Introduction: The Improved Simple Tesla Coil

After finally finding some good sources on Tesla Coils, I set off to see how well built my previous instructable, "The Simple Tesla Coil" was. My findings were grim, it was performing terribly considering that the transformer draws in 990 watts. So I set out to change that. I would recommend that you skim through my previous instructable before attempting this one.

I suggest that you read the entire instructable before ever attempting to build it. You may end up halfway through and realize that you don't have access to a tool or material, and waste time and money/supplies (I only had to buy the magnet wire this time!).

Step 1: Supplies

Ha! This isn't supplies! This is safety! Please read. I am NOT responsible for any injury, property damage, or death that may occur as a result of you building or operating this device. After reading new sources, I have found that fatality is likely if you happen to touch the line in, or primary circuit, so don't! The secondary circuit is a grey area, you might die, you might not, but DON'T TOUCH ANYTHING besides the off/on switch and keep your distance when using this thing.

Alright, for my supplies I used:
-A 15 kV 60mA neon sign transformer (same one as before)
-16 Snapple bottle salt water capacitors/leyden jars (made more than before, check previous instructable to see how to make these).
-Lots of plywood, 1.5" diameter PVC, and some wheels for the supporting structure (Design your own structure out of whatever you have lying around, its cheaper that way)
-Spark gap from previous instructable (1/2" gap now, made from two bolts through opposite walls of 3" PVC)
-Shop vac
-1/4" inside diameter copper tubing, 30 feet long
-Various lengths of HV and/or regular 120V, 15A wire (it works too if you keep it away from other wire to avoid arcing)
-Long metal rod to use as ground (NOT the ground for your house! Bad things will happen to the electronics you love!)
-Extension cord (to stand way back!)
-4" diameter PVC for secondary form -19" long
-800 feet of 24AWG enameled copper wire (aka magnet wire)
-A toriod (previous instructable- 3" minor diameter, 11" major)

Step 2: Things That Will Not Be Covered

To build this project, you should have some experience with Tesla Coils, or at least an understanding of them. Check out "The Simple Tesla Coil" for some basic information, and details on constructing the following (which I shall not cover):
-Snapple Bottle capacitors (aka leyden jars)
-A structure to hold everything together
-Hooking up the step-up transformer to the wall outlet (NST in my case)
-Single electrode static (non-rotary) spark gap.
-A toroid (donut thing on top) made of aluminum dryer duct wrapped around two pie pans (3" vertical diameter, 11" horizontal diameter)

If you know what these are, and can make them, you probably don't need to go to that instructable, and you are ready for the next step.

Step 3: The Math

As always, I suggest patience when building these things. The first one I built was for a school project, and maybe that is why it wound up being so inefficient. The repairs (basically rebuilding it) are just for fun! The first time through I used many online calculators, formulas, and diagrams without ever researching them. This time, I read a few books on the subject, used three different programs, and also did the math by hand, just to quadruple check. The programs I used are: JAVATC, WINTC, and an Excel sheet I found on a science website (I won't even post the name as it is full of errors, and I don't want you to use it or insult the creator). JAVATC as I found out, was very wrong about tuning the coil, and the spark gap. Don't take anything on JAVATC for fact. The most important resource, however, was probably the 10-15 pages of notebook paper full of random notes, numbers, and calculations derived from many websites, guides, and other sources. I spent around 9 hours calculating what went wrong, how to fix it, and testing different setups.

WinTesla is on It was hard to find, and is quite old. But it can do a lot. If you search for it, make sure to include "-Nokia" in your search, as there is a program for unlocking (perhaps stolen) Nokia phones under the same name, and you don't want that.

I also suggest that you read up on Tesla coils on Wikipedia, and check out this place:
It is full of links that I have yet to explore, I had too much information on Tesla Coils to warrant looking at them all.

In the end, you need to make some decisions, and stick with them. Like secondary diameter, primary diameter, and a couple others. There is no "magic program" in which you simply click a button and it feeds you dimensions and specs. The whole point of all the calculators and equations out there is to solve for one variable when given another.

The last three images are from JAVA TC. After finding your dimensions, use it to "test" and tune you coil before you even buy the parts to build it. I found it to be inaccurate, and had to add 10' more onto my primary coil. The program freezes a lot, on account of being a java application in a web browser crunching huge numbers, but you just have to deal with it, as I know of no other such program. It even draws your coil to scale! That way you can tell if all those number dimensions will look funny when translated into reality.

Step 4: My Dimensions

They can be seen on the previous page, if you can decipher the poor image quality. Here they are:

0.25" id hollow copper. ~30' length
Flat Archimedes spiral form
6.5" Inner diameter
13.9" outer diameter
8.25 Turns (I tuned it manually)

24AWG copper wire, 800' length
4" inside diameter
15.15" tall
711.27 turns

Top Load:
Aluminum Torus
3" minor diameter
11" major diameter
Sits 3" above end of secondary coil.

Neon Sign Transformer
15000V output
120V input
990 watts input (similar to a microwave, makes the lights dim)

16x Salt water capacitor Snapple bottle (aka Snapple leyden jar).
Necessary capacitance: 0.0104µF
Actual Capacitance: 0.0160µF (If you do the research, having the exact capacitance is dangerous, less diminishes performance, and more doesn't really do anything, so make more capacitors than you need).

Spark Gap:
Single, static gap with two flat electrodes (bolts in my case)
0.5" gap (for now. It is best to adjust this 0.25", test it, and repeat until best performance is achieved.
I also attached a shop vac to the top of the spark gap for cooling purposes. I set the vac to reverse because the hot gas (ozone) coming off the spark gap might melt the plastic components of the vacuum.

Step 5: Wind That Primary!

I used about 30' of 1/4" copper tube for my primary. At my local hardware store, 1/4" copper is sold in 10', 20', and 50'. I started with 20', because JAVATC said I would need 18.7' or something like that. Unfortunately it was wrong, and I had to add another 10' on, which is not recommended as you want one, continuous piece of coil. By judging the length of the sparks, and then adjusting the lead-in on the primary coil by hand, I manually tuned this coil. The lead-in's final position is at 8.25 turns.

First, I made a 6"x6" square out of 1" thick particle board, with a hole in the middle for accepting 4" id PVC. It would be best to cut about an inch off of the corners, as the coil won't fit with full sized corners.

I then made four 2"x7" pieces of plywood. I then marked them 1, 2, 3, and 4. On all four pieces, I made a line across them (longways) 1" from the bottom. On piece 1, I made a mark 0.5" from the end, intersecting the horizontal line. I proceeded to make another mark 0.75" from the end, 1" from the end, 1.25" from the end, and so on, making a mark every 0.25" along the center line. Drill between the marks where an "X" is. See the pictures. On piece 2, I made a mark 0.625" (1/2" + 1/8") from the end, and then proceeded to make a mark 0.25", 0.5", 0.75", and so on from that mark. The extra 1/16" offset of the first mark is to insure that after a full rotation, the coil is .5" from where it started (making a spiral). Again, drill out the spaces marked "X". The series continues with piece 3 beginning at 0.75" and 4 beginning at 0.875". I used a 0.286" diameter drill bit. Use something slightly bigger than 1/4", as the copper coil is 1/4" inside diameter, the outside is slightly larger. Test to see if the tube fits in the holes before gluing it all together.

After completing the four plywood pieces, glue the particle board with 4" hole in the center of whatever you used for the base of the Tesla coil. Then glue the four plywood forms (with holes drilled), one centered on each side of the board, with piece #1 being at the point where you plan to have the primary windings start. See the pictures for an idea of what I'm talking about.

Now feed the copper through the closest hole to the center in the first piece of plywood. Now through the closest hole to the center in plywood piece #2, then #3, then #4. Now you're back at #1! What do you do? Feed it through the next closest hole. Continue doing this until you've made 10 complete turns (10 holes filled on every plywood piece). As the tuned parameters call for 8.25 turns, go ahead and put it through the tenth holes just to put the extra somewhere. I drilled holes in the plywood base at the beginning, and one at the end (which should be about 1" before the seventh hole on piece #1). Some thick wire I have will be ran through these holes during the wiring process.

I found it easiest to feed in copper from one end, and pull as many of the windings as possible from the other. Simply feeding or pulling one direction only is quite difficult, and will probably break the plywood pieces/braces. Push and pull to make it easier.

Step 6: The Secondary Coil

Now for the not-so fun part: winding the secondary coil.
I used 800' of 24 AWG copper magnet wire that I got on Amazon for under $30. There are cheaper places to get it, but I hate using credit cards online and amazon has a gift card option. I also used 4" PVC pipe that I got at a hardware store ages ago. I cleaned it up before using it.

