Thursday, June 21, 2012

How to : DIY Solar Backpack with Solar Mobile phone charger and LED Lighting

Solar Backpack with Solar Mobile phone charger
The Finished Solar Backpack!


Last year , i was trekking in the mountains and was surprised by the lack of electricity. Although there was an abundance of sunlight during the day, all lighting there during the evenings/night was with oil lamps which not only smoky but provided very little light. Vowing to return next year better prepared,  i made a solar backpack. It can be also used to power widgets such as the arduino, raspberry pi, etc.  Here are the features:
  • Can charge upto 6 mobile phones at one time!
  • 140 lumen high power led lighting
  • 27wh high capacity battery
  • Modular Design for expansion
DIY solar mobile phone charger

Materials Required:

  • 5W Solar panel for 6v battery
  • Old Bag / Bagpack
  • General Purpose PCB
  • Schottky Diode (1n5189/ SS14 etc)
  • 6v Sealed Lead Acid battery
  • 2 pin Terminal plug
Solar Mobile Phone Charger Circuit:
  •  5v 3A LDO (I used a ucc383. You can use an LDO with a lower current capacity also)
  • Heatsink for the TO-220 package LDO
  • USB Port
Light engine:
  • High Power led (Can be 1w-3w. I used a CREE XM-L as it is the most efficient led  the world) 
  • Heat Sink for LED
  • Lens/Reflector for the LED
  • LED Driver


  • Attach the solar panel to the backpack. You can stitch it, use hot glue, epoxy or any other adhesive as you see fit. I used a synthetic rubber based adhesive called FeviBond.
  • Using a general purpose board, construct the following circuit:
Circuit Diagram for solar mobile phone charger

Circuit Diagram for solar backpack

    • The USB port can be used as a solar mobile phone charger to charge phones, tablets etc.   
    • My PCB looked like this:
    PCB for solar mobile phone charger

    PCB of Solar Backpack

    • To make the light engine, i soldered some wire to the Cree XML led and mounted it on the heat sink.
    • Although the Cree XML can be driven with 3 Amps or current giving a staggering 1000 lumens, i could not find a suitable driver. Hence, i am using a 350ma driver.
    Power led mounted on heatsink
    Led mounted on heatsink
    • Some LED drivers, for use as halogen replacements have a bridge rectifier.If you wish, you can remove the diodes as they cause a voltage drop of about one volt. I removed them as they reduce efficiency
    • Mount the led driver on the other side of the heat sink

    Led driver mounted on a heatsink
    Led Driver mounted on heatsink

    • Attach the reflector or lens to the led. 

    Reflector mounted on a led
    Reflector mounted on the led
    Enjoy your eco-freindly power source! In the picture below, it is a solar mobile phone charger!
    mobile phone being powered by solar panel
    Mobile phone being powered by 100% solar power!

    In the picture below, the Arduino Uno is being powered by the solar backpack, making it a solar powered arduino! You can also use this to power the Raspbery Pi, Teensy etc!

    solar powered arduino
    Solar Powered Arduino


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