Nikola Tesla's famous air core transformer--aka the Tesla Coil--was developed in the 1890s as a source of high voltage, high frequency electricity. In those days it was a valuable component in the emerging field of wireless telegraphy, and Tesla had ambitions to charge the earth and upper atmosphere in order to supply electrical power throughout the world without costly and cumbersome power lines. His concept did not work out for various reasons, and the Tesla coil survives today as a project for hobbyists. The design below is based on popular designs published for amateur builders circa 1910 or so. I have modernized the frame by using PVC, but the horizontal coil was very popular with early radio experimenters in that long ago time.

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Step 1: The Frame

The frame of the tabletop Tesla is made entirely of half-inch (12.7 mm) PVC pipe. There's no point giving you exact dimensions of the stringers and risers because they depend on how big your secondary coil is. You can scale the frame up or down as you wish. I used a 12 inch long cardboard tube for mine, making the footprint of my coil 14 inches by 11.25 inches.

Study the pictures and you will see how the frame is made. The configuration as made requires the following joints:

(4) 90 degree elbows;
(8) "T" joints
(2) end caps

All the rest is straight half-inch tubing, cut to length. NO CEMENT WAS USED TO JOIN THE PARTS and none should be used. The friction fit of the tubing is reasonably strong, and leaving the joints unglued allows you to take the frame apart to work on the coil, make adjustments or repairs, etc.

The center uprights consist of three T joints each, stacked vertically. Short lengths of tubing connect these. If you make a bigger coil these length will have to be adjusted accordingly.

The cross piece that runs underneath and parallel to the secondary coil has to be drilled for the primary supports. Find the center point of the cross piece and drill two holes so that the primary form in centered on the secondary. Again, I can't tell you exactly where, because it depends on what you use for your coil forms. But center it and it will be fine. See the page on the Primary for more details of the mounting method.

The secondary is supported by plumbing caps and tubing adapters inserted into the cardboard tube. The tube I used is 1.75 inches in diameter (it's a thick-walled cardboard paper towel tube). I had to experiment at the home center to find off the shelf PVC plumbing pieces that would fit, but I found ones that slip in closely. Again, no glue was used. You want to be able to remove the secondary for maintenance or replacement.

In the two topmost T joints insert plugs to support the brass terminal posts. These can be anything non-conductive--cork, rubber, etc. I found wine corks fit nicely. Push them down equally on each side until they are level with the top edge of the secondary form. Above them fit a length of PVC tubing. Exact height is not too important; they should be tall enough to keep the terminals away from the active coils to avoid arcing. Mine are four inches tall each.

Drill 3/16ths holes in the center of two PVC pipe caps for the terminals. Drill small holes--about 1/8th inch--in the support tubes opposite the ends of the secondary coil to feed the secondary's wires through. See the step about the Terminals for final connections.

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can i change the power supply and reduce the voltage as i am doing this for a school projet and 7200V seems very dangerous.

Mr. Apol (author)  katanadayoshimitsu3 months ago
7500 volts at 30 milliamps isn't as fearsome as it sounds, but you can operate a Tesla coil at voltages as low as 3000. Streamer output will be commensurately less. You will also need to re-balance the capacitance of the system to achieve best resonance.

Frankly, as long as you're in control of your apparatus (and you are a sane, responsible person ;-) ) voltage isn't too much of a problem. Be aware that coil generates RF energy, ozone, and other irritant gases, especially in a small space.


exactly what i was thinking about i dont think that a school project should be something that causes air pollution but thanks for your help.

GeckoScraps11 months ago

Thanks man, this worked well. Made this after trying one out on my own, didn't work quite as well. But still effective.

I am having trouble. When I connect my spark gap, It works. When I connect the capacitors and the coil, it stops working. I am making an oudin coil,and it is wired like this (see image). What could be wrong with it?
Mr. Apol (author)  Kirkthepyro1 year ago
I need more info. What is your voltage source (volts & amps)? How wide is your spark gap? What is the total capacitance of your tank caps? How many turns on the secondary? How many turns on the primary? Are they wound in the same direction? What is your topload and how is it connected?

Here is a toroid I think might work. I am trying to get visible streamers from my coil, but it is fully operational. Note the toroid is hollow.
I am using a 7.5 thousand volt nst. My spark gap is about a 1/2 of a centimeter wide. I have about 2.45 micro-farads in my caps. I will tell you the rest as soon as I get a chance to check it (I am kinda tied up a the moment)
There are approximately 330 winds on the secondary.There are 4-5 winds on the primary. My topload was made of tinfoil squished into a toroid wrapped in HVAC tape. I stabbed a hole in the bottom with scissors. I stripped one of the ends o my primary and stuffed it in. I do not undurstand what you mean by "wound in the same direction". Please clarify. Also, why does my spark gap not work when I attach the coil and the caps, but remain functional when it is isolated. It is connected in paralled, after all?
Mr. Apol (author)  Kirkthepyro1 year ago
More questions, and maybe a few answers.

What gauge is the wire in your secondary? What gauge is the wire in your primary? You say you connected the topload to the primary? I hope you mean secondary. Try to find a simpler topload--an old doorknob will do, or even an aluminum drink can (with all openings sealed with aluminum tape, of course). Wadded foil has enormous surface area. In effect you asking your coil to light up a huge topload.

