[Elecraft] Re: Field Day Battery Capacity

[W5EI@cs.com]

Daniel

If you are using the K2 as a QRP rig, the "jump start" battery might work.  
Current drain on receive should only be 250 mA or less (your mileage may 
vary).  The Wal-Mart type battery I have is a 19 amp-hour one, so 24 hours on 
receive at 250 mA is no problem.  Of course transmitting is going to require 
1.0 to 2.0 amps if you stay at 5 watts or less.  The K2 is rated for 2 amps 
at 10 watts.  Duty cycle for CW is pretty low, 50% or less.  If you are like 
most operators, you will be doing more listening than transmitting.  Let's 
say you transmit 30% of the time.  At the risk of greatly oversimplying 
things, here is the way I would figure it:

For RX:  24 hrs x 250 mA  x 70% time factor =  4.2 amps
For TX:  24 hrs x 2.0 amps x 50% duty cycle x 30% time factor = 7.2 amps

The 2 amps I use for the TX current is meant to be conservative figure; you 
probably won't use that much at 5 watts with a well built K2.  Most of the 
jump-start gel cell batteries I see in the discount stores are 17 amp hour 
ones.  That much capacity should be adequate unless you transmit a lot more 
than the scenario I have outlined above.

Good luck,

Don
K2 #2478


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