I’ve made a little progress with the mini-coil. I have two flyback drivers up and running. Each circuit fits nicely inside a 2″ ABS cup potted with silicone, now dubbed the hockey puck of DOOM.
One flyback charges a capacitor bank, and is held open by the trigatron. I’m not sure when these actual trigatrons where manufactured, but they’ve been available since the 1940s.
The trigatron acts as a very quiet, easily controlled spark gap switch. When the second flyback turns on, it closes the switch, dumping the charge in the capacitor bank across the primary of the Tesla coil.
When actually operating, both coils will charge the bank in parallel, and the trigatron will be fired with very precise timing using a solid state ignition coil.
Although I did get some nice shots, I couldn’t help but feel that they don’t quite capture the full experience of a real live lightning machine. While I can’t do much to recreate the visceral smell of ozone and nitrogen compounds formed by the ionizing sparks, or the reverberating whine of the beautiful but deadly spark gap, I did have an idea for bringing another aspect of the lightning show to the interwebs.
Why that particular camera? Partly because I found someone dumping a bunch of them on eBay for cheap, but also because they run CHDK, the infamous scriptable firmware for Canon cameras. This let me write some code to streamline the process of taking ten photos all at once, and then get them off of the cameras in a reasonable manner. By wiring all of them to the same 10-port USB hub, and using CHDK’s syncable USB remote feature, I was able to wire up a single button to make all of the cameras fire at once. Collect all the photos, find all of the good ones that are actually in focus, get them aligned and color balanced and scaled, and away you go. Bullet time lightning.
This was one of the more challenging projects I’ve taken on in a while. I had to build a physical mount to hold all of the cameras, wire them together to a repurposed PC power supply, recompile CHDK to eliminate as many unnecessary camera keystrokes as possible, write some scripts to facilitate taking and retrieving the photos, then shoot the actual photos without accidentally frying the whole rig. And, of course, build and operate the Tesla coil itself, edit together the stills, and compile the whole thing into a possibly entertaining vid.
I want to take a lot more footage with this camera, but I also wanted to release the results as soon as I could. So here you are.
Aside from Tesla shots, what would you shoot if you had a bullet-time style camera?
It uses a TL494 to switch a MOSFET very rapidly, dumping current into the primary coil of a TV flyback. The air rapidly heats up when the spark is on, and it cools quickly when switched off. This causes the air to vibrate, making sound just like a speaker.
I used a Hitachi flyback (about $10 on eBay) but any flyback with an open primary will work. You can use jumper clips for electrodes (as above), but they will melt eventually. Tungsten electrodes are much better. You can also use anything else that is conductive and will tolerate heat, such as chunks of pyrolytic carbon.
Here is Plasmana’s original schematic. Replacing the IRF540 with a bigger MOSFET (such as the FQA16N50) will let you dump more current at higher voltage across the flyback, making even bigger sparks. Adding a gate driver between the TL494 and the MOSFET would also likely help.
A good heat sink is critical to keep the MOSFET from melting. I used a large copper CPU cooler with an integrated fan.