Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!think.com!eplunix!raoul From: raoul@eplunix.UUCP (Nico Garcia) Newsgroups: sci.electronics Subject: Re: Batteries! Summary: Whoops: posted before re-checking your numbers! Keywords: nicad gel cell Message-ID: <987@eplunix.UUCP> Date: 10 Dec 90 07:13:01 GMT References: <5664@uafhp.uark.edu> <985@eplunix.UUCP> Organization: Eaton-Peabody Lab, Boston, MA Lines: 31 In article <985@eplunix.UUCP>, raoul@eplunix.UUCP (Nico Garcia) writes: > In article <5664@uafhp.uark.edu>, bbs00068@uafcseg.uucp (Joel Kolstad) writes: > >[questions about gel cells] > Hmmm. I won't address your NiCad questions, since I've never worked with > those directly. However, for a Gel-Cell charger, use a LM317 rated for > your maximum voltage from your power supply to provide a regulated > charge voltage, and drop a resistor on the output of it to limit the current > to your batteries. You only need a trickle charge anyway, and a 12 Volt > supply, even if you put the battery in backwards, will only put a 24 Volt > drain on it. Put a 1 K resistor there, and a diode to stop discharges, > and you win. Sorry, accidentally sent this off before checking your power demands. For a 12 Volt supply, with a 10 mAH drain once per hour, you want a recharge of oh, say, 100 mA to charge quickly: and 1/10 your maximum AH capacity as recharge current is 100 mA for 1 AH gel-cells. So, figure a mimimum 1 Volt differential, and a 10 Amp resistor is needed. 12 Volts for a completely discharged battery, and you get almost 15 watts heat dissipation. Gaah, a bit large. You could use a second LM317 as a current limiter. The National books have good application notes on this. Depends on your size and circuitry constraints. Don't forget a 3-Volt drop and minimum currents for good regulation. I've had very good luck with gel-cells left on trickle charge. The Yuasa 12-Volt 0.8 AH have behaved very well, even if their connectors are a bit weird. -- Nico Garcia Designs by Geniuses for use by Idiots eplunix!cirl!raoul@eddie.mit.edu