The form.
The form for this Tesla coil will be 4" diameter PVC with a length of 19.15". The secondary itself will only be 15.15". The extra 4" are for:
1" before the secondary winding, so that there is room for it to fit into the particle board form. The other 3" go after the secondary windings, before the toroid. This is just some leftover room I put in when doing the equations just in case the windings are a bit longer. It also puts more room between the toroid and the primary coil.

So start by cutting a piece of 4" PVC pipe to 19.15" in length (you don't have to be exact, just a bit over 19"). Stick it into the particle board base, and trace around the base, it should be close to 1" from the bottom of the pipe. Now remove it from the base. Prop the pipe up horizontally in a manner that it can rotate. Start winding according to the picture (clockwise if viewed from top of coil). If you want, you can make a motorized rig, but I prefer to turn the pipe myself, as I feel more in-control of it. Put tape around the coil every so often, so that if you drop the wire, the whole thing won't unwind.

After completing the windings, put five or so coats of enamel over it. This will further insulate the coil, and help prevent damage to the fragile magnet wire. I would suggest gluing the base of the pipe to the particle board base.

This step will take a few hours. Find some good music, a good block of time when you won't be busy, and plenty of your favorite beverage, as you don't want to get up halfway through (you can, but you will lose all the windings past the last piece of tape).

Step 7: The Spark Gap

I used the same spark gap as in my previous instructable, but I improved it. I attached a vacuum hose attachment to the top, so that the shop vac could be removed after use. I adjusted the space between the two bolts to 1/2", and I plan to manually adjust it to whatever works best.

Step 8: The Capacitor Bank

I used the same capacitors as my previous coil, but added six more. The ten old bottles had to be removed and mixed up again, as the salt settled out of the water. Also, I had to re-glue the wires extending from the tops, as the old glue had weakened and started to leak. The oil in the old ones appears to be molding (it's been almost 6 months), but I see no issues yet.

I glued all my capacitors to plywood sheets in groups of 4, 6, and 6. The plywood is screwed to the lower "deck" of my support structure. This way, I can remove a set of capacitors easily if there are any problems.

The total capacitance of my bank is about 0.0160µF, as opposed to 0.0104µF that is ideal according to the equation. Having less capacitance can be a problem, as the bank will overcharge and explode. Having exactly the right capacitance (while being nearly impossible to judge when using leyden jars) is a bad thing, because the perfect resonance may somehow damage the transformer. Having more capacitance doesn't really effect anything, and it can help if some of the capacitors fail.

Step 9: The Toroid

I made no changes to my toroid. It is still 3" tall by 11" wide. It sits 3" above the top of the secondary coil, and is connected to the secondary directly by the loose end of magnet wire of the secondary.

Step 10: The Wiring

The wiring is the same as before. It goes as in the images below.

For wire, use what you've got. I used some 15000V rated HV wire, some 600V 100 amp rated wire, and some plain old solid copper 120V 15 amp rated stuff like you would find in your walls. Anything smaller than the standard 120v wire, I wouldn't use. When using any wire that is not HV rated, keep good spacing from other wires/objects. A rule of thumb is 1 inch of air for every 10000 volts of current when using UN-insulated wire. At 15,000 volts, I doubt that insulation on regular wire does anything, in fact, I think that it is a conductor, albeit a poor one. So keep at least 1.5" between every wire that is not HV, but probably shoot for 2" or 3" just in case it shifts during transportation. Also, watch out for coatings on the wood you are using for the support structure. The bottom board on mine is coated with some sort of plastic. I tested it with the transformer, and it is about as conductive as wood. But other coatings may be more conductive. Learn some material science!

Step 11: The Power Switch

This step is optional.

Alrighty then, we are technically done with the coil, it works as is, now for some improvements. First I'll show you one that I should've done a long time ago, a off/on switch. This switch will toggle on/off the 120V going to the neon sign transformer. Check out the image for my setup.

Everything is plugged into a 6 outlet surge suppressor, which is plugged into the wall. There is an off/on switch on the surge suppressor, which controls everything. Turning this switch off will shutoff the Tesla Coil and the shop vac that is cooling it, no matter what position the handheld switch is in. This is a good thing, as you don't want to run the Tesla Coil too long without the shop vac. While the surge suppressor is on, the shop vac will run, and if the handheld switch is in the "on" position, the Tesla Coil runs. So one can turn on/off the Tesla coil from a good distance with a device in their hand.

