[Elecraft] Solar power?

[Rick WA6NHC]

AGM works well or LiFePo4 (lighter, smaller and more expensive, higher 
operating voltage so better for radio, pickier to charge properly)...  
Neither offgas so they're safe for in the home.  AGM can be used down to 
50% charge, lithium 80% without damage, so you have to compensate when 
comparing capacities (apples/oranges). (The days of lead are ending.)

I'd suggest that you define the battery type you want to use, then get a 
solar controller that is both RF quiet (duh) and can help manage the 
battery chemistry effectively.

LiFePo4 was my choice for portable/RV ops and the charger I use can 
charge from 9-20V (because it charges each cell individually at the 
appropriate voltage/current) so I can charge while driving between 
sites.  It wasn't cheap to get started (battery, management board, 
charger[s]), but size and weight matters on the road (half the size, 1/3 
the weight compared to lead).  The radio prefers it to AGM (it's 
cleaner) from the slightly higher voltage.  The lifespan of lead is 3-5 
years, lithium is 10+ years and can be recharged MANY more times 
(factors when considering cost/year, lithium wins even though they cost 
more initially). Lithium maintains a charge much longer than lead if 
unused.  My next move is to get a small solar charger; which will lead 
into more panels, time and expense (so I'm dawdling).

Learning curve:  Lead charges fade over use, making it simple to know 
when to charge.  Lithium goes full tilt, until it doesn't; so you want 
to monitor each cell and don't get to the cutoff voltage.  The 'knee' on 
lithium is subtle.

WARNING:  Battery chemistry with proper maintenance techniques can be a 
HUGE learning curve and there is a LOT of misinformation out there to 
filter out.  I do not claim to be an expert, but I know some who are.

CAVEATS:

     Some solar controller designs manage via the negative lead, which 
if the battery is also bonded to anything else (an RV), can be a BAD 
thing (momentarily exciting but smelly and potentially expensive).  If 
the battery is not connected to anything while being charged (unlikely) 
it's safe.  [Find a controller for your situation, both designs work but 
management via positive is overall safer.]

     Some LiFePo4 bulk chargers (running through a BMS - Battery 
Management System device) are switcher supplies that generate RF noise 
(shouldn't be an issue with a quiet solar charger).  Ask me how I know?  
At home, I use an Astron linear supply, no noise.  If I use the switcher 
(rare), I'm not operating.

That, in a nutshell, are the high points of a month of online discussion 
with my battery guru.

Rick nhc


On 2/6/2017 10:53 AM, Matt Zilmer wrote:
> You might look into CirKits SCC charge controllers. I use the SCCS3 
> here with two 50W 12V PV panels to keep the 75A-H station battery 
> charged.  It's an easy-to-build kit.
>
> cirkits.com
>
> 73,
>
> matt W6NIA
>
>
> On 2/6/2017 10:37 AM, Harry Yingst via Elecraft wrote:
>> My son has my KX3 and I'm building a K2. Both of us have a set of 
>> solar panel that are capable of a lil over an amp at 12v
>>
>> We are both looking for a battery idea and a method of hooking it to 
>> the solar panels to charge it .
>>
>> Thank you