[Elecraft] KX3 internal battery problems

[Mark, ars: KE6BB]

Re: With increasing cycle count, individual cells are showing differences.

Cycle count agravates the differences, but the most common CAUSE is a failure to FULLY CHARGE the series set of cells, so some of the cells never reach their FULLY CHARGED voltage.  Damage occurs during use as the cells are discharged.  The cells that were not fully charged reach the damaging voltage of <1.0V per cell first, possibly before the KX3 low voltage warning is set.  Below that voltage, they will be damaged and will never again have the capacity of the good cells.

Re:  If you don't charge them individually, these differences are getting bigger, as reflected by the numbers you posted.

Individual cell charging is one way to prevent damage, but the KXBC3 can manage this problem as well, saving the cost and trouble of an external charger.  When charged with a properly designed constant current charger such as the KXBC3, NiMH cells in a series configuration are self leveling.  Cells with a higher charge will reach their fully charged CHARGING voltage of about 1.5v per cell (varies somewhat with temperature, charge rate, etc.) and then level off.  The lower voltage cells will then continue to rise to a similar FULLY CHARGED voltage if they are healthy.  Eventually they will all be at the CHARGING voltage.  With the KXBC3's 200mA rate, 12 hours will usually do it for 2000mAH cells, and 16 hours for 2500mAH cells.

I do not mean to knock external chargers or battery managers.  I am simply saying that YOU, along with the KXBC3, can learn to manage rechargable NiMH cells.  This hobby is about learning, isn't it?  BTW, I just checked my 3.5 yr. old Eneloop 2000 LSD cells, and they are all within .04V resting.  I never disharge the set below 8.8V.

Mark,
ars:  KE6BB