On 12/06/2009 09:00 PM, James Cameron wrote: > On Sat, Dec 05, 2009 at 06:56:58PM +0000, Tiago Marques wrote: >> I went to the wiki yesterday and found the information that the >> LiFePO4 batteries have 2 or 4 cells, rated at 22Watt hours. Is this >> rating the same or is it half of that with 2 cell models? > > I think that is unlikely, but I don't know.
Batteries can have n number of cells where n = (Output voltage / Cell voltage) * number of strings in parallel. OLPC batteries have 2 cells in series with a nominal cell voltage of 3.25V. >> From my battery it seems it's 22 Wh since it's rated at 6.5v @ >> 3100mAh. Am I right? No. > I'm not sure. 6.5V at 3100mA is 20.15W. > Here is where I repeat my power mantra that power numbers must include a _specific_ load case or they are wrong. Mfg test specifications are only valid under mfg test conditions. In our case the mAh rating is for a discharge current of .5C (aprox 1.5A) less than that you get more mAh, more than that you get less mAh. Plus you can't do a straight V * I = W calculation because the V of the battery decreases as you use it so Wh calculations have be iterative. -- Richard A. Smith <[email protected]> One Laptop per Child _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
