camera flash circuit using more than one capacitor to be able to fire sequential flashes

Discussion in 'The Projects Forum' started by cvangordon, Aug 29, 2016.

  1. cvangordon

    Thread Starter New Member

    Mar 28, 2016
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    So if you are well versed in electronics but don't know about camera flashes here is an article that should be enough to figure out how to answer my question. This article is also the flash I am trying to modify.

    http://www.diyphotography.net/how-to-build-a-flash-with-an-optical-slave/

    What I was planning to do was to add 2 capacitors so that I could fire the flash then fire it again then fire it again and by the time the 3rd has fired the first capacitor is charged again making me have very short wait times between flashes and the ability to do 3 shot burst photos as well.

    I was thinking I would only need to add the capacitors and some transistors that close after first use and reopen after the capacitor is charged. Not sure exactly how it would be done so some ideas is what I'm looking for.
     
  2. cvangordon

    Thread Starter New Member

    Mar 28, 2016
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    I'm guessing my best option would be some kind of logic gate. It would have to be hooked up to the circuit where the 3 capacitors would charge as normal but then would only a alow the discharge of one capacitor at a time.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    The thyristor fires the capacitor across the pulse coil, so you're going to have to use a 3way switch to pull in the other capacitors, they will all have to be charged at the same time, which will take three times longer.....
     
  4. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Simpler to use a massive capacitor holding enough energy to do the 3 flashes, then use an IGBT switch and trigger circuit.

    The IGBT switch is used to fire and quench the flash rapidly, you then just need trigger pulses.
    A trigger coil can be wired to fire when the IGBT switches on.

    Beware of overheating the flash tube...
     
  5. cvangordon

    Thread Starter New Member

    Mar 28, 2016
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    I'm not well versed in electronics but that's not how this flash circuit works. As soon as the xenon gas is ionized it becomes conductive and that simply pulls the current from the capacitor right out and just gets filled up again as long ad the fladh is still turned on. Yes having 3 caps would make a 3 times longer charge time when you initially turn the flash on but if I could make it only use one cap per flash while it still recharged the used caps it would make my flash recharge times much shorter. Would definitely require more battery power though.
     
  6. cvangordon

    Thread Starter New Member

    Mar 28, 2016
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    You are right it would be simpler with a large cap. I was thinking about using 3 small caps because I want to keep the size of the fladh unit small. From what I have seen 3 small caps is significantly smaller than a cap big enough for 3 flashes. Also 3 of the same cap makes each flash a consistent brightness where as one big one might have some variations in how much energy is coming out each flash. Also like I told the the previous commenter the cap is simply emptied because the xenon gas becomes conductive so any attempt to use only part of the capacitor's energy would require going through a resistor as far as I know. Might be wrong about that but still pretty sure.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    A big question is the peak current through the tube. This must flow through whatever the switching part is.
    3 - 600 V NPN transistors
    1 - CD4017 Johnson counter
    3 - 1N4937 diodes
    3 - capacitors
    Plus an oscillator or some logic to step the 4017 when shooting.

    ak
     
  8. cvangordon

    Thread Starter New Member

    Mar 28, 2016
    11
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    Could you elaborate a bit on this reply? I see a list of parts. Are you saying these are the parts I need or are you asking if the voltage on the circuit can go through these parts safely?
     
  9. Sensacell

    Well-Known Member

    Jun 19, 2012
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    If you make the strobe pulses short enough, the capacitor can easily retain enough charge for multiple flashes.

    The energy delivered is a function of the pulse width driving the IGBT, you can go as fast as 100 us.
    Increase the pulse width on successive flashes to even out the energy delivered?

    Three caps is going to need some stupidly complex switching - you need to switch the discharged caps out of the circuit, switch in a charged one, then fire a trigger pulse.
     
  10. cvangordon

    Thread Starter New Member

    Mar 28, 2016
    11
    0
    Ah, I see. Yeah I thought my idea might be impractical. I don't know enough about electronics to know for sure though so that's why I'm asking about what is possible. This is good info so thank you for that :).
     
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