[Elecraft] [KX3] Boost Buck 13.8 V Regulator

[Mark Goldberg]

How about using a 4S LiFePO4 battery? From fully charged to 15% charge I
get from about 14 V to 12 V in RX and very little sag on transmit. Pretty
much the ideal battery for this radio in my opinion. They are rated to go
down to 10V or so, but since you don't get that much more and you can
permanently damage the batteries if you go too low, I stop at 12V. The KX3
will run full power throughout this range, too. I use real A123 brand cells
with a balancing charger. These do not have quite as much energy density as
LiPo;, but you do not need anything else. I also keep Eneloops in the KX3.
I have not tested it but I think it will switch over if the external
battery goes below their voltage, somewhere about 10 V. If someone could
confirm that, it would be great. Those NIMH Eneloops run below 11V for most
of the discharge cycle, so only 5 W on those but they hold a charge a long
time so they can be used in a pinch.

73

Mark