Introduction: 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 :


-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

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.

Edit - 9/16/2013 

Since creating this instructable, I've figured out how to remove the GFCI circuitry from certain NST's. Since there seems to be a deficiency of online resources as to how this procedure is performed, I've decided to cover it here. The following process will only work with transformers that have the GFCI circuit exposed. In some transformers it is impossible to remove the GFCI because it is surrounded in tar and is inaccessible. As of this writing, I am aware of only two companies that leave the GFCI exposed, those being "Transco" and "France".

The following procedure is for "Transco" transformers, "France" transformers have a slightly different but similar procedure:

Safety Note
NEVER touch EITHER output terminal of the transformer while it is plugged in. 

1. Unplug your transformer.

Remove the access panel from the top of your transformer. "Transco" transformers have one screw and one rivet holding the access panel on, remove the screw and cut off the rivet with some pliers. For this step, please refer to pictures 3 - 6.

3. With the access panel removed, you should see two partitions on the inside of the transformer. The first partition will be completely filled in with tar and is inaccessible, the second partition will contain the GFCI circuitry. The blue box shown in the pictures is the GFCI. See pictures 7 - 8.

4.  Pull the GFCI box out of the transformer so you can get a better look at it. Notice that all of the wires coming from the transformer go through a terminal block to connect to the GFCI box. Use a screw driver to disconnect all of the transformer wires from the terminal block and set the GFCI box to the side, we are done with it. See pictures 9 - 12.

5. With the GFCI removed, we need to figure out which of the remaining wires are no longer needed and which of the remaining wires must be joined together. The remaining wires are green, brown, grey, blue, white and black. The green wire is ground for the components in the GFCI box. Since the GFCI box has been removed, we no longer need the green wire and it should be taped off to keep it insulated and out of the way. The brown wire is used to activate a relay in the GFCI box. Again, since the GFCI box has been removed, we no longer need the brown wire and it should be taped off to keep it insulated. The white wire and the black wire are the ends of the primary inductor within the tar-filled partition. In electrical terms, the white wire is neutral and the black wire is line voltage. The last two wires are blue and grey. The blue wire comes from the "line voltage" (L) terminal on the exterior of the transformer, where the power cord gets attached. The grey wire comes from the neutral (N) terminal on the exterior of the transformer. Connect the grey and white wires, since they both correspond to neutral. Solder them together and use tape to insulate everything. Connect the black and blue wires, since they both correspond to line voltage. Solder them together and use tape to insulate everything. See pictures 13 - 15.

6. Put the access plate back onto the transformer and get ready to give it a test run. Attach one electrode of your spark gap to each of the two output terminals on the transformer. If your spark gap fires when you plug in the transformer, you have successfully re-wired your transformer and removed the GFCI box.


When shopping for a transformer on online sites like eBay, transformers with no GFCI often cost significantly more money because of their increasing rarity. If you can, I would advise you to purchase a "France" or "Transco" transformer WITH a GFCI, then use the previous procedure to remove the circuitry. If you take my advice you could save upwards of $130 - $150.

The transformer I bought from Info Unlimited was $290 because it did not have a GFCI. Don't needlessly waste money like I did.


Step 2: The Base

This step is entirely up to you. You are going to want a strong, sturdy base to hold all of your components. Some people like to use materials that aren't flammable, like plexi-glass. I didn't really find this necessary and decided to use wood, it's been working just fine. Perhaps the most important thing to keep aware of is to stay away from using anything metal. The more conductive materials you use to build the base, the more likely for an arc to jump and hit something that it shouldn't.

Here's the way I did it:

Generally, you're going to want to have two layers. The bottom layer will consist of all of the delicate electrical components that are part of your primary circuit. The top layer will contain the primary coil, the secondary coil, and the toroid. Each of my two layers measure 2'x3'. I chose to use 4 pieces of 1.5" PVC as the legs of my base and they are each about a foot long. To hold the legs in place, I cut 8 square pieces of plywood measuring 5" by 5", and then drilled 1.5" holes in the middle of each of them to accept the PVC. As you can see, my capacitor array ended up being longer than the base of my coil, so I had to cut a separate longer piece of wood for that. To avoid using metal fasteners, I secured everything in place with gorilla glue. I also used 4 wheels from Home Depot to make the Tesla Coil easier to move around. Keep in mind that the components on the bottom layer should be evenly spaced apart, you do not want arcs forming down there.

