[Elecraft] [K3] K3 Off Grid

[Lynn W. Taylor, WB6UUT]

Here is how I'd do it, your mileage may vary.

I'd measure the power draw at 100 watts key-down, and the power draw for 
receive.

I'd assume 50% duty cycle.  You can skip a lot of math by either 
ignoring the receive power draw (if it's low enough) and dividing by 
two, or adding them together and dividing by two (averaging them together).

Multiply that number by the number of hours you need to be able to 
operate -- and that's your target capacity in amp-hours.

That should over estimate the battery, so if that size wasn't 
economical, I'd buy one slightly smaller.

That should insure that the battery does the job for years, even when 
it's starting to fail.  It should also make sure you can keep operating 
if the emergency was longer than initially planned.

Yes, there are a lot of factors, like operating mode that this appears 
to ignore.  I'm simply assuming things like full power or nothing when 
the operator might be running SSB or PSK-31 at 20 watts.

I'm also ignoring portability, which I would not do if I was operating 
for fun.

73 -- Lynn

On 3/5/2014 1:15 PM, Steve Baum wrote:
> There are so many things to consider when you try to calculate battery
> requirements for emergency operation, is it really possible to accurately
> predict how long a given battery will last?