Did you strip the enamel insulation from the ends of all connecting wires? (Don't be offended by the question; with clear enameled magnet wire it can be easy to forget to strip the insulation).

2.45 microfarads is way too much capacitance. It should be more like 2.45 NANO farads. This alone will prevent your coil from operating! Though the NST will make the spark gap fire, there is way too much capacitance in the system to allow the coil to work.

It is often said that if you have a secondary wound in one direction--say, overhand--and a primary wound the other way (underhand), that this interferes with proper resonance. I have tried both configurations, and I can't say it makes a great deal of difference, but any difference in a very small coil makes more relative difference in total performance.
My wire is 24g wire. My primary is 12g I will check my insulation. You said the NST will make the gap fire even if my capacitance is to high, however It wont fire at all when i connect the capacitors, just when it is isolated. Why? I will go fix my topload, now.
Mr. Apol (author)  Kirkthepyro1 year ago
the wire gauges are okay, though 330 turns is a little low for really big performance. It should work fine with these gauges though.

It sounds like you have way too much capacitance. Trying to fire a coil with too high capacitance is like trying to fill a swimming pool with a teaspoon.

The spark gap merely shows you're getting 7,500 volts across the gap. Once you connect the oversized capacitors and coil, your voltage is getting lost in a way too large environment.
I saw your "Tesla's candlestick" ible', and your cap array. would you be willing to sell some to me? If not, where did you get them. Also, where did you get your NST?

Mr. Apol (author)  Kirkthepyro1 year ago

for example.
So I should just lower the capacitance?
Would photo-flash capacitors work? I have a ton. they are from old cameras.
If I solder a bleeder resistor across the terminals of the cap, will that work?
please help!
Machine1 year ago
Your countdown technician does a good job.

Nice Tesla. Thanks for showing us.
(removed by author or community request)
Mr. Apol (author)  Kirkthepyro1 year ago
Yes, that's bad. You will get arcing and poor performance from this. The secondary needs to sloothly wound, unkinked, and without any overlapping.

I will fix this
Check this out. I just finished:
-My capacitors
-the 2 coils
-the spark gap
Here it is:
Comments/constructive criticism welcome
Last minute question here. Would it work if I mounted the secondary vertically, almost like this:
tesla coil.png
Mr. Apol (author)  Kirkthepyro1 year ago
That will work, but it your going to make vertical coil, you might as well make a conventional style one. See my other instructable, "Tesla's Candle Stick."
I am going to build a conventional one after this. I need it to be bipolar because I wont have a source for my ground connection at the fair.(you have to bring a model for engineering. The only reason it is upright is to save space

Mr. Apol (author)  Kirkthepyro1 year ago
You can also build an upright style coil as an Oudin coil, or autotransformer. This involves connecting the lower end of the secondary to the lower end of the primary. This works fine, but it makes the output of the HV terminal more dangerous to come in contact with.

So would it look more like this(note the connections):
tesla coil.png
Mr. Apol (author)  Kirkthepyro1 year ago
No, for the Oudin coil arrangement the lower end of the secondary is attached to the lower end of the primary. There is no pair of top terminals, but a single terminal as with most vertical Tesla coils. Basically you're grounding the secondary into the primary. Be sure to connect the bottom end of the secondary to the bottom end of the primary; if the primary is wound on a cylinder form, use the lower end of it.

Don't touch the output arcs of any Tesla coil BUT ESPECIALLY DO NOT TOUCH THE OUTPUT OF AN OUDIN COIL.

I will probably do that! (I already wound my mag. wire and I will post a pic soon).
I am making a tesla coil like this, but vertical. I have the frame done here:
HI, I read your instructable. I am going to build a tesla coil for a science fair (demonstrating Wireless Energy). This is my first time doing so. Where did you acquire such an amount of mag. wire? also, will the tabletop version work for wireless energy? I am using this instuctrable: for the power supply. Will this work? Also, how do I calculate the capacitance I will need? PLEASE HELP!!!! ASAP! I need these questions answered. anyone please reply. Thanks in advance!
Mr. Apol (author)  Kirkthepyro1 year ago
1. Magnet wire is easily obtained on eBay. Just search for the gauge and quantity you need.

2. as you can see in the video, this bipolar coil will easily light up fluorescent tubes at a distance--the exact distance depends on the output of the coil.

3. Flybacks produce DC. My experience is with AC coils. It simplifies matters if you use a high voltage AC source, such as a neon sign transformer, oil burner ignition transformer, or car ignition coil. DC will work, but it requires a different approach.

4. If you build the coil as described in my Instructable, you will need about 3 nano-farads of capacitance (3000 pico-farads). You can find free or near-free programs to calculate capacitance and other aspects of Tesla coil construction: TeslaMap and JAvaTC are two of the most common.

Good luck,

I'm not skilled very much at all with electrical... Stuff. Do you think that you could email me a list of materials I would need and maybe a simple walk through?
Mr. Apol (author)  doubledogcowboy1 year ago
Al the materials and directions are included in the Instructable.

Cephus1 year ago
I might assume you are familiar with Alfred Morgan's old books? Your coil looks like a modern version of his Tesla coil from "The Boy Electrician." I could only imagine what he might have built so many years ago with modern materials such as PVC rather than shellacked wood or paraffin.
Mr. Apol (author)  Cephus1 year ago
I know the book well, along with Thomas Stanley Curtis' "High Frequency Apparatus."

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