[Elecraft] K2 qrp battery drain estimation

[Don Wilhelm]

Robert,

You are assuming you can draw the full rated Ahr from a battery - that 
is not a good assumption, go with closer to half that amount of energy.  
You will not be able to completely discharge the battery.

Secondly, your transmit current at 5 watts is a bit low, it will 
generally be closer to the 1.4 to 1.9 Amp range (I just measured a K2 
with T4 wound for "high efficiency at 5 watts" and it was drawing 1.2 
amps with a 13.8 volt supply).  Remember that the K2 tries to maintain 
the requested power output, so as the battery voltage drops, the current 
must increase to maintain the same power output. If the overall transmit 
efficiency is 30% (you have to run the entire transmit chain, not just 
the PA), you will have to put 15 watts in to get 5 watts output.

73,
Don W3FPR

On 6/14/2013 6:28 PM, Robert G Strickland wrote:
> If I'm operating a K2 at 5w cw, in S&P contest mode, I compute the 
> current drain under the stated conditions as follows:
>
> conditions:
> 50% listening, 50% transmitting
> CW 50% duty cycle
>
> current:
> 200ma receive, more or less
> 1.0a transmit, more or less
>
> current draw per hour:
> 100ma [30min rcv] + 250ma [30min xmit @ 50% duty cycle] = 350ma per hour
>
> 10Hr requires a 3.5Ahr battery
> 20Hr requires a 7.5Ahr battery
> etc...
>
> Is this more or less accurate, or have I missed something? Thanks.
>
> ...robert