[Elecraft] Running the KX3 and KXPA100 Off Battery

[Fred Jensen]

Phil,

It appears that there are three types of batteries with lithium in their 
names ... Li-ion, Li-poly, and LiFePO4.  Li-ion, in one or another of 
the variants, usually power laptops, cell phones, and Tesla's.  They're 
pretty stable, you can take them on aircraft although there are some 
limits on total weight and packing.

Li-poly are very small and light with a high energy density and are used 
mainly by RC hobbyists.  I have a 750 mAh one for my KX1, it's a little 
smaller than a small matchbox and weighs an ounce or so.  They're 
somewhat unstable, I wouldn't recommend internal mounting.  I had one 
catch fire while I was operating, it was on a pigtail which I pulled 
loose and tossed it over the deck rail onto our gravel driveway.  I 
always charge my current one outside.

LiFePO4 seem to be very stable.  I have a 4S1P A123 2.5 Ah pack for my 
K2.  At full charge, it is almost 14 V which drops quickly to around 
13.5 where it pretty much stays until almost depleted.  With my K2 on CW 
in QRP field contests [flight of the bumbles], it has powered 3-4 hours 
of steady operation.  So far, I get tired and hungry faster than I can 
run it down.  It does require a cell-balancing charger, mine is a 
CellPro-Multi4 which will charge a variety of chemistries.  Considering 
all, LiFePO4 seems to be the best choice ham use.

Use great care with Li batteries of any flavor.  They have an incredibly 
high energy density for their size and weight, and incredibly low 
internal resistance, so fuse the leads and don't ever short it.  My 2.5 
Ah pack will easily deliver 10 to 15 times that [25 - 40 A] into a 
short.  You can spot weld with them and some of the larger ones would 
probably start my truck.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
- www.cqp.org

On 5/26/2015 11:42 AM, Phil Hystad wrote:
> Thanks Jim,
>
> I took a look and they appear to be cheaper than the A123 packs (the
> brief scan I did) — I may buy one or two.  But, with my two 4S1P A123
> battery packs have performed very well with the KX3 so far.
> Although, this is a KX3 running QRP to 10 watts.