Introduction: The Simple Tesla Coil
This is a guide on how to build a medium sized Tesla coil. I built this one from parts I had laying around, all I had to buy was magnet wire, in all I spent less than $30! For those building their first coil, I would not suggest using this a standalone source of instructions. This is my first coil, and I used a multitude of sources to make it. Also, I did the boring math part behind it. At first I tried to skip some of the math, and just "wig it" but that didn't work. For the math part I would suggest deepfriedneon.com, but I found a much simpler site : http://www.classictesla.com/java/calculat.html#WireFreq . Once you know what materials and dimensions you will use, go to this site to get the whole resonance thing synced up as closely as possible. Read this entire guide, and maybe the comments section, before doing anything. Also read some other guides and maybe the Wikipedia article on Tesla Coils before deciding whether or not to embark on a shockingly frustrating, but rewarding journey. I built this for a high school science project, and although I finished at the last minute, it didn't take more than maybe 20-30 hours of work. I entered a few contests with this so you should vote for me if you enjoy this instructable.
I also must say that by using any information in this guide you assume all risks involved with the components, operation, and construction of Tesla Coils or any part of the circuitry described. I do not take any responsibility for injury or damage resulting from the use of this information. Tesla Coils CAN KILL YOU! Whether it be the streamers, 15kV NST output, or the simple (and most dangerous) 120V wall outlet input. All the currents involved with this project are dangerous! I would recommend working with someone experienced with high voltage if you are not. Also, this device is a major FIRE hazard. Use it only outdoors. To sum it all up, this project is risky, be careful.
Step 1: My Understanding of the Inner Workings of a Spark Gap Tesla Coil
From what makes sense to me, the Tesla coil is a magnetic resonator, otherwise just a really powerful transformer. Wall outlet current is converted to 15000 V by the NST, which then charges capacitors, which (once fully charged) allow electricity to temporarily "jump" the spark gap, which allows current to temporarily flow through the primary coil, generating a magnetic field, which the secondary picks up, and converts it back to a current (of higher voltage), which then flows into the ground and into the air (What a sentence!). This process happens 120 times per second or something like that. The Tesla Coil not only steps up voltage but also frequency, which makes the pretty streamers of death that obviously fascinate you (that's why you are here). Due to this high frequency, your nerves would not feel pain from the streamers conducting into your body, but they still cause damage! Basically, your insides would cook and you wouldn't feel a thing, but that is not going to happen because you are not to touch the streamers! Don't do it! Oh yeah, the diagram is from Wikipedia, thanks to another instructable to pointing out to me which one to use. Use the bottom diagram. The top one didn't even work when I tried it, and the bottom one makes more sense.
For the High Voltage transformer, I used a 15kV NST.
For the spark gap, I used two bolts in opposite sides of PVC pipe at a set distance.
For the HV capacitor, I used salt water "Leyden jar" capacitors made of Snapple bottles.
For the Primary, I used .25" diameter copper tube.
For the secondary, I used 24AWG magnet wire wrapped around 1.5" PVC.
For the Torus, I used Aluminum Dryer Duct that I cut open and wrapped around two aluminum pie pans.
Step 2: The Materials
Check out the other Tesla Coil Instructables and get an idea of what you want. I used the following materials and tools to build mine:
-Lots of plywood (about 12 sq ft)
-Lots of 1.5" diameter PVC (about 10 ft)
-Liquid Nail (1 tube)
-Electrical Tape (1 roll)
-High Voltage Wire (about 15 ft) I actually used some 8 gauge 600volt rated machine wire and left a lot of space between the wires to prevent arcing, but I still get the occasional arc, and fire.
-10 Snapple bottles
-Regular copper wire (about 5 ft of the single solid strand stuff used to wire your house)
-Canola Oil (Vegetable Oil might work, haven't tried it)
-Hot Glue Gun with a lot of glue
-800' 24AWG Magnet wire (got it from Amazon)
-10 ft of 1/4" diameter copper tube
-Spray on enamel (1 can)
-1.5" diameter Floor Flange (quite expensive, you could probably get by with drilling 1.875" holes in plywood and gluing pipe in)
-1.5" diameter PVC screw thing (attaches PVC pipe to floor flange)
-Aluminum dryer duct (length & diameter depend on your calculations)
-Two aluminum pie pans
-Long metal rod, 4'-6' preferable (it's a grounding rod, so it will be pounded into the ground)
-Small section of 2" or 3" diameter PVC (about 6" in length)
-Two bolts of any size with four matching nuts and washers
-A fan or blower is optional
-An Input Transformer!!! I used a 15kV 60 mA Neon Sign transformer <- GET THIS FIRST!!! Your entire design should hinge on the specifications of the transformer that you can get your hands on!
