Homemade flashbulb

Discussion in 'Lighting' started by Eugen Mezei, Feb 28, 2011.

  1. Eugen Mezei

    Eugen Mezei Member

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    Hope I'm in the right subforum. Have not found one about DIY.

    I intend to build my own chemical flashbulbs. It will be an oxygen filled and sealed glass recipient with aluminium foil snipplets.

    What I don't know is how to ignite the aluminium.
    I thought about running two electrodes with a tiny gap between them inside the recipient and connect them to a loaded condensator (best a high capacity goldcap) to produce a spark. Was this done so in the industry produced flashbulbs? Or was the ignition by incandescent filament?

    What I know is that in the industry produced flashbulbs a chemical ingitor (a priming paste or powder) existed inside the bulb that got hot and was sputtered around to ignite the aluminium or magnezium foil or wire.
    Can somebody point me to information what the chemical used as primer was, how it was applied and how it got ignited and provoqued to sputter?
     
  2. ath

    ath Member

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    Don't use a goldcap, the internal resistance is too high. Use a standard electrolytic capacitor with low resistance, e.g. one designed for switch mode supplies.
    Don't know anything about the involved chemistry.
     
  3. Steve Smith

    Steve Smith Subscriber

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    A standard flashbulb firing circuit would connect a battery, a capacitor, a resistor, the flashbulb and the shutter contacts all in series. When the bulb is inserted it completes the circuit and the capacitor starts to charge. The resistor is included to limit the current flow so that the bulb does not fire as soon as you plug it in.

    The shutter contacts are wired such that when they are closed, the capacitor is connected directly across the bulb therefore dumping its full charge into the bulb.

    It is done this way rather than simply connecting a battery via the contacts as a battery has a relatively high internal resistance which would give a bit of variance on the point in time in which the bulb fired. The capacitor's lower internal resistance allows it to deliver a short high current pulse which will set off the bulb more consistantly.


    Steve.
     

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  4. Eugen Mezei

    Eugen Mezei Member

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    Steve, I know the circuit, it is how I build mine too.
    Andreas, didn't know about the high impedance of the goldcaps. Just thought goldcaps have the highest capacity at the lowest physical volume. Speaking about goldcaps, I thought about using them for another application too. I wanted to use the spark to perforate thin alufoil to make pinholes. Do you think I am better of with normal electrolytics for this application too?
     
  5. DWThomas

    DWThomas Subscriber

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    I believe flashbulbs had some sort of combustible material coated on a filament (sort of like the sparklers seen around here at holidays). The material ignited rapidly in a burst of very high temperature which then ignited the foil. Don't know what the stuff was, but trying to buy it today would probably put me on a watch list here! I would guess it probably involved powdered magnesium and an oxidizer in some sort of binder.
     
    Last edited by a moderator: Feb 28, 2011
  6. DWThomas

    DWThomas Subscriber

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    That's the later "refined" versions; I'm pretty sure the earlier units that used two or three C or D cells were just plain brute force. A D cell can pump out many amperes (briefly). Going to the capacitor types allowed use of a battery that was much smaller physically, and often 15 or 22 volts. (I sort of lived through that transition. :whistling: )
     
  7. glbeas

    glbeas Member

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    I think many flash bulbs used zirconium foil if I remember right. Not sure if thats any better than aluminum and probably way harder to find.
     
  8. tiberiustibz

    tiberiustibz Member

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    ever used model rockets? Try nichrome wire.
     
  9. Steve Smith

    Steve Smith Subscriber

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    Have you ever pushed a 9 volt battery into wire wool?

    [video=youtube;gbK-W460vuo]http://www.youtube.com/watch?v=gbK-W460vuo[/video]

    Once it gets going, it continues to burn. I think flashbulbs are similar.



    Steve.
     
  10. Mike Wilde

    Mike Wilde Member

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    Actually, rocketteers who 'roll their own' hunt down ag1 flash bulbs as a relaible ignitor.
     
  11. patanderson

    patanderson Member

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    Good Idea! Now I'm learning a lot. A homemade flashbulb seems interesting to learn. Thanks for posting this topic.
     
  12. ath

    ath Member

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    You are right about goldcaps but in this case you want to draw significant current (after all that's why the energy is stored in the capacitor and not drawn directly from the battery). It may work with a goldcap though.

    Regarding the pinhole, are you sure that works? Goldcaps were developed for low current applications (e.g. buffering ultra low current electronics like static RAM for weeks or longer). Generating sparks is not low current. I would start with electrolytic caps or, if higher voltage is required, with foil capacitors.

    Shorting a 4700µF cap charged to 30V already gives some welding effect.
     