Building this switch properly is important. Out of all the electricity worked with in the project, 120V 15A is by far the most deadly. Use proper electrical wiring, conduit, and circuitry here. I used a 15A interrupter switch (a common type of light switch) that I got for about $1.50 at the hardware store. There was another kind of light switch for only $0.70 there, but I decided that I wanted the higher quality one for this circuit (it is under a large load!). I am sure that the cheaper kind will work, but it may wear out sooner. I also used some 1/2" PVC, an electrical conduit box (with a removable plate, and two 1/2" connections), some HEAVY DUTY extension cords, liquid electrical tape, hot glue, and electrical tape. It is important that you use heavy duty extension cords because cheap thin ones can overheat, melt, arc, and start a fire/burn/electrocute you. Make sure that the extension cord is tick and rated for at least 15 amps.

If you have no experience with 120VAC wiring, DO NOT attempt this switch. It is only for aesthetic purpose (you don't need it) and wall outlet voltage is lethal.

Cut the 1/2" PVC into two 3" long sections. Glue these sections using PVC glue into the slots of the conduit box. Now unscrew the face plate of the conduit box, and remove it. My switch did not fit in the conduit box, so I used a jigsaw to cut a slot into the side of the box that would fit the switch. Cut the extension cord about 5 feet from the male end. Separate and strip the wires inside. Feed them into the long end of the box. Attach the ground to the switch, one color wire to the screw on the switch, and the other leave hanging. Take the remaining 20 or so feet of the extension cord (the female end) end stick the split end into the other end of the conduit box. Attach the ground to the ground screw (along with the other ground wire). Attach the loose wire from the male end to it's matching color from the female end, and attach the only remaining wire to the other end of the switch. Now seal the heck out of this thing using electrical tape, liquid electrical tape, and hot glue (probably in that order).
Basically we are just making a light switch, but in middle of an extension cord, as to turn the current on/off in the cord. If you do not understand, do not attempt! Wall outlet voltage kills!

You can use an extension cord without a ground cable, as the ground is not used on a Tesla coil. If you use one with a ground cable, you might as well wire it to the switch, so that you can use this switch-able extension cord with other appliances.

Step 12: Breakout Point

Yet another optional optimization step.

Want to give general direction to your streamers? Want to make one large streamer instead of many small ones? Look no further than a breakout point!

Most "professional" coilers (is there such a title?) choose to place a breakout point on top of the topload of their coils to encourage a direction, and increase streamer length. The breakout point can be as simple as a piece of bent wire resting on top, or it can be part of the topload. Do what you want, you may find something that works amazing. Here's what I did:

1. Take a piece of plain solid core copper wire (bare), and bend it like so:

2. Place on top of topload.

3. Enjoy.

Perhaps you could bend it to make streamers go different directions. The possibilities are endless!

For an even better breakout point, use thicker wire! I noticed in some of the overexposure pictures that arcs were running parallel to this wire just above its surface, meaning that it was probably too small to take all of the current (skin effect means that it can carry very little).

Step 13: Pics!

While this improved version of my old coil wasn't as awesome as JAVA-TC would suggest (43" streamers, yeah right!), I was still satisfied. It looks better and works better than the old one. I would guess that the arcs are about 16" at the longest. What will I do next? I am not sure, but it will definitely involve a bigger transformer(s) and some quality components, as well as many months of intense research.

As a wise man once said, pics or it didn't happen!

And video:


More videos will become available once the weather warms up! Hopefully I can shoot some where you can see something other than the streamers and a florescent bulb!


NitroRustlerDriver made it! (author)2012-02-17

You might be better off using this type of electrical box:|0&pl=1¤tURL=%2Fpl_Electrical%2BBox_4294821892_4294937087_%3FNs%3Dp_product_price%7C0&facetInfo=

It is made to hold a switch and the breakout holes in the back/sides allow you to use these to clamp the wires in place so they can't tear out:|0&pl=1¤tURL=%2Fpl_Conduit%2BFittings_4294821891_4294937087_%3FNs%3Dp_product_price%7C0&facetInfo=

It would be bigger then the box you used, but then the switch would be more securely mounted and completely concealed inside the box instead of hanging out slightly.