This is the one part of the project that you can get creative with. There are plenty of designs that are better than mine so feel free to experiment with it.

Step 3: The Spark Gap

Designing the spark gap is an important step in Tesla Coil construction. Basically, after electricity flows through your transformer, an electrical charge will start to build up in your capacitor array. Once that charge becomes powerful enough, it will arc across the spark gap. The spark gap should be enclosed, It produces dangerous amounts of ultraviolet light that can damage your eyes. The spark gap also needs to be kept cool. If it is not, the electrodes will need to be replaced frequently and the Tesla Coil will not perform as well as it could.

My spark gap is simply 2 3" brass bolts, which are being used as the electrodes. There is a 1" brass ball threaded onto the end of each of these bolts. You must use some kind of spherical shape at the end of each bolt. If you don't, the threads of the bolts will act as individual breakout points and you will never get consistent results. I chose to enclose my bolts in a piece of 3" diameter PVC, the length isn't overly important. I simply drilled a hole the whole way through the PVC pipe, roughly the same size as the bolts I used, then threaded the bolts through. On each bolt I used 2 nuts and 2 washers to lock them in place, this way I know that the bolts will be secure but the gap can still be easily adjusted if need be. To keep my spark gap cool, I chose to drill a hole through the center of the base and mount a 12VDC computer fan. I glued the fan underneath of the hole, then glued a 3" to 4" PVC coupling over the hole, that way the air will blow up through my enclosure. With this 3" to 4" coupling in place, it is much easier to remove your spark gap for purposes of tuning and examination. See the pictures to get a clearer understanding.

I wired the leads from the computer fan to a battery holder and attached a switch to keep the fan from running all the time. The battery holder I used holds 8 AA batteries, creating a total of 12V. If you use a smaller fan, obviously you will need a smaller battery holder. AA batteries are 1.5V each, so make your adjustment accordingly. The final adjustment of my gap was ~5/16", but this measurement may vary depending on your specific transformer and electrode diameter.

The procedure that must be followed to properly space your gap is as follows:

Make an electrical circuit that is comprised of only your transformer and your spark gap. Set the bolts at an initial gap of ~1/2". Turn the transformer on and observe the spark gap to see if the bolts are firing. You should see a steady stream of electricity flowing from one bolt into the other, if not, slightly shorten the gap. Continue to do this in increments until you see electricity flowing across. You need the gap to be adjusted so that every time you turn on the transformer, electricity immediately begins arcing across. If you turn on the transformer and there is a 2 or 3 second delay before you see the electricity, shut the transformer off and shorten the gap a little more. Keep bringing the gap in until you can consecutively turn the transformer off and on without witnessing a delay. As I said, my final gap was 5/16". Results will vary depending on how powerful your transformer is and the size and shape of your electrodes. Once you have the gap set, tighten the nuts to lock it in place and DO NOT make any future adjustments to the gap. It is a common misconception that widening the gap while you are in the process of tuning the Tesla Coil will help to achieve a higher output. Making the gap excessively wide won't accomplish anything except shortening the life of your components and possibly damaging your transformer.

It might be important to point out that the size of your electrodes will directly influence the quenching capabilities of your spark gap. Larger electrodes will act as heat sinks and dissipate the heat better than smaller electrodes. This will ultimately result in better performance and long electrode life.

I'll go through how to wire it later, but hopefully you can begin to see how I have the spark gap wired from some of the pictures.

Step 4: The Capacitor Array

I'm going to start off by saying that the homemade "Leyden Jar" type capacitors are not the most efficient. They may be the cheapest, but if you want a quality Tesla Coil, it would be better to buy actual capacitors. Be aware however, most types of capacitors are not made for this particular kind of application, and as a result they will blow. When browsing for capacitors, make sure that they are made for high voltage use. Through much trial and error, I think I found a capacitor that is perfect for this application. Cornell-Dubillier capacitors, (Model# 942C20P15K-F), work like a charm. These particular capacitors are rated for .15 MFD, with a maximum voltage of 2 kV. You may be wondering how these capacitors will work if they are only rated at 2 kV, since we are working with a 15 kV transformer. I'll get to that in a second. For this particular Tesla Coil, I calculated that I would need a total capacitance of right around .015 MFD. To play it safe, the general rule is for your capacitors to have a maximum voltage of at least twice as much as what you are putting into them. In this instructable, we are working with 15 kV so it would be ideal for the capacitors to have a maximum voltage of at least 30 kV. When you wire capacitors in series, their voltage rating increases and their capacitance rating decreases. As capacitors are added in series, you add up each capacitor's max voltage rating to get the total rating. The total capacitance is determined by adding the reciprocal of each capacitor's capacitance. To make a long story short, if you wire 20 of these capacitors in series, you will end up with a max voltage rating of 40 kV and a capacitance rating of .0075 MFD. Adding additional capacitors in parallel will increase the capacitance, while not affecting the voltage rating. Because of this, I ended up using two strings of 20 capacitors each, with the two strings wired in parallel. This arrangement gave me a final value of .015 MFD at 40 kV.

