AA Battery Powered "Tesla Coil"

First things first:

DISCLAIMER: I am not responsible for any injuries or property damage that may befall you from following this instructable. High voltage electricity can be DANGEROUS and should only be worked with at your own risk. Proper safety precautions should always be followed. 

That out of the way, welcome to my first instructable. Seeing as this is my first, any suggestions for improvements are greatly appreciated. Just go easy on me.
This is intended to be a how-to guide for a newbie to high voltage (like myself) looking for a quick, cheap, and relatively safe project. Although this is not a true tesla coil, as it does not utilize a resonant air-core transformer or operate at high frequencies, in effect it is similar. It still throws out plasma discharges from the top load and about 3.5 centimeter arcs to ground. Estimated output is about 100kv.

Step 1 Parts and Pieces

There aren't many parts to this build, and most can easily by scrounged from old TVs and other electronics or be bought for cheap. The following is needed:

Bug zapper racquet: This can be purchased from Ocean State Job Lot for about 5 bucks, and is nifty for fending of mosquitos or high voltage experiments. There are probably other types of devices very similar, but I would recommend finding the racquet pictured to insure the internal circuitry is the same.
Flyback transformer: Any flyback transformer will do, though the bigger the better. Don't kill yourself looking for an old non-rectified design, since there are no benefits of it for this circuit.
Random assorted hardware: This circuit requires a spark gap to be constructed. The design of the spark gap can vary, as long as the two ends where the arc jumps is rounded, and the gap adjustable. For mine, two Erector set brackets were used. One had a ball bearing soldered to it, the other a nut over top the hole, so a bolt with an acorn nut on the end can be threaded through. See the attached picture for the details. 
2xAA battery holder: Can be purchased from Radioshack or the bug zapper handle can be used to hold the batteries.

Optional: 
Additional Capacitors: Should be rated for at least 1.6 KV. The Bug zapper already contains one, but for bigger sparks more can be used.
Toggle Switch: The switch on the board of the bug zapper can be difficult to use, and because of the design of the bug zapper circuit, floats at high voltage, leading to a shock hazard when it is exposed. Because of this, a new switch is recommended.
Pen body or other plastic tube: To elevate the top load
Top load: I used a ball bearing, but anything smooth and without sharp edges or points can be substituted. 

Of course, solder and a soldering iron as well as other general tools are needed, and wire for connecting everything together

Comments

[BrunoG]

Good project but what is the range of the value of the capacitor bank is it in the range of 10 to 500pF or 20 to 600nF or 1 to 20uF?
Please respond.

[JoeBeau]

To say it simply- I dont know. Each of the large red capacitors are .1 uF, but the blue ones are unmarked except for "1.6 kv" Seeing as this project does not use resonance like a true tesla coil, the capacitor bank does not make a huge difference. I would guess that my cap bank is between .2 uF and .4 uF. But dont worry abou it too much.

[BrunoG]

If it helps

[f22archrer]

a little help here please... i want to make this for my phy project..and have successfuly done..till what you have done!! thanks alot for that..

now i was just wondering if I could show the teacher...a small LED bulb glowing with this tesla coil... is that possible with 1k voltage???

please answer

[JoeBeau]

1 kv is kinda high for an LED, bt they do gow, yes, at voltages like that. This circuit can be used for that. What would probably be a better idea is to use a flash bulb from a disposable camera. You can actually see the spark travel through it. Or, a small neon bulb

[tesla man]

One more question. When you said the racket had capacitors, what did you mean?

[JoeBeau]

There was one large storage capacitor allready in the racket, as well as a voltage multiplier circuit with 4 more small caps. I had a broken reacket lying around, so i used the stroage cap from that and the caps from the multipier circuit as well as the storage cap from the racket that the circuit is from to build the capacitor bank.

[tesla man]

Would You leave the capacitor in the racket circut board thingy, or take it out?

[Extreme Intellect]

You would leave it in.

[f22archrer]

can i get a led glowing out of it??..

[-max-]

its better if all your capacitors are identical, and wired for more voltage (series) and have at least a 1M resistor across all of them. you might consider making your own out of aluminium foil, and plastic sheets

[Nicola Tesla]

what does the resistor do?

[-max-]

it evens the voltage across all the capacitors. you learn in science class "a series circuit divides voltage across all the loads" (capacitors, in our case) well, caps are tricky, if they are not EXACTLY the same, some will charge with more voltage than others, and that can cause the overloaded capacitor to fail, and conduct, then its a chain reaction, the voltage is now divided among fewer capacitors, and are charged to higher voltage, causing them to fail.

