On Thu, 20 Dec 2001 00:32:09 -0600 (CST), Chris Brogden wrote: > On Thu, 20 Dec 2001, Doug Franklin wrote: > > > I'd love to see the graphs their labs have of current/internal > > resistance during a "catastrophic discharge" like a dead-short. You > > _know_ they do those tests. > > How would a curious person go about trying this at home? :) Is there a > nice and easy way to make a battery do this?
OK. And no shitting. Step one is to get a _very_ efficient fume hood. Do some research and see if someone has published exactly what comes out of those bad boys when they vent, but you're _going_ to vent the crap out of the cell (battery) doing the test. It may be harmless gasses, but I would _NOT_ bet on it, since the cell is full of cadmium, nickel, and/or some other biochemical nasties. Step two is the equipment under test. Part two.one is a NiCd cell or battery (cell makes the computations easier). Part two.two is a piece of #8 AWG (or larger) copper or silver wire long enough to connect the cell's (battery's) positive and negative terminals. [I've seen a battery pack burn #12 AWG stranded copper wire clean through. You might want #4 AWG or larger.] You need wire that can take a couple of hundred amps of continuous current for up to a minute or two, for safety's sake. Step three, if you're interested in real measurements, is the measurement apparatus. You're going to have to measure cell (battery) internal resistance indirectly by measuring the current through and voltage "drop" across the cell (battery) as the test progresses. I don't know enough electronics to say much more than that. My guess is that you need a couple of integrating scopes that can tell you the area under the voltage and current curves and record the data they capture during the test. Step four is some cannon fodder (e.g., the next-door neighbor's idiot kid who's after your daughter) to actually hook up the "dead short wire" and the measurement probes. :-) Step five is to connect the wire across the terminals of the cell (battery) and get the hell out of the way while the scopes record the data. Step six is to analyze the recorded data to calculate the cell (battery) internal resistance changes over time. I'd caution _strongly_ against breathing any of the gasses, vapors, or anything else emitted from the cell (battery). Let it "burn down" until it's not only ceased any electrical activity but also cooled back down to "human" temperatures. I've never measured it, but I've seen a shorted pack draw blisters on the pit crew's hands before. Entomb the remains in the most chemically resistant container you have and take it to a battery recycler. Radio Shack will recycle batteries, but I doubt they'll take a plastic bag full of cells, juice, and emitted solids. :-) TTYL, DougF - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
