Building a Tesla Coil In 9 Easy Steps!

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Over the past Summer I built two Tesla Coils. The first one didn't work, so I started building this one. This instructable will outline the steps I took.

Before I begin, I feel it is necessary to go over some safety guidelines. Please read each of these points thoroughly before starting this project.

-Tesla Coils are potentially dangerous devices and precautions must be taken before every operation to help prevent possible damage to property, injury, or death. Prior knowledge of high voltage electrical safety is required, and assumed.

-The arcs from the Tesla Coil produce ozone and other gasses, which can build up to toxic levels in unventilated areas. Do not allow this to occur.

-Tesla Coils can damage or destroy hearing aids and cardiac pacemakers in the proximity of the unit. This means that Tesla Coils are capable of killing a person wearing a pacemaker. It is imperative to verify that anyone using one of these devices maintains a good distance from an operating Tesla Coil.

With that being said, here is what you're going to need for this project.

Materials :


-4' of 1.5" PVC
-8 pieces of 5"x5" plywood
-2 pieces of 3'x2' plywood
-4 caster wheels


-15kV 60ma transformer with no GFCI

Spark Gap:

-1' of 3" PVC
-2 brass bolts the same size, plus 2 nuts and 2 washers that fit the bolts
-2 1" brass balls
-1 Computer fan
-1 8 AA battery holder

Capacitor Array:

-40 Cornell-Dubillier capacitors, (Model# 942C20P15K-F)
-40 10MΩ resistors
-Material to mount your capacitors to (I mounted mine to sheets of lexan, with ceramic stand-offs as legs.)

Primary Coil:

-4 pieces of 10"x3" plywood
-50' roll of 1/4" copper tubing
-20' of 3/8" copper tubing

Secondary Coil:

-2' of 4" PVC
-1 piece of 4.5"x4.5" plywood
-~1200 ft. roll of magnet wire


-2 aluminum pie pans
-Aluminum dryer duct
-Nylon nuts and bolts


-3 copper lug terminals
-High voltage wire
-Gorilla glue
-Drill press
-Table saw

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Mickjohno2 months ago

Mate, you're a legend! I've been on a bit of a Tesla coil quest for months now, I've built it to the stage I can test it but nothing but a spark across the spark gap is all I have been able to get. I'm brand new to instructables so already had mine mostly built when I read this but your instructions are one of the better that I have seen that's for sure. to start with despite no lack of trying I had my spark gap & capacitors around the wrong way (so I'm guessing that wasn't helping!). Also my top rail was a full circle & u said not to do that. Plus the basic wiring up of the thing was poorly described in every other vid or write up I've seen so well done.
But unfortunately I still need some help if u can please. I'm running 2 MOTs with a voltage doubler off 240volts which I think is giving me close to 8kVAC, then I've got 2 MOCs in parallel & an assortment of capacitors in series I've been trying to get right. I don't have any like yours, those suckers are expensive. I have several small capacitor banks made up & soldered together in series but I have no idea how to work out what the total capacitance would be & can't follow how to do it. I understand when I put 2 together I just add the voltage & the capacitance halves etc. But what about when I combine 2 totally different capacitor values?
My primary is 3' x 3.5" wound with 24G magnet wire & the secondary is a 1/2" tube with about 7 wraps ( I used exactly half of the reel). The spark gap improved 10 fold once I removed the capacitors & ran just from the voltage doubler & MOCs.
I'm guessing once I get the capacitors close I'll be right..?
Any ideas or assistance would be much appreciated..
Thanks heaps!
Mick :)

My main drama/question I think is how do I add up my capacitance when I have 2 separate banks with totally different capacitors in each?
Cheers! :)

WHY would you want this deleted? It was featured, and it won a contest. Looks to me like it was a great ible' before you removed all the content.

milandin6 months ago
My son and I are getting started on this Instructable and I rolled the dice and ordered a Franceformer off eBay. It's a 15KV 60mA but it arrived packed terribly and two of the ceramic terminals are bashed up badly. Two questions: Are these replaceable and if so, where can one buy these parts? I've been looking online for a while but no good so far.
twotower milandin5 months ago

I'm sure you figured this out by now that sadly, the transformer is shot and most likely is not repairable. It might be possible to mold some new separators using epoxy putty. Could be worth a shot. Couldn't you get your money back?

sheydon5 months ago

Beachley is now selling this instructable for sale on Ebay in the form of a pfd document. I am really disappointed as well as I have numerous links to this site from my own tesla web site. - Anyone one is free to meet me there. I offer all of the information necessary to build a tesla coil. I will have to expand informationally in areas where I was relying on Beachley's instructable. This is mainly in regards to the design and construction of the base for the primary coil.

neoberchman6 months ago
Beachley, what happened to your instructable? My son and I were using your instructions as a basis for his science project. Logged in today and *poof* it just says "Please Delete." Your instructions and images were some of the best available. Any chance of sending me a PDF? I can send you my email. Let me know.
Did you use any diode in your circuit ?
Beachley (author)  matthews martins8 months ago
Did you use any diode in your circuit ?
intead i use the same capacitor you use, can i use 146 capacitor with 2,2 uf and 250 v?
I forgot to say that they are electrolytic capacitors
or is better if i use polyester capacitors with 2,2 uf and 250v?
Beachley (author)  matthews martins8 months ago
(removed by author or community request)
I just have one more doubt, can I wire the primary coil with a AWG 12 wire?
Beachley (author)  matthews martins8 months ago
Using a conductor with a different width for the primary will change the primary inductance, which will change the required secondary inductance and the required capacitance of your capacitor array. If you plan to follow this instructable you cannot use 12 AWG, it will change a lot of the parameters I used.
I am now using 100 capacitors with 1,5 uF and 400v each made of polyester, that should work better, I couldn't find capacitors made of polypropylene here in Brazil
Beachley (author)  Beachley8 months ago
I really advise using polypropylene. 146 of these capacitors wired in series will give you a capacitance of 0.01506 uF and a max voltage rating of 36,500 V. That should work fine.
I am making a Tesla coil and I am only needing two parts the primary coil and plywood. But could I use adhesive to keep my toroid togethere? And what would be a good breakout point for the toroid?
Beachley (author)  Merlinthegreat1009 months ago
You can use adhesive to keep the toroid together, it doesn't really matter what you use as long as there aren't gaps anywhere. I like to use a piece of copper wire for my breakout point. Bend one end of the wire into a circle to make a base, then point the wire straight up into the air and lay it in the middle of your toroid. I also like to take a straight piece of copper wire and tape it to the side of the toroid, pointing outwards.
Beachley (author) 1 year ago
The first point you bring up, about the size of my primary, can easily be explained. As the size of the primary decreases, the size of the secondary must increase and vice versa. I chose to make my primary longer because it is easier to do that than to wind a longer secondary.

I can't explain the spark gap, I remember reading that you should close the gap until it first starts to fire. I started at 3" and nothing happened. I shut the coil off and adjusted the gap to 2.75", nothing happened. I repeated this process until the gap fired at 2.5".

The bottom of my secondary is laying flush on top of the plywood. The plywood is acting as the plexi-glass in your example. Underneath of where I have the secondary placed, I've drilled a very small hole in the plywood. The end of magnet wire coming off of the bottom of my secondary goes through this hole and attaches to a copper lug terminal, as you describe in your comment.

So I guess the only thing I can't explain is the spark gap!

Let me know if you have any other questions.
Beachley (author)  Beachley10 months ago
I just wanted to clarify that you were correct and my spark gap was not done correctly. I have since updated this instructable to reflect the corrections that I made. Thank you for pointing this out to me.
twotower Beachley10 months ago
Hi Beachley,
Thanks for the update, and you can see on my TC, that I had to increase the size of my primary to 12 winds. I'm clipped onto the 11th wind for optimal performance.