[Nicola Tesla]

oh thanks for telling me! =)

[JoeBeau]

Just to clarify- my spark gap under normal operation is less than a millimeter in diameter. sometimes, its even smaller.

[-max-]

for every millimeter of spark in the air, is 1000V (this means a inch long spark is 20,000 volts! )

[tesla man]

thats not potentially true... a taser is 10,000v but across the leads,an at least 2 inch spark can be formed.(depending on the taser.)

[-max-]

i always see them rated at 500,000V to a few million volts. and they have pointed electrodes, i forgot to mention that, the 1000V per mm. is for smooth polished electrodes in the ideal atmosphere.

[JoeBeau]

What can change the spark length however is the roundness and size of the electrode. The estimation stated above is for a rounded electrode of a certain saize. (i found a chart online that gives a voltage estimate based on the distance between two round electrodes of a certain diameter) A taser usually has pointier electrodes.

[Nicola Tesla]

ok thanks i'll try it out when my better caps arrive

[-max-]

do you know about basic electronics, you shouldn't build this if you don't. also, for a more true Tesla coil, you need a really old huge flyback transformer. every now and then, a good one comes along eBay, and you can get one out of a really old TV. for a even more realistic coil, make your own primary and secondary coil. only then will you have a true "Tesla coil"

[Nicola Tesla]

yes i now "Basic Electronics" and i don't plan on making a bigger one

[-max-]

good, you should also know high voltage safety precautions. a real tesla coil doesn't need to be large.

[-max-]

i dont have too many high voltage capacitors, all of them have different values, i make my own with wax paper and foil.

[-max-]

OK. but still, be on the safe side

[tesla man]

So, what is the voltage output of the spark?

[JoeBeau]

from the racket it is in the neighborhood (from my estimates) to be 1.5kv. From the flyback itself it is over 100,000. again, that being an estimate

[tesla man]

So, from my understanding, It starts out at the racket circut board, goes to the flyback transformer, which goes to the switch. Then the spark gap and cappacitor, and finally the primary, seconday, and topload. Is this correct????

[JoeBeau]

not quite. the switch turns power on from the batteries to the racket board. it then steps it up, and charges the capacitors, connected in parallel to the output side of the board. From the caps, it goes into the primary side of the transformer. While one wire from the caps goes directly to the tranformer, the other side goes through a spark gap. On the secondary of the transformer, one side goes to the top load, the other to ground. Steps 4 5 and 6 have pictures with ladels showing where each wire connects.

[tesla man]

Thank you!

[techno guy]

Can you make a schematic of that driver circuit thing?

[JoeBeau]

i could, yes, but unfortunately with school/work/sports that could take a while. i can tell you that the circuit is very simular to the single transistor flyback driver, with what looks to be a feedback coil and everthing.

[mmaaz]

can you show me back of capaciter's bank

[JoeBeau]

Sorry it took so long but i didnt have a camera. I realized that the caps are glued onto the board, so a picture of them couldnt be taken. But i drew a diagram of how they are wired.

[JoeBeau]

All the capacitors are wired in parallel, so there are two parallel traces along the back of the board that the capacitors are wired into. I'll get a picture up once i have a chance.

[EEduino]

Would it be possible to make a singing tesla coil with this? I think all I would have to do is change the circuit a bit and use fiber optics to send the signal from my computer. I'm just trying to find a low cost way to do this, and I love how simple this is setup!

[JoeBeau]

To make a singing tesla coil, it needs to have a modulated signal and be solid state. With a spark gap, this coil is not solid state. Also, the circuit is not capable of modulating an audio signal. If you were to search instructables, you'll find circuits for a singing tesla coil. Unfortunately, this setup is too simple to allow modulation.

[D.L.Downs]

Enjoying the info, I was wondering instead of the spark gap could I use a 555 or a simply relay with a cap to buzz off and on? Also could I use 9v in place of the AA? to get a small bit more on the out put? Thank you

[JoeBeau]

The bug zapper circuit is not meant to run off a 9 volt battery, so i would be afraid that it would fry. The spark gap has around 2 thousand volts pulsing through it, so a 555 might not be able to handle it. As for the relay, i have used something similar fro making a quick and dirty pulsed supply for driving a transfromer, but here it might not be a good idea. The voltage stored in the capacitors is great enough that it would use the small gap between the contacts in the relay as a spark gap, and you would not get consistent opperation. But both these alternatives seem to be more complicated than the spark gap.

[isaksena]

Joe, in the first photo what is the rod-like thing near the ball bearing with which you're getting such long bolts ?