DIY Stun Gun With 18650

Hi Folks,

i don't even know how to introduce this project because it came out of nowhere. Actually, it came from an high voltage converter, purchased to build spark gap "entertaining devices" like Jacob's ladder and others.

Then i got bored and i decided to see if i could realize a portable stun gun with this generator. Well, i can!

Disclaimer: i've never test this device on humans! (or pets!) I can't say anything about how harmful it could be, it could just give a temporary pain o it could be deadly, i don't (obviously) know. It can't provide a lot of current, its battery can't shock you with more than 5 watts, and that's a good thing because it's the current that will kill you, not the voltage. For instance, you phone charger might be way more powerful but it has unharmful voltage (5V).

Didn't i just wrote that the issue is the current and not the voltage? Actually the issue is the HIGH VOLTAGE but only because it can create enough potential difference to create CURRENT under you skin, which can interfere with your nervous system (that's the concept behind tazer after all).

Don't use this thing to injure people and take precautions not to hurt yourself using it and building it!

While i'm quite sure that this generator doesn't actually provide 400 Kilo Volts (as stated in the product description), it can definitely provide 45-50KV. In fact the air's dielectric strength is 3KV/mm, and this generator can produce 15-20mm sparks, so 45-60KV are available.
Well, in practice that's even better! Imagine a real 400KV generator: in air it can create sparks as long as 13.3cm, so even a reasonably sized grip (like this one) doesn't really keep you safe because your bare hand is in the spark range. Your really don't want to have hundreds of KV, even professional devices don't reach this voltage, or they would have the same self-harm spark issue, but they still work quite well.

Do i have to mention that all this concepts are valid as long as you are in a dry eviroinment, with dry hands on a dry plastic case? Ok, it seems quite obvious to me but i'll tell you anyway: keep your hands and the plastic case always dry!!!

PS: i'll never carry this thing outside my house but depending on your local laws it could be forbidden to even build such a thing. Do your check!

To build this device you need few tools and some electric components.

I've collect the electric components in this page (Amazon, Bangood). You will only need to cut and solder few wires. In case you don't have a soldering iron and other soldering tools my DIY electric kit is collected here.

Actually you'll need also two M4 screws, with 4 nuts and washers, and few centimeters of whatever thin conductor you have at hand (better explained in a following step). I didn't put these things on the components list because they'll be way more expensive to buy online than the local hardware store.

The M4 screws are the electrodes, and i guess they are supposed to be pointy because they have to break through possible insulating layers, like clothes or hairs, that would compromise the stun effect.

Any abrasive surface can be used to sharp the electrodes, you can use a file, sandpaper... I've used a drill and a bench grinder. If you tight the screw in the spindle and push it against the grinder (with the spindle counter rotating respect to the grinder) you'll have the job done in few seconds.

The plastic case is 3D printed, you can download the 3D files here (scroll to the end of the page, after the video, the only red line).
The case can be closed with two countersunk M3x15mm screws, or you can glue the edge, the case has been designed for both sealing methods.

The wiring process is quite easy, you have to:

- Solder the 18650 in parallel, and then to the battery pads on the TP4056 module.

- Connect the TP4056 output to the H.V. generator input, adding the momentary button and latching switch, in series, to the positive wire.

- Connect the H.V. generator output to the electrodes.

Keep always in mind that the 18650 li-ion cells are intrinsecally dangerous! Soldering on them is not trivial at all, it could be done of course, but you really have to understand what you are doing. 18650's gurus like this guy actually prefer to solder the cells instad of using a spot welder, and they know what they are doing. I'm quite sure that a 18650 cells' soldering tutorial is available in pretty much every language, so please spend few minutes to understand the process and the risks in your mother tongue (or whichever language you are fluent in). For instance, pretend to have a drop of tin falling in the small gap near the positive pole, shorting the cell, impossible to remove within seconds. Well, that's why i do this kind of stuff with a bucket filled with water near me. Never actually used, but better safe than sorry, right?

The battery pads on the TP4056 are labeled B+ and B-, easy to find (check the polarity).

The TP4056 output pads are also clearly labeled, but in any case the attached wiring diagram shows the right wire in the right place. The momentary button has only two poles, so no doubt here. The latching switch has 3 poles but it doesn't really matter: if the central pin is used then the wiring is ok, it doesn't matter which wire you connect to the center and it doesn't matter on which side you connect the other wire.

The H.V. module has two pink wires on one side and a green and red wire on the other side. The pink wires are the high voltage wires, they should be connected to the electrodes, the red and green wires are the positive and negative wires.

It's definitely hard to solder the H.V. wires on the screws. Don't worry, you can connect the H.V. wires to the electrodes just by removing some wire insulation and using the nuts on the screws. Put the wire between the nut and the washer and then tight the nut. That's all.

When the wiring is done you can use few drops of hot glue to fix everything in place, use few drops also on the cables to help with the cable management.

One really important thing: in the first photo you could see that the spark didn't happened between the electrodes' sharp ends but somewhere in the middle instead. There are two small wires, connected to the electrodes nuts, that are few millimeters apart. These two small wires can be realized by stripping down a common electric cable and fixing it on the case with hot glue, it doesn't matter. What's really matter is that they should be only few mm apart, five to ten.

If you have a small distance from the main electrodes you'll have less effect on the hypotetical target becuse your device hit involves less muscules and nerves. A big electrodes distance, on the other hand, doesn't allow the spark to happen because the high voltage isn't high enough to break through the air's dielectric strenght. If you power up the H.V. generator, but it can't discharge itself by creating a spark, it will overheat and break.

Good news, the solution is easy: you can have the main electrodes far apart, so they'll hit harder, and you can use small secondary electrodes that are few millimters apart, to keep the H.V. generator in a safe condition. These secondary electrodes won't "steal" any hit strenght because when you hit someone (don't do that, it's just to explain) his/her/its tissues have an electrical resistance way lower than the surrounding air, so the current will flow through the target and not the air.

In fact aslo commercial devices have the same concept so you can trust this design.

The usage is really simple, toggle the latching switch to enable the momentary button and then press the button just when you want to fire. The latching switch is only a safety switch, i just wanted to avoid electrical shock by unwanted button pressing, so turn it off when not in use.

You have a micro USB port to recharge the batteries, no other mainteinance.

I really don't know what you can do with this tool, the only reasonable use i've found so far is to kill the green bugs that enter my house. I've attached two semi-rigid wires to the main electrodes, so i can touch the bug with both without crushing it. It works, they are thunderstruck dead in fractions of second and they don't even have the time to release their stink agent. I don't think that's cruel, at the opposite, it's way faster and cleaner than the common methods (toilet? poison? smash?).

How about humans? I really don't know what could be the effect. I've never tried, i definitely won't try and i was smart enough to avoid "unscheduled" test on myself (because of accident or distraction). Don't even think to hurt someone, you, dogs, cats and so on. Please keep this things just funny to build, don't use it for stupid things.

My guess is that this device can't even be considered as a self defence device. If you consider the power you can take from the battery controller, little more than 5 Watts (1.2Ax4.2V), you could use it to calculate the available current on the high voltage side. Well, 5W divided by 30kV are close to a tenth of milliamp. Electrostimulators can provide tens of milliamps, so it seems to be quite uneffective on human scale. The first objection is that the spark is not constant, so there could be a power buffer that can increase the current by a lot. In the end my guess is that this device will cause some real pain but that's all, it won't actually stun an hostile adult human. Aynway. always remember: this is only my guess, as far as i know it could be lethal.

That's all, have fun but keep everything safe.