On 3 February 2011 11:45, Olin Lathrop wrote: > V G wrote: >> I figured a simple way to profile them was to measure under-load >> voltages while draining the cells with some resistors at around 500 >> mA. But this would mean current drain would decrease as the battery >> voltage decreases. > > That's not a big deal. =A0Make really sure you have a circuit that cuts o= ff > when the battery gets low enough though, else you will damage it. =A0You = could > simply measure the time from fully charged until the circuit cuts out to > compare capacity of different cells. =A0You may not know the exact capaci= ty, > but the comparison will still be valid. > > NiMH cells don't drop that much in voltage over most of their life, so > you'll actually have a pretty good absolute idea of capacity too. > > If you really want to measure capacity, you can measure the voltage over > time. =A0Since you know the resistance, you know the current, then integr= ate > that. =A0Even once per minute would be good enough since you're talking a= bout > a discharge time of a few hours. > > > ******************************************************************** > Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products > (978) 742-9014. =A0Gold level PIC consultants since 2000. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > If you are going to be using them in a laptop or similar, you may want to consider testing them with a constant power load. (e.g a DC -DC boost converter with its own load). In this case the current will increase as the voltage falls. For most testing though, a resistive load will give a good indication. RP --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .