In a message dated 10/16/04 2:15:31 AM Eastern Daylight Time, [EMAIL PROTECTED] writes:
> It seems to me that with [ 2 x 6v (3.0Ah) = 12v (3.0Ah) ] while [ 2 x > 12v (3.0Ah) = 12v (6.0Ah) ]. That's correct. You'll have twice the capacity. But for the same size and weight, it should be possible to find two 6V 6AH batteries to put in series. > > > 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? That depends entirely on how much time (percentagewise) is spent at each condition. Here's how to make the calculation: First off, I'll assume CW. Analysis of typical plain-language Morse Code has shown that the key-down time in a typical transmission is 44%. (derived from the standard word "PARIS") In the case of a QSK transmitter like the K2, it means that *while you are transmitting*, the rig draws 2A 44% of the time and 150 mA 56% of the time. The "key down" time is only 44% of the transmit time. But how much of the time are you transmitting? Unless you're sending bulletins, a lot of messages, or calling CQ a lot, you probably spend at least 60% of the time listening and 40% transmitting. So the actual keydown time is 40% times 44% (.4 x .44 = .176) = 17.6%. To allow for tuneup and such, let's say 20%. So the K2, when operated in CW under the conditions assumed, draws 150 mA 80% of the time and 2 A 20% of the time. So in a typical hour of operation, the K2 will use up: .15 x .8 = .12 AH receiving 2.0 x .2 = .4 AH transmitting .4 + .12 = .52 AH total Using a 6 AH battery, you could get up to about 12 hours operating time as described above. However, such calculations are very approximate. For one thing, they assume that your battery is fully charged at the start and can deliver name-plate capacity. Also assumes that your keydown time is as calculated. Less keydown time produces a lot more operating time. For example, if you listen more and send less, the operating time increases dramatically. Look at what happens if the operating is such that the rig then draws 150 mA 90% of the time and 2 A 10% of the time. So in a typical hour of operation, the K2 will use up: .15 x .9 = .135 AH receiving 2.0 x .1 = .2 AH transmitting .2 + .135 = .335 AH total Using a 6 AH battery, you could get up to about 18 hours operating time at the lower duty cycle. Note also that battery capacity isn't linear. Lead-acid battery capacity is specified at a certain current demand level. At lower levels it increases, and at higer levels it decreases. If a given lead-acid battery can deliver 2 A for 8 hours, (16 AH at the "8 hour rating"), do not assume the same battery can deliver 8 A for 2 hours - you'll be disappointed, because it will run out of juice before then. OTOH, at 0.2 A it will probably last longer than 80 hours, indicating a capacity greater than 16 AH. Last time I used my K2 on FD (all CW), a single "7 AH" battery lasted more than 12 hours and was still going strong. 73 de Jim, N2EY _______________________________________________ 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
