DIY Taser

[kulakovs]

Hello. So I decided to construct an electric taser for my potato gun. The only schematic I was able to found is this (first). So I don't understand a few things:
1)What kind of transformer can I use? I've got few simple step-down transformers, but there aren't any audio transformers even in my local electronics shop. And what does "200k to 1k" even mean?
2)As I understand, the 555 timer controls the tasers spark. Is there a way I can control the spark with a switch?
3) (this is dumb one) Doesn't the spark short-circuits the circuit? Or not because of air huge resistance?
And maybe someone knows a better DIY taser schematic?

 

[Blueteeth]

Hi,

A 'taser' is designed to provide arelatively slow series of very high voltage (and current) short-period pulses. The average power isverylow, as to not 'kill' the victim, and the pulses are very short to prevent burning.

For a 'potato gun', I guess all you really need is a rather fat spark to ignite the propellent. Although typical BBQsparkers will do, a larger spark will no doubt ignite more of the gas when it triggers, providing a much quicker combustion, and therefore, longer range for the poor potato. I see no reason why you would need a 'taser', as its over kill. Unless you're potato gun is automatic (doubtful lol) you only need a single spark once every say.... 30 seconds max?

1) 200k to 1k, refers to impedance. Generally such transformersare signal transformers used for audio, to convert high impedance signals (weak ones) which arelow current and can't drive inputs to mixers/amps, to a low impedance. Although many DIY designs for high voltage use them on the internet, they are woefully inadequate for the purpose of high voltage. Their insultation is generally in the order of 200V before they break down (arcing inside the transformer between windings). Not to mention the many windings provide a lot of DC resistance, meaning you can't really put much power through them. In many situations, people wind their own transformers, or use ones designed for the purpose. An example would be a car ignition transformer. Or those used to automatically ignite gas heaters. - Both are designed to output enough voltage for a 'spark'.

2) The 555 timer used in many of these applications arenothing but an oscillilator. You pwoer them with DC, and they produce a small signal (low power) which turns on and off at a freqeuncy determined by the value of the components used. This signal is used to turn onoff a power transistor which is used as a switch to control power through a transformer winding. Transformers don't work with DC, they can only transfer energyfromone winding to another via a changing current. This is either AC (alternating current,voltage regularly changes polarity), or chopped DC (DC that is switched on and off).

In what way do you wish to 'control' the spark? are you talking about triggering it? or its power?

3) Sparks are essentially short circuit. There IS significant resistance in air, but when a spark occurs, the extreme voltage (combined with the distance of the spark gap) breaks down the air, creating a channel of plasma, which has much lower resistance than normal air. This is why sparks die when you widen the gap... lower the voltage, or increase the distance and the 'voltage/distance' drops below a threshold to keep the air in that state, so the resistance suddenly increases, and current stops flowing.

That said, at high voltages, plenty of current is allowed to flow through the air (remember V=IR, therefore I= V/R, the higher the voltage over a resistance, the morecurrent can flow). But usually sparks come directly from the output of a transformer, which is electrically isolated form the rest of the circuit. TO the transformer, a spark gap appears as alow resistance current source. And usually such high voltage transformers are configured as 'flyback' transformers (not, thats a type of transformer, not just the ones used in tv's).

Essentially, unlike standard 'forward' transformers, flybacks store energy. You charge up the primary like a capacitor,energy is stored as a magnetic field in the core. You then suddenly turn off power to it...and the magnetic field colapses, trying to maintain magnetic flow. This creates a large voltage spike on the secondary (and primary !!), in order for the energy to leave the transformer, it will do anything it can to discharge it. In this case, out the secondary,and across the spark gap. Because the spark only occurs when you turn the power OFF to the transformer, it doesn't short anything. Those high voltage circuits which produce constant (DC) high voltage have much tougher components to cope with the constant 'short circuit' of the output, and limit the power output in other ways.

That was a very long winded explaination, but believe it or not, its pretty complilcated lol

One verycheap (and excellent) way of producing a rather large spark is to use a photoflash circuit from a disposable camera. These step up the samll (1.5 - 3V)voltage from oneor two AA batteries, to approximately 300V ata verylow current. This is used to charge a large high voltage capacitor. When you 'fire' the flash, a high votlage is produced (again,very low current) around 4-6kV which triggers the xenon tube. It momentarily, ionizes the gas inside, making its resistance drop, essentailly, making the gas conductive. This allows the huge amount of energy formthe cap to discharge through the tube.


If you cut one of the wires to the tube,and insert the primary of a transformer, you can use the xenon flash as a 'switch' to switch the high voltage pulse from the capacitor into the transformer primary. Depending on the turns ratio of the transformer,the secondary of it will develop a voltage. So,using a cheap mains transformer say, 115V-> 6V, in reverse... its ratio is about 19:1. wired backwards, thats 1:19. Your 300v 'pulse' will get stepped up to 300 x 19 = 6kV ish. Doesn't sound like much, but given the vast ammounts of energy this 'pulse' contains, it'll be a FAT spark, more than enough to ignite a lot of your gas in your potato gun immediately.

Using a car ignition transformer instead (along with the camera flash circuit) you should get a VERY big spark. As the turns ratio is remarkably large. Altohughof you have one of those transformers, you may be able to get away with not using the camera flash, and just using a relay to switch 12V into it. The sudden 'chop' on/off of the relay will create a very high voltage on the output - its enough for cars engines....

 

[kulakovs]

Thank you for detailed explain.

 

[Raul]

you can cheat and just get one of those ballasts that run fluorescent fixtures like the kind they use to make pretty neon signs etc.
I have one of those an it's puts out a Doozie of a high voltage spark.
Any one with a busted neon sign may be willing to just let you have the whole thing.

 

[boscoe]

Or you could even go as cheap as a electric fly swatter?

 

[Raul]

Electric fly swatter?
I have always had this sick twisted fantasy about chasing a fly around a house with a shotgun (ala Elmer Fudd). There just seems something complete about the whole idea.

 

[DerStrom8]

If you've got an old electric fly swatter, the transformer puts out somewhere around 1-3kv, but you would need a TINY spark gap. I'm not sure if it would work. I would just use an old neon sign transformer or an ignition coil. You can find good ignition coil driver circuits all over the internet (just google it ;-) ). Good luck!