Hi Doug, You're right: 2 x 12 is better than 2 x 6 (because you get twice the current capacity from the two 12 packs). But a caution... you can't just wire the battery packs in parallel. If one battery has even a slightly different voltage than the other, the higher voltage battery will discharge into the lower voltage battery which could be a disaster. I've seen circuits for putting batteries in parallel (they're called 'battery isolators'); there might even be one in the handbook or maybe someone on the reflector can point you to one. Otherwise a Google search would certainly find it for you. It could be as simple as a pair of Schottky Barrier Diodes (they have a lower voltage drop than normal silicon diodes). I seem to remember seeing a circuit in QST lately (meaning 'in the past 5 years or so'). An article search on arrl.net might find something.
As far as calculating battery life, it seems straightforward, but you have to make a lot of assumptions to do it. For example: if you assume you listen (0.15A) 90% of the time, and transmit (2A) 10% of the time, your average current drain is (0.15 + 2 x 0.1)A = 0.35A per hour. At 0.35A/hr, a 3AH battery would last about 8.5hr. A pair of batteries would last about 17hr. The big assumption in that example is the 10% transmit time. If you're using CW, your average current draw is much less than the "key-down" current because you're only drawing 2A during the key-down times, and 0.15A the rest of the time. If you're on SSB, you have a similar situation, only with voice peaks instead of key-down. So that 17hr is a really conservative estimate, and could be off by a factor of 2. In addition to the calculations, you should do a "real-world test". I went through the same calculation scenario with my little K1, concerned that a 2.5A gel cel wouldn't be enough. The actual usage however showed that I came home from my camping trip with a lot of capacity to spare, plus an extra gel cel that never got used. Hope this helps. 73, ed - k9ew ----- Original Message ----- From: "Doug Forman" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, October 16, 2004 1:14 AM Subject: [Elecraft] Two battery questions - K2 portable operations > I'm assembling a portable kit in which I can fit two small sealed > lead-acid batteries. > > For my specific size requirements, I have the option of putting (2) 12v > (3.0Ah) batteries in parallel, or (2) 6v (3.0Ah) batteries in series to > obtain the 12vdc I need. (the specific batteries I am considering are > the PowerSonic PS-1230 - Mouser # 547-PS-1230 or the PowerSonic PS-630 - > Mouser # 547-PS-630) > > It seems to me that with [ 2 x 6v (3.0Ah) = 12v (3.0Ah) ] while [ 2 x > 12v (3.0Ah) = 12v (6.0Ah) ]. Maybe the simplicity of this makes me > question this assumption, or maybe it's been too long since I did these > kinds of calcs ;-) > > Could someone please confirm or deny my thoughts here? > > Also, I'm trying to calculate (roughly) the useful battery capacity > based on considering the minimum current draw from a rig, and the > maximum current draw from the same rig. For example, given the battery > configurations above, and considering the K2 approximate minimum current > draw of 150mA and approximate maximum current draw of 2A (at 10w), what > is the potential operating time ranges available from the batteries? > > Thanks in advance & 73, > > Doug N7BNT > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 > _______________________________________________ Elecraft mailing list Post to: [email protected] 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
