Building a Tesla Coil In 9 Easy Steps!

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:

Base:

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

Transformer:

-15kV 60ma transformer with no GFCI

Spark Gap:

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

Capacitor Array:

-40 Cornell-Dubillier capacitors, (Model# 942C20P15K-F)
-40 6MΩ resistors
-Material to mount your capacitors to (I mounted mine to 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

Toroid:

-2 aluminum pie pans
-Aluminum dryer duct

Miscellaneous:

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

Step 1: The Transformer

Before you start this project, you may want to consider finding a good transformer. This will likely be the most expensive part of the project and the hardest thing to find. Most transformers today have a built in GFCI circuit, this circuit is designed to shut down the transformer if it senses any unusual fluctuations. These types of transformers are terrible for Tesla Coil use, due to the Coil's sporadic nature. Transformers with a GFCI circuit will have some sort of reset switch and an LED indicator light. There's a website called Info Unlimited that sells very nice ones with no GFCI, that's where I got mine but if you can find one cheaper then go for it. 

For this instructable, I will be using a 15kv 60ma transformer from Info Unlimited.

Comments

[divided_eye]

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

[divided_eye]

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]

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.

[divided_eye]

Great! Thanks for the timely response!

[jgyger]

where did u connect the top wire from secondary coil? if you said somewhere else i missed it .

[Beachley]

The wire coming off the top of the secondary will go directly to the toroid.

[twotower]

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
http://www.twotowers.com/tesla/tessie_1_tesla_coil.html

[Beachley]

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

[twotower]

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.

[Beachley]

I'll get back to you on the other question. I'm at work right now.

[cjones71]

how much did this cost.

[cjones71]

in total.

[twotower]

Hi beachley, Just wanted to share a link for my own tesla coil page. It is still under development. Like your site, it will be a comprehensive guide for anyone wanting to build a coil. I also give you and the geek group credit for their contributions and I have linked back to your sites! Have a look.
http://www.twotowers.com/tesla/tessie_1_tesla_coil.html

[Beachley]

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!

[twotower]

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!

[sheydon]

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

http://www.youtube.com/watch?v=99EERVYhZtI
http://www.youtube.com/watch?v=p_BGBGVEiss

[sheydon]

Hi. Just an update. I finished my coil yesterday but was having difficulty getting any noticeable activity on the top load. To make a long story shorter, I would up extending my primary coil from 7 to 11 winds. That was all I had space for. I clipped onto the 11th wind and I was getting beautiful sparks up to 12" or so. On about the 4th test, Kickback from the tesla coil fried my transformer. I will be installing a variac in front of the new transformer in order to reduce the possibility of this happening again. Good news is that I do have a nice working coil. I will upload photos with sparks as soon as I round up a new transformer.

I used an alternate series-parallel configuration for the same forty Cornell Dublier .15MFD caps in order to save space and to be able to fit the MMC neatly under the primary and secondary coils. I'm uploading images of this cap layout. If anyone is interested I can upload a link to a pdf file. A large format printer would be ideal to print this larger that 8.5'X11". I got the idea from thegeelgroup.org. It works great.

[twotower]

Hi Beachly, First I would like to thank you for taking the time photograph your Tesla coil in such detail and posting the pics along with assembly instructions. As you already found out, there is not a lot of step by step info on how to build a tesla coil. That said I also found a good video tutorial on thegeekgroup.org. I am nearing the completion of my coil. I still have the secondary coil and my capacitor bank to assemble. I will submit photos when the TC is complete.

I have a friend in Vegas, who was building monster tesla coils when I was still a young teenager and I am now 52. Some of his coils are now in museums. A few of his recommendations differ from from how you and the geek group built your tesla coils. His biggest difference is the size of the primary. He said if you look at the primary coils on Tesla Coils build by really experienced TC builders, that the primary coil is usually not more than four or five winds. He was completely perplexed by your primary that had 15 or 16 winds. He was even more perplexed that you are clipping onto the 13th or 14th winding. Because of his suggestion to make it smaller promary, I have constructed my primary coil with 7 winds, in which I will most likely clip onto the 4th or 5th.

Another issue my friend was concerned about was the spark gap. According to him, a static spark gap is usually not more that 1/2 in distance at its MAX. My friend was scratching his head about your SG being 2.25 inches across.

Of coarse, I know very little and have to rely on what he tells me and what I read online. Your second coil attempt seems to work quite well! So you obviously have done something right!

