[Elecraft] K3 and KX3 questions for Wayne

[Jim Brown]

On Sun,5/22/2016 11:46 AM, N6MQL wrote:
> Although I appreciate all of your answers I specifically asked these 
> questions of Wayne because I was making a point to let him know of my 
> disapproval of the fact that the KXPA100 amp is incapable of running a 
> full 100 watts on a standard 12v battery.

Michael,

A careful reading of the online data sheet for the KXPA100 is 
instructive here.

http://www.elecraft.com/KXPA100/kxpa100.htm

The first line says "100 watts at 13.8 V, 1.8 to 29.7 MHz and 80 watts 
50-54 MHz PEP CW/SSB/DATA; ± 1 dB"

Two points: First, the amplifier is rated for 13.8V, NOT 12V. Second, 
the rating is +/1 dB, which is +/- 20% power. Thus, 80W on the HF bands 
is within spec for 13.8V at the amplifier terminals.

The second line says "13.8 VDC powered; 20 A typical current drain (11 V 
with lower output. 15 V max)"

This clearly means that the unit is designed and rated for 13.8VDC, can 
be operated from 11V to 15VDC, and will have reduced output at lower 
supply voltages.

Obviously, Ohm's Law dictates that resistance of the DC supply 
conductors will reduce power supply voltage at the amplifier terminals, 
so while we may have 12V or 13.8V at our battery terminals, the voltage 
at the end of 6-12 ft of cable will be a bit lower with a 20A load. For 
example, the drop in 6 ft of #10 is 0.24v; for #12, it's 0.38V, and for 
#14, it's 0.6V.

As others have noted, the operating voltage in so-called 12V DC power 
systems using lead-acid batteries is not 12V, but rather 13.8V. If you 
buy an AC power supply for ham gear, it will likely leave the factory 
with its voltage regulator set for 13.8V. Open the manual or the spec 
sheet for nearly all ham gear and you will find the supply voltage 
specified as 13.8VDC.

73, Jim K9YC