[Elecraft] [KX3] KXBC3 Battery Charge Times

[eric norris]

A while back I uploaded a file to the KX3 Yahoo Group giving the percentage charge remaining by KX3 voltage display, and suggested charge times.  This was based on the Sanyo datasheets for the Eneloop XX (I also uploaded both Eneloop XX and 2nd gen Eneloop (2000mAh) to the files section).  I found in practice that the chart was quite inaccurate.  I think this was due to I**2R losses in the battery pack spring clips, and battery leads. These losses in spring-clip battery packs have been documented by other hams.

To update the figures, I partially discharged my KX3 Eneloop XX internal pack, then removed the batteries and put them in a battery analyzer.  Knowing what their actual remaining capacity was, I then took another look at the Sanyo chart, and scaled the results to the datasheet.  My pack was discharged to the 60% remaining capacity level, so I am very confidant for that data point.  I'll have to repeat the experiment for other levels of remaining capacity to confirm the new table.  

I removed the old table from the files section of the KX3 Yahoo Group and uploaded the new one.  If you don't want to join that group (I certainly understand why) email me and I will send you the PDF file.    

Remember, you must measure the voltage of the internal pack when it is under load at the 5w CW level--just going by the internal pack voltage when the KX3 is in receive will give you a very inaccurate number.  To confirm this, I made both measurements and found the battery voltage in RX would change by .1 VDC vs. the voltage under TX would change by .3 VDC during a single 1/2 hour measurement period.  

To answer the flames I will get (again):  1.  No, this data is not in the manual.  2.  Yes, I specified measurement UNDER LOAD.  3.  For 2nd-gen Eneloops (2000mAh) I suggest reducing the charge times by 20% as a starting point, since that is the approximate difference in capacity.  

If you are unsure of the charge time to specify, aim high.  If you aim too high, the KXBC3 will terminate the charge when the pack gets warm.  Also be sure your source voltage to the KX3 is high enough.  It should be 13.8 VDC or higher.  

73  Eric WD6DBM