Quick update on an early prototype of the "Portable Energy Scavenging Kit", after a intense hackathon this weekend with Ben Garmari:
This first version of the kit is able to charge phones that require 5 Volts, 500 mA, and it can also power a small LED light (suitable for lighting a small space, or usable as a flashlight). It uses a rechargeable battery (the amount of energy the battery can store is 6600 mAh -- a typical smart phone battery capacity is about 1500 mAh) which can be charged either by house current (via an adapter), or via a small solar panel (3.4 Watts, 6 Volts). We haven't yet tested how long it takes to charge fully a battery of this size; but the panel typically outputs 500 mA in bright sunlight, so acquiring 1500 mAh (one smart phone battery's worth) should take around 3-4 hours.
More photos here:
* 3.4 Watt 6 Volt Solar Panel ($30, voltaicsystems.com)
* Solar / DC / LiPo charger ($25, adafruit.com)
* MintyBoost v3 kit ($20, adafruit.com)
* A 6600 mAh LiPo battery ($40, adafruit.com)
* Buck Puck DC Power ($20, superbrighleds.com)
* A 1 Watt LED ($3, adafruit.com)
* Piece of PVC junction ($.49 at hardware store)
* USB Mini-B, USB Micro cables ($1 ea on Ebay)
* Altoids-like tin (< $2)
* Design a custom PCB. The next version will simply combine the MintyBoost, Solar Lipo, and Buck Puck charger circuitry in order to reduce costs. And hopefully subsequent version will use an Arduino-like chip to allow for charging other battery chemistries and for optional output of, e.g., the 700 mA that a Raspberry Pi prefers.
* Design a case for the battery and electronics
That's a good point, Jiansheng -- the panel is rated at 3.4 Watts, but Adafruit said they usually got around .5 Amps (~ 3 Watts, for the 6 Volt solar panel) ... maybe the way that manufacturers rate these devices is rather optimistic?
Is this a question? Click here to post it to the Questions page.
Gregor -- thanks for that link! I hadn't seen bootstrapsolar -- they're using almost precisely the same circuitry (though they went ahead and combined the two separate open hardware projects into one, nice board) -- and, as you say, they located cheaper components. Great find! I'll contact the fellow, point him to what we've done, and look to collaborate / get advice ...
The Adafruit circuits are fairly inefficient, and in practice solar panels are already only like 10% efficient. Story time:
Over two years ago I was working on a Maximum Peek Power Charging (MPPT) circuit for lithium ion batteries based around the LT3652. The first set of boards I printed had a missing wire, and by the time I'd fixed it I was 1) busy writing grants for Public Lab in my free time rather than doing that, and 2) the dude who was letting me use his surface mount soldering gear turned out to be a crazy bank robber (true story).
so I dropped the project... I figured I was fighting uphill against the innovator's dilemma and that someone would have built such an OS MPPT circuit by now, but I can't find any such thing.
The files are on the Yahoo Charge Controller Group, and, using my admin privileges, attached to this research note. I hear by bequeath them to you!
They include the circuits, parts lists and item#'s at Digikey, datasheets, and some other stuff. I actually don't know if the circuits really work, but the background work I did should give you a good start-- I built a spreadsheet around the parameters of the datasheet for picking components.
So rad you're working on this! the world needs a good, non-proprietary field charger for small electronics!
You're like a combination Lucius Fox (Batman) / Q (Bond) / Merlin (Arthur)! But, in addition, you actually employ in the field the tools you create, so you're also, e.g., the Bond to your own Q. The most parsimonious explanation I can think of is that, like Merlin, you are living backwards in time and delivering us the fruits of your future research.
Incredibly helpful post. I'm going to share all of your info -- circuits, parts lists, datasheets -- with Ben, and have a sit-down with him when I return to Amherst on the 28th. Will also look into the Yahoo Charge Controller Group.
And I'm going to want to hear the bank robber story at the next meetup.