A Much More DYI Air Gap Flash Unit

In reaction to the other air gap flash unit we featured a few days ago, [Eirik] sent us a tip about another one he recently made. In his setup, the duration of the flash peak intensity is around 300ns (1/3,333,333 of a second). As a reminder, an air flash unit consists of a circuit charging a high voltage capacitor, a circuit triggering a discharge on demand, a high voltage capacitor and the air flash tube itself. The flash tube contains two wires which are separated just enough to not spark over at max potential. Isolated from the other two, a third wire is placed in the tube. This wire is connected to a trigger/pulse transformer, which will ionize the gap between the two capacitor leads. This causes the gap to breakdown and a spark to form, thereby creating a flash of light.

[Eirik] constructed his flash tube using an olive jar and a glass test tube. As you can see from the (very nice) picture above, the spark travels along the glass test tube, making the quenching much faster than in an open air spark. [Eirik] built his own high voltage capacitor, using seven rolled capacitors of roughly 2nF each made with duct-tape, tin foil and overhead transparencies. For ‘safety’ they are stored in a PP-pipe. A look at the schematics and overall circuit shown on the website reveals how skilled [Eirik] is, making us think that this is more a nice creation than a hack.

Disclaimer: As with the previous airgap flash, high voltages are used here, so don’t do this at home.

38 thoughts on “A Much More DYI Air Gap Flash Unit

    1. Plug it in a socket on the end of an extension wire. That way you can plug and unplug it without having to get near it.

      For the cap, either don’t go near it, or use some sort of string-operated mechanism to short it out once it’s done. Or a servo if you’re going for bonus points.

      Exposed wires are fine as long as you don’t actually touch them. It’s not something to leave plugged in with kids running round while you go make a cup of tea. Just use your brain.

    2. Aaaah I love the smell of xrays in the morning (device looks like its on a kitchen counter)

      I love the disclaimer:
      Disclaimer: As with the previous airgap flash, high voltages are used here, so don’t do this at home.
      So the takeaway is go make one of these yourself but do it at someone else’s home….

    1. I think the circuit and the operating principles are quite simple. Meaning, if you know enough about it to operate it safely, you may as well build one yourself. Olive jars and bits of tinfoil don’t really count as a “kit”.

      If you don’t know how to build one, you shouldn’t have one. Lots of things are like that. It’s too dangerous to give to people who might leave the cap charged overnight without thinking. You don’t just need to know the rules, you need them drilled into you like instinct so you -almost- never forget. This all comes with the greater knowledge.

    1. Surely that would be PE pipe? ;-)
      (or if you want to watch it in high-definition then you’d need HDPE pipe!)

      I wonder how many people realise what the different types are beyond their acronyms (let alone their different material properties – chemical inertness, strength, density, etc)?

  1. Don’t do this at home? Seriously? Look but don’t touch kids, sparks are dangerous. I’m not saying you should lick it or anything, but where would we be if Thomas Edison had “not done this at home?” I was just about to look up how to make my own capacitors when I read that. Disappointing.

    1. Grow a sense of humor, and I’m pretty sure nobody cares if you’re disappointed except for your mother, your significant other and your dog. Alternately, the righteously indignant line forms up beside the people who moan about how one should only use GPL software, which is just to the left of the people who freak out every time a project comes up that involves working with mains power.

      Any article that frames “safety” in quotes is alright by me.

    2. Side note:
      Thomas Edison electrocuted cats and elephants (among other things,) on public display, in order to show alternating current electrical technology was too dangerous for public use, and to convince everyone they should use direct current instead. His proposed DC power grid had a coal-fired power plant every 4-5 blocks because of the massive voltage drop across such short distances, compared to AC which could go tens of miles with very little drop at high voltages.

      If that scare tactic (among other bullying techniques Edison used) had worked, and Westinghouse in conjunction with Nikola Tesla hadn’t pushed AC technology into the common place, you wouldn’t have a computer to type on. Actually, there’s a good chance you probably wouldn’t exist thanks to medical science still living in dark ages.

      TL;DR Thomas Edison was a stubborn asshole, didn’t invent anything other than the fallacy that he was much more than a CEO, and that myth shouldn’t be perpetuated

      1. Why the lecture out of the blue on something by now everybody already knows?
        Next you are going to tell us there was this huge war in the 40’s right?

        Oh and medical science still is in the dark ages.Bur I guess you mean MRI’s? And in that case I think that even if homes had DC they’d simply use a standalone generator when needed for such things in science and medicine. It’s not like you can run a MRI machine on your home circuit anyway. And many scientific and medical devices use non-standard supplies.
        And incidentally, cars are full of modern electronics, all running from a DC supply.

      2. Sorry you activated an aggravation of mine. Speaking of fallacies. When it come to long distance power transmission AC is subject to the same resistive losses as DC, even more when skin effect is taken into consideration. AC transmission has reactive losses that DC doesn’t. The main reason AC won the day is because that the higher AC voltages where easily transformed down to lower voltages at the consumption point. AC is more efficient is one of those incomplete facts that get’s parroted. Like it’s the amps that kill not the voltage, or it costs less to run a 1/2 horse motor using 240 volts than running it with 120 volts. I’m neither an Edison or a Tesla fan boy, I’ll let others defend them.

  2. A “peak intensity is only 300ns” is pretty useless to photographers. They care more about T5 and T1 times which I’m pretty sure will be the same as the other airgap flashes out there.

    The safety of this design is pretty scary. Conductivity of wood increases greatly in humid environments. The really cool part about this build is the details about making capacitors. That’s awesome!

    1. Although, when lacquered it has the advantage of not being conductive at least. But it’s flammable and pretty heavy, so not very portable, and on the picture it looks unpainted so it can adsorb both damp and grease.

  3. In case people wonder why arrays of white LEDs aren’t used, the problems are twofold.
    1) capacitance of the device, yielding >1mS (ie useless) flashes
    2) the phosphor used to convert blue light into green and red is quite slow to decay

    People have used arrays of discrete LEDs for this however, you can get red, green and blue >5W diodes now and if you can compensate for the device capacitance this approach is quite effective, see work done on amateur optical communications.

    Another worthwhile trick for generating high voltages to charge up the capacitor is connecting CCFL inverters in parallel using diodes on their outputs and about a 22K resistor from -HV to Gnd on each inverter to balance things out.
    This approach vaporised steel pins in a shower of sparks when I built it a few years ago so please be careful!

    #include “DangerofAcuteCaseofDeath.h”

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