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Photo Forum / General Photo Topics / General Topics / March 2005[Q] DIY flash external battery pack?
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 instead? > 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 [quoted text clipped - 14 lines] > building something like the Quantum that deals with higher voltages > instead? 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. > 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 [quoted text clipped - 14 lines] > building something like the Quantum that deals with higher voltages > instead? 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 ____________________________ 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 test@gesg.com (Sir Loin of Beef) wrote in news:4246ba96.4974937 @news.starhub.net.sg: > 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 [quoted text clipped - 14 lines] > building something like the Quantum that deals with higher voltages > instead? 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. 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? >test@gesg.com (Sir Loin of Beef) wrote in news:4246ba96.4974937 >@news.starhub.net.sg: [quoted text clipped - 7 lines] >hour capability than AA cells. The result is a simpler design that >achieves the objective of more exposures between recharging. > How about if I make a battery pack of 4 x 4 sets of 2100mA AA cells > connected in parallel instead? 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? ________________ > Will this give me faster recharge times, or just a higher number of > flashes before the batterys run out of power? Recharge time wouldn't change. -- dadiOH ____________________________ 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 >> How about if I make a battery pack of 4 x 4 sets of 2100mA AA cells >> connected in parallel instead? [quoted text clipped - 8 lines] > >Recharge time wouldn't change. Eh? Flash recharge time *will* improve if you continue to add more batteries in parallel. This is due to an increase of available current. 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' section: http://www.nikonusa.com/template.php?cat=1&grp=4&productNr=4801 "Quick Recycle Battery pack SD-800 holds a fifth AA - size battery for faster power recycling" -- Owamanga! http://www.pbase.com/owamanga > Flash recharge time *will* improve if you continue to add more > batteries in parallel. This is due to an increase of available > current. Yep. > 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. 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 something? >> Flash recharge time *will* improve if you continue to add more >> batteries in parallel. This is due to an increase of available [quoted text clipped - 20 lines] >it'll take twice as long to recharge them. Maybe I missed >something? 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! http://www.pbase.com/owamanga >> Flash recharge time *will* improve if you continue to add more >> batteries in parallel. This is due to an increase of available [quoted text clipped - 20 lines] > it'll take twice as long to recharge them. Maybe I missed > something? 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 > 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, [quoted text clipped - 3 lines] > batteries can delivery (not the individual batteries, mind you, but the > battery bank as a whole). 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. >> No, he's talking flash cycle time. A low internal resistance battery >> will [quoted text clipped - 19 lines] > sized NiCad cells? I'm not talking about lightweight RS cheapos, > but the higher capacity, heavier, sintered plate NiCads. 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 > As to internal resistances, lead acid batteries have extremely low internal > resistances. For car batteries it's imperative to have low internal [quoted text clipped - 5 lines] > Alkalines, NiCds, Lead Acid would be the order from > high internal resistance to low. 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. >> As to internal resistances, lead acid batteries have extremely low >> internal [quoted text clipped - 25 lines] > size, but only verifiable data will confirm it and show how large or > small the differences may be. Maybe this will help: http://www.buchmann.ca/Article4-page2.asp However, this article only discusses rechargeable batteries so he's comparing rechargeable alkalines to NiCds and Lead Acid. -Bruce > Maybe this will help: > > http://www.buchmann.ca/Article4-page2.asp > > However, this article only discusses rechargeable batteries so he's > comparing rechargeable alkalines to NiCds and Lead Acid. 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. :) > Good evening ladies and gentlemen. Welcome to the Northwest > Photographer's Association Handicap Stakes. In lane 6 is Ansel > Adams, bearing a handicap of 56 sets of batteries. In lane 7 . . . > > On your mark . . . >>> How about if I make a battery pack of 4 x 4 sets of 2100mA AA cells >>> connected in parallel instead? [quoted text clipped - 28 lines] > "Quick Recycle Battery pack SD-800 holds a fifth AA - size battery for > faster power recycling" 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 ____________________________ 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 > (snip) Let me ask you this... > Suppose you have two identical flash units, [quoted text clipped - 4 lines] > recharge faster? No way, Jose. Not in my > experience. (snip) 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. Stewart >>>> How about if I make a battery pack of 4 x 4 sets of 2100mA AA cells >>>> connected in parallel instead? [quoted text clipped - 30 lines] > >Which is in series with the other four giving 7.5v, no? 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. >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. 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. >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. 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." http://www.pcphotomag.com/content/2005/mar/powerguide.html 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. >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. Okay... -- Owamanga! http://www.pbase.com/owamanga [ all data provided below is fictitious, meant only to represent reasonable values that might be seen if actually measured ] > 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 [quoted text clipped - 6 lines] > 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. 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, 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. 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 tote. 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. Regards, JDR > 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, > (snip) In your opinion, is this a worthwhile > project, or should I look at building something > like the Quantum that deals with higher > voltages instead? 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. Stewart |
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