[Power] $30 resin panel in my hands from eBay

[Mike Lee]

Richard,

Your response is effectively a testing manual. Thanks! Hopefully my intern
and I will get started at least on the prep tomorrow if I get the soldering
done tonight. We have 2 XO-1s ready to have the log scripts installed. A
few responses below:


On Thu, Jun 20, 2013 at 7:36 AM, Richard Smith <richard at laptop.org> wrote:

> On Thu, Jun 20, 2013 at 2:16 AM, Mike Lee <curiouslee at gmail.com> wrote:
>
> > Hi,
> >
> > In case your last 2 days are a quieter ramp down rather than a frenzy...
>
> :)  I've cc:ed power@ so that this is archived and can be referenced
> later.
>
> > I ordered this $29.99 12 volt, 10 watt resin panel from eBay in the hopes
> > that it might be a serviceable and affordable replacement for the
> original
> > 10 watt GP unregulated solar panel for G1G1 XO-1s.
> >
> >
> http://www.ebay.com/itm/10W-Solar-panel-10-Watt-12-V-Garden-Fountain-pond-Battery-Charger-Diode-cable-/251190599766?ssPageName=ADME:L:OU:US:3160
>
> > It arrived today (Wednesday) from Xiamen Fujian, China by China Post in
> only
> > 7 business days and one weekend.
>
> Sweet find. Finally!  At $3/W its absolutely a replacement.  It won't
> be quite as good though as that looks like its a poly-Si panel.  So
> its going to have a lot more derate when it heats up to NOC.  Ask the
> supplier if they can provide you with a VI curve.   Also ask if they
> have a 15W version.
>

I've contacted the seller to request the VI curve and to see if they have
15 watt or larger in the same panel. Maybe I'll hear from them tomorrow.

Here are some initial photos:

http://www.flickr.com/photos/curiouslee/sets/72157634232528701/



>
> > I'm hoping to install the supplied diode on the positive lead and solder
> on
>
> Not necessary for the XO.  The XO input already has diodes in the
> path.  Additional ones will only result in more loss.
>
> > an XO power cord to do a quick 2-point measure test today or Friday with
> an
> > XO-1 running 12.1.0. Let me know if there might be any gotchas I should
> be
> > aware of. I will run Power Log Collector.
>
> Use 2 XOs one with the old GP panel and 1 with this new panel so you
> can do a relative compare.  Do a crossover test as well where half-way
> through you swap the panels so that each XO gets run from each panel.
>

Never would have thought to do crossover.



>
> You are using the olpc-panelpwr-log test right?  Not just
> olpc-pwr-log?  panelpwr is what you want for panel testing as it puts
> the XO into the lowest possible power mode that you can still log data
> from.
>

Yes, olpc-panelpwr-log. It took a couple extra pokes in Google to find that
zip package on GitHub.


>
> Oh and make sure you discharge the batteries in the XOs down to the
> same level. My suggestion would be that you run each XO on battery
> until powerd shuts the system down.  Then charge each XO from the wall
> for 10 minutes.  Just so they have a bit of juice to run on.  Then put
> them out in the sun for 30 minutes, swap panels and then let them run
> until they charge up or your sun dies.   A voltmeter on the panel
> output while connected would be nice too especially if you have one
> that can log readings.
>

The meter I currently have is pretty basic. But I will have my intern
record some readings off the two solder points of the panel using some
alligator clip jumper wires.


>
> Ideally you would run multiple runs of each XO+panel combination with
> a battery discharge cycle in between each run so the starting point
> was the same for each test.  But thats a much longer test.  You want
> to see 2 things.  How does it perform in the bulk charge zone when the
> XO is trying to draw more power than the panel can provide (about 1 to
> 1.5 hours) and then what happens as the battery charges and the
> required power draw drops below the output of the panel.  This is
> where the XO-1 gets into problems with unregulated panels as once you
> cross into that zone the voltage on the input to the XO will begin to
> rise and if it crosses the 18V threshold then the XO-1 can go into
> overvoltage mode.  I say 18V because thats the worst case but typical
> is about 20V.
>
> This also can happen when the panel is put in the sun unconnected to
> the XO.  In that case the load on the panel is zero and the output
> voltage will be at it maximum value.  If thats > 18V (20V typical)
> then when you connect up to the XO it might think its overvoltage and
> shut off the input.  This is why the GP panels for XO-1 have a 18V
> limiter in them.
>

We'll make it standard practice to place the panel face down before
plugging it in. Then flipping it over to start the test.


>
> > With a successful test, my hope is that for the ongoing contributor's
> > program granting XO-1s and the steady trickle of donated units, this
> could
> > be a solution we can point to for the tinkerer or suitcase deployment
> > voluntourist.
>
> I look forward to the test results and hopefully you have made a great
> find that small deployments can use to get solar panels in qty < 100.
>
> --
> Richard A. Smith
> One Laptop per Child
>
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