Battery power requirements

[Randy Johnson-8]

I have operated Field Day with my K2 in the QRP mode and one "normal" car battery. No problem.  

I made 460 contacts so calling stations and giving the exchange maybe took 20 seconds. THat means the transmitter was on only on for perhaps 20 seconds per QSO or 8 minutes per hour. Hardly seems like much of a drain.

I am going to try QRP again, but I am a realistic and it may well be that with conditions as bad as they are today, QRP might be a wasted effort. If it is too frustrating, I'm going to switch to 100 w. That means I will make more contacts that QRP and I would call CQ.  My question is, "Under these circumstances, can I expect the battery to last for the more or less 18 hours that I will be operating?"

Obviosuly, if not, buying a second battery is a not-very-expensive option.  

Randy W6SJ
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[KD7PY]

  My question is, "Under these circumstances, can I expect the battery to last for the more or less 18 hours that I will be operating?"

Obviosuly, if not, buying a second battery is a not-very-expensive option.  

Randy W6SJ

The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts.

[KD7PY]

Just doing the math...I would assume that you would draw aprox 20 amps at 100 watts..
you would not be at 100% duty cycle so that would help.
I don't think that your rig would work very well when the battery dropped down to 10.5 volts
what I would think would be useable would be a battery with a 400 amp hr rating..
400 divided by 20 = 20
that would give you some head room...
prob.. a deep cycle/RV type battery

just a guess...

Ed