[Solved] Cost effective solar + LiPo

I'm working on a solar powered project (automated garden) and I have the solar bits working out fine (great in fact) with a 3.7V 2000mAh LiPo battery, a 6V 2W solar panel, a USB, DC, and & Solar LiPo, and a Mintyboost primarily from Adafruit. Trouble with it is that it seems to me that it's a bit overly expensive, particularly the charger and booster. While I'm happy to support Adafruit as I've learned quite a lot for their beginner friendly tutorials, I'm interested in producing more of them for friends who have expressed interest and I'd like to keep the cost down.

I'm still quite new to this and don't YET possess the knowledge to design something like this from the ground up, though I'm capable enough at following schematics.

I found from another post on this forum a 5V boost regulator for what I think is a pretty good price, http://www.pololu.com/catalog/product/798 which looks to be a good replacement for the mintyboost but I'm not sure what to do as a replacement for the charger.

I've also found through my rudimentary and most likely incorrect math that the project could probably continue to run just fine on a smaller mAh battery and panel so that should help but I'll do some more load testing on my current configuration before deciding on that bit.

For ~$12 these things would be worth a shot.

http://www.ebay.com/itm/New-Multi-Function-Panel-USB-Power-Solar-Battery-Charger-for-Cell-Phone-MP3-Red-/400522167204?pt=US_Cell_Phone_PDA_Chargers&hash=item5d40fb43a4

Hmm, I have a feeling that particular item won't hold up being mounted on a fence and left out in all manner of weather conditions. I doubt it's waterproof and I bet that battery will explode in 100+ degree temps. but I hadn't previously considered solar cell charging kits so great avenue to start looking in to at least, so thanks!

But on that point, I do have the electronics (Arduino, components, batteries) in a separate weatherproof case that will live in the shade so while I will definitely look in to more chargers akin to the one Chagrin suggests, I would also like to hear any suggestions that allow for a separate battery and panel.

Also since you're already reading this, take a moment to really contemplate the irony of solar panels that aren't weatherproof. It gave me a few moments of amusement :).

If you use a small lead-acid battery (or, perhaps some NiMh cells) instead of the LiPos you could probably dispense with all the charge controlling stuff.

...R

This works well, but it is not particularly cheap: http://www.adafruit.com/products/390
I use it with the inexpensive solar panels from Seeed Studio http://www.seeedstudio.com/depot/1w-solar-panel-80x100-p-633.html

Thanks everyone!

Based on these suggestions I've seen here I've seen some very inexpensive options.

  1. With that highly inexpensive solar panel that jremington linked plus the booster I linked originally I think I can still justify using Adafruits charger since I can save so much elsewhere.
  2. Using some lead-acid or NiMH batteries in a paralell configuration for trickle charging like described here http://www.evilmadscientist.com/2008/simple-solar-circuits/ should also do pretty well. I was able to find some lead-acid batteries for quite a low price.

Now I'm just left with which to choose. But for all intents and purposes I would call this one solved and will flag it as such. Thanks everyone!

I think you could pass over the charger, and let arduino and a couple mosfet transistors do your charge controlling.

jackwp: I think you could pass over the charger, and let arduino and a couple mosfet transistors do your charge controlling.

I'm vaguely familiar with mosfet's, I'll Google to find out more, but how would one use the Arduino to do the charge controlling? I tried to find information to that end but without luck.

The rough basics; All grounds common. Setup a voltage divider (2 resistors) on each of the batteries to be charged. Drop the voltage down to what can be read by the analog inputs. Let arduino sample those voltages, and turn on and off the FET to charge the battery more (from the solar panel) if needed, but stop the charging if battery is full.

You want to charge the batteries as much as you can, without over charging them (which could destroy them). Google "arduino battery charger".

That actually mostly made sense.. I must be making progress! I will look in to that. Does it need any more than one analog input? I'm considering using the Pro Mini from Sparkfun in future builds and IIRC I would only have one spare analog connection. With the Uno it's fine of course, I've plenty left.

I thought you were charging two batteries. It will need one analog input for each battery you want to monitor.