[Q] DIY flash external battery pack?

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

  1. I have been toying with the idea of building an external flash battery
    pack. However, I don't wish to deal with high voltages, and my idea is
    mainly to eliminate swapping AA cells when you need to fire off that
    essential shot the most.

    So what I have in mind is to have a beltpack, just like the Quantum,
    which holds 4 sets of 4 Ni-MH AA cells. There will be a connector and
    cable to the flash battery compartment, via a set of false batteries
    which provide the contact points.

    The idea is to allow only 1 set of 4 AA cells to power the flash at
    one time, but the moment I feel that this set is getting slow, I can
    flick a switch to advance to the next set of batteries. I plan to use
    a 4-position switch for the 4 cell sets.

    In your opinion, is this a worthwhile project, or should I look at
    building something like the Quantum that deals with higher voltages
    Sir Loin of Beef, Mar 27, 2005
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  2. Sir Loin of Beef

    dj_nme Guest

    It sounds like an okay sort of project to me.
    The flashgun that you describe runs off 6 V and be damaged by higher
    voltages, the control electronics may not handle it.
    Perhaps making an external pack using 4 C or D sized cells for extended
    operating life would be a less bulky and simpler?

    Years ago, I made a battery pack for my Olympus D-600L that attaches to
    the tripod socket and contains 4 C cells; it allows over 120 pictures
    compared to just 30 shots from a set of 4 AA cells in the camera alone.
    dj_nme, Mar 27, 2005
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  3. Sir Loin of Beef

    dadiOH Guest

    Nothing wrong with the idea that I can see but if I were doing it I'd
    use "D" or "C" cells rather than "AA". I don't recall the ampere/hour
    ratings but I'd think one set of the bigger batteries oughta give you at
    least the equavalent of fours sets of "AA".

    Quantum uses high voltage batteries and rectifies the output to 6v
    nowadays? Used to be they just used bigger 1.5v batteries as above.


    dadiOH's dandies v3.06...
    ....a help file of info about MP3s, recording from
    LP/cassette and tips & tricks on this and that.
    Get it at http://mysite.verizon.net/xico
    dadiOH, Mar 27, 2005
  4. Sir Loin of Beef

    Mono Guest

    (Sir Loin of Beef) wrote in @news.starhub.net.sg:
    There was a how-to article in (I believe) Petersen's many years ago
    describing precisely this kind of battery pack. The critical difference,
    however, was that it used rechargable D-cells that have a greater ampere-
    hour capability than AA cells. The result is a simpler design that
    achieves the objective of more exposures between recharging.
    Mono, Mar 27, 2005
  5. Sir Loin of Beef

    Flavius Guest

    A *MUCH* better approach is an SLA (Sealed Lead Acid) battery. Use 6v @ 4.5
    amp hours. With a 500milliamp UBC two stage charger you can leave it on the
    charger 24/7 at home until you are ready to shoot. Just grab and go knowing
    you have 1500+ flashes at your beck and call. If need be, the unit can be
    left off the charger for up to three months without significant loss of
    charge.! Battery cables with adapter modules to interface with many
    different flashes are available from Quantum Instruments ( and B & H ). Use
    the cables made for their "Bantam" module. BTW the Bantam is great, except
    it is WAY OVERPRICED and you only get about 450 or so flashes. (Of course
    flash power setting has a lot to do with flash count. These numbers
    represent FULL power flashes).

    You can also get the unit ready made at a fraction of Quantum's price from:

    http://www.aljacobs.com .

    Al builds a GREAT unit for about $99.00 depending on how much custom bling
    you want.

    FYI, I have done a significant redesign of the Jacobs pack. Same power, 25%
    smaller, and more reliable. I don't yet know if I will be building any for
    sale though.

    Flavius, Mar 28, 2005
  6. How about if I make a battery pack of 4 x 4 sets of 2100mA AA cells
    connected in parallel instead?

    Will this give me faster recharge times, or just a higher number of
    flashes before the batterys run out of power?
    Sir Loin of Beef, Mar 28, 2005
  7. Sir Loin of Beef

    dadiOH Guest

    You mean four sets of 4 - AA batteries in series, each set of four in
    parallel? Why not just use one set of 4 - D cells in series?

