Solar AA mintyboost

by jonsleepy on Thu Dec 20, 2012 12:23 pm

Hi,
I've picked up a Mintyboost v3.0 and I'm very interested in adapting it to solar. I noticed you have made a solar powered Mintyboost, but it abandons the AA platform in favor of lithium polymer.

I'm wondering whether/how I could connect a solar panel to charge the AA batteries using some combination of the circuits from the mintyboost and/or the usb/solar/lipoly kits (and/or why you've opted to bypass the AAs for liPoly and whether I should, too)?

Is switching from AA to lipoly a major leap forward in efficiency (even if I used 4 rechargeable AAs in series instead of 2)? ...My main motivation for Mintyboost was the use of rechargeable NiMH AA's - I have lots of them floating around in circulation, and until I decide to trash them all, I'd like to continue to use them due to the convenience of their interchangeability for different uses.

Right now I'm stuck on how to solar-ize my Mintyboost. Any thoughts would be appreciated!

Jonathan
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Re: Solar AA mintyboost

by nginx on Thu Dec 20, 2012 1:35 pm

In my experience solar charging is more a gimmick than anything. Just look at the size of the solar panel you can possibly fit on top of a mintyboost. If you think a panel of that size is gonna give you any juice you are out of your mind. If you can carry along a 5W panel may be it will be worth your while but then you lose mintyboost's portability advantage.

The reason for not charging AA with solar is because AA batteries either need to be slow charged at steady 0.1C for 16 hours or fast charged with delta peak termination. Solar panel's current output is highly variable in nature. OTOH Li-ion charging with proper circuitry can be terminated at 4.2V irrespective of current rate (as long as its under 1C).
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Re: Solar AA mintyboost

by jonsleepy on Thu Dec 20, 2012 2:40 pm

Hmm.. I see the issue..

The usb/solar/li-poly charger still appeals for its principle, because for days I can't carry a large solar panel, I could still charge by more conventional manners (but if I'm on an extended road trip, having a solar panel would be a great advantage).

The Adafruit USB/solar/li-poly charger linked to a Mintyboost (without the AA's, right?) can convert solar input to USB output, with a lithium battery in the middle.

The charger here on Amazon can use USB input to charge AA's.
http://www.amazon.com/Rayovac-Everyday- ... aa+charger

Can the solar circuitry pass current directly to mintyboost, without the lithium battery? If so, it would seem like you could add a third circuit (or do a modification of mintyboost) to make the circuit go Solar --> usb <--> AA . Maybe a switch would could determine which direction the current flows between the usb and the AA (or I'd just reverse the direction of a diode), and I could only either recharge the AA's or discharge the AA's into my cell phone, but not both at the same time.. or something like this?

I'm not going to try too hard here, but it seems like there is (or could be) a way to make this work?

Or maybe just toss out my AA's and switch to lithium, eh?
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