-Various drill bits
-Large diameter drill bit that makes holes that the PVC fits in nicely (mine was 1.875" diameter)
-Table Saw (circular saw can work if you are good at straight lines!)
-Long extension cord
-Type C Fire Extinguisher
Just Basic DIY project tools, I probably forgot a few...
Step 3: Get a Transformer!
I called around local Neon Sign dealers and repair shops, and browsed the internet. Just before I bought a new one on Craig's List (or maybe it was Ebay...) I got a call back from a neon sign shop a few towns over. They gave me an old one for free that worked just fine. So call around Neon sign stores, electronics shops, electronic recycling centers, or anywhere you can think might have something like a neon sign. Maybe you can get one for free!
Also Oil Burner Ignition transformers work, and so do microwave oven transformers. I don't know anything about using those, except that it is more complicated than just 120V in 15000V out. If you can't get a NST then go check out some other guides on using those transformers. In fact, even if you can get an NST go check out other guides anyway to get a better understanding of what you can do to build a Telsa Coil. The more info the better!
Step 4: Apply Math!
The inevitably boring part. Fortunately the computer can do most of the math for you! Go to http://www.classictesla.com/java/calculat.html#WireFreq or http://deepfriedneon.com/tesla_frame6.html to find out all the dimensions and statistics of your coil. Unfortunately I did not copy down most of the stats of my coil, but I do have the dimensions. The Capacitors have a capacitance of 4µF for each bottle, so I have a 40µF bank of 10 capacitors. The spark gap should be 9mm, but I shortened it to around 6mm or 7mm because it overheats quickly, a problem I am trying to solve with a more powerful fan. The Primary coil is helical with an inside radius of 4", an outside radius of 9", a height of 6", and 5.5 turns (It actually has 5.75 turns but the outside wire is connected at 5.5 turns). The Secondary Coil has a radius of 1.875" and about 1000 turns of wire. I lost the height measurement (I have had this finished for months but am just now getting to the instructable) but that is how I estimated the number of turns. I didn't actually sit there and count each turn, I just found the diameter of the wire and multiplied it by 1000 to get the desired height. I have two tops, a ball and a toroid. The ball I didn't measure and don't really care about (it's a softball wrapped in aluminum foil!!!) but the toroid I worked on (as seen in later step). It used to be almost perfectly round, but with all the traveling to and from the high school it got damaged. It used to be 10.5" diameter, and 3.5" tall (at it's tallest point, otherwise known as diameter 2 on deepfriedneon's topload calculator).
If you skip this step, your coil will not perform optimally, or not perform at all, as mine did after just guessing most of the math. Just do it now to avoid a re-do later.
Step 5: Assemble Capacitors
To build the salt water capacitors, also called "Leyden Jars", you will need 6-10 empty Snapple glass containers, a bunch of table salt, water, canola oil, a bunch of aluminum foil, a bunch of electrical tape, and some regular old indoor 120v 20amp copper wire (the stuff that comes in white sleeve with three solid single wires inside). The number of bottles will depend on your transformer, each bottle is about 4µF according to another Tesla coil instructable that I can't seem to find. According to Glen781's comment on DevCoder's Tesla Coil instructable, if you are using a 15000V transformer, as am I, 6 bottle capacitors will blow up! Use more! I used 10, and have had no problems. The higher the voltage, the more capacitors you will need. As you can see in the pictures, I used bolts instead of copper wire in the bottles. This didn't work very well as the bolts rusted. I have since replaced them with the copper wire.
1. Start by removing the labels and all the glue left behind. Also wash the bottles.
2. Put a tablespoon of salt in each bottle, consistency of the salinity is critical!
3. Add water until the water level is about two inches from the top in each bottle.
4. Mix salt and water by any means necessary. Wait a little bit for some of the salt to settle out, then mix some more!
5. After the salt and water are thoroughly mixed, add a layer of oil on top of the water, maybe 1/2" thick. This will combat coronas inside the bottle (I still get some).
6. Wrap the bottle in a few layers of foil, making sure to keep the foil 1" from the top of the bottle. If it is too close to the cap an arc may form. Then wrap some tape on to keep the foil in place.
7. Drill or poke holes in the caps, and put a length of copper wire in, make sure it has plenty of contact with the salt water, and not touching the sides of the container.
8. Use hot glue to seal the top, so that the mixture doesn't leak. I still wouldn't turn them upside down, though.
9. Connect all the capacitors in parallel. Wire to wire and foil to foil. The wire/cap is one side of the capacitor, and the foil is the other. I recommend connecting the foil together with wire, as any gaps caused by just taping the bottles together may cause arcing and fire.
10. I attached my capacitors to a separate piece of plywood that I can unscrew from the rest of the coil, so I can remove them if any problems arise. You don't have to do this though. I think that you have to mix up the salt water every now and then if you leave it in storage for long periods, so this might be a good idea.
Step 6: Make the Spark Gap
The spark gap is very simple on this coil, it is just two bolts set at a distance apart. I put them inside a pipe because that was easy and the light coming off the spark CAN BLIND YOU! Do not look at the spark gap while it is in operation under any circumstance. It is as bright as an arc welder and it emits UV light. Now that I explained the safety part, it's time to build.
You will need:
-3" Diameter PVC (4"-6" length)
-Two bolts, with four matching nuts and washers
-Drill with bit slightly bigger than bolts
-A fan (optional, but recommended)
1. Drill two holes, on opposite sides of the 3" PVC pipe
2. Put the bolts through the holes, with two nuts and two washers on each bolt, one nut/washer on inside of pipe, one on outside.
3. Adjust the gap between the bolts until it is around 8mm or 9mm. This measurement is for 15kV transformers. If you has a lower voltage transformer you will need a smaller gap.
4. If you want, you can put a fan at one end of the pipe, to cool off the spark gap. The bigger the fan, the better. I am currently attaching a hairdryer fan to mine, as the computer fan wasn't enough for constant operation. Mine overheats after about 10 seconds. Some people choose to use a shop vac to suck air through the gap, but I would be careful as the hot air might melt the hose.
Step 7: The Secondary Coil
The secondary coil is going to take a few hours, so before beginning work make sure that your schedule is open. You can either hand wind it, or use a machine. I prefer the hand winding as I felt too rushed by the motor I used. I propped up the PVC horizontally on two pieces of bar-stock so that I could spin it, and then I put the magnet wire on a pencil (to act as a spool). I used the thickness of the magnet wire to determine how long 1000 turns on my PVC would be. You can use other gauges of magnet wire, but I would recommend between 22 AWG and 26 AWG.
Edit: I think that you should stick with a larger diameter PVC to form the secondary. Maybe 3" diameter. Remember to update your math, as this will make a difference. I plan to try a larger diameter secondary and will post the results.
You will need:
-A length of magnet wire (depends on the diameter of your PVC, I purchased 800ft and used a good amount of it).
-A 3ft length of 1.5" diameter PVC (others seemed to get better results with wider PVC, check out some other sources, maybe 1.5" is too thin)
-Some electrical, masking, or duct tape.
-Spray on enamel
1. Find a way to hold up the PVC horizontally so that it can spin.
2. Attach the magnet wire 1ft from one of the ends of the pipe.
3. Start winding. Be careful not to cross the wire at any points. Some like to watch a movie while winding the coil, but don't! Attention should be directed at the wire.
4. Attach tape every now and then, just in case you drop the wire or something and it all unwinds, only one section will unwind (see picture).
5. After you have done about 1000 turns, put tape over each end of the coil, and remove the tape from the middle sections.
6. Spray on the enamel. I did three coats. The enamel will protect the weak magnet wire from damage, and it will help to insulate it more.
Step 8: The Top-Load
The top load, or the donut shape on top, acts as a very small capacitor in the secondary coil's circuit. I used pie pans and aluminum dryer duct to make it. I cut myself a few times while cutting the aluminum, so once again, be careful! As you can see in one of the pictures, I used a butane torch to solder the two parts together. That was a bad idea because the heat would warp the aluminum, then when it cooled it would change back to its original shape, and the solder would break off. I found that I didn't need any adhesive to hold it together.
You will need:
-3 ft of Aluminum dryer duct
-Two Aluminum pie pans
-Scissors that you don't care about
-Maybe some hot glue and a glue gun (Mine held a donut shape without any glue, but you might have to glue it in shape.)
1. Invert one of the pie pans, and place it on top of the other. Apply tape around the seams.
2. Cut the dryer duct from one end to the other. Try to fit it to the pie pans. If it doesn't fit (mine didn't), it may be necessary to cut off some excess duct, to make a "C" shape.
3. Now that you have an aluminum donut, cut a hole in the bottom of it where it can fit on top of the PVC of the secondary coil. Or you can just set it on top. I like the hole because I did not glue or tape it in place, only gravity is holding it on. I found out that I had to remove it when driving it around in the truck bed as the top load would just blow away in the wind.
