Build Your Own Stun Gun Introduction Do you feel the need to protect yourself in the event of an attack? Live in a country where stun-guns and most other weapons are banned? Then this page might be for you. It discusses the construction of an electronic shocking device called a stun-gun. It’s nonlethal according to the companies who make them commercially, and it is fairly easy and cheap to build. This page is really for people who already have experience with electronics, or those who wish to learn. Having said that, you don’t need to know how it works (although it helps with trouble shooting), and the only skills you need are soldering and recognising components. In its current state, experimentation by the constructor is required if a decent weapon is to be built! It is probably best to use it for intimidating the attacker, and only actually used as a weapon as a last resort. Also please remember that this device is intended for self defence against the many people in this world who like to start fights unprovoked.
Circuit Description The first “block” is a multivibrator (oscillator). The purpose of this is to turn the DC into AC (pulsed DC in this case) by switching the power transistor on and off very quickly. The power transistor sends a current through the primary winding of the transformer every time it’s switched on, creating an electric field in both primary and secondary coils. The field changes as it’s switched off, creating a high voltage in the secondary winding. This high voltage is fed into a voltage multiplier, which increases the final voltage (by the amount fed in, peak to peak AC) at every stage. This is used to give a bright spark at the electrodes.
Construction of the first stage I built the first stage on stripboard, apart from the transformer. The power transistor Q3 was mounted on a small square of aluminium to act as a heatsink, but the transistor doesn’t get hot with my setup. The component values are rough, as I used the one’s I had lying around. The resistors should be about that value, and the capacitors can be between 0.01uF and 0.1uF. The resistors/capacitors in the first “block” (apart from R5) determine the frequency that the device operates. The optimal frequency is fairly low. At high frequencies, the device simply won’t work as the power transfer from the oscillator to the transformer is so small. I use a preset for R1, and vary the frequency for maximum efficiency. For Q1 and Q2, just about any NPN transistor should do, so long as they can withstand the voltage/current, same with Q3. When originally testing this circuit, I used a car ignition coil as the first transformer. It has 3 terminals, just mess about connecting it up until it works! With a 9.6v battery pack made up of 8 AA ni-cads, I was getting a 4mm spark from the secondary winding. Using a 9v PP3 battery, I got a smaller spark (the battery may have been flat). I also tried using a mains transformer. I used the low voltage winding as the primary, and
the mains winding as the secondary. I don’t know the spec of the transformer, but I was getting a 1mm spark.
Construction of the Voltage Multiplier The capacitors and diodes should be able to withstand the peak to peak RMS voltage output at the secondary coil of the transformer. They should be well spaced out so that sparks can’t jump from one stage to another, and possibly encased in some type of insulating epoxy (potting compound) or oil.
Power I got many emails asking where to connect the battery and switch. I can see why it wasn’t clear, so here you go: Connect the negative terminal of the battery to the ground (0V) of the circuit, and connect the positive terminal of the battery to one terminal of a switch. Connect the other terminal of the switch to the +9-12V input of the circuit. Be sure the switch is off whilst you’re doing this!
Stripboard Layout I’ve finally got round to sketching the layout for the stripboard. The arrow indicates the direction of the copper strips (vertical). Q3 is mounted on a heatsink, thus it isn’t on the board, and I have used a preset for R1 so that I can vary the frequency. The tags on Q1 and Q2 indicate the position at which they must be mounted. If you use different transistors, it is likely that you’ll have to mount them differently. Just check the listings for them in an electronics catalogue for correct pin outs. Also note that the ‘-‘ sign in the circle means connect the lead to the negative battery terminal. I’ve numbered the tracks on the board for easy reference when constructing. The bridge shaped lines on the diagram are simply wires to connect tracks together. Using this layout, there is no need to ‘break’ any copper tracks.
My Results I built the circuit described above, only I used lower value components because these were the only ones available at the time. I wound my own transformer. This was made using 8 turns of 1mm ECW (enamelled copper wire) for the primary, and between 900 and 1000 turns of 0.125mm ECW for the secondary. This was wound on an RM10 core kit. My voltage multiplier consisted of 6 1kv capacitors and 6 diodes, giving a 3 stage multiplier. This gave a small bright blue spark of between 3 and 5mm at the output of the voltage multiplier. Recently the secondary winding of my transformer shorted out, so I rewound it using 1400 turns for the secondary. I was getting some 8mm sparks using a 10 stage multiplier, made up of 10000pf 1kv capacitors. The higher the capacitance, the fiercer the spark. I also wound another transformer, this time with 1500 turns in the secondary. I connected the two in series, and made up a 5 stage multiplier using 2200pf 7.5kv capacitors, and 8kv diodes. Using this setup, I got sparks of 13mm! All this was done using a 12v input (8 AA Alkaline batteries).
Mini update Rewound the primary on one of the transformers, using 20 turns of 0.25mm ECW. The spark length is about 10mm, and the circuit will operate at higher frequencies.
