Introduction: Solar Pocket Charger
Hello Friends! Today I will share the recipe of my 3.3W ultra-portable solar mobile charger. It will fit easily into your pocket. It is the smallest of the foldable solar chargers and is perfect for powering cell phones, MP3 players, PDAs, and more.
It is also waterproof and you carry it in your pocket or use it with your backpack and keep all of your electronics charged up while you are on the go.
Step 1: Bill of Materials (BOM)
1. 0.55W, 5.5V Solar Panel (6 pcs) (gearbest.com)
2. LiPower - Boost Converter (sparkfun.com)
3. Standard USB Connector (female)
4. Jumper Wire
5. Waterproof Fabric
1. Soldering Iron
2. Glue Gun
4. Sewing Machine
Step 2: 3D Print the Panel Base
I will attach all the panels (total 6) with a waterproof fabric in a foldable fashion. As the panel has no clip or hole to attach to the fabric I made a 3D printed base with 6 pairs of holes so that I can easily sew the base to the fabric. I will use hot glue to attach the panel in the base. I designed the base as 1mm thick to keep it slim. I attached the designed file (.STL) with this step.
Step 3: Making the Fabric Cover
I took a 400cm X 200cm waterproof fabric from an old backpack. I folded it once at the middle to make it double. Then I sew the surrounding according to the size of the panel (height = 3 * width of the base + 2cm for gap, width = 2 * base length) as I arranged the panel as 3 X 2 matrix form.
Step 4: Attaching the Base to the Fabric
After making the fabric cover ready I sewed all 3D printed base one by one to the fabric as shown in photos. I did not keep any gap between two bases in each row but keep 1 cm gap in between two rows so that I can easily fold it.
Step 5: Connecting and Placing the Solar Panel
I made a hole to the top layer of the fabric and insert a 2 wires jumper inside the fabric. I soldered one terminal of the wires to one solar panel. I selected two wires of separate color otherwise it will be hard to identify +Ve and -Ve wire connected to the solar panel. I choose green wire for +Ve and white wire for -Ve.
Then I made another hole to the second base and bring out the wires from inside the fabrics to solder another solar panel according to the previous polarity.
Following the same procedure, I soldered all the remaining solar panels. Keep in mind that all the panel must be connected in parallel. Because we want to increase the current maintaining the same voltage of each solar panel because 5.5 V is enough for mobile charging.
Step 6: Fixing the Panel With Base
After connecting the wire to the solar panel I added some hot glue around the inner sides of the base and then I placed the panel into the base. Then I added slight pressure into the panel and keep it for approximately one minute to tightly attach the panel to the base. I repeated the same for all the panels.
I prefer hot glue over any other epoxy because you can easily remove the attached thing if required without damaging the surface.
Step 7: Testing
After connecting all the panels and attaching to the base cover it is the right time to test it to check either all connection is OK or not. To check the panels I used a digital multimeter. First, I observed the voltage of one row with the multimeter. I tested it in very low light because during testing weather was very bad. At that low light (actually with no direct sunlight) I found approximately 5V which proves that the row is working and the connection is ok. Then I tested the second row and found the same result.
After testing I connected two rows in parallel. So, all the panel is now connected in parallel. The voltage will remain same but current will be six times of each separate panel.
Step 8: Connecting Buck Boost Regulator to USB Connector
The output of the solar panel is 5.5V which is moderately safe to directly charge a mobile phone but not recommended. Besides, the output of a solar panel is directly related to solar irradiance and temperature. So for reduced irradiance output can be reduced. To get a stable output from the panels I used LiPower - Buck-Boost Converter from Sparkfun.
The LiPower board is based on the incredibly versatile TPS61200 boost converter. Though the board is configured to be used with a LiPo battery, has solder jumper selectable 5V and 3.3V output (default is 5V), and an under voltage protection of 2.6V this can be easily connected up to a 5.5V source to get stable 5V from the output. Even, the board can also be used as a general purpose buck and boost regulator with an input voltage as low as 0.3V (default UVLO is 2.6V).
- Input voltage 0.3-5.5V
- Output voltage 3.3 or 5V
- 5V @ 600mA max
- 3.3V @ 200mA max
- Undervoltage lockout at 2.6V
- Quiescent current, less than 55uA
So, using this regulator I can get a stable 5V output for changing input voltage from 0.3 to 5.5V and is perfect for our application. The charging current is 600mA so first charging is not possible.
For connecting this regulator to a standard USB connector first note the pinout of the USB connector. Then connect VCC of the regulator to the 5VDC pin of the USB connector. After that, connect GND pin of the regulator to the Ground pin of the USB connector. Be careful about the polarity as the board has no reverse polarity protection.
Step 9: Connecting & Placing Regulator to Solar Panel
In this stage, I will connect the regulator circuit I mentioned earlier to the solar panel. The connection is very simple. Just solder the positive (+Ve) wire from the panel to the +Ve input pad of the regulator. Then connect the ground wire from the panel to the -Ve input pad of the regulator.
So, all the connections are now completed. We connected all the solar panel in parallel. Then we connected a buck-boost converter to the panel to get a stable output from any weather condition. We also connected a female USB connector to make the charger universal.
One last thing. We should hide the circuit board and USB connector for good locking and protection. To do so, first I added some hot glue to the circuit board and soldered points. Then I placed the circuit board within the fabric and sewed the connector head with the fabric.
Step 10: Final Product
If you completed all the previous steps accordingly then Congratulation!!!
You successfully made your own Solar Pocket Charger. Now, you can easily carry the charger in your pocket and use it to charge your mobile phone, mp3 or tab.
You can also you it in a backpack and keep all of your electronics charged up while you are on the go.