[Q] DIY flash external battery pack?

Discussion in 'Photography' started by Sir Loin of Beef, Mar 27, 2005.

  1. Sir Loin of Beef

    BillB Guest

    Ok, thanks for the info., it's the lead acid batteries I'm more
    interested in. I'm familiar enough with rechargeable alkalines to
    know that their internal resistance would be practically the same as
    primary alkalines. They're also of no real concern here. They can
    be useful in very low drain applications, but in digital cameras
    they can be ruined very quickly. Unlike NiCads, manufacturers of
    rechargeable alkalines recommend that they be recharged often, while
    at least 75% of the capacity remains in the battery. Failure to do
    so shortens can drastically shorten their life.

    So if in one hypothetical camera NiMH AAs would provide up to 300
    pictures per charge and primary alkalines 100, you'd want to remove
    the rechargeable alkalines after only 25 pictures have been taken.
    Hardly worth the effort. On a trip away from home without a
    charger, two sets of NiMH batteries (one in the camera, one spare)
    is practical. To take the same number of pictures using standard
    alkalines would take 6 sets of batteries. Expensive, but not too
    outrageous. To be able to take the same number of pictures without
    abusing the rechargeable alkalines would require 24 sets of
    batteries. Sorry, but no thanks. :)
    BillB, Mar 30, 2005
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  2. Sir Loin of Beef

    BillB Guest

    On Tue, 29 Mar 2005 21:28:37 GMT, dadiOH wrote:

    [ all data provided below is fictitious, meant only to represent
    reasonable values that might be seen if actually measured ]
    Oh yes, most definitely. Alkalines are not like NiCads or NiMH
    batteries in that their output voltage is pulled down significantly
    under load. Four fresh AA and D cells would both start at a bit
    above 6 volts with no load. But at the high load presented by the
    flash unit, the voltage provided by the AAs and Ds might start out
    providing something like 5.3 and 5.8 volts respectively. With use,
    the voltages would decrease, with the AAs decreasing faster. I
    remember using an external flash with 4 fresh AA batteries that
    started out with a recycle time of about 7 or 8 seconds. By the
    time the batteries were half exhausted the recycle time exceeded 10
    seconds. I'm pretty sure that if I had the same flash unit powered
    by D cells the initial recycle time might be 5 or 6 seconds, take
    far longer to become half exhausted (at least 5 or 6 times longer).
    And even at that point would have a shorted recycle time than the 10
    seconds needed by the half exhausted AAs, possibly 8 or 9 seconds.

    Now you're cooking . . . :) Back in the 60's I could only dream
    of such equipment, but even then knew it was more than I'd care to
    BillB, Mar 30, 2005
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