Hi > > If your laptop or other hardware is more efficient, or you get a > > bigger battery, then you get more run time, at the expense of charge > > time. 7.2V rechargeables are sold at hobby shops to run remote control > > toys. > > Those sound like an interesting idea. Small, lightweight, fairly > easily available. I haven't used one in like 20 years, they were all > NiCad's back then. Are the available as NiMH or lithium ion now? I know you can get NiMH ones, I can see two from where I'm sitting. At least one source claims to have a 4400mAH Li-Ion pack, as well as some Li-poly packs in lower current ratings [3]. I think those prices look good, and the energy density is better than what I currently have. > > That thing looks pretty cool. The line "The Powerpack has a nickel > > metal hydride (NiMH) battery you can recharge using household > > electricity or 12 V DC power from a vehicle DC outlet" makes it sound > > like if you can supply 12V at some reasonable current, you may be able > > to charge it off solar cells. Whether you can wear a sufficient solar > > cell is another question entirely. > > Charging the battery off DC actually requires an inverter, it does not > charge directly off DC. So that was my concern: that the solar panel > wouldn't be able to provide enough power to power the inverter and > charge the battery. > > > If you don't mind long charge times, then using solar energy becomes a > > lot easier. You can get a big solar array, and charge one set of > > batteries at home while you use another set out in the world. The main > > downfall of modern photovoltaics is the power to size ratio is poor, > > but if you don't have to carry it, that's not a problem. In my > > opinion, this may be the way to go for solar until the energy density > > gets higher. > > I was thinking I'd get a little charge out of the backpack that I > would be wearing around anyway, and then be able to use that for a few > minutes once or twice a day to power an AC device. I can't see any reason you couldn't do it that way, but you'll have to do the math yourself as far as what current loads you'll be using, for how long, what batteries you use, and how much time you have to charge it. It is unfortunate that you can't use DC instead of AC, as the inverter will cause some loss. Admittedly, most modern inverters are quite efficient, around 85-95%, but it complicates things [1]. > > like that guy did, they are enormously heavy. I get away with using > > 7.2V toy car cells because I built my own power regulation board. They > > So you have a single 7.2V battery and then regulate the power to some > other voltage? 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 got recently. Even with a heat sink, the previous regulator got too hot to touch by the time the system finished booting. Since I'm driving the motherboard, a small scan converter, and USB device chains off this supply, the heat is hardly surprising. I also needed an excuse to add a battery monitor. The MAX923 is what I'm using for that, as it's dead simple and available as a sample or in very small quantities [2]. The 12V DC-DC converter was also a sample part. It is available from TI, and probably Digikey as well. The part number is PT5041N. I didn't need high current at 12V, as the only thing the motherboard uses it for is serial ports, which only source a few tens of milliamps. Once I get the power board upgrade complete, I'll do some tests and post battery life numbers. -Abe [1] http://www.solar-electric.com/solar_inverters/inverters_for_solar_electric.htm [2] http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1218 [3] http://www.superbatterypacks.com/ _______________________________________________ Wear-Hard mailing listhttp://www.haven.org/mailman/listinfo/wear-hard
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