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On Tue, 30 Jul 1996 08:54:49 -0700 (PDT), you wrote: >Are these in fact the batteries that AUL uses? It's hard to tell what's >under all that red, white and blue duct tape. Certainly Arnold uses the >Shumacher charger, which is available in most Sears/Penneys type stores. > >The reason, Arnold told me, he uses the 5.25" x 14" acrylic case is that >the light is almost neutrally buoyant with the lead battery. Drop (not a >good metaphor :( - the diameter to 5" and it's 4 lbs negative. That's what >I'm stuck with as a replacement for the one I broke over the weekend, as >he'd out of acrylic. Pete,he's right,with that diameter,length tube,the thing is virtually neutral.I made my own when io had access to a machine shop;I used irrigation pipe,which is aluminum with an O.D. of 5.25" and a wall thickness of .123" very durable,& the buancy characteristics are close to acrylic due to the thinner sidewall. Of course here,you have problems with the conductivity of the case.I wrapped my pack in bubblewrap packing material;not an elegant solution,but it provides good insulation & the batteries dont shift in the case. The quick & dirty way to calculate capacity is to divide the wattage by the voltage to get amps.The only disadvantage to this is you wont get that high a yield from lead acid batteries,i.e.,if the battery is rated at 7 amp hours,that rating is based on a disharge rate of 10 or twenty hours for full discharge (i forget which).If you discharge the battery in 1.5 hours you get a significantly smaller capacity.So,for your 250W light to burn 1.5 hours,youll need AT LEAST 20 amphours of capacity at 12 volts,or 10 amphours at 24 volts,depending on what the bulb is,and will probably need more than that.Now,I THINK nicads have a beeter capacity response at higher discharge rates,but George is the one to ask about that,My nicad info is years out of date. I had a 21 volt 200 watt bulb i used to overdrive at 24 volts that gives the equivalent light output of a 250w bulb,and this 14 amphour pack (7 ah at 24 volts) gave me the about 25 minutes of burn time;it DID get pretty yellow the last 5 minutes.HOWEVER,there are significant problems with overdriving bulbs;they have a greatly reduced lifespan,and are prone to blowing at any time.Maybe not a serious problem for a video light (if you can repeat the shot on another dive) but NOT a good thing in a primary lighting system. Anyway,to get the pack you describe as a lead acid system,youd need one about 4 times bigger than an AUL pack. Asfor the nicads,the big problem is expense.I think I remember George saying the pack you're describing is about $1500 for the batteries alone,but he can answer that better than I can. Bottom line is the bottom line.You can get cheap bulky lead acids or you can get expensive compact nicads,but as far as i know,you cant get cheap compact packs.There aint no such thing as a free lunch. POSTSCRIPT:I just saw an item on the next step tv show about a new manufacturing process for lead acid batteries that's supposed to significantly reduce the size of lead acid batteries.Seems i recall it had something to do with the lead being bonded to a polymer fiber & woven into a sort of mesh,but they were talking about automotive batteries,which are not designed for deep cycle use.Dont know anything more about the technology,but maybe we'll get lucky & help is on the way. John L. Dunk Tallahassee,Fl. screwloose@ne*.co*
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