Arno, >>All eight cells are now at 1.4V. When I turn the TRX on, the integrated meter shows 10.5 V now. I think this morning, when I checked after the full charge, it showed 11.6V
Excellent. All appears to be normal and is almost exactly what I typically see on mine. Immediately after charging, the voltage is highest. It usually settles pretty quickly down to about 10.5 or so volts, even if I don't actually use the batteries much. You can see this in the discharge curve shown in the Eneloop data sheet: www.eneloop.info/fileadmin/EDITORS/ENELOOP/DATA_SHEETS/Datasheet_-_HR-3UTG.pdf (Sorry, I have not been able to find a datasheet on Rayovac rechargeable NiMH cells). The voltage over the majority of the discharge curve is between 1.3 and 1.2 volts per cell, or 10.4V and 9.6V for the 8 cell battery. Once you get down below that 9.6V, you can see that the voltage drops off rapidly down to the 1v per cell level, or 8 volts for the battery. That is roughly how you will see the voltage drop when operating. By the way, a little study of the charge/discharge curves will help you understand what you are seeing on the KX3 voltage display during charge/discharge cycles. >>Kent briefly contributed his opinion that a wall wart would not be good for >>charging the KX3 but did not give his reasons The output voltage of wall warts varies pretty wildly with load. It is hard to really know if your particular wall wart would work well or not. I don't really like to see voltages on the display higher than 15V (14V some places in the KX3 Owner's Manual), because that is the maximum Elecraft recommends; however, the radio does have excellent protection circuits so that may not be a problem. There have been lots of cases of "greater than 15V" supplies applied to the KX3's, and I haven't heard of a failure yet. The KX3 simply shuts down at about 16V. Maybe others on the list have more experience with this. In a later post you mentioned: >>So the batteries were still quite >>full and thus got warm soon and repeatedly. I agree. There are a lot of things going on during charging that generate heat, but in general, as the battery approaches full charge, less and less of the total power applied to the battery is used for the chemical change, and a larger percentage simply gets converted to heat by the internal resistance of the battery. Try to charge a fully charged battery of cells, and the KX3 will get warm since there is no more chemical conversion going on, and all of the power delivered by the KXBC3 is converted to heat by the internal resistance of the cells. In this case, the KXBC3 will cycle off occasionally keeping the temperature below 40deg C. That is completely acceptable to 2000maH (or larger) cells since the current remains at about 200ma, and the temperature remains below 40 deg C, well within the manufacturers specs. Bedtime. Mark KE6BB ________________________________ From: Arno Dienhart <a...@broadweave.net> To: Elecraft@mailman.qth.net Sent: Thursday, June 6, 2013 8:08 PM Subject: Re: [Elecraft] KX3 and charging batteries (when, and why do they get hot?) Mark, Thank you for this excellent response. This is exactly what I need: solid advice with rationale behind it. I checked a few things. All eight cells are now at 1.4V. When I turn the TRX on, the integrated meter shows 10.5 V now. I think this morning, when I checked after the full charge, it showed 11.6V. Not sure if that is a good sign after only having it on for a bit, tinkering. The BAT MIN was at the default setting of 10.0 V. I changed it to 8.5. Kent briefly contributed his opinion that a wall wart would not be good for charging the KX3 but did not give his reasons (I will not operate it off that adapter). What is your opinion, particularly regarding the wall charger's specs of 13 - 15.8V (@960mA). Is this peak voltage potentially too high? Other than that, I fail to construe even one reason why this adapter would not be fit to feed the 200mA charger or cause my heating issue. Thanks a bunch! 73, Arno Kg7bjm ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
