Did you measure the TX wattage on an external meter or the KX3’s internal meter? I have found that my KX3’s wattmeter is not accurate…
On the internal meter, which I have found to be quite accurate on my KX3…
So I was curious whether it was the battery holder’s resistance that was preventing me from getting my 15w output, so I put a single NiZn cell on a West Mountain Radio CBA and ran a test at 2.5amps draw. The cell very quickly dropped below 1.5v, which a pack of 8 would need for 12V output.
I also tested my Ultralast LiFePO4 AA cell at 1.25 amp draw (because I ran them 4s 1p) and saw that the LiFePO4 cell was able to maintain itself above 3v for some time, which would be required for 12v.
Unfortunately though, even without the resistance of the stock Elecraft AA holder, neither type of the cells I have tested so far could get me the 12.8v Elecraft recommends for 15w…but the LiFePO4 did come closer, and my tests suggest that .3 voltage drop could be due to the stock Elecraft AA holder.
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This is interesting. I looked at these as an alternative a while ago and based on the specs thought that they wouldnt have the output to do the job . Your testign has proved this, thank you.
Has anyone used/considered the Lithium Titanate chemistry yet for SOTA use?
I see about an 80 mV drop in total under load (10 W carrier TX) between the cells in the internal holder and the 6-pin connector (P4) that connects the holders to the control panel PCB. However, the reverse polarity protection diode (D10, CMS04 type) causes about a 350 mV drop under load.
Got 8 LiFePo4 AA cells from China, labelled “Etinesan LiFePO4 LITHIUM Rechargeable 600mAh”. I could not find any specs for this cell, but similar ones are spe’d as follows: Max charge 4C, max continuous discharge 3C, max discharge pulses 10C.
Here are my results after having tested a single cell: Specified capacity was reached at C/6 discharge. A real surprise was the low internal resistance of 0.018 Ohms (measured with a DC battery impedance meter).
At 1C discharge I measured 95% of the specified capacity, still 80% at 2C and 38% at 3C (all with 2.8V discharge cutoff). The discharge voltage remains almost constant throughout the major part of the discharge phase.
Interesting cell for portable QRP activities. Keep them separate from conventional AA cells in order not to damage equipment by overvoltage…
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I have found a solution that works for me.
First, I found my factory build KX3 had been calibrated incorrectly at the factory, and Elecraft had to correct that problem.
Next, I rewired the 8 in series AA case to a pack of two 4 in series packs in parallel.
Each 4 cell series pack has 2 fully protected KLARUS Lipo14GT-80UR 14500 cells, and two MPIFR 3.2v 14500 LiFePO4 cells, and this setup will get me my 45 min+ of 15w SSB talk time.
Before putting the cells into the holder I put down a non sticky (doubled over) strip of duck tape so that I can easily remove the cells from the holder back at the QTH for charging.
Its a bit of a pain but boy is it nice to be so compact, lightweight and have my 15w as well.