Electric shock generation

[yiancar]

Hello everyone, so I am trying to make a small bracelet like device which would produce a high voltage and very-low current, ie electric shock.

i have found some schematics online but i would like some explanation to why they work.

in the above first attached schematic i do understand the 555 timer to produce a pulse of specific frequency but i do not understand how a 1:1 600ohm audio transformer is able to "multiply" the voltage

in this schematic
i should assume that the cap is charged and then as the transformer is 1:125 in the case of 3 volts input you would get 375 volts out ?

is there any way to produce such high voltage without a transformer at all?

[tomlut]

Well the transformer will step up the voltage by the turn ratio from the primary to the secondary side of the transformer. However the resistance ratio is not the turns ratio as different gauges of wire can be used to wind the primary and secondary.

Another thing to keep in mind is that the audio transformer secondary insulation may not be rated for the voltages produced. You might be better off with a flyback transformer.

Generating high voltages using single inductors is also possible. The voltage (V) is equal to the inductance times the change in current (di) divided by the change in time (dt),  V=L(di/dt). So the faster you can change the current the higher the voltage developed.

[Psi]

It will work better if you change R1 to 33ohms and move C1 so it's in parallel with the push button.
C1 should be a 100 to 400nF mains filter cap. (The kind that is in every electronic device across the 230V supply)

The HV pulse will occur on the output when the pushbutton is released (not pressed)

If you want to play things super safe, start with R1 at the current 5k6 and then drop it as needed until the shock is strong enough for what you want.

[yiancar]

so here is the datasheet for the suggested transformer in the 555 circuit, http://www.mouser.com/ds/2/410/TY-145P-223980.pdf

the turn ratio is 1:1. now i am confused

[Psi]

Audio transformers are often just used for isolation. So 1:1 makes sense.
Other times they are used to impedance match audio signals and will have a different ratio.

For generating a small shock using a DC battery all you need is a tiny mains transformer out of an alarm clock (or similar small device).
One of those little mains transformers about the size of a golf ball. 6-12V <--> 110/230V.
Use the circuit i described before. A battery in series with a mains filter capacitor in series with the 110/230v side. Then have a pushbutton in parallel with the capacitor.

NEVER wire any mains transformer up to a AC wall adapter.
It's very dangerous to take 9V AC from a power pack and step it back up to 230V. It can kill you just the same as 230v from the wall directly!

[yiancar]

Thank you for the help, I think a golf ball is a bit too big for what i had in mind, Ill check if i can find something smaller

[Psi]

If you can find a smaller mains transformer it will work.
Infact any transformer will probably work to some degree, even the 1:1.

When the button closes it shorts DC across the coil of the transformer and the core is magnetized. When you let go of the button the field collapses and the energy in the core comes out as back EMF at a much higher voltage. This charges up the capacitor to this high voltage and starts an oscillation between the capacitor and the inductor (transformer winding). It obviously works better when the transformer ratio is a step-up but you will probably feel something even with a 1:1.

Do you have any relays laying around?
If, while hanging onto both relay terminals, you apply and disconnect power to the relay you will get a small shock.
(Just make sure its a normal relay and not an automotive relay. Those have internal diodes to prevent exactly this from happening.

[yiancar]

Oh now i get it, thank you.

does a transformer like this http://au.rs-online.com/web/p/current-transformers/7157024/ would do the job or its not safe enough?

[Psi]

Ideally you want an iron core inductor/transformer.

That one is ferrite, it might work but would be tricky. You'd probably have to match the capacitor value so it resonates at a high frequency and maybe add a few extra components. If it even work at all.

[MagicSmoker]

....
i should assume that the cap is charged and then as the transformer is 1:125 in the case of 3 volts input you would get 375 volts out ?

The turns ratio is the square root of the impedance ratio; in this case it is ~1:11. You could get a bit of voltage multiplication from the resonance effect, but small audio output transformers tend to be fairly lossy so I wouldn't count on that.

[Psi]

These things are pretty small and will give you a strong shock from 5V input
http://www.digikey.com/product-detail/en/NMT0572SC/811-1583-5-ND/1927144

Make sure you put a resistor in series on the output to limit the output current to 1mA or less.
Its unlikely to cause injury but the current is high enough to be worrying so adding a 100k in series with the 72V output terminal will make it safe.

[yiancar]

this is a dc to dc converter not a transformer?
i think i  really dont know what i am looking for. my problem is that i want the whole device to be as small as possible

[Psi]

Its got a little transformer inside plus all the electronics needed to take 5V DC input and produce a constant 72V DC (although its more like 150V under no load)

[yiancar]

Oh I see, thank you.
As I am trying to keep cost low, what I should look for a transformer?

[Psi]

i doubt you will be able to make anything smaller than that without SMT design skills.
That module is only 21.8mm x 7.6mm x 11.2mm

[yiancar]

and i could vary the shock using a pot right?

perhaps a transformer like this would work?

http://www.instructables.com/id/How-to-build-the-Worlds-Smallest-Electronic-Shock/?ALLSTEPS

[yiancar]

i doubt you will be able to make anything smaller than that without SMT design skills.
That module is only 21.8mm x 7.6mm x 11.2mm

I assume that the capacitor needs to be of the specific value for the oscillation to work right?

[rickselectricalprojects]

Well the transformer will step up the voltage by the turn ratio from the primary to the secondary side of the transformer. However the resistance ratio is not the turns ratio as different gauges of wire can be used to wind the primary and secondary.

Another thing to keep in mind is that the audio transformer secondary insulation may not be rated for the voltages produced. You might be better off with a flyback transformer.

Generating high voltages using single inductors is also possible. The voltage (V) is equal to the inductance times the change in current (di) divided by the change in time (dt),  V=L(di/dt). So the faster you can change the current the higher the voltage developed.

i wouldn't recommend a flyback transformer at all because the current they can put out can be very dangerous. as psi mentioned use a 9v battery and a small mains transformer instead.

[Macbeth]

Very crude electric shock device I made as a daft kid - 9v battery, relay, mains transformer in reverse. Wire the relay right and it switches on and off and finds it's natural resonant frequency, makes a nice racket as you zap your victim. Work out the relay circuit yourself. That was more fun than actually zapping people. (I will add I only zapped humans, definitely no animals, and the humans were all my friends and family and forewarned...)

Now I recall it was an audio transformer (from the 1970's ladybird book on building a transistor radio) that I wired the wrong way around and clicked on the terminals of a 9V battery that zapped me that led me to this more dastardly version.

I didn't even know the 555 or oscillators back then, just realised I needed to have a switch that ran like the clappers.

[Stonent]

My favorite shocker was simply a relay that the normally closed switch part was wired in series with the coil, so it would buzz when powered from a 9V battery.
If you touched the coil terminals, you'd get shocked. (Won't work with relays that have a snubber diode.)

[tomlut]

i wouldn't recommend a flyback transformer at all because the current they can put out can be very dangerous. as psi mentioned use a 9v battery and a small mains transformer instead.

Yeah, good point.

[yiancar]

I feel really stupid, I cannot get it to work, i can only get a few mV of shock according to my multimeter, I am going with PSI's approach , I think the transformer is not resonating... I dont have a scope to check tho. any ideas?