[Elecraft] K2 Batteries - NiMh and Lithium Polymer

[Alan WB6ZQZ]

An update on my K2 Internal Battery project:

Trying again, the Mime stripper really trashed it last time.

Thanks to the comments regarding my earlier NiMh query. From that I found a 
better source of 10-AA holders (www.mouser.com) and I was again reminded of 
the Lithium Polymers. I see this morning that Dan has tested his out, and 
Oliver KB6BA has given me some info on his experience. I also heard about 
using 4/3A NiMh cells that worked well, but did not fit in the battery tray.

My goal is to have batteries that are capable and light and fit on the K2 
battery tray. Dual sets of AA NiMh (two sets of 10 in parallel) should 
handle the radio well, deliver about 4AH capacity, and have moderate weight 
(less than the SLA, more than the LiPo). They would be the best for Air 
Travel due to familiarity and commonality. I think I will try them later.

The LiPo cells, available from www.batteriesamerica.com and others are 
quite interesting. The 1600 mah size (P611 3.7v  1600mAh 2.35"L x 1.3"W x 
0.33"thick 34 gms (1.2 oz)   $12.95 ea) will easily fit on the K2 battery 
tray (2.4x1.3x7). In fact two sets of three will easily fit and provide 
11.1v at 3200 mah with weight under 8 oz. They can provide over 9A of 
current, so the K2's transmit demands will not be a problem. According to 
the LiPo users manual from Kokam at www.fmadirect.com the cells can be 
paralleled if the charge capacity and charge state are the same, so I plan 
to make two series sets of 3 cells and parallel those. I plan to use 5A 
fuses in each series set to protect against problems.

There are many warnings regarding Li-Ion and Li-Polymer batteries catching 
fire, etc, if they are abused. From what I've read it seems that the 
Lithium Polymer cells have much less tendency to do this than the regular 
Lithium-Ion probably due to the minimal gel electrolyte they contain. It is 
very important to use the proper charging equipment and insure they never 
get charged incorrectly. Various laptop manufacturers have had some trouble 
with this, but generally they do not seem to burst into flames when the 
system is designed properly.

My thought is to develop some confidence in this new pack by charging and 
discharging it externally from the K2 for several cycles just to make sure 
all is copacetic before charging them internally.

So my plan is to use commercial chargers, external from the K2, and insure 
that the Lithiums never get accidentally charged from any other source. 
Oliver KB6BA recommends using a separate jack on the rear of the K2 to 
bring power in and out of the internally mounted LiPo battery. A short 
jumper is used when powering the K2 from this battery, and the connector he 
used on the rear panel from the Li-Po  batteries is not the same diameter 
as the K2's power connector, so the only cables that fit to the Li-Po's are 
the two specific ones - the charging cable and the jumper to run the K2. I 
will probably use this technique also.

To charge the Li-Po batteries Oliver found an excellent small portable 12v 
to LiPo charger for 1-4 cell packs made by Kokam from www.fmadirect.com. I 
think I will start out with the MaHa C777 Plus II that I already have, 
which has LiPo capability, and then later move up to the Kokam.

So the batteries are on order...

Thanks again for your comments,

-- Alan WB6ZQZ