Dave, ab9ca/4 wrote: This isn't right. The capacity of the battery in watts is 110x12 or about 1320WHr. If the load is 122w/hr the battery should be totally exhausted after about 11 hours. ---------- yep, I confused AH with WH, so that does not explain the problems the original writer had. Another way to analyze would be using just the current load: 2x17a = 34a x 30% = 10.2amp
Then 110 A-H/10.2 A = 10.8 hours (theoretically) But battery discharge curves display the actual battery operating voltage one can expect to see. so one would probably reach an unworkable voltage sooner than 10.8 hours. The only good analysis would be if you have the discharge curve for the battery. These usually assume a <10% load (e.g. < 11 A). Using the discharge curve you can predict battery life under load. I used a 30% duty cycle which provides the time weighting factor (integration factor). You can argue that in FD operations the duty cycle could be something other than 30%. I assumed that one does a lot more calling in FD than normal assumed Tx/Rx ratios that commercial radio industry uses (10%). In my professional observations of radio using backup battery power the useful life never approaches the theoretical expected battery life. Most of the time the system becomes unusable in about half the time expected from a battery bank. This is on a properly floated battery bank with periodic equalization (hams normally do not do this). Theoreticals are only a good starting point as they assume fully charged new batteries (rarely is either true). The 120AH solar charging system "theoretically" provides 10A at 12V which would lead one to believe it would supply the operating load of two radios. I rarely have seen solar panels output their full rated power. In the brightest sun it is normally running about 80% of label ratings. So there was something else occurring to cause the voltage to sag to 10v in the original posters operation. 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-? DUBUS Magazine USA Rep [email protected] "Kits made by KL7UW" http://www.kl7uw.com/kits.htm ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