Step 9: The Primary Coil
The primary coil of a Tesla Coil can be of two shapes: a flat, spiral coil; or a helical coil. The dimensions of which are determined by the equations mentioned earlier. Changing the number of turns on the primary coil is how you tune the resonant frequency of the primary circuit to match that of the secondary (which increases the efficiency, and the length of the streamers). My secondary is made with .25" diameter copper tube (common among Tesla Coils due to the skin effect), wrapped in a helical coil. The inside diameter is 4", the outside diameter is 9", and the height 6". It has an overall length of about 5.75 turns, and the topmost wire is attached at 5.5 turns (according to the equation). I originally used a flat spiral primary coil, but switched to this when it didn't work. It turns out my wiring was at fault, but I kept the helical coil anyway.
You will need:
-10 ft of .25" diameter copper tube
1. Get the tube out of the box it came in and DO NOT straighten it. If you noticed it is already in a spiral shape, and the more you bend copper the harder it gets, so do as little bending as possible!
2. Form it into a flat spiral of 4" inside diameter and 9" outside diameter. Try to keep the spacing between the tube consistent.
3. After that shape is formed, then grab the outside edge, and lift until it is 6" tall.
Step 10: The Structure
Your done! Right? What will hold all these parts together? The support structure, although not on your mind, is probably the most important part. It has to hold all the parts of the coil (mine weighs a good 75-100 pounds) and be non-conductive. I used plywood for mine, and used 1.5" PVC as the legs that hold up the "shield" that keeps the streamers from striking the important stuff. I also used liquid nail at almost every joint, because real nails are metal and therefore conduct electricity. I found some shopping cart wheels in my garage (no idea what they came from) and put those on the bottom so I could transport it, as I knew that I would be moving it a lot.
You will need:
-A lot of plywood
-1.5" diameter PVC
-A 1.875" diameter drill bit (to drill holes for the PVC to fit in)
-Circular or table saw
-Liquid Nail or similar adhesive
-Caulk gun for liquid nail
-.25" diameter drill bit
-Floor flange and PVC screw fitting (if you choose to do it this way)
-PVC primer and glue (if you choose the floor flange)
-Some screws for the floor flange
1. Cut a piece of 2'x3' plywood as a base.
2. Cut a 2'x3' piece of plywood as a top/shield (I forgot this and put together two different pieces of plywood on mine).
3. Cut the PVC into 5 sections 1ft long each.
4. Cut 10 small pieces of 3"x3" plywood. Then drill PVC sized holes in each.
5. Screw the floor flange 1ft from each edge of the base plywood.
6. Using the liquid nail, glue each piece of PVC sized hole plywood in a corner of the base, and one in the middle.
7. Repeat step 6 but do it to the bottom of the top/shield piece.
8. Put PVC in each hole before the glue dries. Put the top on the base, and it all should fit together.
9. Clamp all that down and let it dry overnight.
10. Drill a 1.875" diameter hole in the shield board directly above the floor flange.
11. Insert the non-coiled section of the secondary coil into the hole, so that it rests on the floor flange.
12. Using the PVC glue and primer, glue the screw fitting onto the secondary coil's bottom, and screw it into the floor flange.
13. If you don't want a floor flange (they're like $10!) you could just make another 3"x3" piece of wood with PVC sized hole, and glue the bottom of the secondary in that.
14. Drill two holes in the shield, one at the beginning of the primary coil, one at the connection point (5.5 turns). Make sure that the primary is centered around the secondary before you do this.
15. If your capacitors are on a separate piece of plywood, like mine, you should screw them down to the base somewhere along the edge, that way they are accessible. I used screws instead of liquid nail because they can be removed in case I need to repair or replace the capacitors.
16. Attach via tape or glue, or both, the spark gap to one of the outside legs. Make it easy to access as you may need to adjust it often.
As you notice, I didn't follow these steps when I built mine, I just did whatever. These steps would probably work better, but feel free to copy what I did if you want.
Step 11: The Wiring
If something goes wrong and your Tesla Coil doesn't work, it is almost always something wrong with the wiring. There are two ways to wire up a Tesla Coil, but I found the second to be most effective. The image is from the Wikipedia page on Tesla Coils. High Voltage wire is the best for this, but if you can't get any, just do what I did and get some heavy duty wire, and leave lots of space between them to use air as an insulator.
Good rule of thumb- Use 1 inch of air per 10000 volts as insulator. Because my transformer is 15kV, I used 1.5 inches between any wires, usually more just to be on the safe side.
