DIY xenon trigger transformer

Discussion in 'General Electronics Chat' started by takao21203, May 29, 2016.

  1. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    Im going to proceed with this experiment tomorrow.

    Basically I want to try if a 2200uH RF inductor can be used as xenon tube trigger transformer.
    Ive added about 8 windings AWG30 wire on top of the enamel coating.
    The charging resistor for the 220nF capacitor is 1 M Ohm.

    Ive seen schematics using as little as 22nF.
    Only a tiny high voltage charge seems to be required.
    As SCR I will use a XL1225.
    The tube is a small 26mm kind.
     
  2. Hypatia's Protege

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    Mar 1, 2015
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    I apologize that I don't see a question in your post? - FWIW most 'standard' Xe flash-tubes require a trigger pulse amplitude of ≤ 4kV -- Hence, if you wish to preform a 'dry run'. you need merely arrange a ≈ 2 mm spark gap across the 'secondary' then observe same while manually connecting the charged cap to the 'primary' in a darkened room (following ≈ 20 minutes 'visual adaptation')...

    Best regards
    HP

    PS
    Out of curiosity I've just measured the 'secondary leg' of a 6kV trigger coil at 2.5 mH -- Hence it would seem you're in with a chance at 2.2 mH:) -- IOW if your arrangement fails to preform satisfactorily - 'profitable' adjustment of the primary should be possible:cool:
     
    Last edited: May 30, 2016
  3. takao21203

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    Apr 28, 2012
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    Here a picture of the culprit of this thread...
    Didnt find the patience to do it since I was tired and thats no good when making high voltage circuits.

    Dont need sparks just need the small tube to trigger.

    I cant show the full schematics since I use a capacitor bank to prevent fuse switching off.
    But the flasher is very basic. Most schematics on the net are very similar.

    I use a blue neon lamp for the gate!

    Later I could power it from lower voltage or change the storage capacitor.
    Its 4x 0.68uF though I have some larger electrolytic kinds. They scare me honestly.
    Shortening the bank with copper wire, makes some snapping noise.
    Then it recharges and the blue neon goes on and becomes brighter.
     
  4. Hypatia's Protege

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    Indeed, I suggested the spark gap as a means of verifying production of requisite potential (prior to assembly of the circuit) -- If the induced EMF is insufficient to jump a 2 mm gap it will not reliably trigger the tube...

    As an aside - I concur with your cautious approach - For, while owing to the negligible current involved, a shock from the trigger coil would be of no consequence - The flash caps hold potentially dangerous energy levels.

    Best regards and good luck!
    HP:)
     
  5. ian field

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    Oct 27, 2012
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    A typical figure quoted for xenon trigger secondary is around 4kV.

    An RF choke may not last very long before breaking down.

    The ratio isn't as high as most people think - the trigger transformer usually has a capacitor discharge arrangement on the primary.

    Put simply; the least number of secondary turns you can reliably get away with, the better.
     
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  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    A ready made one can be had generally for free. Any place that still develops film will usually give you used disposable cameras, the flash in them is a xenon bulb and that means the have a battery (AA cell usually) and high voltage charge pump. Just make sure to short the flash capacitor before messing with the circuit, they hold their charge for a long time.
     
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  7. takao21203

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    Analogue film is pretty finished here. I had many of these coils around just interested in the technology.

    There are 1M discharge resistors.
     
  8. shortbus

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    Wow I know it's not as popular as digital, But would think they are still available. At least they are here. Any of them I have taken apart don't have a cap discharge resistor in them. One when I first took it apart blew a big chunk out of me favorite small screwdriver.
     
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  9. Hypatia's Protege

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    Ditto! -- A current limiting resistor in the flash-tube circuit would be self defeating (note that connected as described, a circuit incorporating a flash Cap charged to 400V would be limited to a peak flash current of 400uA!!!:confused:) -- FWIW I submit that the OP was referring to a resistor in the triggering circuitry (As suggested by the below quoted text):

    Best regards
    HP:)
     
    Last edited: May 31, 2016
  10. Mary Johanssen

    New Member

    May 28, 2016
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    Look for Edgerton's flash book. He wrote the bible on xenon flash though his fame for creating air gap flashes is misplaced. Fox talbot pioneered those in 1870
     
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  11. takao21203

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    What stops me using same kind resistors to discharge the capacitors (after powering off)?
     
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  12. ian field

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    Can't remember how much - but a local shop told me get paid by the bag for scrap disposables. Worst case scenario, you may get charged up to GB£1 per camera.

    The xenon tubes are tiny, and the trigger transformers are dimensioned accordingly - they're pretty fragile for general experimentation.
     
  13. Hypatia's Protege

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    Ahhhh! You're talking a 'bleeder resistor' now I get it!:D:D:D

    Best regards
    HP:)
     
  14. shortbus

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    Probably wrong on this, but, was under the assumption that the trigger on a xenon bulb was voltage related not current related. Unless they have changed the disposable camera circuits, there are no bleeder resistors on the flash discharge caps. At least any that I've played with.
     
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  15. ian field

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    You seem to be answering 2 different posts in the same sentence - I never said anything about bleed resistors. All I said was; the transformers in disposable cameras are tiny and a bit fragile.
     
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  16. takao21203

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    I think the days where they had bags of disposeable camera scrap are over.
    There are some for sale in a 2 Euro shop dont know if they have flash or not.
    But I guess nobody buys them.

    Instead we have small shops everywhere with windows full of used mobile phones.
    Not to speak the shops selling new ones.
    Photography shops are a few small ones and most they have is lenses and digital cameras.

    I really want to try making my own transformer.
     
  17. ian field

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    A horizontal driver transformer from an old CRT VGA monitor might work.

    The secondary (almost) directly drives the B/E of the horizontal output transistor. Many Philips (and some other makes) powered the driver primary from about 250V HT rail. The turns ratio is very high, so they might work as a xenon trigger - as long as the turns don't break down.
     
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  18. Hypatia's Protege

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    Correct! - The function of the 'transformer' is development of the (relatively high EMF) triggering pulse -- As a practical matter, current is irrelevant...

    BTW -- The OP is advised that reliable (i.e. sensitive) triggering may require the triggering electrode to 'cover' more area than shown in the images - please note that, as manufactured, the 'reflector' serves as 'part' of said electrode (so to speak)...

    Ditto! -- I've not seen them either:confused:

    Best regards
    HP:)
     
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  19. ian field

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    You could always strip one of those tiny transformers in a disposable camera.

    Its mostly the turns ratio you want, most of the rest can just be scaled to whatever you want.
     
  20. shortbus

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    Yeah my mistake. The ones I messed around with had a small PCB size transformer in them, Around a 0.650" cube.
     
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