[Power] The new 10 watt panel from iLoveMyXO in the wild

[Richard A. Smith]

On 11/13/2010 04:44 PM, Mike Lee wrote:

> There are a couple video clips of the oscillation noises in the photo
> set. The noise was quite noticeable when charging the XO-1.5. Cici and
> I took the opportunity to use the set-up as a Light Theremin:

Sorry its take me so long to respond to your post.  The oscillations are 
expected.  It basically means that the XO is trying to draw more power 
than your panel can provide.  Sometimes it will settle in between 11 and 
10V where the effective input resistance of the XO's DC/DC converter 
supply starts to increase rapidly but there are also lot of cases where 
it oscillates.

You indicate that it was a early model 1.5 if the model number that OFW 
prints on it boot screen is less than a D4 then the oscillations are 
going to be much worse.  We worked on that and the changes hit the line 
in either D3 or D4 but I  can't remember which.  If you can get a hold 
of a current production XO 1.5 then give it a re-test should be much better.

My MPPT code in the EC was also supposed to help this but its not active 
right now.  I was able to make a positive difference in the low power 
cases but it had a negative effect at the higher powers.  I need to 
return to it sometime but the changes in the later model XO 1.5 made the 
MPPT much less necessary.

Also, Judging by the angle of the panel in your pictures if you really 
had good solar axis alignment then your sun was really low on the 
horizon.  You won't get very much power in that case.  Try more 
experiments when the sun is much higher up in the sky.

Oh and if you are using the newer builds with powerd then there is a 
powerd log that will measure how much power you put in the battery.  It 
logs by default.

Since the XO has to be running for powerd to log. Mapping the battery 
power to the input power it tricky but if you have positive charge into 
the battery and the XO is idle you know it was at least 4-5 W or more

I also have some scripts you can run that force the XO into suspend and 
then use fast wakeups to take readings from the battery.  Because of the 
low power suspend mode the battery input is approx equal to the solar 
input. (Within 1W)

Let me know if you want to play with them.  I'll dig up my instructions.

-- 
Richard A. Smith  <richard at laptop.org>
One Laptop per Child