Making An Airgap Flash

[Maurice] and his team just finished the airgap flash they’ve been working on for a year now. This kind of flash is useful for very high speed photography such as photographing shooting bullets. With a duration of about a millionth of a second it is 30 times faster the normal flashes at their fastest settings. In the video embedded after the break, [Maurice] first explains the differences between his flash and a conventional one which normally uses a xenon flash tube, then shows off different photos he made with his build.

Even though this video is a bit commercially oriented, [Maurice] will make another one detailing the insides. In the mean time, you can checkout the schematics in the user manual (PDF) and also have a look at an other write up he made which we covered in the past. We should also mention that trying to make this kind of flash in home is very dangerous as very high voltages are used (in this case, 16kV).

20 thoughts on “Making An Airgap Flash

  1. The guy wants an extortionate 2000 USD for one, and seems to be really uptight about selling them to others as he thinks they’re “dangerous”. It’s got a case! Might as well not sell people power supplies because they’re “dangerous” too.

    1. Hmm, it would be interesting to build. I have some HV power supplies that would probably work pretty good for this.

      From the manual: “In the case of an open ground the case potential is 58 Vac, which could be felt but is not dangerous.”

      Wait, what? Where is this 58v coming from? Is it not isolated from the case.

      If he is actually going to sell this there should be some changes.

      The grounding stick has got to go. Build in a shorting bar that shorts out the cap through a resistor when the case is opened. You can make it so it can be overridden for service with a latch which would be reset when the lid closes. I dont think you should be able to access the lamp to service it without opening it and activating the shorting bar.

      Another thing, it should be made to automatically discharge when it is powered down. Something simple as firing the trigger transformer.

    2. The giant capacitor involved might be part of the reason for that price. The old design used a Maxwell 37667 which, may be on ebay cheap as surplus, would be pretty pricey if ordered new from GA. And the failure of even 0.03uF at 35kV would be spectacular in a ‘refurbished in hong kong’ ebay find.

      My brain just scrambles thinking of the liability issues in ‘selling’ an item like this. It’s not the 16kV part that scares the heck out of me, it’s the leakage voltage (can the cap feed that in any failure mode, like a bug crawling in?) and the screws places so close to the air gap shield (bug/dust/humidity, will any of those turn a screw and then the case into one pole of the cap?) And why not just take the extra step and ISOLATE THE ELECTRICITY FROM COMMON GROUND! Really, spend the extra time with a medical grade isolation transformer, and be much happier that the case can’t kill you in an untested failure mode.

  2. Nothing about this post is good. It’s not a DIY flash. It’s a “hey, I made a thing, here’s how”. or even “here are great examples of images made with this”.

    It’s “this device is dangerous so I won’t sell it to you. Unless you’re a photographer, then sure”. Because…one, it’s more dangerous than, say, the inside of a CRT? Not really. And two, what on earth does being interested in high speed photography and being “trustworthy” around dangerous electronics have to do with each other?

    And talk about a misleading freaking title. This doesn’t cover ANYTHING about “making” this product. It just helps sell it.

    1. If you’ve played around with old potato masher flash heads and the associated battery packs and trigger systems, you’ve probably run into some rather high volt machines. Even normal camera top flashes for SLRs could range up to and over 500v exposed at the two points that connect to the camera (don’t put those on a dSLR without a protection circuit!). And don’t tap your finger to the extension cord, it stings a bit.

      So, photographers who play with their gear, and hack back together pieces that other photogs discard, regularly tinker with HV stuff. It’s just a part of the field.

  3. Obviously, anything with a flyback transformer is too dangerous for home use…

    (counting the number of devices in my possession with flybacks and running out of fingers)

    1. You know how it’s said in the low-voltage world that it’s not the volts, it’s the amps? In this case, It’s not the volts, it’s the joules.