    Recharge time wouldn't change.


    dadiOH's dandies v3.06...
    ....a help file of info about MP3s, recording from
    LP/cassette and tips & tricks on this and that.
    Get it at http://mysite.verizon.net/xico
    dadiOH, Mar 28, 2005
  8. Sir Loin of Beef

    Owamanga Guest


    Flash recharge time *will* improve if you continue to add more
    batteries in parallel. This is due to an increase of available

    Assuming the flash keeps 4xAA in series to give it 2100mAh at 5v,
    adding another series gang of 4xAA in parallel to the existing set
    would give it 4100mAh at 5v. Other limitations aside, this would half
    the recharge time.

    If you don't believe me, I'd ask you to check the following
    specification of the Nikon SB-800, especially the 'Power Source'


    "Quick Recycle Battery pack SD-800 holds a fifth AA - size battery for
    faster power recycling"
    Owamanga, Mar 28, 2005
  9. Sir Loin of Beef

    BillB Guest

    Really? And I'm not referring to 4100mAh, which might actually be
    closer to 4300 than 4200, since typos don't count. :) How would
    recharge time (you're now talking about battery recharge, not flash
    recharge time, right?) be cut in half? Wouldn't the best case be
    if the charger only recharged 4 AAs, so a second charger would be
    needed, and they could both be used simultaneously? In that case
    whether the custom flash unit used 4 or 8 AAs, the recharge time
    would be the same. I've seen some chargers though that use a
    constant input current. They tend to be higher power units. With
    these, the output current is divided among the charging batteries,
    so if you double the number of batteries that are being recharged,
    it'll take twice as long to recharge them. Maybe I missed
    BillB, Mar 28, 2005
  10. Sir Loin of Beef

    Owamanga Guest

    Typo it was, and no, I was always talking about flash recharge time.
    Sorry if that wasn't clear.

    A better phrase would have been recycle time (for the flash).
    Owamanga, Mar 28, 2005
  11. Sir Loin of Beef

    Bruce Chang Guest

    No, he's talking flash cycle time. A low internal resistance battery will
    increase cycle time. That's why a lead acid battery can cycle so quickly,
    while alkalines and NiCd's can only try to keep up. If you were to put
    Alkalines and NiCd's in parallel, you've effectively reduced the internal
    resistance the flash circuit sees and that increases the max current the
    batteries can delivery (not the individual batteries, mind you, but the
    battery bank as a whole).

    Bruce Chang, Mar 28, 2005

  12. I just wrote a message in another thread ("Olym;pus FL-50 Battery Door")
    relating to this very subject. In that, I described the construction of an
    external battery pack using "D" size batteries. Since it relates somewhat to
    your plans, you may want to read that message. I've made several of these
    home-built battery packs to use with different flash units and would be glad
    to answer any additional questions you might have.

    Dwight Stewart, Mar 28, 2005
  13. Sir Loin of Beef

    BillB Guest

    Very clear now.
    BillB, Mar 29, 2005
  14. Sir Loin of Beef

    BillB Guest

    Yes, the flash recycle time was made clear. But didn't you mean
    that a lower internal resistance will decrease cycle time? I
    understand about connecting batteries in serial and parallel, but
    I'd only want to put alkalines in parallel with alkalines, and
    NiCads in parallel with NiCads, which I'm sure is what you meant. :)

    From what I've read in the past, NiCads have far lower internal
    resistance than alkalines, NiMH or lithium batteries. They just
    don't have particularly large capacities, but can provide much more
    current while it lasts. I'm only slightly familiar with lead cells.
    Do they really have a lower internal resistance than comparably
    sized NiCad cells? I'm not talking about lightweight RS cheapos,
    but the higher capacity, heavier, sintered plate NiCads.
    BillB, Mar 29, 2005
  15. Sir Loin of Beef

    Bruce Chang Guest

    You're right, decrease cycle time. I suppose I was thinking increase cycle
    time performance.