MistaStokes made it! (author)MistaStokes2012-02-17

Yeah, I would suggest this to anyone attempting that step. I only did it my way because I didn't want to buy one, and had a small one lying around.

ramstew made it! (author)2016-10-07

5V USB Portable Tesla Coil

teslacoilman123 made it! (author)2015-11-18

Hello once again, I am looking for clarification regarding your idea of the Leyden Jars. If you could so kindly notify me about more details on how to make them, that would be great. Thanks. ~teslacoilman123

harsh_dwivedi made it! (author)2015-03-25

can any other transformer work in place of NST because i dont have it and it would be great if you tell me the input output voltage for tesla coil's transformer.

luxdaxor made it! (author)2013-03-30

would you any particular tape for this?

luxdaxor made it! (author)2013-03-14

Could we use particle board, instead of plywood? I only say this because I have some lying around.

MistaStokes made it! (author)MistaStokes2013-03-14

I think so, it depends on how conductive the glue or resin holding the particles together is. A simple test I did to test the plywood was to hook up the transformer to the wood, with the wires contacting points on the wood several inches apart, then turning on the transformer (plugging it in since I had no switch at the time, and seeing if it arcs or burns the wood. I'm pretty sure particle board would not be conductive, even at 15kV, but I'm no lumber expert.

Credible Halter made it! (author)2013-02-12

EXPENSIVE transformer!
i need to find a inexpencive neon transformer

disappearingshadow made it! (author)2012-05-13

what type of wire did you use? Like what type of high voltage wire? and where can i get some?

disappearingshadow made it! (author)2012-04-15

sorry to keep bothering you, but when you covered the capacitors with aluminum foil, did you cover the bottom? Also I'm having trouble on how to connect them together. Say i had 10 capacitors. would they be attached in a single file? or would they have a figure 8 pattern to them

MistaStokes made it! (author)MistaStokes2012-04-16

No problem! I did cover the bottom of each capacitor. They would be connected in "parallel", meaning that all the foil would be wired together, and all the nails or wire would be connected, just like when you wire light bulbs in parallel.

disappearingshadow made it! (author)2012-04-13

I'm gonna make this for my third term project for my high school engineering class. It looks like a fun build. May i please have a copy of the pdf file. Oh and for the capacitors did you stick a nail in them or was it a piece of wire? -Irene

MistaStokes made it! (author)MistaStokes2012-04-13

For the capcitors, I used wire. Nails would work, too. What .pdf are you referring to? The instructable?

disappearingshadow made it! (author)disappearingshadow2012-04-13

I was wondering if I can have a copy to both of the instructables on pdf file

R.A.T.M made it! (author)2012-02-14

so height frequencies goes on the outer of the skin and low starts to penetrate but you have be careful because some height frequencies coils may feel fine and look ok but can cause nerve damage so unless you are a pro you wont know what is what

MistaStokes made it! (author)MistaStokes2012-02-16

Yes. Even if it doesn't hurt, it can be harmful.

R.A.T.M made it! (author)R.A.T.M2012-02-21

No i wass telling i know you had some questions in the guide

bpark1000 made it! (author)2012-02-16

Replace the spark gap with a "segmented gap" (4 to 5 shorter gaps in series). This will reduce the heating in the gap and increase output.

MistaStokes made it! (author)MistaStokes2012-02-16

I am thinking about doing this. I need more identical bolts first!

wanabop made it! (author)2012-02-14

Why do you have the toroid? I think there would be a greater spark if a grounded wire was brought about 1 foot from the toroid.

Some large caps can be made using aluminum flashing, and sheet plastic, then enclosed ina PVC sealed, pipe filled with mineral oil.



MistaStokes made it! (author)MistaStokes2012-02-14

Thank you for commenting, Dennis!

The toroid acts as a small capacitor (all conductive metals have a capacitance, be it a small one), the toroid shape is ideal for building a small charge around its radius during the nano seconds between the high frequency pulses generated in the secondary circuit. This charge helps the energy to "leave" the circuit and for arcs.

Placing a grounded wire near the toroid does create larger sparks, as the electricity in the toroid is attracted to the ground. I've done this in my instructable, see images 4, 19, 20, 21, and some others. The tall thing next to the coil in certain images is actually the ground rod that I used, as I didn't hammer it in all the way.

I have heard of people creating capacitors in similar fashions, I plan to do that on my next coil, whenever that is. I used glass leyden jars just because they were simple and cheap, and I had all the materials lying around.

About This Instructable




Bio: I like to play with the more dangerous DIY stuff, but don't worry, the ones I upload are pretty safe if you follow the ...
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