Capacitors for Bulb Flash

Discussion in 'Lighting' started by brooklynkid, Sep 25, 2007.

  1. brooklynkid

    brooklynkid Member

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    I have two old flash bulb flashes. The power supply for each flash is a battery and a replaceable capacitor. I have been able to find replacement batteries at Radio Shack, but the flashes still wont fire even with the new bateries. My feeling is that the capacitors need replacement. However, I cannot find a supplier for the capacitors. Does anyone know where they can be obtained? I have done a web search without luck. Thanks.
     
  2. greybeard

    greybeard Member

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    Any of the online electronics suppliers should carry something that you can use, although some will have minimum orders that may be more than you want to pay. The voltage and capacitance should be marked on the original units; you can use anything rated at equal or higher voltage, and comparable or higher capacitance. You will have to make sure that the replacement is not physically larger than the space available for it.

    I would suggest Moser, Digikey, or Allied, in that order, but there are others as well.
     
  3. Jim Jones

    Jim Jones Subscriber

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    The voltages of battery and capacitor aren't really critical as long as the battery voltage doesn't exceed the capacitor working voltage. Readily available capacitors, such as those at Radio Shack, may not have the mechanical specifications of the original capacitors, but probably can be adapted.

    Electrolytic capacitors like those used in the battery/capacitor flashes can deteriorate with time. Sometimes they can be rejuvinated by applying appropriate voltage over a period of time. A series resistor will limit current if the capacitor is shorted. Power supplies from small disgarded appliences are handy for this. A variety is available in second-hand shops.
     
  4. Mike Wilde

    Mike Wilde Member

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    capacitors - seconding jim's comment

    yep, I have done this. I got a dead old little 2" agfa tully for ag-1's , from my wife's long deceased grand father's pile of stuff. The 45+ year old cap was dead - all dried out. So I dug around, and came up with some 10V caps that I had been using to diagnose a dying minolta x-700 with. 2 of them in series actually fit the available space better than a single modern 25V unit. Tested it with a 12V bench power supply. bingo- the bulb goes pop/flash.

    Now to the battery...15V photoflash batteries these days can costmore than I want to spend once the mail cost adds on. I sniffed around my local electronics wholesaler and found that modern car keyless entries are powered from a little 12V alkaline battery, for I think $3.

    I also stocked up on LR-44 for my pH meter, light meter and cameras, at far better than photo store prices. I know, killing the traditional photo retailer, but at $2 vs 5.5 , and I bought 10, I could not resist.

    So the old zinc carbon battery case got pried apart, and the dead guts removed and replaced with the 12V alkaline battery, and a short length of 1/4" copper water pipe I cut to the right length to extend the 12V terminals to reach the terminals in the old case.

    So now I have the flash unit working, and the motivation to scrounge old flash bulbs at camera shows. If it stayed broke I would be a bit less inclined to further indulge my GAS habit, because I would not have as strong a reason to go to the shows.
     
  5. dferrie

    dferrie Member

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    A lot of the actual manufacturers will actually order "samples" often free of charge. You could try Cornell Dubilier, as far as I can remember they are one of the "big" manufacturers of capacitors and I think I saw photoflash capacitors in their catalog at on point, a google search for Dubilier should find them.

    David
     
  6. Mike Wilde

    Mike Wilde Member

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    not a big cap is required

    with flash bulbs the energy is in what is being burned. With electronic flash the energy is in sustaining the arc. So flash bulbs don't need a big cap - I recall that I used about 50 uF-100uF rated at 20V but quite suitable when triggering at 12V.
     
  7. sun of sand

    sun of sand Member

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    Radio Shack. You would've been popping flashes already, man.
     
  8. Steve Smith

    Steve Smith Subscriber

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    The capacitor value for a bulb flash is not critical. Probably 22uF to 100uF would do.

    The reason for the capacitor is that the battery alone cannot provide enough initial current to start the bulb burning due to its relatively high internal resistance.

    The capacitor is charged in a series circuit by the battery via a current limiting resistor and through the bulb (i.e. current only flows with a bulb fitted).

    The cameras flash contacts short out one side of the capacitor to the bulb, the other side being permanently connected to the other side of the bulb so that at the time the shutter is pressed, the full charge of the capacitor is discharged into the bulb.

    As I said above, this arrangement was to overcome the shortcomings of the battery's internal resistance to ensure that the bulb fired within the time it was supposed to.

    Battery technology has advanced since the days of flashbulbs and it should be possible now to find a battery with a lower internal resistance which could fire flash bulbs efficiently in a simpler bulb - battery - flash contacts series circuit.


    Steve.