My resistor setup for discharging the RC racing batteries was designed to bring a six battery pack of 1800 ma/hr cells to approximately 1 volt in four minutes, which is the run time for a race. Part of the idea was to train the cells to discharge fully during the race. I had a slew of resistors hooked up in parallel along with one automotive taillight bulb. I had to have a cooling fan to keep it all from getting too hot. I'd watch the light bulb and when it was almost out, i'd disconnect the battery pack. Sometimes I hooked up a voltmeter as well as a safety check, but the lightbulb method made it quite easy to catch it before full discharge. Paul -------------- Original message ---------------------- From: graywolf <[EMAIL PROTECTED]> > Ohms law will tell you that 2 ohms will discharge a 2500ma/hr cell to > dead in 1 hour*, I would recommend a larger resistor (maybe 5 ohms) for > a slower discharge rate. Of course, you do not want to discharge to > dead, so put a digital voltmeter in the circuit and discharge to one (1) > volt (NiMH/NiCad, do not try this with a Li-Ion cell). Going below one > volt can permanently damage the battery. > > ----------------- > | | | > voltmeter resistor battery > | | | > ----------------- > > By the way, Paul, a dead short is zero ohms, if there is a resistance it > is just a short. > > *Yes, I am aware that is not quite accurate because we are dealing with > a dynamic system (voltage changes with charge state), but it is close > enough to work with. > > -- > graywolf > http://www.graywolfphoto.com > http://webpages.charter.net/graywolf > "Idiot Proof" <==> "Expert Proof" > ----------------------------------- > > > Paul Stenquist wrote: > > When my son and I were racing electric radio control cars, I made a > > discharge unit that was basically a dead short with resistors in > > between the contacts. Worked fine. I had it set up to discharge at a > > very high rate to mimic the way the car's motor discharged. (It was > > about 1 ohm resistance.) I would think that a dead short with > > something like 20 ohms resistance wired in between would provide a > > nice discharge for the NIMH batteries. > > Paul > > On Jul 25, 2006, at 7:07 PM, Scott Loveless wrote: > > > >> On 7/25/06, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: > >>> Obviously these batteries aren't holding a full charge. I know > >>> that cycling > >>> batteries (drain, charge, drain, charge, etc) is supposed to help > >>> NiMH > >>> batteries regain their former capacity, but I haven't any ideas > >>> how to drain > >>> the batteries in a relatively short period of time. > >>> > >>> I suppose I could stick them in a flash and repeatedly hit the > >>> test button over > >>> and over until there's nothing left, but I've got a feeling this > >>> wouldn't be > >>> good for the flash tube. > >>> > >>> Does anyone have any ideas for discharging AA batteries? > >>> > >>> Or, should I just bite the bullet and buy all new sets? > >>> > >> I had the same problem recently. Cheap flashlights are notorious for > >> quickly draining batteries. I loaded up a couple of AA flashlights, > >> turned them on and walked away. The whole experiment was a big > >> failure and I saw very little, if any, improvement. Just get some new > >> batteries. > >> > >> > >> -- > >> Scott Loveless > >> http://www.twosixteen.com > >> Shoot more film! > >> > >> -- > >> PDML Pentax-Discuss Mail List > >> [email protected] > >> http://pdml.net/mailman/listinfo/pdml_pdml.net > > > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net
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