Edit 9/23/2013
I had posted this in the comments section, but I thought it might be helpful if I posted it here as well:

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 *

If you are not familiar working with capacitors and you have any questions about how to wire them, just leave a comment below and I'd be happy to help you out. The next challenge you may run into is finding some way to mount your capacitor array. Veroboard would be a good option, but the capacitors are heavy and I'm not sure

Veroboard would be able to support the weight. The material I ended up using was lexan, with ceramic stand-offs. Again, you have some freedom with this step so do whatever you see fit. I secured a copper lug terminal onto each end of the capacitor array, allowing me to easily attach the capacitors to the rest of the circuit. You can find these terminals at Home Depot for fairly cheap.

The following step is optional but recommended*

These capacitors will be holding a lethal charge, and it will take awhile for that charge to dissipate. To avoid any injuries, I chose to wire a 1/2 watt, 10M? resistor in parallel with each of my 40 capacitors. Resistors are cheap, and they could end up saving your life.

Step 5: The Primary Coil

It may be easier to construct the support for your secondary coil before beginning this step. To do this, follow these 4 steps:

1. Cut a 4.5"x4.5" piece of 3/4" plywood.

2. Drill a 4" hole exactly through the center of this piece.

3. Gorilla glue the piece exactly in the middle of the top layer of your base.

4. Drill a small 1/4" hole through the top layer of your base, right through the center of where you just glued the support for the secondary. This hole will be explained later.

Now, back to making the primary:

The primary coil generates the magnetic flux needed to allow all of your components to work together. As current is pushed through the primary coil, it will resonate at a certain frequency, coupling it to your secondary coil. It is necessary to be able to tune this resonance for the best results, so I took that into consideration when coming up with this design.

Your first step should be to acquire a 50' roll of 1/4" copper refrigeration tubing. This kind of tubing can be found at Home Depot or at online vendors like eBay, if you prefer. Be careful when working with the tubing, it can be easily kinked and I found myself wasting a large portion out of carelessness. When you purchase the tubing it will be wound into a circle, do not unwind it. Instead, use this shape to your advantage and gently start to spread the layers of copper tubing apart to form your coil.

Each turn of the coil is going to need to be separated by a 1/4" gap. In order to accomplish this I made 4 wooden braces measuring 3"x10" each. The wooden braces can be kind of hard to explain, so I drew a diagram and attached it to this step.

1. To start, I measured 1.5" up from the bottom of each piece and extended a center line down the entire length.

2. Next I numbered my pieces, 1, 2, 3 and 4. On piece 1, I made a vertical line .5" in from the end. I then continued to make vertical lines every 1/4" until I reached the opposite end.

3. Next, I made an "X" between the first two vertical lines I drew in the previous step. I then left a gap and made an "X" in between the next set of vertical lines, continuing this pattern until I reached the end.

4. Finally, I drilled 9/32" holes wherever there was an "X".

5. Pieces 2, 3 and 4 followed the same method, except the first vertical line that I made on these was not .5" in from the end. On piece 2, the first line was .625" in. On piece 3, the first line was .75" in. On piece 4, the first line was .875" in.

6. Unless you have an extremely steady hand, it is almost required that you use a drill press for this step. If you are not precise the copper tubing WILL NOT fit into the braces correctly.

7. If you notice, the first vertical line of each piece is offset 1/16". This way, as the copper tubing makes one complete turn, it will form a 1/4" gap between rows.

8. Now I went back to that original center line that I made in part 1 of this step. Using a table saw, I cut the brace in half along that line. This allows you to pop your copper tubing in from above, rather than trying to worm it through the holes.

