On Fri, Nov 12, 2010 at 12:40 PM, Dwayne Reid wrot= e: > My experience has been that you don't need any electronics at > all. =A0Inexpensive battery-powered USB chargers that I have purchased > confirm this. > > Both NiCd and NiMh batteries have a very flat discharge slope. =A0The > terminal voltage ranges from about 1.25V (fully charged) to about > 1.1V (less than 10% charge remaining). =A0That means that a 4-cell pack > will range between 4.4V through 5V. > > A standard USB port will supply somewhere between 4V to 5V under load. > > Take note that you should NOT ever use alkaline batteries in your > box. =A0One of the battery-powered USB chargers that I purchased took > care of that possibility in a typical Far East fashion: they had 3 > large (5W?) 5.1V zener diodes connected in parallel right across the > battery pack. =A0The obvious intent was to force alkaline batteries to > discharge quickly so that the terminal voltage was less than the zener vo= ltage. > > Bottom line: a small battery pack with 4- high-capacity NiMh > batteries should be all that you need. That's a VERY sensible solution. Thank you! --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .