Electronic Circuits and Projects Forum

Although I generally never say 'never' - you won't get 500kV out of a transformer without some serious insulation. The output voltage claimed by stungun manufacturers are misleading for the purposes of advertising to those who don't know/care about how they work (consumers don't need to know at all). The maximum output voltage is determined by the sparkgap length and conditions of the air/medium in that gap. Since the output of a transformer driven by a capacitor discharge is essentially a current source, it's voltage will to whatever voltage is necessary to make current flow - often the breakdown voltage in the insulations of windings.

If you have a 1mm air gap, a stungun rated at '250kV' won't output 250kV, but most likely in the order of 2kV.

Also, stunguns are rather crude devices with manufacturers making claims about 'tetanisation' or how long it will keep an attacker of a certain weight on the floor. Whilst there are certainly devices specifically for creating tetanisation, it is impossible for the manufacturers to know the circumstances in which devices will be used, and so, their claims cannot be proved/disproved. What may 'sting' a bit for someone, can quite easily kill another, and visa versa.

I've been unfortunate to conduct mains on a couple of occassions, as well as brush my hand across the terminals of a 800uF cap charged to 420V and whilst the fact I'm still here means I could say 'naa its not that dangerous', others have been killed from far less - not to mention the secondary effects.

The way I see it with so many 'wanna build a stungun' posts on the web is, if you truely want to build one, then you have the tenacity to take the time and effort to reseach the electrical, and electronic engineering to work things out for yourself. I think the OP can understand why so many are guarded, given the (il)legality and dangers.

Originally Posted by Blueteeth

I've been unfortunate to conduct mains on a couple of occassions, as well as brush my hand across the terminals of a 800uF cap charged to 420V and whilst the fact I'm still here means I could say 'naa its not that dangerous', others have been killed from far less - not to mention the secondary effects.

I am glad that your heart is not in your hand. Your heart is in your chest. If you brush 420V on your chest or between your hands then your heart will probably stop beating.

Originally Posted by audioguru

I am glad that your heart is not in your hand. Your heart is in your chest. If you brush 420V on your chest or between your hands then your heart will probably stop beating.

Probably, but it was from a cap My other hand was grounded via a static-wrist band. The burn was more of a concern at the time, but it was enough to kill... The '15mA' figure varies person to person, and thats 15mA across the heart - not the chest. Otherwise defribulators for external use wouldn't have to use 2000V @ 300J, and electric chairs could run off NiCads. Continuous power is far more dangerous, AC, or DC, but at the right time, in the right conditions, a pulse of >120V, even from a smaller cap IMO, would be enough to meet the angels :/

I wasn't showing off recounting how many times I've been dumb enough to get electrocuted, just that, any numbers referenced talking about 'whats dangerous and what isn't' are misleading, both in over-stating dangers, and understating. Too many variables to come up with a definate 'safe level'

At work before they closed the place down. We had a computer room that had the phone lines in it. Most of the blocks are punch down but some of the older lines have blocks that have nuts to hold the wires. It was a real hot day and I bumped into the blocks You talk about a shock the block hit my back I could feel my body draw up it was so strong of a shock. The T1 lines can have over 190 volts on them

I really think if I had fell on this I would of been a goner. I fell away from the block. I been shocked before but never like this. I learned some new respect for any line with voltage on it

Originally Posted by 4pyros

You need to do your turns ratio.

600ohms to 120000ohms

1 to 200 ratio

15 volts x 200 = 3000 volts

This is wrong.
Z2/Z1 = N^2, so N = SQRT (200) = 14.14

Turns ratio only *really* applies directly when you're feeing a transformer with constant AC. Under pulse conditions with the secodary as open circuit - its really behaving as a coupled inductor, as the secondary is open, it might as well not even be there. The magnetic field builds in the coil during the pulse, then colapses creating back EMF (flyback) in the primary and secondary. If the turns ratio is say 1:10, and your pulse reaches 300V peak, the back EMF could easily reach 3000V. Multiply that by the turns ratio and you have 30kV. So, what looks like something that would require a 1:100 turns ratio transformer, could actually be done with a 1:10. It's how flyback transformers work.

Of course the turns ratio is important, but the voltage 'gain' is part of the primary, just multiplied by the secondary.

Audio transformers are less than ideal for any high voltage apps. Low voltage insulation, and high inductance (they are dealing with audio frequencies after all...) make them useless for anything >1kV. I'm sure one could get a good spike of voltage out of them grater than 1Kv, but in terms of efficiency, and reliability - its wasteful, and would be disappointing.

I suggest that you use an EHT transformer from an old CRT television set.

However, colour TVs have an EHT of about 25 kV, so be sure to discharge the tube before handling.

Microwave ovens have a transformer that provides about 3 kV.

But be careful.

There is a capacitor in them that can store the 3 kV for a long time, so it needs to be discharged before you start removing parts.