9. The copper tubing fit nice and snug in the holes I drilled, but I occasionally used a dab of hot glue for extra support.

10. These braces will be under stress due to forces acting on them from the tubing. I found it necessary to use gorilla glue beforehand to hold them in place. Glue the braces perpendicular to the support you made for the secondary, one on each side.

Trying to force the copper tubing through the holes rather than dropping it in from above will be very frustrating and you'll probably kink it numerous times along the way. Because of this, I highly recommend you design your braces as I did in this step.

It is also important to note that the inner turn of the primary should have a diameter of approximately 5.5". If you follow the dimensions I used in this instructable you should get exactly that.

If an arc from the Tesla Coil happens to extend down and strike the primary coil, a majority of your electrical components could be destroyed. In an effort to prevent this, it is common practice to utilize what is known as a "Strike Rail". The strike rail is a separate piece of 3/8" copper tubing that is placed approximately 2" above the primary and attached to ground. This way, any arcs aimed downwards will be directed at the strike rail.

When creating your strike rail, it is very important that your copper tubing does not form a complete circle. If it does, it could throw off the resonance of the primary.

Step 6: The Secondary Coil

The secondary coil receives the magnetic flux generated by the primary in the form of induction, and uses it to produce tremendous voltages.

For this step, you will need a 22" long piece of 4" PVC and roughly 1200' of 26 AWG magnet wire.

Make a mark roughly 1" from an end of your PVC, this is where you will start winding the magnet wire. Drill 3 small holes side by side on this mark, guide the magnet wire through the first hole, bringing it to the inside of the pipe. Feed the wire back out of the pipe through the second hole and feed it back in again through the third hole , leaving at least 4"-5" of wire on the inside of the pipe. This will hold the wire in place as you wind the rest of the turns. This end will be the bottom of your secondary. Some people choose to use tape to hold their magnet wire in place, this works fine but it leaves the ends of the magnet wire on the outside of the PVC and, in my opinion, looks sloppy.

With an end of the magnet wire secured, you can now begin to wind the secondary. For this instructable, you are going to need approximately ~1100 turns. Go slow, this process will take lots of time and patience. Make sure you don't accidentally cross the wire anywhere and don't leave any gaps in between turns. Use painter's tape to hold the turns in place as you continue to wind, this way you can take breaks without having to worry about the wire unraveling.

Once you've counted roughly 1100 turns, temporarily tape the wire down. Drill 3 more holes on this end of the pipe, just as you did on the other end. Now repeat the previous procedure to secure it in place. If done correctly, you should now have a few feet of extra magnet wire on the inside of the pipe. Bring this extra wire out through the top end of your pipe and cut it about 2" above where the pipe ends. Using aluminum foil tape, create a conductive path around the top edge of the secondary. Don't make this path go the whole way around, leave a little bit of the top edge of the pipe bare. Using 1200 grit ultra-fine sand paper, remove the enamel from the 2" of magnet wire extending from the top end of the pipe. Use a piece of aluminum foil tape to secure this end of magnet wire to the conductive path around the top edge of the secondary. I chose to tape pieces of electrical tape around the inside and outside of the top edge of the pipe, this gives it a cleaner look and prevents the aluminum foil tape from discharging along the inside and outside of the secondary. See the pictures for clarification. This creates the connection for our toroid.

You must cut the ends of the magnet wire to the specified lengths. Leaving the ends of the magnet wire too long will cause the Tesla Coil function improperly and there is a very good chance you will fry some of your components.*

At this point it is a good idea to apply some type of protective enamel to your windings. Enamel will greatly help to hold the windings in place and prevent them from gradually coming undone. I used Dolph's AC-43 insulating varnish. Once 2 coats of enamel have been applied, you can safely remove the tape that was being used to hold everything in place. Now apply enamel again to cover the area where the tape was.

Once the enamel has dried, you can mount your secondary into the support structure that was made in the previous step. As you press the secondary into the support, guide the extra 2"-3" of magnet wire (that we left at the bottom of the secondary) through the small hole we drilled in the previous step.

Under the top layer of your base, where the magnet wire is now protruding through, I attached another copper lug terminal. I wrapped the loose piece of magnet wire around the lug terminal and bolted it in place. This terminal will provide a path to ground later on when we do the wiring.