    As to internal resistances, lead acid batteries have extremely low internal
    resistances. For car batteries it's imperative to have low internal
    resistances so that it can supply a starter with high current. A higher
    internal resistance will not supply as high of a current as a battery with
    low internal resistance. It's effectively adding resistance to the circuit
    and more resistance means less current (if voltage stays the same)

    Alkalines, NiCds, Lead Acid would be the order from high internal resistance
    to low.

    Bruce Chang, Mar 29, 2005
  16. Sir Loin of Beef

    dadiOH Guest

    Which is in series with the other four giving 7.5v, no?

    I don't disbelieve what you say but my experience with small battery
    (not high voltage) powered flashes over 50 years has been that a
    slightly higher voltage decreases flash recharge time, increased mAh
    gives greater quantity of flashes.

    Let me ask you this...
    Suppose you have two identical flash units, one powered by four AA
    cells, the other by four D cells...same voltage but the D cells have a
    much higher mAh rating, right? You think the one with the D cells is
    going to recharge faster? No way, Jose. Not in my experience.

    Now, if you want *fast* recharging, use a 510v battery (or 2-240v as in
    the old Stroboflash). Has to go directly to the flash capacitor(s)
    though, not to the flash innards where the low voltage is normally
    bumped up.


    dadiOH's dandies v3.06...
    ....a help file of info about MP3s, recording from
    LP/cassette and tips & tricks on this and that.
    Get it at http://mysite.verizon.net/xico
    dadiOH, Mar 29, 2005
  17. Sir Loin of Beef

    BillB Guest

    Again, you're not telling me anything not already known. I
    understand that lead acid batteries have low internal resistance,
    but you can't directly compare them with NiCads because of the great
    disparity in size. About 20 years ago I had a Sears emergency
    light that used two lead cells that were approximately the size of C
    cells. Back then I think that I read about hi capacity NiCad D or F
    cells that if subjected to a short circuit could produce at least 50
    amps of current. It might have been 100 amps or more, I don't
    really recall, and it would certainly not be able to produce such a
    current for very long. There's a huge difference between the
    current capacity (or internal resistance) of alkalines vs. lead.
    Simply placing NiCads between alkalines and lead cells gives no
    indication whether they are more similar to alkalines or lead cells.
    Lead cells may have lower internal resistance than NiCads of similar
    size, but only verifiable data will confirm it and show how large or
    small the differences may be.
    BillB, Mar 29, 2005
  18. Sir Loin of Beef

    Bruce Chang Guest

    Maybe this will help:


    However, this article only discusses rechargeable batteries so he's
    comparing rechargeable alkalines to NiCds and Lead Acid.

    Bruce Chang, Mar 29, 2005

  19. Are you talking about recharging the batteries or recycling the flash
    unit? Recycling commonly refers to the time needed for the capacitor(s)
    inside the flash to reach the power levels necessary to achieve the flash
    unit's rated flash output. If you're talking about that, recycling, my
    experience is very different than yours. Given the same load, four "D" size
    cells will generally deliver quicker recycling times then four "AA" size
    batteries, up to the maximum imposed by the electronic circuitry inside the
    flash. Further, those quicker recycling times will remain consistent over a
    much longer period.

    Dwight Stewart, Mar 29, 2005
  20. Sir Loin of Beef

    Owamanga Guest

    Possibly, but I don't have that attachment with me to check if the
    configuration is parallel or series. It *might* be safe to bump the
    voltage by another 1.25v, but this can't go on for ever.
    From a electronic background standpoint, yes, both are capable of
    reducing recycle times. Increased mAh would also give greater quantity
    of flashes, increased voltage alone would not.
    It has to do with internal resistance (sometimes called 'cell
    resistance'), which is halved by ganging the two sets in parallel. I'm
    not at all familiar with D cells and how they perform for this task,
    but I assume their internal resistance is the limiting factor
    preventing them from recycling a flash quickly.

    Check the following page:

    "In flash units, NiMHs recycle your flash in half the time than fresh
    alkaline batteries."

    This has also been my experience. Now, I know the NiMH and alkaline
    output voltage are similar but internal resistance is significantly
    different, which would account for the faster recharge time.
    Owamanga, Mar 29, 2005
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