Inherieted a bunch of Nexcell "10000mAh" D cells and some Imedion "5000mAh" C cells. What's the maximum charge and discharge rate these may tolerate?
I'd like to do some quick and dirty capacity assessments and it will take ages doing them 1-2 at a time. The likely regimine for the C / D I'm hoping for is 2 / 5A charging and 1 / 2A discharging to 0.9v
Hi Ualnosaj. The best way to find out the maximum charge and discharge rates for your cells, is to look up the specs on the manufacturer's website. Checking quickly on Maha's site though, I couldn't find any specs.
Many C and D sized cells have a maximum recommended charge rate of around 0.3C. This no doubt will not apply to every cell, but should work for any C or D size cell. As for maximum discharge rate, 1C is a good general rule of thumb, for NiMh cells. Again, this may not apply to all cells.
Keep in mind that the general purpose of C and D size cells, in all chemistries, is to extend runtime, and not necessarily to increase power, although the size difference compared to an AA cell usually provides some additional available current. Put another way, the larger C and D size cells are usually designed to supply the same basic power level as AA cells, and are geared more towards extending runtime. Considering this aspect, they may need to be charged and discharged at rates closer to those used for AA cells, regardless of their superior capacity.
There are of course exceptions, such as high discharge rate cells used in the R/C hobby and cells used in tool battery packs etc. For the most part nowadays though, these have been replaced by LiPo packs, or other types of cylindrical Li-Ion chemistry cells.
Not sure why, but when you charge more than one cell in series, hobby chargers seem to do fairly well with -dV termination, particularly with C and D cells. It doesn't always trigger, but it works a lot better than when attempting to charge just one cell. I have only minimal experience with charging AA cells, and none with AAA cells with a hobby charger. I think -dV termination is maybe more of a problem with smaller size cells. I use my Maha C9000s most of the time anyway, for them.
If you use the 0.5C rate, I'd just make sure the cells don't get too hot. I think that's probably why many D cells, such as the Powerizer 10,000mAh, are limited to 0.3C. The larger "can" likely holds heat in more so than the smaller AA and AAA cells.