One Question I have for you....
Is your secondary coil completely open a the bottom or do you have some kind of cover down there? In one of your photos. it look like the secondary is open at the bottom. My friend says it is very important to have the bottom of e secondary sealed off with a piece of plexi-glass that is glued in place. He says that the only thing that should be protruding out the bottom plate, is a small bolt with nuts that you attach the ground to.

Thanks again for your efforts. It has been a great help! I hope we can enjoy personal Tesla communication over the phone sometime. I live in central California near the coast.

Peace

[Beachley]

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.

[sheydon]

Hi Beachley,

Did you ever wind up using a safety gap, reactor or variac to limit the possible kickback into the transformer? My 'tesla coil expert friend' is recommending that I include a reactor (basically a large resistor) on the "hot" line voltage lead before the Transformer. I don't recall you using anything like that in your design. I was just wondering if you have experienced any issues with your transformer just using the basic tesla coil schematic that only utilizes a transformer, spark gap, capacitor, primary coil. secondary coil and a top load? I'm adding a photo of my Tesla coil so far. I just need to build the MMC array. Caps should be arriving tomorrow!

[Beachley]

The Tesla Coil looks really good! The best way to protect your transformer is by utilizing a Terry Filter, you can find a page on Terry Filters here:

http://www.hvtesla.com/terry.html

When I built mine I chose to stick with what you call "the basic tesla coil schematic." The main thing that needs to be avoided in order to prevent damage to your transformer is to make sure the arcs generated at the toroid NEVER strike the primary. I have never had this happen because I used a strike rail, and from your picture it looks like you used one as well. The strike rail has been sufficient enough for me and I've been running my coil off and on for the past 9 months or so.

As far as the variac is concerned, that's up to you. It gets hooked up just as you described in your comment and it basically acts as a large potentiometer. It's kind of cool to be in control of the input/output of the coil, but I wouldn't call it necessary. I might add one to mine in the future but, at the time, I was low on cash.

[nerd7473]

Well done Beachley, this is an awesome Tesla coil i want one do you think I should make one or buy one?

[nerd7473]

This is the coolest ever I want a Tesla coil

[whon1015]

My Tesla Coil

[whon1015]

Thank you so much for putting this instructable out here on the internet. It helped me very much in creating my tesla coil. This is my first one and it works beautifully, it has so far been able to produce up to 4 foot sparks. I still have a bit of tuning to do, but it is amazing. Again, thank you for putting in the time and effort to create this instructable.

[Beachley]

That's awesome!

Thanks for sharing it with me, I'm really glad to see it run so well. I put a lot of effort into this instructable and it's nice to see that it's helping people.

[sheydon]

I seem to be unable to upload images form my Mac. Too Bad.

[whon1015]

Also, does it matter if i use aluminum lug terminals in place of the copper lug terminals?

[Beachley]

I would stay away from using aluminum, it's a lot less conductive than copper.

[whon1015]

When you bought the material to mount your capacitors on, did you use a 12"x72" board of lexan? Also, how thick was the lexan?

[Beachley]

The lexan was 12"x72" before I cut it down, I think the thickness was 1/4". I used 10 gauge wire for all of my components, I'm not sure exactly how much I used. I'd suggest a 20' roll, that should be plenty. The ceramic standoffs can be found on eBay.

[whon1015]

Where did you get the ceramic standoffs?

[whon1015]

Oh and how much wire and what gauge wire did you use? Thanks

[whon1015]

When soldering the capacitors and resistors, do you solder one end of one capacitor and an end of the next capacitor together with an end of the resistor?

[Beachley]

Exactly. Upon close examination, you'll be able to see that, when wired this way, the two leads of any particular resistor only have continuity with two leads of a single particular capacitor.

[whon1015]

I checked the color bands on the resistors in the pictures (it looks like brown-black-blue-gold) and that is a 10Mohm resistor with 5% tolerance. You said you used 6Mohm resistors.

[Beachley]

The resistance value makes no difference, the resistors are simply an optional step included for safety purposes. The coil will not perform any differently no matter what resistor you use. Higher resistances are going to be better due to the fact that they are going to drain the capacitors more quickly after you've shut off power. You're correct that these are 10 Mohm resistors, I built this awhile ago and my memory was a little hazy when I was preparing this instructable, thank you for the correction. I should also note that these resistors are 1/2 watt

[whon1015]

exactly what type of resistors did you use? there are many different types of 6Mohm resistors out there. Also, can you please tell me if there would be a problem with using 10Mohm resistors? Thanks

[agis68]

nice project. I guess the most difficult thing was the coils.maybe i missed on text but how many turns is the secondary coil?

[Beachley]

Thanks for the compliment.

To answer your question, I briefly mention the secondary has ~1150 turns in "Step 6"