You will need:
-Some type of heavy duty or high voltage wire
-Liquid electrical tape if you want
-Wire cutters suitable for the wire (I ruined a pair of regular wire cutters on the 8 gauge wire)
1. Put the capacitors, spark gap, and transformer as far apart from each other and from the secondary as possible (on the base).
2. Run a wire from the bottom of the secondary coil (connect the heavy duty wire to the loose end of the magnet wire) to your ground rod. DO NOT connect it to a ground of your house! Anything else connected to this ground rod will be fried!
3. The ground rod optimally will be 5 ft into the ground, but less works too, and isn't nearly as hard to get out when you are done.
4. Connect the transformer to an extension cord, so that you can turn it on or off by simply plugging it in.
5. Connect one output of the transformer to the tops of your capacitors. Connect the other output to the sides of the capacitors.
6. Connect the top of the capacitors to one side of the spark gap.
7. Connect the other side of the spark gap to the top of the primary coil, putting the wire through the hole you drilled in the shield for this purpose.
8. Connect the sides of the capacitors to the bottom of the primary coil, through the hole in the shield drilled for this purpose. Be careful around the place where the secondary connects to the ground wire. It is best to wrap this and that connection in as much electrical tape as possible. It may arc 3 or more inches if not properly insulated.
9. Connect the toroid to the loose end of the magnet wire on top of the secondary coil.
10. Double check all connections, and apply tape where any loose connections are made.
A good idea is to include a safety gap. Just make another spark gap that is just a hair too wide for the transformer to jump, and connect it across the two output terminals of the transformer. That way, if residual magnetism of the secondary coil causes a feedback into the transformer, a feedback that is more than the transformer's voltage, it will spark and dissipate the charge.
Step 12: Operation
This is the moment that you have been working toward- the first operation of your Tesla Coil! But you need to make sure that you do not jump the gun and do something stupid to mess it up. It is not uncommon for an electronics project to not work on its first run, so don't get your hopes too high, as I did. There are only a few more safety things I must cover, so bear with me.
First of all, Operate this OUTDOORS! There are so many bad things that can happen if you do this indoors- fire; destruction of appliances, and why would you not want your neighbors to be afraid of the mad scientist next door? Also, it is best to use this at night, as the sparks are not very bright, and you can barely see them when there are other sources of light. The only drawback of using it at night is the noise- Tesla coils are LOUD! It's mainly the spark gap, but the streamers add to the noise. It is about as loud as power tools, so don't use it too late or the police might show up and write you a ticket for noise/disturbance. Also, like I said earlier, Do not operate this device near any living things, as it can turn them into non-living things. Just use common sense and don't use it near anything you don't want broken.
Another safety tip that is essential is have a Type C rated fire extinguisher within arm's reach! This is rated for electrical fires, so it will work best. If fire occurs, unplug the device first and then spray it down. Mine didn't catch on fire until the third or fourth time I had it on, so be ready for fire every time you use it, even if it has a flawless past.
Now for the operation.
Put the Tesla Coil on the ground about 20 feet away from anything you don't want broken, including people. Make sure that it is grounded properly, or it will not work. Plug in the extension cord, and hopefully you get what you want! If nothing happens, put a "breakout point" on top of the toroid. I put a metal rod on top. This should help let the streamers escape the donut. If nothing happens this time, check your wiring, all of it. Try again. If nothing still happens, make the spark gap smaller and try again. Even if your equations are wrong, the coil should still produce some discharge, so you don't need to trash it if it still doesn't work. Check out some troubleshooting guides, such as deepfriedneon's. Eventually you will get what you want.
The only fun things to put on the Tesla coil that I found were Fluorescent Bulbs. They will glow, even if they are many feet from the Tesla Coil. Another fun thing I did was put a metal tiki torch pole near the toroid. A large streamer jumped to the pole and that was the biggest I got with my original configuration (I haven't tested the updated version at the time that I am writing this instructable). It was about 10" long. I think that my design could get bigger sparks if I tune it more properly. Another fun thing was I took off the toroid and replaced it with a softball wrapped in aluminum foil. The ball produces hundreds of small streamers instead of a few big ones.
If you have a camera with adjustable shutter speed, take an over-exposure of the streamers. You get results like the one pictured. If you plan to video tape it, use a camera with nightvision. I found that my old sony nightshot worked way better than my 1080p digital camera, just because you could actually see something.
I end this project with two tips:
Be safe, and have fun!
Here is my YouTube channel with the videos that I took of the original Tesla Coil. If I get it better tuned, I will upload more.
Here are all of the places I used for information. Check them out, they may help you:
Finalist in the
The Mad Science Fair