--- Brooke Clarke wrote: > Hi: > > I'd like to test the Sanyo eneloop Ready To Use (long shelf life) > Ni-MH AA > cells to see what their shelf life really is. Has someone already > made up a > small PIC based tester to do this? Or have any ideas on how to > proceed? > http://www.prc68.com/I/RTU-Batt.shtml <- my eneloop page > First you cannot draw any current from the battery if you want to measure it's shelf life while it's on the shelf (given). Second NiMh chemistry is very difficult to measure the capacity left in without discharging the battery completely, the only method to measure capacity therefore is to perform a complete discharge and periodic intervals after the battery has been fully charged. Third charging the battery to determine lost capacity is not a valid method to determine lost capacity. This is because total capacity of batteries varies between cells. If you are just testing these for your own use .. do what's cheapest and gives you an idea. However if it's for any product you should make a fully quantifiable and verifiable method and procedure to perform your tests. In other words you need it to be documented very throughly to the point anyone can repeat the test and get similar results. Otherwise any conclusion you make is going to be questioned due to methodology of testing. Best idea I can think of is charge the batteries then discharge them through a constant current sink (200ma is fine). Look for the battery knee (sudden voltage drop during discharge) and watch precisely when the battery gets below 1V stop discharge at that point (do not further discharge said cell either or you will ruin it). You should then begin the charge cycle afterward and wait whatever interval you want before discharging it again. This gives you the capacity loss over a fixed period of time (IE say 604800 second multiples (604800 == 1 week in seconds). It's best to do this on multiple batteries simultaneously. Likely 2 4 6 8 10 12 week intervals should give you enough information on the self discharge. You might consider first qualifying each batteries known capacity by charging and discharging each battery. This value can be represented as a battery agnostic quantity known as C and the curves can be scaled based on that. That's a bit of a start. Testing batteries requires a bit more than a ni mh charging system and voltmeter I guess. The only time a valid measurement of voltage over time is available is during discharge. Stephen __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist