Hi all! Just a brief instructable on this solar phone charger. Made it in a jiffy, with some random parts lying around on my desk. First up, the parts list.
High quality 2W 6V solar panel by Voltaic Systems or other panel you wish to use
Adafruit Solar lithium charge controller
5000mAh 3.7V lithium polymer battery
DC to DC voltage regulator, 5V 1A from eBay
3.7V single cell lithium protection board from eBay
small plastic rocker switch
several JST 2pin connectors or similar
5mm yellow LED
100 ohm resistor
1N5817 or similar diode
3mm lock nuts
Barrel plug that fits the adafruit charger board
USB type A male plug
For the case, I designed and fabricated it using my Ultimaker 3D printer. I think the case is quite compact and the whole thing looks store bought (neglecting the standard switches and LEDs).
For the first step, I shall give you an overview of the solar charger. Most of the reasons why I did what are shown in the picture. Some of the cons of this charger are:
-It lacks a full charge indicator. I was too lazy to add one.
-No thermistor to monitor battery temperature. I am relying on the bubble wrap to insulate the battery from heat. You can add a thermistor to adafruit's solar charger board to better protect the battery from blowing up.
-The eBay parts are probably unreliable. the over discharge protection from the lithium protection board is most likely insufficient to keep the battery healthy if you drain it completely. The DC step up regulator is also running quite hot and therefore inefficient.
- The real output of the solar panel is about 1.4W at best, as demonstrated by Voltaic Systems themselves in one of their blog posts. On a sunny day, ideally, the battery will charge from 0-100% in 13 hours. On a cloudy day.., the battery will charge from 0-100% in... never. Imagine how long it would take an altoids solar charger(commonly posted in instructables) using a 1W panel to fill a decently sized battery(~2000mAh) completely.
Its not really practical to rely on this gadget to charge in the sun, but it was a great little project to test my skills at integrating the different parts together. Do notice that I have taken into account the importance of mounting the hardware properly within the case. Whenever I had the option to use fasteners, i use them.. if not, hot glue is the best alternative. I have also designed walls within the case to isolate the parts to prevent shorting.
In case you haven't noticed, the solar panel screws into the wall of the case, and the wall of the case is fastened to the base which holds the electronics.
Next up, the wiring.