This is the guide to make a device which runs on a battery and produces sparks at tens of thousands of volts very rapidly.
You can do a lot of things with it but it's on this site because you can also use the high voltage sparks to ignite and thus fire a combustion potato gun.
How it works:
The capacitor charging circuit from a camera is used to charge a small capacitor. Not the electrolytic capacitor from the camera. A different one.
When the capacitor reaches X volts then a spark gap which arcs at X volts will arc across and dump the capacitor through a high voltage coil.
The high voltage coil then puts out a very high voltage spark on the other side.
The capacitor loses its charge, the spark gap stops conducting and it all starts again with the camera circuit charging the capacitor.
All that will happen about 20 times a second.
How to:
First you need the capacitor charging circuit from a disposable camera. Any will do but the easiest way is to get a Kodak Fun Saver camera. The Wedding and Custom Kodak cameras are the same thing by the way.
Get the battery out of it, and short out the capacitor before removing the circuit:
Chop off just that corner with the charging circuit on it (click to enlarge):
Solder two pins and add four wires to make it usable (click to enlarge):
That's the difficult bit done.
The rest is plug and play. These are what you need (click to enlarge):
The spark gap in this example is a 350V gas discharge tube (so it will arc at ~350V). You may also get by with an open air gap as commercial stun guns use which is two strips of metal crossing each other separated by a thin insulator.
To assemble follow the video:
[youtube][/youtube]
Finally, pack it up into a practical size:
I doubt anyone could make it smaller but feel free to try....
Making It Smaller Challenge Accepted - By Me
Here is the current incarnation of the circuit fully boxed up, complete with battery.
[youtube][/youtube]
Reminds me,
Safety:
This circuit produces tens of thousands of volts. Be extremely careful with the output, it can and will jump gaps of several centimetres.
Ideally, use a momentary switch so that if you do get electrocuted by it, it's easier to switch it off.
The capacitor will store a voltage of several hundred volts even when the circuit is turned off, short it out before working on the circuit.
The high voltage sparks are VERY likely to cause interference and damage to nearby sensitive electronics even if the sparks do not make contact. Don't run it near an expensive phone or computer...
Bear in mind the sparks cause ozone and nitrogen oxides to be produced as they ionise oxygen and nitrogen in the air.
Both gases cause irritation and damage to eyes and lungs. Try to be in a ventilated room or outside if allowing it to spark for any notable length of time. A small closed room is not ideal.
Credits:
Chap on here called Spudgun on Crack asked me in 2007 about how the camera charging system worked. I told him and showed him a working circuit with the bare minimum components.
A year later in 2008 he gets back to me and tells me he's found that instead of unsoldering components to make the circuit, a certain Kodak camera has the entire charging circuit in one corner of the board which can be easily cut off.
This was the Youtube tutorial he did: Click Here.
Bear in mind he added a redundant diode, there is a diode already on the board, another is not needed.
And if you're interested...
Spark Energy
The spark generator here is being described for gas ignition so it must have sufficient energy in the sparks for ignition.
If we examine the minimum energy for the ignition of gases:
Source 1 reports a minimum energy of 0.02mJ to 0.18mJ.
Source 2 reports a minimum of 0.1mJ to 0.3mJ for most gases.
Now that's a minimum, throw in problems with bad fuel mixing, wrong fuel/air ratios and the energy is going to need to be higher for reliable ignition.
The circuit I've demonstrated discharges a 0.22uf capacitor at 350V.
Energy in the capacitor is ½ CV^2 = (0.00000022 x 350 x 350)/2 = 0.013475J or 13.475mJ
Even considering some losses in the circuit, the energy in the spark produced will be significantly greater than the minimum needed for ignition.
On top of that, the circuit doesn't just spark once. Spark rate depends on voltage but typically with two fresh 1.5V alkaline batteries a few dozen sparks per second can be produced.
A single spark may be sufficient but generating a shower of sparks each with the potential to ignite by itself provides greater reliability and due to the rate the circuit can cycle at, minimal delay between triggering the circuit and the first spark being produced.
If it takes 1 spark or 5 before it ignites you wouldn't notice. On the other hand if you used piezo ignition you'd notice if the first few didn't work.
Further stages
A) Replace GDT with SIDAC and see how that compares, initially suspect it won't like the high spark rate and may require a resistor to slow things down. That or dropping input voltage to 1.5V.
330V SIDAC incoming.
Done that, SIDAC works fine. Simple and direct replacement for the GDT in this circuit.
B) Crank up the power from 13.5mJ per pulse to 500mJ per pulse as used in certain high power electroshock devices. Requires a higher voltage switch, changing the capacitor, adding a voltage multiplier and perhaps beefing up the power supply.
1KV GDT, 1KV 1uF capacitor, bunch of caps and diodes and second power supply in the pipeline.
C) Pack up the coil driver into the smallest possible package. A much physically smaller capacitor and a SIDAC should do the trick.
Also done, see boxed circuit clip above or page 3 of this thread for details.
