Simple Tesla Coil




Introduction: Simple Tesla Coil

About: Just do things, electronics, woodwork, etc.

Hello! Today I’m going to show you how I build a Tesla coil! Probably you may know this device from computer games, movies or some “music tesla show” whatever they call it. If we ignore the mystique around the Tesla coils, it's just a high-voltage resonance transformer working without a core. So as not to get bored from theory let’s jump to practice.

Step 1: Circuit

There is a

circuit of coil, as you can see it’s very simple and we need only few components.

- power supply, 9-21V, also it’s gonna work from batteries with same voltage

- little heatsink

- Transistor 13009 or 13007, or almost any NPN transistors with similar parameters

- variable 50kohm resistor

- 180Ohm resistor

- cooper winding wire 0.1-0.3mm, I used 0.19mm which is 36 American wire gauge, about 200 meters.

Also we need a frame for secondary coil, it’s could be any dielectric cylinder diameter of approximately 5cm and length of 20cm. In my case it’s piece of 1-1/2 inch pvc pipe from home depot.

Step 2: Coils

Let’s begin from the most complicated part – secondary coil. It has 500-1500 turns turn to turn, my is about 1000 turns. Fix the beginning of wire and wind, actually you don’t need to count every turns, simply multiply diameter of wire to number of turns you planning to make - it’s going to be your winding length. When you done fix wire with some tape or better by couple layers of varnish.

Primary coil is much easier I put paper tape sticky side out, in case to save the ability to move it, and wind on it 10 turns of regular wire in pvc insolation.

Step 3: Soldering

Next is soldering, all under the circuit, PCB is not necessary. Be careful when soldering variable resistor! 9/10 coils didn’t work because of wrong soldered resistor. Connect primary and secondary coils, latter has a special insulation which must be scraped off before soldering.

Step 4: Turn On

So we done. Before you turn on the power at first time, place the variable resistor in middle position and put light bulb near to the coil, because usually you’ll not see high voltage sparks immediately and only thing notice that it's working is light bulb. Turn on power, and slowly turn the variable resistor. It's quite weak coil, and you can not get electrical shock because of skin-effect, but any way be careful and don’t place any electronic devices such as cellphones, computers etc. near to the working coil and notice that high voltage sparks is made of plasma and it's actually very hot, be careful when touch it. If Tesla coil doesn’t work, try to flip wires from primary coil, usually it helps, also you can try add or subtract a couple of turns from it.

Step 5: Final

Now lets talk about improving results, first you can do is rise voltage, but I don’t recommend go over 25V at this circuit. Second is playing with primary coil, logic is simple, fewer turns – more current equal more power and more hitting, I stopped at 5 turns, also try to move it around secondary.

But to be honest this circuit is so-so and can run only like simple model for beginners, next time I’ll show how to built real device. If like this instructable don't forget to check out my YouTube Channel :)

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30 Discussions


Question6 months ago

do u have a backup battery circuit

Is the schematic correct? The HV coil goes to the base of the transistor? I would think it would go to Battery Ground. But I looked online and that is how others show the schematic. And this one seems to work. Huh.

1 reply

The schematic is totally perfect dude connect in that way and circuit gonna work.

I used 20 turns in primary side and 2200 turns at secondary side but there is very less amount of spark at output what can I do for enlarge the spark

I am trying to make it for my science project, i have already tried the following method -

(by roman ursu hack)

but it DID NOT work.

can you please help me understand how this works in simple english and guess probably why this didnt work.

and CAN I USE 2 dc batteries of 9v used in remote controls?

and not use the heat sink

2 replies

I made a little tesla coil and powerd it with a "small" wimshurst generator we had in school.


I have just tried to build this project myself and have run into a problem. Does it matter which way the primary and secondary coil are wound? should they be oposite?


I finished the coil using almost the same steps.

I used a BD135 transistor, one Resistor - 47k 1/2w, 9V battery, 6 turns primary coil, 2400 turns secondary.

There is no spark, but it successfully lights lamps. There is though a small problem. When I approach a lamp to the coil, the lamp lights but if I leave it there
the lighting lasts only for 80-90 seconds and then fades away.

I have to close the circuit for some time and open it again to make it light again.

Could this be a heating problem? Can you help me with this?

Thanks for your help

Being pedantic, this isn't a Tesla coil at all, it is a simple Induction Coil.

A Tesla coil works on a totally different principle and generates far more spectacular results and is well worth taking the extra effort to make. Just Google Tesla Coils and you will find dozens of sites telling you how to make one.

8 replies

It is a Tesla coil if the secondary's coupling to the primary is low, and the secondary is resonant. When a relatively large secondary is made, the capacitance to ground tends to dominate, making this a Tesla coil if the primary is driven at that resonance. That is forced as he is using current feedback to the transistor's base.

What I would do is add an "anti-parallel" diode (most likely a 1N4148 or 1N914) across the BE junction (cathode banded end to B, anode to E) to carry reverse cycle of AC safely around transistor's BE junction, otherwise transistor could fry. Also a smooth metal toroid or ball on top would improve voltage output, and the E lead/battery minus lead should be grounded.

How long of a spark do you get?

I think your Idea is interesting, Could you edit the circuit diagram to show where you would add the diode?

The unmarked capacitor is selected to tune the primary's resonance to match that of the secondary. Diode, earth ground, and sphere on top are shown. What you do is: wind secondary, and put sphere on top. Drive bottom end of primary with signal generator (or kludged-together oscillator) connected through a 1K resistor. Ground other terminal of generator. Do not make any other connections. Put meter from ground to the 1K/secondary node. Turn on generator to a couple of volts. When you are out of resonance, meter will read generator's voltage (as expected, you have no circuit "connection"). Sweep the generator. When you hit resonance, the meter will show a dip in voltage. (This should happen at about 1 MHz). You know you have it when waving hands around secondary disturbs meter reading.

Wind the primary over the secondary, tape it, and then slip it off the secondary, but keep the form intact. Connect cap in series with primary, and sweep with generator as for secondary, except "far end" of primary is grounded. Adjust cap value until primary resonates at same freq as secondary.

Slip primary back on secondary, connect cap in parallel with primary, and proceed with Tesla coil assembly/test.


What is capacity of that "unmarked capacitor"???

That is explained in detail in my previous comment. My guess it will be in the 0.01 uF range. It is selected to resonate with the primary alone, at the same frequency that the secondary resonates with its top loading sphere only, with the bottom grounded. I can't give value, as that depends upon the diameter of the secondary, number and spacing of turns, and the loading capacitance of the sphere you choose. I would have to build an exact "carbon copy" of the coil to determine that. That's why I included the long-winded explanation of how to determine the value in the previous comment.

If you don't have test equipment, you can build an oscillator from a CMOS chip, a capacitor, a resistor, and a pot. Wave shape is not important, but stable amplitude is, which a CMOS oscillator will give you. The important thing is that you can "make the same frequency twice" by marking the pot position when you test the secondary, and tuning the primary to "dip" at the same pot setting.

Not pedantic.

I also clicked through thinking this was a tesla coil, when in fact it was not.

That is not to say its not well-executed, well-photographed, and very interesting.

Apart from maybe the start of a very dangerous electric fence energizer, what else could this be used for? Could the spark be used for some interesting process?


1 year ago

I realized after a few seconds that the red was a coil, and I wept for you.

That must have been an absolute bi-yatch to wind.,,,,,,,,,,