[Elecraft] K2 alive again, yay!

[jerry]

On 2021-07-18 19:50, Douglas Hagerman via Elecraft wrote:

> Next step, adding the the immensely heavy internal lead-acid battery.

*** I wonder how hard it would be to add instead a much lighter 
lithium-ion
battery pack?  Individual 18650 cells are now routine at 2.5A-H, and 
available up
to 3.5A-H.  The technology has gotten standardized, and you can buy a 
BMS ( Battery
Management System ) card off the shelf.  The only hard thing is spot 
welding the tabs.
A 3S1P ( three cells in series, 1 in parallel ) pack would probably do 
fine.

   I just got back from the garage where I repaired such a pack.  It was 
out of an 85W
cordless vacuum cleaner.  Just four cells.

    Like any battery, the voltage varies with charge.  These cells are 
about 4.2V fully
charged, and 3.4 when dead.  For three cells, that would be 12.8V fully 
charged, and 10.2
when it's time to recharge.

    I got all set up to weld the cell tabs for an ebike project.  The 
ratio of energy storage to battery weight is much better than lead-acid.


                       - Jerry KF6VB