[Power] [support-gang] 3 portable solar choices for XO-1? (and other XO laptops, if poss!)

[Richard Smith]

On 01/15/2014 12:46 AM, James Cameron wrote:
> Please do continue to include power at lists.laptop.org, thanks.
>
> On Wed, Jan 15, 2014 at 12:17:01AM -0500, Adam Gordon wrote:
>> It is said to use 1mA average while connected to a 12v battery which
>> would be 99.91% at 14W. Once the sun moves back into the northern
>> hemisphere I'll do some testing.
>
> That 1mA draw from the battery is not a specification of conversion
> efficiency, but rather how much current is needed to operate
> overnight.
>
> There is _no_ specification of efficiency in that product
> description.  You might ask them about it.

James brings up a very valid point about operation of that when 
connected to the XO-1.  The XO-1 will present a load that looks very 
different than a LA battery.  If it makes that charge controller think 
that it needs to go into soak or float phases you won't get much 
charging from it.  I think using that to charge an XO will be very 
problematic.

There are DC-DC converters with adjustable output available on ebay that 
are a much better option.  I'll find you some links.

Note that you will take about a 10% loss using a DC-DC converter. 
Really good ones can operate in the 97-98% range but thats usually under 
very specific conditions.

Re: the 18V limiter loss.  The design of the limiter in the GP panel is 
a mosfet in line with the output that only restricts if the voltage 
reaches 18V.  In the normal case the mosfet is fully on and thus has a 
resistance of milli-ohms.  The loss across the mosfet when its not 
limiting is negligible.  Its on the order of the same loss you get in 
the cable or in the connection resistance of the DC jack.

For the panel voltage to be 18V you have to have a load thats less than 
the rated output of the panel therefore there is spare power in the 
system and the overall system loss is zero because its power you were 
not drawing to begin with.

-- 
Richard A. Smith