Has anyone tried running 1.6v NiZN AA cells in a KX3 for higher TX power?
It would seem that the actual running voltage of the NiZn cells is closer to 1.7v and when fully charged is near 1.8v, which seems like a nice match for a KX3 to run 15w from an internal pack with little modification…that is of course if the resistance of the stock AA holder isn’t too high. But if the cells hold up (I have them on order) I would think the next step would be to upgrade the AA holder…
I can’t comment on NiZn, but what I’ve done with my KX3 is rewire the two internal 4 x AA battery holders to be in parallel instead of in series. Now I can fill it with 8 x LiFePO4 AA cells (eBay has lots of them; the silver ones marked “MPIFR” worked well for me) and get 15 W for quite a while before it drops down to 10 W. Obviously the cells needs to be taken out for charging; I never bothered to try and fit a balancer in the KX3’s case.
Would be interesting to hear about NiZn experiences though!
I thought about the LiFePo4 AA cells, but they all seem to have such low Mah ratings…what is the capacity rating and maximum draw current on the AA cells you got? How much SSB time do you get at 15w? And then how much more time do you get at 10w?
Good to hear though that the AA holder’s resistance does not preclude 15w…
8 x 600 mAh, so nominal 12.8 V at 1200 mAh. It‘s been a while since I last used my KX3, but for typical SOTA SSB operation with frequent calling and mini pile-ups, I would say about 45 minutes at 15 W, and after that, an hour at 10 W. If I remember correctly, max. TX current is around 2.5 A at 15 W, and the LiFePO4 cells have no problem with that (rated at max. 3C discharge current).
Consider the Watt-Hour rating of a cell rather than a mAh rating. Looking only at the mAh rating does not take into consideration the much higher nominal voltage of a LiFePo4 cell vice a traditional NiMh AA. I suspect you’ll find that a LiFePo4 cell has a higher watt-hour capacity than a NiMh cell.
Its not the capacity that concerns me as much as the maximum discharge current. The highest discharge current AA LiFePo4 cells I can find are only good for .6 amp current–so my parallel pack would only be good for 1.2amp max draw.
There are lots on eBay that are rated at 2C continuous, which works out to 2.4 A in this configuration, but considering that the 2.5 A TX current is only during SSB peaks, they should be fine – for example:
My cells look exactly like these, and I haven’t had any problems with them so far after about 50 cycles.
I have tried the AA size LiFePO4’s in my Yasu FT-817. Wired the battery tray for two @ 4 battery sets. Success? Yes in that they powered up the radio. No in that they lasted about 25 minutes. Your Mileage May Vary.
So my first tests of the PK Cell AA NiZn cells were not encouraging. The open circuit voltage several hours after charging was a healthy 1.85V per cell, however in receive that quickly went down to 1.7v/cell. On 20m FM TX to a dummy load the set of 8 cells dropped to about 11.5V.
I think I am going to run them down and see if with “exercise” they get better, but reports online seem to say they get worse with exercise.
I am also going to test another brand to see if they are any better.
These are lithium ion chemistry (3.7v nominal, 4.2v max) will have a different voltage profile than the LiFePO4 chemistry (3.2v nominal, 3.6v max.) There are a few companies that make lithium cells in the AA (or 14500) cylindrical format, with the highest capacities being just above 800mAh. Fenix makes a decent cell, I’ll link the review below. As with most batteries a higher current draw will reduce the overall watt hour capacity, as demonstrated by the test results.
P.S. If you’re trying to decode the number code for the AA battery, the first two are the diameter (14mm in this case), the next two are the length (50mm for AA), and the last 0 indicates that it is a cylindrical cell. So an 18650 cell is 18mm wide, 65mm long, and round. There is commonly some drift here as there may be protection circuitry or raised terminals.
Interesting that the NiZn cells performed worse than expected. I did some testing with my KX3 today:
KX3 firmware 2.90
TX/RX ratio 50% (CQ message repeat)
Ambient temperature 22 °C
8 x MPIFR LiFePO4 AA cells bought two years ago, about 50 cycles, in internal battery holders wired in parallel, fully charged
The voltage displayed by the KX3 during short SSB peaks dropped to 11.7 V almost right from the start (later down to 11.4 V; 12.6 - 12.8 V during RX), but the KX3 nevertheless operated at 15 W for 1 hour and 15 minutes, with TX current peaks up to 2.4 A. Then it dropped down to 12 W and then 5 W in less than 5 minutes, and at 10.8 V in RX, I stopped the experiment.