On Tue, 9 Jun 1998 07:55:36 +1000 Clyde Smith-Stubbs writes: >On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote: >>battery to power a Pic and a bunch of other electronics >for about >> 20 hours. The current consumption of the parts would be about >300mA/hour. > You mean the operating current is 300 mA (at 5V, I assume)? This is quite a bit of power. The battery is going to be rather unweildly. It would be advantageous to look at reducing the power by using micropower techniques or implementing standby/sleep modes. On the other hand, if the capacity required is 300 mA-hr, (operating current of 15 mA for 20 hours), just about any sort of medium sized battery such as 4 "AA" cells will have lots of capacity. Specify a battery with plenty of extra capacity, then it will be less necessary to have a gas gauge or rapid charge. Also the battery will wear out more slowly, and it's "useful life" will extend further into the wear-out phase. (The rest of this is assuming 300mA * 20 hr = 6 A-hr) >A lead-acid gel-cell battery would be the best choice, unless weight >is critical, >in which case you might want to look at Nimh (Nickel-metal hydride) or >Lithium-ion >batteries, but the gel-cell will be cheaper, I think the lead-acid is about the only practical choice. If the weight (about 5 lbs for a 10 A-hr 6V gell-cell) is a problem you will do much better to reduce the power consumption rather than deal with exotic batteries. and can be float charged >with constant >voltage. The others require fancy charging circuitry. A "gas-gauge" >for a gel-cell is >basically a voltmeter. Yes, easy to charge with just a constant-voltage, current-limited arrangement. However, it is not recommended to charge faster than 4 hours. Measuring the voltage does give a meaningful indication of the energy remaining. Be sure your circuit has a cut-out that will keep the battery from overdischarging, as this is very bad for them. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]