" AA LiFePo4 cells appear to have a rating of about 600 mA-hours."

I've noticed this also, which seems odd, as my understanding is that LiFePO4 
has (at least) comparable energy density as NiMH.  However, I did run across 
these cells:

http://www.aliexpress.com/store/product/High-Capacity-LITELONG-AA-1200mah-14500-3-2v-lifepo4-Rechargeable-Battery-Consumer-Battery-Free-Shipping-4pcs/816574_1302272496.html

which would be better than the NiMH solutions that I've found.

-----Original Message-----
From: Elecraft [mailto:[email protected]] On Behalf Of Wayne 
Burdick
Sent: Wednesday, February 11, 2015 5:52 PM
To: Jim Wilkie
Cc: [email protected]
Subject: Re: [Elecraft] Internal LiFePo4 for KX3

The charger could in theory be redesigned to work with a 12.8-V LiFePo4 pack (4 
cells), but there are several disadvantages to this:

- AA LiFePo4 cells appear to have a rating of about 600 mA-hours. As a coarse 
metric, 4 cells at 13 V would provide about 7.7 watt-hours, which is very poor 
compared to 8 NiMH cells; the NiMH pack rovides roughly 2500 mA hours at 10 V, 
or 25 watt-hours. There's room for 8 cells, so NiMH makes better use of the 
existing space.

- Even though you'd get 13 V from LiFePo4 cells, and could thus run full power, 
you'd only be able to operate for a third as much time (roughly). The KX3 can 
put out as much as 5 W from 10 V, and since this is only 3 dB down from full 
power, it's probably a better trade off for a weekend of casual operation. Your 
antenna and propagation will generally outweigh this 3 dB power factor.

- Being able to use just about any type of AA cells in a pinch is important for 
ad-hoc field use of the radio. You can then borrow AA cells from other devices 
in an emergency. So if you used 4 LiFePo4 cells, you'd want to leave the other 
socket in place and insert some sort of placeholder cells (easy to lose) or a 
bypass switch.

- LiFePo4 cells are not as readily available. You can get NiMH cells a drug 
stores, supermarkets, Radio Shacks [before they close], etc.

Wayne
N6KR



On Feb 11, 2015, at 1:03 PM, Jim Wilkie <[email protected]> wrote:

> Andt, will wait for the experts to answer, but I think the nimh charger vs 
> the lopo charger would be a problem.
> 
> Jim Wilkie WY4R
> 
> 
> On 2/11/2015 2:18 PM, Henshaw, Andy wrote:
>> Has anyone looked into hacking a replacement battery case for the KX3 that 
>> featured LiFePo4 cells?  I've seen external LiFePo4 packs being used, but it 
>> seems like an internal solution might be workable.  With a 13.2V supply 
>> (four cells in series), one can run the KX3 in full-power mode.  In 
>> addition, the discharge curve of LiFePo4 is much better than NiMH.
>> 
>> I'm asking, because I'd like to take my KX3 on some backpacking trips and it 
>> just seems wasteful (of space) and slightly awkward (for setup) to have to 
>> carry an external battery pack in order to get full-power.
>> 
>> It appears that AA size LiFePo4 cells are available.  So, wouldn't it be 
>> feasible to arrange them in a 4S2P configuration that could replace the 
>> existing battery holder?
>> 
>> Andrew Henshaw
>> 
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