SpudFiles

I had heard about this on the 'net before, and decided to try it out myself. Basically, you get the step-down transformer from some old electric applience (I used an old clock radio), and run pulses of DC current through it, the wrong way (ie, the primary becomes the secondary and vice versa) Whenever the power is taken off, a small spark can be seen.

When running off somthing like a lantern battery, it seems fairly safe. I have zapped myself numerous times with single pulses, and the other day I got a nasty shock when I found out that the path of lowest resistence was my hand, and not the xenon tube (I was prepared for the shock, it went through one finger and out the other of one hand, so it was fairly safe. I was curious, because I know when I have a small neon globe attached to it the current flows through the globe, and not your hand even when touching both the wires. The xenon tube had a bit more resistence, and so I got 4 or 5 pulses through my hand as I rubbed the wire along the spring on the lantern battery)

In the vid I am using a small rare earth magnet from a hard-drive to pulse the electricity very very rapidly (the wire moves due to the electricity, and when you get it in just the right spot with just the right pressure it pulses the electricity at an extremely fast rate) I'm careful not to get zapped when doing this, because while one spark from this isn't too bad, I would hate to feel a few hundred zaps in a fraction of a second.

The way the transformer steps up the voltage while decreasing amps makes it relatively safe, so long as you don't get zapped across the chest I doubt you could hurt yourself with this setup. Using a more hefty power supply would probably be a bad idea

Most of you would probably have an old wall transformer or broken vcr laying around, so I suggest you try this. It works very well for what it is. The only problem is that these arn't made for such high voltages, and the transformer you see in the vid developed some internal sparking so now it doesn't work so well.

EDIT: Thanks jsr... couldn't get it to work for some reason.

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Insomniac wrote:Hmm... embedding seems to be broken.

No it isn't

[youtube][/youtube]

Maybe I'm dense this morning but I don't get what the neodymium magnet was doing. How was it causing the wire to switch touch on and off very fast?

Also, this circuit as you have constructed it has the real potential to be lethal! Take care....

starman wrote:How was it causing the wire to switch touch on and off very fast?

I imagine it somehow interacted with the electromagnetic field around the wire when there was current running through it.

Say if there's current, the field pushes the two apart, disconnecting it. Then due to the lack of current, the two come together by the natural springiness of the materials.

Much like an older style of electric door bell, you know, the half-ringy/half-buzzy ones.

This is basically the same thing as an ignition coil, but good find!

Ragnarok wrote:I imagine it somehow interacted with the electromagnetic field around the wire when there was current running through it.

Actually, saying that, it gives me an alternate idea.

What about hitching this up to a DPDT relay?
Power the transformer through one of the poles on the relay, but use the second pole on the relay to act as a short for the relay coil.

So you provide power to the relay coil, it connects the transformer, but at the same time shorts the relay coil, which then disconnects it all again, and repeats very rapidly.

I did it myself once, and it provides a respectable number of pulses per second - of the order of 50 I think when I tried it. It would save messing around with holding wires in a particular way.

Ragnarok wrote:

starman wrote:How was it causing the wire to switch touch on and off very fast?

I imagine it somehow interacted with the electromagnetic field around the wire when there was current running through it.

Yeah those magnets have amazing gauss levels and the current from the lantern battery is considerable. Still cool to see it act on a single small length of wire like that.

I'll have to fiddle around with that sometime.

Ragnarok, what you are describing is usually called a "buzz coil" and was used as the igntion system in early cars. You can also use the buzz coil to pulse the current to a flyback transformer (instead of a 555 based timer). (like this piss-poor example)

Automotive relays, when run from a strong 12V source, will oscillate at a couple hundred hertz when wired as a buzz coil.

jimmy101 wrote:called a "buzz coil"

That was it, the term had escaped me.

It might not be the most elegant solution in the world, but it is probably the simplest and least involved way to achieve the goal.

Just a question regarding ignition coils. The shocks from this little transformer are fairly safe, and would I be correct in assuming an ignition coil driven from the same power supply wouldn't be overly dangerous? Just running directly from the 6v battery, no capacitors or anything to bump up the current, would an ignition coil be any more dangerous than this?

I understand that you can't get power for nothing, and this is why I think it would be fairly safe, but I'm not entirely sure.

Insomniac wrote:Just a question regarding ignition coils. The shocks from this little transformer are fairly safe, and would I be correct in assuming an ignition coil driven from the same power supply wouldn't be overly dangerous? Just running directly from the 6v battery, no capacitors or anything to bump up the current, would an ignition coil be any more dangerous than this?

I understand that you can't get power for nothing, and this is why I think it would be fairly safe, but I'm not entirely sure.

You don't have a charged cap but you do have the collapsing inductive field of the transformer...can be just as potent as a discharging cap...depending on the "farads" of the cap and the "henries" of the transformer of course.

That lantern battery can put out close to 3 amps and even at 6 volts could supply plenty of umpf to cause human heart failure from your little sparking device there. Remember most stun guns use a mere 9v battery with much less current carrying capacity...and stun guns can be lethal under ideal circumstance. You get heart failure in the 50-100 milliamp range, loss of muscle control way before that.

Jus' be careful with it.... 8)

Yeah, I only ever zap myself across the hand, never let the current flow near any organs lol.

I don't think the current from the sparker would be lethal, because say the transformer draws 3 amps from the battery @ 6V, and steps it up to 1000V (based on the spark length, it is probably a bit more than that), then that means it is boosting the voltage to around 166 times the imput... that means the amps go down to a 166th of the imput, and that gives a measly 18 milliamps. Also, even if this calculation is way off and it does give potentially lethal amps, would I be correct in thinking so long as the shock is localized to something away from my heart (in one side of my hand and out the other side) it shouldn't do much?

I wonder if the collapsing magnetic field boost the amps up for a fraction of a second? If so, I wonder how much?

Insomniac wrote:I wonder if the collapsing magnetic field boost the amps up for a fraction of a second? If so, I wonder how much?

The amps won't rise. However, the inductance of the coil tries to keep the current moving, but without a complete circuit, it can't.

The inductance therefore causes a huge peak in voltage to try and keep things moving. It's the basic principle of a variety of DC-DC converter called a boost converter - charge the inductor, then suddenly turn off it's supply, then redirect the increased voltage elsewhere.

At least, that's what my poor electronics tells me.

Ah, I guess that explains why I can get decently long sparks from this thing... the voltage output is thousands of times the imput, whereas it was only designed to step the voltage down to say a 20th of the imput. When wired backwards one would expect it to only step the voltage up to a few hundred volts, but the spark length indicates it is in the thousands. I'll have to ask my dad about it a bit more, seeing as he is an electrician.

Ragnarok wrote:The inductance therefore causes a huge peak in voltage to try and keep things moving. It's the basic principle of a variety of DC-DC converter called a boost converter - charge the inductor, then suddenly turn off it's supply, then redirect the increased voltage elsewhere.

At least, that's what my poor electronics tells me.

Well, sort of. Actually DC-DC convertors or even AC-DC switching power supplies operate by first rectifying the input signal to DC (if it is AC of course). The resultant DC voltage is then switched on and off at a very high rate, usually well out of the audio range say at 100khz and applied to either a step up or step down transformer, depending on the application. Because of the high frequencies involved, transformers and capacitors can be much lower values and smaller than if trying to operate on 60 hz AC....a fairly inconvenient frequency to work with actually.

FWIW, aircraft power operates at 400 hz and allows a much improved component girth and space savings...not ideal for audio applications however.