[Elecraft] K2 voltage and battery charging questions

[Rick Wheeler]

Finally after 7 years or so my K2 (Serial No. 2001) internal battery would no longer hold a charge. After replacing it I poked around and got some voltage readouts which I am questioning. I wanted to ensure the battery was getting the proper float charge.

I have now set my input voltage as measured by my DMM at 14.04. And the voltage BEFORE D10 is DMM measured at 14.04. The voltage AFTER D10 is DMM measured at 13.70, a drop of only .34 volts, the expected drop of about .3. The book states the battery should be charged at 13.70, hence the 14.04 input. The K2 reads out 13.5 volts.

But going strictly by the K2 readout and trying to increase (by increasing my power supply voltage output to 14.25) to a K2 readout of 13.6 (just .1 volts more as K2 indicated before) results to a DMM measured voltage of 14.18 AFTER D10 (now it is 14.25 BEFORE; I assume D10 does not drop linearly with voltage increases from the power supply). Now the battery would be charging at 14.18, too high according to the manual. But the K2 voltage readout would state it is in spec, 13.7 +/- .2 (which it is obviously not and would get much higher if I increased it to 13.7 or even +.2).

And one other question. When connected strictly to battery power and in receive, the K2 readout voltage is 12.1 volts, but the battery voltage measures across the terminals at 12.6 volts according to my DMM. Now it is off by 4% or so. 4% does not seem like a lot but when it "shows" your battery at 12.1 instead of the DMM reading of 12.6 it seems as if it is not at a peak charge as it should be.

I have understood in the past the K2 internal voltage readout should be fairly accurate (about 1% or so if I remember correctly). And from 13.5 to 13.7 is only about 1.5 percent off. 

So should I use my DMM as the final say for internal voltages in the K2? Is it normal for the K2 voltage readout to vary as described above from my DMM (13.5 K2 vs. 13.7 DMM when plugged to an external supply, 12.1 K2 vs. 12.6 DMM on battery only)? Where is the K2 pulling the voltage measurement for its readout?

BTW, the DMM is a $40 or so Sperry DM-4100A. I assume it to be accurate but obviously not lab grade...

Rick 
K4LX
No. 2001






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