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

The Finished Solar Backpack!

Introduction

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

Success!

Materials Required:

Backpack:

• 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

Instructions

• 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 backpack

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

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.

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 heatsink

• Attach the reflector or lens to the 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 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