[Elecraft] 14 volt batteries?

[Jim Brown]

Hi Charlie,

Since your question is likely of interest to others, I'm responding to 
the reflector.  My system is float charged using a Genasun MPPT solar 
charge regulator designed for LiFePO4 batteries. My solar array is quite 
small, composed of 4 panels gifted by a friend who recovered them from a 
dumpster after they had been replaced in instrumentation setups. Because 
I'm in a redwood forest, they get far less illumination than they would 
in a more typical installation. During the summer months, they're 
producing charging current from about 9:30 am to about 4:30 pm. From 
early fall to late spring, they're barely illuminated at all.

When the sun is not enough, I disconnect the panels and use an old 
computer laptop power supply to feed the charge regulator.  That's 
enough to run a single K3 for contesting at full power, but not for two 
K3s in heavy SO2R. It is enough to run SO2R at the much lower power 
levels needed to drive my power amps.

I've done two things to address that. First, the LiFePO4 battery only 
runs the radios. Other 12V gear in the shack runs from a big Costco deep 
discharge battery, floated in the same manner from another old laptop 
power supply. Second, for 100W contests, I reduce K3 output to what it 
takes to get 100W from my power amps, which varies from 5-8W, depending 
on which amp and which band.

You asked about a 10Ah battery. W6JTI used my KX3/KXPA100 for two 
ridgetop expeditions (3 miles up a trail that climbs 2,000 ft) to 
activate the rare CM79 grid on 6M. He was joined on one trip by K6EU, 
and on a second by N6ZFO. The first trip was for two days, and they 
carried three 20Ah batteries. On the second trip for only one day, they 
carried two. On both trips, they got through most of the day with one of 
those batteries. The first time around, they were not familiar with the 
KX3 power hookup, and by accident ran the KX3 on the internal NiMH AA 
pack. That also got through much of that first day. it was a CW-only 
operation. To gauge operating time, they were set up and on the air by 
about 8 am and shut down between 6 and 7 pm (on the second trip, in time 
to make it down the trail before dark).

So -- I'd say a 10Ah pack would be good for nearly continuous CW with a 
barefoot KX3 all day. And, of course, there's the internal pack, which 
for my batteries, is about 2.7Ah.

73, Jim K9YC

On 8/21/2017 4:32 AM, Charlie T, K3ICH wrote:
> Interesting comment Jim.
>
> I would have suspected that a 10 Ah battery might not be big enough.
>
> Assuming you have the 100 W K3, can you run full power using the LiFePO4
> battery?
> How about operating time?  Again, assuming casual not full contest mode.
> Also, do you leave the charger connected at all times? I'm guessing it is
> designed to operate like this.
>
> Currently, I have an old 2' X 4' solar panel charging a regular 24 size car
> battery with a diode isolated 3 Amp power supply in case the sun doesn't
> cooperate, all feeding a home brew switching type charger.
> It DOES make some beeps and squeals on the six meter band, but just a couple
> obvious spikes in the panadapter that I've learned to live with.
>
> Ultimately, if I converted to the newer battery, I'd still want the ability
> to use the solar panel to charge. I'm thinking that would take quite a bit
> of extra circuitry to accomplish.
>
> I typically get around ten years of life to a car battery in this situation.
> I'm hoping the LiFePO4 battery would have better lifetime considering the
> cost.
> Of course, when I started this set-up years ago,  you could buy a Wal-Mart
> battery for $29.95.  They're not that far from a LiFePOP4 battery pricing
> now days, especially if I could get away with a considerably lower Ah
> rating.
>
> I'm hoping this goes to you directly since I don't want to prolong an OT
> thread.
>
> 73, Charlie k3ICH
>
>
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
> Sent: Monday, August 21, 2017 12:17 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] 14 volt batteries?
>
> Right on!  For about a year, I've been running the radios in my shack from a
> 10Ah LiFePO4 battery from Bioenne Power.  I never see the voltage drop below
> 13V on the K3 voltmeter.
>
> 73, Jim K9YC
>
>
>