[Elecraft] Battery voltage on KX3 seems high...

[Mark Petiford]

Andrew,Phil hit the nail on the head.  When you have the power supply attached (or an external battery with a voltage greater than the internal battery voltage), the KX3 Battery Voltage displays the UNLOADED voltage of the internal NiMH cells.  When you remove that external power, the internal battery powers the KX3, so the KX3 Battery Voltage displays the LOADED voltage of the internal NiMH cells.  The difference between the loaded and unloaded voltage is primarily due to the internal resistance of the NiMH cells.  The LOADED voltage reading will vary depending on what the load current is.  If you see 10.2V during receive, and you key the rig with few watts of output, you will see that loaded voltage drop a bit farther due to the added current draw.  That is the effect that internal battery (cell) resistance has.The internal resistance of the cells has a good effect, too.  It is partially responsible for the self leveling effect (the tendency for
 a group of cells in series to end up at the same voltage after charging) that is inherent in NiMH cells.The KXBC3 is strictly a constant current charger.  You turn it on for a length of time, and it tries to keep the current at a constant of about 10% the capacity of the cells...about 200ma in the case of the KXBC3.  I don't believe there is a trickle charger as a design feature in the KXBC3; however, there appears to be a very small reverse current leakage that may tend to reduce the effects of the self discharge properties of the cells.  It is probably small (a few microamps?) in relation to that, but my LSD (Low Self Discharge) Eneloop 2000's seem to stay charged longer if I keep the radio hooked up to a 13.8v supply.  I haven't quantified this yet. The self discharge rate is so low with these cells that it is difficult to tell.  As Don pointed out, it may depend on the source voltage, so there is another variable thrown in.MarkKE6BB

Hope this e-mail works out.  I did it on a Yahoo Win 8 mail app that sometimes formats everything to be incompatible with the Elecraft list.