I 've just had a very entertaining evening playing with my new toy. Just a simple cardboard mine, but ignited by a 15kV arc from a neon sign transformer, giving me remote ignition and immediate reloading.

The mine:
A 33mm ID cardboard tube is glued upright on a solid timber base. Two 90mm nails are driven into the tube just above the base, from opposite sides of the tube, leaving a 5mm gap between the points. Wires connect each nail to the terminals of a 15kV, 400VA neon sign transformer (scavenged from a rubbish skip in perfect working order :cool: ). A nice long mains lead puts me at a safe distance, next to the main switch. I had drawn a pretty pic but the imagestation account doesn't work anymore.

A spoonful of BP in the mine, casual stroll back to the switch, and when you're ready >Flick<, >WUMPF<. And back to the mine with the next charge!

Entertained the kids for a couple of hours with this tonite, launching flaming paper balls, the odd handful of stars, bits of sparkler, spoonfuls of naphthalene, and just plain old BP for the thump.

I must have got something right with that last batch because a couple of spoonfuls (and nothing else - just the open ended mine) gave a good solid thump, not a whoosh, along with a nice mushroom cloud. Thankfully Guy Fawkes is tomorrow, so nobody pays much notice.:D

sounds impressive :)
I didn't get the bit about how you ignited it... I am not good with electronics or anything of that sort. How did the BP light without a spark or some generated heat?
You said the nails weren't touching, and there wasn't anything like nichrome wire between them...
and what about the transformer.... What is that for???
:confused:

Perhaps I shouldn't speak for the author, but I can answer your question. High voltage (40,000V in this case) will arc across a gap. The length of the arc depends on the voltage and the matterial filling the gap (loose powder, air, in this case). The "heat" of the spark is dependent on series resistance of the transformer, wires, connections, and terminals (very low in this case, which is good for a hot spark). The transformer is required to step the voltage up from 120 to 40,000. A neon sign transformer is en excellent choice because they not only produce the high voltage, they are designed to pass a considerable amount of power. Notice how bright those signs are? All that has to pass through the transformer.

Thanks grandyOse. I guess I forgot the fine detail ;) .

The other reason for using a neon sign transformer is that the output is current limited, in this case to just 30mA. That means you can short circuit the output and run it all day without the transformer overheating - ideal when you consider that an arc is pretty close to a short circuit. The arc off this particular transformer is hot enough to light a piece of paper in about 1/2 sec. Makes a great demo for explaining to the kids why you shouldn't mess with the power sockets in the wall - electricity is too abstract for a 4 year old, but fire is very real and visible :D