  13. Steve Smith

    Steve Smith Subscriber

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    A normal, cheap electrolytic should work. Nothing fancy was used in bulb flashguns many years ago.


    Steve.
     
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  15. ath

    ath Member

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    Steve, that last recommendation was for punching aluminum foil...
     
  16. haclil

    haclil Member

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    While this is a bit OT, any outdoor photographers out there might be interested in my spin-off idea. First off, we know that steel wool burns with a nice warm glow.

    Now sometimes I want lighting (at night) that simulates the warm glow of a fire. (Usually I shoot in arid areas where there's precious little wood.) Next time I want faux-fire lighting I'll just light a wad of steel wool with a match or a 9V!
     
  17. tkamiya

    tkamiya Member

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    I think the old flash bulbs used magnesium....

    I would think the regular electrolytic capacitor would work just fine. It may have higher internal impedance and slower frequency response but at the speed we are talking about, especially considering its application, it's irrelevant.

    Metal fibers will burn explosively in pure oxygen environment. Please be careful.
     
  18. bobwysiwyg

    bobwysiwyg Subscriber

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    Why do you want to do this? I am not being judgmental in asking at all, just curious.
     
  19. nickrapak

    nickrapak Member

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    What you are looking for is a pyrogen. You can find these compounds online via fireworks supply stores, as they are used to make electric matches for fireworks shows. Be careful, though. Purchasing the equipment and supplies to make e-matches is completely legal for anyone, but in order to buy premade e-matches, you need a BATFE Type 54 explosives license. Of course, the above only applies if you are in the USA, as I have no idea as to the laws in other countries.
     
  20. railwayman3

    railwayman3 Member

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    And don't forget that commercial flashbulbs had a clear (or blue) lacquer coating to prevent the glass shattering from the heat when they were fired.....
     
  21. Mike Wilde

    Mike Wilde Member

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    The coating also was also often a colour temperature adjusting filter.
     
  22. Eugen Mezei

    Eugen Mezei Member

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    Thank you all for your answers.

    Now I have a doubt: Is ignition by spark or by fuse in comercial bulbs?

    Well... I intend to use aluminium foil as this is what I have handy. (I eat a lot of chocolate.) Of course magnesium foil or zirconium wire would be better, but where to get? I also think some of the big bulbs avaible from manufacturers were filled with aluminium foil.

    Yes, I will coat the glass. I think laquer for wood or metal will suffice, I will try to get a thick one.

    Final achievment of the experiment should be bigger bulbs that the ones avaible comercially. But I will begin with small ones out of safety considerations.

    Steve, is that wire wool the thing used to clean/scrub hardened residues from dishes?
     
  23. mopar_guy

    mopar_guy Subscriber

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    Chemical Primer compounds?

    If I remember correctly, Class M flashbulbs utilized a chemical on the ignition electrodes to stabilize/improve ignition. I am not sure what sorts of chemicals may have been used.

    Class F flashbulbs such as the GE Speed Midget (SM) had no metal filaments that burned and the "flash" was all from a Chemical which burned in an oxygen atmosphere.
     
  24. Marc B.

    Marc B. Member

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    "What makes a flashbulb flash? Well, flashbulbs have, placed between their terminals, a piece of tungsten or zirconium filament. This wire is covered with an explosive primer paste. When current is applied, the wire heats up, igniting the paste, which then ignites the tin, aluminum or (in later years) aluminum wire (or wool). An oxygen atmosphere would increase the brilliance of the flash. Some bulbs were also filled with nitrogen gas to actually slow or delay the burn"

    The statement above is from the link below.
    http://www.darklightimagery.net/flashbulbs.html
     
  25. holmburgers

    holmburgers Member

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    I'm really excited about your project. How will you make the actual glass bulbs?

    I'm (slowly) working on an IR-transmitting coating for flashbulbs (a la GE #5R) and I intend to coat the bulbs in gelatin. Gelatin might be another option over varnish, though varnish would probably be easier; just dip and hang.
     
  26. greybeard

    greybeard Member

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    Yes, I will coat the glass. I think laquer for wood or metal will suffice, I will try to get a thick one.

    Not, I sincerely hope, a nitrocellulose lacquer :smile:

    Commercial flashbulbs use a very thick layer of plastic, probably cellulose acetate or something similar. They tended to have a very characteristic "toasted" smell when fired.

    You mentioned making large bulbs; if you do, be very careful: as a kid of about eight or nine, I found some of the bulbs which are the size of a 150-watt incandescent, and fired one by touching it to the terminals of a lantern battery. It blistered essentially all of the palm and fingers of my left hand, even though the envelope didn't break and I dropped it more or less instantly. The radiated power, at close range, is awesome.