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[on:]

Continuing the threads from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1257210571
and http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1294864688

...
Seems there are several elements at play here. 
Driving an Uno from a solar cell / battery pack is the goal to avoid power lines to inconvenient places.

Factors (as I understand them)
a) Batteries like to either be giving charge or receiving charge, not both at the same time
b) Li-po batteries have very specific rules for charging
c) Solar cells give variable power, from zero, to some, to enough to drive a 5v Uno, to enough to *both* charge a battery *and* drive a 5v Uno
d) It is useful to have USB around to charge up when the battery is dead and it's dark outside.

An ultimate solution would
a) balance USB (when available), solar, and battery sources to give continuous 5V (or 3.3v) to the Uno
b) charge the battery from solar / USB as according to available source, while keeping the Uno well supplied.
c) report voltage of solar and battery for management and low-battery warnings.
d) do so unattended, as solar /USB power can change moment-by-moment.
e) not ignite the battery, at least, not often

Just imagine how a standard published schematic could free all those Arduino's from the tyranny of power cable tethering...
Could one of the brilliant honest-to-goodness engineering types comment or point to a solution?  We'd all be grateful.

Thanks,

[Reply #1 on:]

I got one of these http://www.seeedstudio.com/depot/lipo-rider-p-710.html and it works quite well. It uses the solar panel to charge the li-po battery, and switches to charge from usb when connected to that.

But how much are you going to connect to it?

I only got the smallest battery they got http://www.seeedstudio.com/depot/lithium-ion-polymer-batteries-980mah-p-593.html and it can power an duemilenova with 6 leds on for a night. My plan is to order the biggest http://www.seeedstudio.com/depot/lithium-ion-polymer-batteries-pack-6a-p-602.html 6Ah li-po they got, and test how long it can power the same setup as the small 980mAh.

I also tested the 980mAh with an Arduino Nano and one servo motor, also only powered by the li-po rider. I had it running the sweep example for an half hour, then turned it off because the sound from the servo was getting annoying.

The li-po rider does not support battery voltage readout, but it should be possible to connect the 3,7V cell to an analog input to read it. But not sure if it really is that easy with li-po, isn't they like full voltage (or almost) the entire time, then a sudden drop?

[Reply #2 on:]

Thanks to bld for the links!

It will be driving a few sensors, status LEDs and a GSX b/g WIFI.  It should add up to max theoretical burst of nearly 350mA.
Sleep consumption (majority of time) will be much lower.  Still it exceeds/challenges  the max 350mA of Li-po Rider output.
The Uno wants a minimum of 7V going in, so a step-up will also be needed.  This will lower the effective mA output further... need to do more math.  Unless there are better ideas out there?

Cheers,

[Reply #3 on:]

No, the UNO wants 5v on the usb, 7v there would be a bad thing.

The lipo rider outputs the voltage you need, and the output current can be pushed a bit too, but might not be recommended. I actually had an 2x16 LCD on, a duemileanove, and a wishield... Not sure how much it exactly is, but I think it is over the double of what the specs say...

But might not work for long term use, I was just abusing it to see what it could take of beating.

[Reply #4 on:]

I made it using arduino fio.

Take a look at video and pictures.
http://arduino.cc/forum/index.php/topic,49986.0.html

The fio has a built-in max1555 li-po charger and you can plug your solar cells/panel directly to fio. Also you can transmit serial communication using the integrated xbee socket.

actually I don't know if I need a diode or no on my solar cells. I made a post about this and I'm hoping somebody help me:
http://arduino.cc/forum/index.php/topic,50338.0.html

[Reply #5 on:]

Thank you again bld for setting me straight: keeping to 5V instead of 7V.

With the confidence of the ignorant, I'll go ahead and abuse it and will report on results.
It'll take a while with shipping, construction and burn time, and further questions will arise, so please stay tuned.

Wagner Sartori Jr, your project looks great - good luck with the remaining pieces!