[Elecraft] K2/100 Power Requirements

[G3VVT at aol.com]

In a message dated 03/06/05 04:10:11 GMT Daylight Time,  
tbeltran at earthlink.net writes:

Given  the size and weight of batteries, I had hoped to use a 36 Ah battery,
and  then recharge it with solar power.  But it seems that these  batteries
charge rather slowly, and that might not be possible.  For  example, I think
it is powerportstore.com that has a 1.2 amp flexible solar  panel recharger
that puts out approximately 5.6 - 7 Ah per day.  The  solar panel is about $
500.00.    The general size/weight and  price is ok, but it doesn't appear
that such output would be sufficient to  fully recharge a big battery. 



Reply: ------------------------------
 
The problem of recharging the battery from the 1.2A solar panel (about 16  
-18W capacity) is related to the solar panel being rather lacking in capacity  
and would not do much more than delay the battery being run  down considering 
the drain of a K2/100 on TX. It all depends on the TX to  RX ratio used with 
the K2/100 and the mode of usage to how long the battery  will last. RX is no 
problem with the K2 as that is in the 0.25A range, but the  100W on TX can draw 
something in the region of 20A at full output.
 
However a 1.2A solar panel would be very usable with a basic K2 which has  
much lower TX current requirements of usually 2.0 to 2.5A at 13.8V. Even with  
this a charging controller would probably not be needed as the battery would  
provide much of the needed voltage regulation. A diode would be needed in  
series with the solar panel to prevent the battery discharging back into the  
panel when the solar insolation is insufficient to provide any charge.  This diode 
is provided internally with most of the larger solar  panels.
 
For use with a K2/100 a much larger solar charging capacity would be  better, 
probably in the 55W range (4A at 13.8V) or higher together with a  suitable 
charge controller to prevent any possible over charging of the battery  and 
consequent over voltage being applied to the K2/100.
 
With the solar powered communications systems I was involved with from 1981  
to 2002, these initially used multiple 55W panels (approx 3ft x 1ft) with  
individual controllers on each to provide the charging for the battery plant.  
Later 15kW systems used 200 x 75w panels (approx 4ft x 1.5ft each  panel) and 
switched the solar panels in banks controlled by an intelligent  charger system. 
A matter of balancing the required charging voltage  with the amount of 
panels on line. This was needed to provide for the current  drain of the comms 
systems and allow for days when the sun did not appear,  where the available 
charging current would be insufficient to balance the  24 hr drain. With the latter 
systems running a microwave site it was normal to  see 120A or greater charge 
current at 54 to 58V when the battery  plant was in the morning full charge 
cycle.
 
Bob, G3VVT