I really like the look of your new Spark Gap with the ball electrodes. I'm currently looking into building a rotary spark gap. I hear the performance increase is incredible! Alan from sells a kit so one can put together one's own synchronous rotary spark gap. He also sells a pre-made high pass filter that he has had great success with and also the components to build one's own Terry Filter.
my coil 2.jpgmy coil.jpg
Beachley (author)  twotower10 months ago
I have heard similar things about using a rotary spark gap and I've been considering going that route in the future. In fact, it seems that most people that want to get serious with their Tesla Coils use a rotary gap. Static gaps like the one seen here are definitely in the minority. I would highly recommend purchasing parts from Alan, I've bought some items from him in the past and he is very helpful and ships fast.
Beachley (author)  Beachley10 months ago
I also wanted to say that your Tesla Coil looks great!
I would build one tesla coil just like yours, all the things are the same, but my transformer is a 15000 v with 30 mA only. It will work the same way? Because if don't work I would buy another one and put them in parallel, so I can get 15000 v and 60 mA (but it's more expensive).
Beachley (author)  matthews martins11 months ago
Since your transformer is only rated at 30 mA there will be some differences. The output you observe at the top load will be significantly less than what is seen in this instructable, your capacitor bank will also need to be slightly altered.

I would suggest you go ahead and buy another one to wire in parallel.
I would build one tesla coil just like yours, all the things are the same, but my transformer is a 15000 v with 30 mA only. It will work the same way? Because if don't work I would buy another one and put them in parallel, so I can get 15000 v and 60 mA (but it's more expensive).
Hi there--I'm building a coil as my final project for one of my classes this quarter, and I really like your Instructable! I appreciate that you put in the effort to come up with a solid, clean design, and your instructions are overall pretty clear. I'd like to use this Instructable as one of my primary guides while building my TC... but I have a 12kV 60mA transformer (the only 15kV 60mA ones I could find online are going for upwards of $280--no luck looking locally, either), and most of the D.I.Y.s online use a 15kV one (like yours). What adjustments to your design would I need to make in order to follow this Instructable with a 12kV transformer instead? (I'm also using the DeepFriedNeon website as a reference, and I've read through dozens of other TC-building guides already). Thanks for your time!

I'm hoping to see some big TCs at the Maker Faire this weekend :D
By the way, what I mean by "adjustments to your design" is adjustments to the design of the base/structure for the TC; I know that I'll need fewer capacitors and whatnot [I'll do those calculations on the DFN site ;)]. I'm just trying to figure out what materials I'll need//how much it's gonna cost me to put it together. Also--do I really need to buy a whole 50 feet of 1/4" copper tubing? I'm working on a fairly tight budget... The transformer I got was $125, and I'm hoping to keep it under $250 for the whole project. Thanks again (in advance)!
Beachley (author)  divided_eye1 year ago
With your transformer, I would build the secondary and primary exactly the same as I have. I used a 50' roll of tubing to play it safe, using 50' provided me with many turns to ensure I would be able to achieve the proper resonance. Since your power supply is smaller you will likely need to tap the primary at a location other than the one I have. You can use whatever length you want, but make sure you have enough turns to tune your resonance properly. For capacitors, I recommend going with two strings of 16 capacitors, making a total of 32 capacitors. This is assuming you use the same capacitors as the ones I've used.
Great! Thanks for the timely response!
twotower1 year ago
Hi Beachley, A couple of questions if you have time....

What mathematical formula did you use to calculate your capacitor value? As you know, I followed your design and used 40 of the Cornell Dublier caps in a series/parallel configuration. However, this does not seem to jibe with the formula others are using to calculate the correct capacitance for a tesla coil. In my case the equation looks like this:
C = 1/(2π*60Hz*15000V/0.060A) = 0.00000001061033 = .0106uF

If I am not mistaken, the capacitance of our MMC is 0.3 (0.15 + 0.15) MFD 40,000V (20 X 2000).

