank, due to the unavailability of the exact capacitors in the instructable, the ones I used had a capacitance of .015uF, and a voltage rating of 1.6kV, i posted an ebay link to these earlier, but due to the slightly different capacitance, they must be arranged in 8 rows of 12 capacitors, rather than the 10 rows of 10 directed in order to achieve the 0.01uF necessary for this coil. This configuration also has a max voltage rating of 19.2kV.
just to ask two questions. why were there insicions in the speaker wire and is the secondary coil connected to the primary. because i dont know were to put the loose ends
also, the &quot;incisions&quot; in the speaker wire are where the insulation was stripped to connect the test clip, in order to experimentally tune the coil i believe.
Bottom of secondary is connected to a ground, top wire is taped to the top load, or bolted to the toroid if you went fancy
sorry to be bothering you so much, but i also cant find any capacitors rated for 1.5kV 0.01uF... where did you get yours?
i take it the resistors need to have a max voltage rating of around the same as the capacitors? what was the rating on yours and where did you get them?
ok, im back, Found what appears to be a REALLY great deal on a pair of 9kv 30 mA very-used-but-still-working-guarunteed neon transformers, the only problem is they have GFI, but seller claims they have a switch to bypass it, would they be suitable? (id show you the auction but I'm afraid someone will grab them first looking at the comment, email?)
daniel (dot) kramnik (at) gmail (dot) com<br><br>I can't guarantee that I'll be right, but I can try to tell!
Ok so I'm going to try and build one of these coils, should be pretty impressive, but I noticed you listed the price of the neon transformer as $35, I have not found one for anything under $90, and that is a substantial price jump as I'm trying to stay under or around $150. can you suggest a supplier of a $35 transformer? or better yet, a link? also, i have not found capacitors of the appropriate exact type anywhere on ebay, so a link would be nice for that too if possible. Thanks!
I had to wait several months to find that deal on eBay - it was the whole reason I decided to make an SGTC in the first place!<br><br>Given that you could make the difference between $35 and $90 in a couple days' work, that's probably the best idea if you want your coil project to happen in the near future - I'm sorry if this is the not response you wanted to hear! =/
Hi- <br> To any one not willing to build there own tesla coil or wants to support Xellers, (if I wasn't so poor after building my own four inch TC, I would) he has posted a listing on ebay for this coil running up to feb 28, 2012.<br>Go to: http://www.ebay.com/itm/250-000-Volt-TESLA-COIL-Assembled-2-Foot-Tall-8-12-Sparks-/180826521311?pt=LH_DefaultDomain_0&amp;hash=item2a1a19bedf#ht_500wt_1303<br><br> Xellers- great coil sad to see it go, though.<br><br> -OzL
http://www.ebay.com/itm/015uF-015-uF-1600V-5-Radial-Film-Capacitors-100-/380266725123?pt=LH_DefaultDomain_0&amp;hash=item5889a9bf03<br><br>.015uF .015 uF 1600V 5% Radial Film Capacitors (100)<br><br>$24.99<br><br>Will these work?
Yes these are Metallized PP Film Capacitor's from the manufactures website (panasonic). PP = polypropelene
would an electrolytic capacitor work?
i live in India so ebay not possible.Should i use same type of capacitor that you used in this project???
Does nobody on eBay ship to India?<br><br>If you can find an Indian supplier of the capacitor you need, that should work just as well, however. I'm afraid I won't be able to help you find a part distributor in India, though. If you find a capacitor you're not sure about, you can post a link and I'll help you determine whether it is suitable.<br><br>Have you registered on 4hv.org? If not, that's the place to start when it comes to Tesla coils - you might even be able to find someone else in India who knows where to get the parts you need.

About This Instructable


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Bio: My name is Daniel Kramnik - I like building Tesla coils, quadrotors, and robots!
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