Rick, The K2 voltage display is determined by Control Board R9 and R10 which are 1% resistors. If you need really accurate voltage readings on the K2 display, you can consider trimming one of those resistors to produce greater accuracy. If your K2 display is too low, you may increase the reading by reducing R9 (parallel a high value resistor - likely greater than 3 megohms - across it). Use the formula for parallel resistance to determine the correct value. Similarly, if the K2 reading is too high, decreasing the value of R10 will decrease the K2 reading.
Seven years is a long lifetime for an SLA battery, and if it performed good for most of that period, you may just want to leave well enough alone. If really proper battery charging is required, I would suggest that you consider adding a direct (but fused) connection to the battery terminals and use an intelligent charger (Smartcharger) to keep the battery topped off. You can see how I did it on my website www.w3fpr.com. The optimum terminal voltage for the battery will vary a bit from one battery to another, but the Smartcharger approach circumvents those differences. 73, Don W3FPR Rick Wheeler wrote: > 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 > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
