Hi, > Voltaic shows it takes 8-10 hours to fully charge the battery pack > that comes with the backpack: 10h * 4W = 40Wh, that doesn't match up > the numbers below. Going backward (see below) 15.84 Wh / 10H = 1.584 > Watts. Maybe that's what it averages if not angled directly as the > sun--or is my math wrong? or my thinking (quite likely ;-)? My guess is that the batteries are not 100% efficient when charging. I know some batteries get warm while charging, which is some energy getting lost as heat. > > I have a pair of 3000mAH 7.2V NiMH packs, in parallel for 6000mAH. > > That runs into a board that has a 5V 3A regulator and a 12V 1A DC-DC > > converter. I need to upgrade the board to use a 5V 5A regulator that I > > How big/heavy/safe/hard to build is your board? It's about the size of a credit card, and has a heat sink that's a bit over an inch high comming off it. It doesn't weigh much more than a few ounces, no big caps or transformers on it. Safety-wise, it seems OK. So far I've only booted the system twice, and I didn't catch fire either time. It doesn't have any dangerous voltages or anything like that. Construction is fairly simple. It's on a piece of perf board now. The regulators are easy to work with, just read the datasheets and use the recommended input and output caps. If there's interest, I can put up schematics, and eventually PCB art. Two of the parts are available as samples, and the one that isn't is $8. Even buying everything (resistors, perf board and all) wouldn't go much over $30. > Would it be bigger/heavier/less efficient to have a 12V regulator in > parallel with the 5V regulator instead of regulating then converting? That's how I currently have them. > Same question if you reversed it and had a 12V regulator then a DC-DC > conversion down to 5V. Well, in my particular case, no, as the 5V is hooked up to a 7.5V battery, so it drops 2.5V rather than 7V. If I was running off a voltage greater than 12V and doing a down-conversion to 12 and one down to 5, then it would be more efficient in terms of power loss to regulate the 5 from the 12. However, that would run into the issue that the power supply at any point could only put out the current of the lowest current regulator in the chain up to that point. Even though I have a 1A 12V converter and a 5A 5V regulator, I'd only get 1A out of the 5V regulator before the 12V converter burned/shut itself off. -Abe _______________________________________________ Wear-Hard mailing listhttp://www.haven.org/mailman/listinfo/wear-hard
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