The other question I have is regarding my Safety Gap. I know that you do not use one. However, I fried my first NST only minutes after I ran the tesla coil for the first time, due to a voltage spike that kicked back from the primary and secondary coils and fried my NST. The problem I'm facing at the moment, is that no matter how I try to adjust the safety gap and spark gap, that the safety gap fires way too much. The coil may run fine for 10 seconds or so, but then all of a sudden the Safety Gap begins to arc repeatedly and I need to shut the coil down.

Any ideas? I'm about ready to build a rotary spark gap. Have you built one yet?

Peace, Steffan
Beachley (author)  twotower1 year ago
When calculating the capacitance, I used a very basic rule. One of the first things I learned in electronics class was how to add resistors and capacitors in series and parallel.

For resistors in series,
Add the value of each resistor. The acquired sum is your total resistance.

for example,

Let's say we have five 2 ohm resistors in series.

Total resistance = 2+2+2+2+2=10 ohms

For resistors in parallel,
Add the reciprocals of each resistor. Divide that number into 1.

1/2 + 1/2 + 1/2 + 1/2 + 1/2 = 2.5
Total resistance = 1/2.5= .4 ohms

The method for capacitors is the exact opposite.

For capacitors in series,
Add the reciprocals of each capacitor. Divide that number into 1.

for example,

In this instructable we have twenty .15 MFD capacitors in series.

1/.15 + 1/.15 + 1/.15 + 1/.15.......and so on..........= 133.33
Total capacitance = 1/133.33 = .0075 MFD

For capacitors in parallel,
Add the value of each capacitor. The acquired sum is your total capacitance.

In this instructable we have one string of capacitors with a total capacitance of .0075 MFD and then we have another string of capacitors with a total capacitance of .0075 MFD.

So... when we combine these two strings in parallel,

Total Capacitance = .0075 + .0075 = .015 MFD
The Geek group was using the same formula. I was always under the impression that the capacitance value of capacitors connected in series does not change; only the voltage rating?? Apparently I have been mistaken all this time. Adding the reciprocal of the value for each capacitor and then dividing that into 1 provides the accurate capacitance of the MMC. Thanks! I think I get it now.
cjones711 year ago
how much did this cost.
in total.
Beachley (author) 1 year ago
Your site looks good, thank you for referencing me. I really like your vacuum method to keep the spark gap cool, I'll have to give it a try one of these days.

I'm glad your Tesla Coil turned out so well!
twotower1 year ago
I just want to share a Tesla coil update. First let me say that I am getting up to 3.5 foot sparks off of my top-load. I opted not to mount a battery operated computer fan underneath the lower table which had a hole cut out and sucked air through the 4" PVC Pipe Spark Gap above it. I opted to mount a 120V computer fan from above and blow down onto the spark gap. I drilled a series of half inch holes at the bottom of the PVC pipe spark gap housing in order to vent the exhaust. That did not work at all. Then I watched a video where a guy built a suction spark gap out of a PVC conduit fitting. When the vacuum was engaged, the spark output off of the top load was nearly doubled. Very clever! It gave me the idea to merely flip my fan motor around and see if pulling or sucking air through the spark gap housing would make a difference. I also taped up all but two of the 1/2" holes at the bottom of the PVC housing in order to create a true negative pressure inside the spark gap housing. The two holes left (one on either side), are perpendicular to the spark gap electrodes. I thought this would provide the best quenching effect. SUCCESS! My spark output nearly doubled and I can also now run my coil for up to 30 seconds at a time. The 120V Computer fan I purchased from Radio Shack (Catalog No. 273-242) is much more powerful than a 9V battery operated fan and may be considerably more effective for quenching and cooling. I recommend giving my method a try.

If you like I can upload images of my modified version of your gap. I was completely surprised by how well is quenched.

I also run my coil through a variac now. Once you have a variac, ... you never go back!
sheydon1 year ago
My Tesla Coil Is now working again. I put another 15KV 60mA NST into service after my first transformer got fried from kickback from the tesla coil. I now included a safety gap across the capacitor and a variac. Its easy to do and I recommend doing it to save your expensive NST. A variac alone will not prevent your NST from getting destroyed from T. Coil kickback. Below are two youtube links to videos of my coil in action. Enjoy
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