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Solar Cell Booster Pack


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This is my first attempt at a booster pack design.  The design is inspired by the TI/Element 14 Fuel Tank Booster Pack.  I wanted to improve on a few of the aspects of the Fuel Tank as well as add a few features to it.

 

Fuel Tank Cons:

  • Non-standard pinout.  The I2C pins are not brought out to 9 and 10 as they should be on the BP standard
  • Not solar friendly.  The charging IC on the Fuel Tank supports solar charging, but it's not easy to add it.
  • Battery is in parallel with load.  The battery is always powering the LP, even when charging current is available
  • Not low-power friendly.  The regulators fitted on the board have a PowerSave mode, but it required soldering a resistor to enable it.  Also, LEDs cannot be disabled
  • Fuel Gauge is not configurable for a different sized battery.  The FG IC used requires a new "golden file" to uploaded to the IC to change any LiPo cell parameters (design capacity, etc).

Solar Cell Changes:

  • Change I2C pins to comply to BP standard
  • Add DC jack to make connecting solar panel easier
  • Change charging circuit (credit to Adafruit for the charging circuit http://www.adafruit.com/product/390)
  • Add breakouts for the PS and EN pins for both regulators, add jumpers on all LEDs, add the ability reroute I2C (more on that below)
  • Change FG IC to a more configurable one.  BQ27425-G1 is used which uses a generic LiPo impedance curve, and has a configurable design capacity

Solar Cell Cons:

  • Use of QFN and BGA IC packages makes it impossible to hand solder
  • More to come...

 

I use a CC3200 launchpad and one of my biggest annoyances is that the green and yellow led are shared with the I2C pins.  I wanted to add the ability to move those signals on the booster pack to an alternate location.  This way, no power needlessly wasted on these LED's when not in use.  I also added an INA219 high side I2C current monitor which would give similar abilities to measure current and voltage of the solar panel as the FG IC gives on the battery side.

 

I wanted to get feedback from the community on the design as well as make it open source so I have placed my entire KiCad project on GitHub.  At the moment, I don't really have any plans to manufacture them or sell them.  This was essentially a personal project for me, but I wanted to share.  I look forward to hearing thoughts on the design!

 

Schematic:

SolarCellBoosterPackSchematic.pdf

 

GitHub repo:  https://github.com/svcguy/SolarCellBoosterPackHW (The docs folder contains pdfs of the schematics if you're not a KiCad user)

3D renderings:

post-39193-0-44410200-1421207241_thumb.jpg

post-39193-0-31127000-1421207251_thumb.jpg

 

Thanks,

Andy

 

 

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