Step 7: The Toroid

The toroid is the point at which the stepped up voltage will discharge from the Tesla Coil.

The size of your toroid will make a difference in how the electricity is discharged. If you use a smaller toroid, electricity will be discharged more rapidly, but the arcs will not be as long. If you use a larger toroid, electricity will be discharged less rapidly, but the arcs will be much longer.

My toroid ended up being 4"x15" and it produces fairly long 3' arcs. To make it, I used two 8.5" aluminum pie pans that I found at Wal-Mart and a piece of aluminum dryer duct from Home Depot.

1. I bent my aluminum dryer duct into a circle around the bottom of one of my pie pans. You don't want to have any gaps between the dryer duct and the pie pans, so I bent it around the pan tight.

2. Once I formed the dryer duct into a shape I was happy with, I used aluminum tape to secure the two ends. I found that using glue and other adhesives will cause the toroid to underperform.

Place the dryer duct off to the side, we will come back to it later.

3. Bring the two pie pans together, bottom to bottom. While holding them in place with your hand, drill one hole through the center of the pans, and 5 other holes evenly spaced along the outer edge of the pans.

4. Place the dryer duct between the two pans and thread ceramic nuts and bolts through the six holes we just drilled.

5. Tighten the nuts until the lips of the two pans securely tighten up against the dryer duct.

6. Keep tightening the pans together until the dryer duct is firmly sandwiched between them.

The nuts should be tight, but not so tight that they crush the dryer duct.

Center the completed toroid on the top of the secondary. It should make contact with the aluminum foil tape from the previous step.

Step 8: The Wiring

When I started building my Tesla Coil, I had a hard time finding a tutorial that went in depth with how to do the wiring. After a lot of research I was able to piece it together and it is pretty simple.

In this instructable, I'm going to attempt to explain the entire process step-by-step. I uploaded numerous pictures and some of you can probably figure it out just by looking at them. If there's anything that you're unsure about just ask and I'll respond as soon as possible.

You may be wondering why I have chicken wire rolled out underneath the base of my Tesla Coil. This chicken wire actually serves as my ground. If you don't have access to a good ground, or if you don't want to pound a grounding rod into your backyard, just use chicken wire. It works great, I never had a problem with it. If you use this type of ground, the chicken wire must be at least 10'x10'. I couldn't find a size that big so I ended up using two rolls of it side by side.*

Please note that all wiring used in this step should be at LEAST 12GA.*

1. To power the transformer, use a long extension cord. This will keep you at a safe distance when you plug it in. I chose to wire my extension cord through a light switch, that is entirely up to you.

2. One wire will run from each output of the transformer to opposite ends of the spark gap.

3. From here, a wire from one side of the spark gap will go through the upper layer of your base, and clip onto the inner turn of the primary.

4. A wire from the other end of the spark gap will go to one end of the capacitor array.

5. A wire will come out of the other end of the capacitor array and attach to the outer turn of the primary. For my coil, I found that it performed best when attached to turn 14.

This wire may have to be adjusted to properly tune the coil. In an effort to make the wire easily adjustable, I created a clip-like device that can be used to clamp the wire to the the primary. To create this device, I used a modified 30A fuse holder from Radioshack. I uploaded numerous pictures of this "clip" in an attempt to show how I did it.*

6. A wire will wrap around the strike rail and travel down to ground.

7. A wire will travel from the copper lug terminal underneath the secondary and go to ground.

Step 9: Fine Tuning and Operation

Your Tesla Coil is now ready for use! The first time you power it on, keep an eye open for any sparks at the bottom of your secondary or at your capacitor array. If you see this, shut it down immediately. This is an indication that your secondary is not properly grounded.

The Tesla Coil may need to be tuned before it will run properly.

Try clipping the wire onto different turns. For me turn 14 worked the best, for you it might be different. If you're having a problem, adjusting the primary in this fashion should take care of it.

DO NOT touch the primary coil or any component on the lower layer of your base while the Tesla Coil is running! The results could be fatal.

Before operation, always use an ohm meter to make sure the toroid is properly grounded.

It pretty much goes without saying, but please do not attempt to make adjustments to the Tesla Coil while it is running!*

Thank you for taking the time to read my first instructable, I hope it was helpful to you. If you end up making a Tesla Coil please send me pictures/videos of it.
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