[Elecraft] FW: [K3] K3 Off Grid

[Chester Alderman]

Gosh Engineers...why not just suggest to Paul that he use the most simple
method of finding out the voltage and current the K3 draws by pressing the
K3's METER button????

73,
Tom - W4BQF



-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Lynn W. Taylor,
WB6UUT
Sent: Wednesday, March 5, 2014 5:23 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] [K3] K3 Off Grid

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?

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