Solar Powered USB Charger


Recently I went on a two week backpacking trip and I wanted to make sure my cell-phone and camera had enough battery juice to last for the whole journey.  I could have bought a bunch of extra batterys, but I wanted something renewable.  Luckily for me, the sun outputs  384.6 yotta watts of power!  I decided to harness a small slice of this power with a solar panel that I could use to charge Li-Po batteries or USB chargeable devices.  This project is based on the MCP73871 Battery Charge Management Controller and the design here.

Charging the battery on the mountain pass!


My goals for the charger:

  • Built-in Li-Po battery that could store energy to charge USB devices even when the sun wasn’t out.
  • USB output for charging my camera and cellphone.
  • Intelligent charging to optimize energy from the solar panel.
  • Small and Portable.

Parts List:

  1. 1300 mAh Li-Po Battery
  2. Adafruit Li-Po Solar Charger board
  3. Mintyboost kit
  4. 6V Solar Panel
  5. Altoids Tin

In total everything cost about $80, a bit expensive, but it works well.

Building the Charger:

Using some velcro and careful planning, I was able to cram all the components into a regular Altoids tin.  Since I didn’t really have the tools to mount the components correctly I just used Velcro to stick everything in place.  I also soldered the optional thermistor into place and angled it so that it rested against the battery.  After cutting holes for the USB and solar panel connectors it was done!

Everything fit!


Here is the data I collected for the charger in different lighting conditions:

Max current: 330mA @ 6V.

(more coming soon!)


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