[Elecraft] slightly OT: need reference for solar charging system for 18AH battery

[Jim Wiley]

So, what do you want to know?   
 

To answer your questions, whatever they may be,  some preliminary 
information is needed. 


How much operating time do you plan on doing each day (what is the duty 
cycle)?  


Will you be in any one place long enough to have a solar panel 
stationary (for best charging)? 


Will you be attempting to charge the batteries (or operate) while in 
motion? 


Where is the Salmon river (what state)?


Is the river "out in the open" or running down a steep-walled canyon? 


Do you have,  or have access to,  a solar battery charge controller?


Do you already have, or have access to,  one or more solar panels, and 
if so, what is their rating?


If not, what is your budget to purchase panels?


I am assuming the battery in question is a sealed gel-cell, using 
lead-acid chemistry.  Is this correct?  If so, remember that the maximum 
charge rate for best battery life is about 3 amperes ( a charge rate no 
more than 1/6 of the ampere-hour capacity is the rule of thumb for 
gel-cells).  Using that as a benchmark,  it will take approximately 7 
hours for a full recharge - the other rule of thumb is that you will 
have to "return" about 120% of what you take out to recharge the system.


Is any source of power (other than solar cells) available - for example, 
from the charging circuit of the boat (if it has one) or from "shore 
power" when you are stationary for an evening?   Are you bringing along 
a small generator for lights, entertainment systems,  or food 
preservation (a refrigerator)?


How long (in days) is the excursion scheduled to last?


Do you have, or have access to, a small wind turbine generator (to 
charge batteries at night)?


What time of year do you plan on doing this (the amount of solar energy 
available varies with the seasons)?


Do you plan on using the K2 on CW or SSB, and at what power level?


Be aware that a fully charged 18 Ah battery will  run the K2 for a 
significant amount of time with no additional charging. Others on this 
list may have more information, but I would expect to get 20 or more 
hours of actual operation if you are on the air a lot (contest style 
operating), and substantially more hours if you are doing casual 
contacts?  20 hours is 4 hours a day for 5 days  quite a long time, 
actually, when you consider that most of your daylight hours are likely 
to be involved with the actual navigation of the river, and not pulled 
out to shore.  If it were my choice, and I were considering a rather 
"radio heavy" schedule, I might opt instead for a 2nd fully charged 
battery and not worry about recharging until you get back home.  .A 
second battery will be substantially less expensive than buying a solar 
panel that is capable of any serious amount of recharging in the short 
intervals that are likely to be available, and quite possible less 
intrusive from a  physical size and "carry weight" point of view as 
well.   


Once you have developed the answers to these questions, then it becomes 
possible to offer some ideas for your project.


- Jim, KL7CC


  . 

Allan Taylor wrote:
> I know someone who checks this reflector is heavily involved in solar
> charging for small (QRP) station use. I have
> a fresh 18 Ah battery that I wish to take along to power the K2 on a
> white water raft trip (Salmon River, Middle Fork).
> This has proven an impetus to finally inquire about a solar charging
> system. Can someone point me to this
> person (or others) to get me off dead center??
>
>