      A CRT is hard to measure (hmm, I should actually time it with an HV probe the next time I have one open!), but if it hasn’t self-discharged, probably doesn’t hold more than a few hundred nanofarads or so, and at typical 20kV voltages holds a fraction of a joule. A brief spark and a “zap” if you discharge it improperly to ground, a painful jolt and potentially dangerous if you’re the path to ground. Exercise caution.

      Let’s take a look at this cap. Oh dear. White nylon exterior. One of *those* caps.

      0.03uF at 35kV is .03*35000*35000/1000000 = 36J
      0.03uF at 16kV is .03*16000*16000/1000000 = 7J

      The instant you see an oil-filled capacitor made with that waxy-white nylon plastic material, you’re well past the “dangerous” range aind into the “deadly” range. You’re no longer in TV-land, you’re in Tesla-coil territory. (You still have a few orders of magnitude to go through before you get to “coin-shrinker land”).

      Everyone’s comfort zone is different. Many years ago, I saw some caps like this in a surplus store. I passed when I realized that the only thing I’d feel comfortable doing with them was building a big safety-wired metal connection between the two terminals, in case the existing not-as-big, not-safety-wired piece of hookup wire between the two terminals ever failed as they sat in my closet. (In other words, I left them for an experimenter with better skills than I had, and I hope they found a good home, because I was damn tempted…)

  4. Looks like Hackaday is going commercial on us. Yesterday they were promoting the $650 CNC machine; today they promote the $2000 Flash. I wonder how much commission they make from this?? This is disappointing. If it continues, then I will go to another tech web site.

    1. I agree, this video didn’t rate anything in my give o crap meter. I don’t mind promotion if the content has value but the only value on this one was, hey an air gap flash might be useful for high speed photography. So many more questions then answers, what does he consider HV? Expensive parts? OK like what a pulse rated cap? Direct shorting, wouldn’t a resistor be more cap friendly even to a pulse rated one? I thought you could leave a small resistor attached to something like this as long as the power supply kept up with its discharge rate that way when the unit lost power it was rendered safe in say 3-5 minutes or less like a lot of TV’s etc. What kind of results did this provide?

      Anyway ya HaD you muffed this one.

  5. All you need to know is in Edgerton’s theses/books, available at any good engineering school library. I’ve been working on refining an airgap flash, and they are deceptively simple — all you need is a triggered sparkgap with a hell of a capacitor. 16kV is kinda low — most are between 18-20kV. You can’t skimp on the cap on these, and bought new it isn’t inexpensive. The other tricky component is the trigger transformer. That’s really all these flashes are.

    Here Hackaday — if you want to make one of these, here’s how:

  6. Matthew, I’ve got a funny story related to your ham radio comment. One of my beta testers actually had his garage door opened once when he triggered this device. We suspect it put enough RF into the air that it bipassed the code feature and just activated the open feature directly :-) Just so people don’t worry about this too much this probably wouldn’t work from outside because the flash would be too far from the door opener.

    For those concerned with the safety of the device, I did have it reviewed by en expert in these kinds of devices and implemented all of his suggestions expect his optional feature of an interlock. Designing such a system reliably would have added considerably to the design time and I wanted to get something out. I appricate all the comments above, but if I had to pick one out that really gets the closest to my concerns it would be “Old CRT Dude” with his joules comment.

    The cost is largely driven by the cost of the capacitor and the liability issuance. On that note, it sounds like I might not be able to sell these to photographers. The insurance company I was working with seems to have changed their mind after giving me a quote. If I can’t find someone to insure me, I’m not going to sell it. It is kind of frustrating because I did due diligence to make this safe and they agreed I’ve done enough for this class of equipment, but they are now deciding they won’t insure it for unspecified reasons. So for the time being these aren’t going to be sold. I really believe this is safe when used properly and there is a class of photographers that are very interested in such a device that nobody in the world sells for photography. If anyone here happens to know of a company to sell this kind of product please contact me. I’m happy to work with them on this. My main goal here is to enable photographers to take photos that just aren’t possible with xenon flashes.

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