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 non-lethal 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. 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). 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).
14 Feb 2001 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.
Conclusion
I am always looking for feedback on the circuits. If you have got any
suggestions, please email me. If you are having trouble building them, please
email me. If you have built the circuit and got some good results using
different components, let me know. I'm also looking for information on
transformer winding.
My email address is thejuice2000@bigfoot.com
Construction
of the first stage
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
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