[Elecraft] Powering a K3s from a battery?

[Jim Brown]

On Tue,12/29/2015 7:57 AM, John Macrae wrote:
> I run /P on a 35aH lead acid battery. Whilst there is a noticeable voltage
> drop, I have worked dx till the battery voltage falls well below 11v
> without any noticeable effects on signal quality (I asked)!

It is well known that IMD (splatter, clicks) with a K3 is least with 
higher DC supply voltage, and increases as the supply voltage is lower. 
By 11V, it's increased a lot.

IMD is also reduced when the K3 operates at lower power. This is helpful 
when you're driving a power amp. The KPA500 needs about 25-30W for full 
power, my big 1.5kW tube amps need about 50W.

There is a menu setting for the DC voltage below which the K3 will not 
transmit. Check the manual.
> I have also run from a battery in the shack with a charger connected. No
> problem.

I currently run from two big 6V golf cart batteries that are 
float-charged by a regulated DC supply. With the charger connected, I 
get about 13.4V on TX. Without the charger, the voltage falls below 11.5 
V when the batteries are getting low. Because I'm usually driving an 
amp, I have my K3s set to cut off at 11V.

> Clearly the larger the battery,  the less problems you will have.

Yes, but the battery chemistry also matters. The "normal" operating 
voltage of LiFePO4 batteries is at least a volt higher than lead-acid, 
and the discharge curve is flatter. The problem is that LiFePO4 is 
currently a lot more expensive, and the chemistry requires a special 
charger.  Prices are gradually dropping, and eventually that's likely 
where I'll end up.

73, Jim K9YC