Solar MintyBoost using AA batteries?

[jpettit]

I'm looking at building a Solar MintyBoost using the blog post:
http://www.adafruit.com/blog/2010/07/09 ... r-gadgets/

I was thinking of using the MintyBoost v3 Kit and moving it into a larger tin and then all the parts could fit in.

Is it a requirement to use the mentioned Lithium Ion Polymer Battery or can I simply attach it to the MintyBoost v3 Kit (with the 2 AA batteries)?

Thanks
John

[adafruit]

yes the charger does not charge AAs, only lithium polymer

[jpettit]

is there a charger that can charge AAs?

[adafruit]

no

[ScottHW]

What about using Li-ion AA form-factor , aka 14500, batteries? Would this charger work with those?

[scott-42]

The charge controller is designed for a single cell. So if you used a single LiIo or LiPo 14500 AA size 3.7V battery it would work just fine. The problem with this is that you would get about 700mAh out of a cell that size. While it is tempting to parallel two cells and thus get 1400mAh of capacity, it is not supported with the charger. You'd be better off just fitting one of these http://www.adafruit.com/products/258 in place of the two AA size and getting 1300mAh out of it.

Technically you could use multiple cells and trick the charger into thinking it is a single cell, but that requires knowledge of how to balance the cells.

[jvschwarz]

jpettit,
I've had success with a simple usb AA charger, $6, a LDO linear regulator, LT2940-5, and shards of solar cells with OC of .88 amps and 5.5 volts. The usb charger was an Igo with output characteristic of ~190 ma for both AA and AAA. Worked, only it took all day to charge 2 AAA. I'm upgrading to an Eneloop usb charger, ~$13 w/ 2 new AA's, should arrive tomorrow. I started look with the simple instruct-able online but didn't like the likelihood of frying my batteries. For the price you can't build the protection circuits from scratch that these cheap chargers provide. Good luck.

[golemB]

no

I'm no engineer, but I, too, wish for a solar AA smart charger with Minty 5V USB output. Based on what I've read so far, am I correct in guessing that this isn't practical as a DIY kit is that it takes expensive circuitry to make a decent NiMH smart charger, especially with small solar panels?

On the non-DIY side, the closest I've seen to my wish is the Goal Zero Guide 10 kit (2 panels about the size of the 2W/6V panel sold by Adafruit, plus a fairly slow 4xAA NiMH charger that outputs 12VDC and 5V USB).

Any chance that a similar system could be made via a future kit?

[adafruit]

its more difficult to charge Nimh's with solar than LiIon - and a lot more people want LiIon!

[jvschwarz]

Ada,
It appears you have me at a disadvantage. You sly devil, you knew I'd run headlong into a wall, wink,wink. As indicated above, I used an Igo and solar panels to charge AA & AAA batteries. Small panel, small load. Everything worked according to my evil plan, or so it seemed. As indicated, I wasn't happy waiting all day or two for my batteries to charge and thus I purchased a quicker USB charger , Eneloop, rated at 500 ma. After playing around all day yesterday I've come to the same conclusion you commented on in your USB/ DC /Solar Li/po charger product design document, "instability confuses battery chargers," should have read that before I.... Oh well, it was a learning lesson, and fun too. The little Igo still works but not much better than my original, dumb, little aa & aaa solar lamps, ticks I called them because they're suspended all over me while hiking. Yours is obviously the superior logic. While not an EE I can still read.

Finally my question, drum roll, would it be possible to substitute, obviously with mods, capacitors for the lipo cell in the USB/ DC /Solar Li/po charger design as a pass through to the USB? You've obviously given this problem a lot more time and consideration than I have or ever could. All my research indicates that everyone is looking at the Lipo solution, which is great for obvious reasons, but not in my case, or other hiker's for that matter.

[jvschwarz]

scott-42,
Question, which I think you've already answered, but I'll ask anyway. If not the AA form 14500 Li-ion, how about the larger banned's. More rigid construction, 2.2 ah, max 6 amp charge rate, Over-charge/discharge protection (not that I'd trust it). If so, sign me up .
http://www.tenergybattery.com/index.php ... &Itemid=27

[adafruit]

Finally my question, drum roll, would it be possible to substitute, obviously with mods, capacitors for the lipo cell in the USB/ DC /Solar Li/po charger design as a pass through to the USB? You've obviously given this problem a lot more time and consideration than I have or ever could. All my research indicates that everyone is looking at the Lipo solution, which is great for obvious reasons, but not in my case, or other hiker's for that matter.

that's a very good question. the secret answer is - yes...it does work (somewhat) but because its totally not meant to do that it acts really oddly and will confuse your phone. even the smallest lithium cell will help. we do plan to carry banned's shortly, but we are waiting for a shipment of the battery holders to come in (unfortunately there is no ETA)

[scott-42]

If not the AA form 14500 Li-ion, how about the larger banned's.

Yes you can use that form factor too. Single cell or balanced groups of them. Adafruit sells them in balanced three packs. It is actually what is inside this battery pack Lithium Ion Battery Pack - 3.7V 6600mAh. You can use the pack as is or tear it apart and use the cells individually.

[jvschwarz]

Thank you to both of you. I look forward to your next allotment of solar lipo chargers.

[adafruit]

thanks for understanding, we did design a 'solar' AA charging mintyboost but really, it was not going to work nearly as well. we want people to be satisfied with their purchase