Last year, I made a 3.3W ultra-portable solar pocket charger and I published it in Instructables (link: https://www.instructables.com/id/Solar-Pocket-Charger/). After using of several days I discovered one problem with it.
- In a full sunny day it works great but on a cloudy day or in shade the output voltage cannot reach to 5V and for that, it cannot charge any device.
In today's instructable I will show you how I solved this two problems. I will rewrite the complete instructable with the solution of the problems so that you can make it without reading the previous instructable.
I am calling it pocket charger because it fits easily into a pocket. It is the smallest of the foldable solar chargers and is perfect for powering cell phones, MP3 players, PDAs, and more. You can 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)
- 0.55W, 5.5V Solar Panel (6 pcs) (gearbest.com)
- LiPower - Boost Converter (sparkfun.com)
- Standard USB Connector (female)
- Jumper Wire
- Waterproof Fabric
- Soldering Iron with some solder
- Glue Gun
- Sewing Machine
- 3D Printer
LiPower - Boost Converter: The LiPower board is based on the incredibly versatile TPS61200 boost converter. The board is configured to be used with a LiPo battery, has solder jumper selectable 5V and 3.3V output, and an under voltage protection of 2.6V. However, 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). With such a low input voltage and quiescent current, the board also works well in energy harvesting applications that use low input voltages.
I set the output voltage at 5V. Now the output voltage of the charger is always 5V in full sunny or cloudy weather.
Step 2: 3D Printing of the Panel Base
Most of the small solar panel available in the market have now clip or such thing to connect each other in an easy and flexible way. Same is true for my case. So, I decided to make a 3D printed thin base with some hole for every panel so that I can attach all the panel in a waterproof fabric. I am using fabric because I want to make it foldable. I made the 3D printed base with 6 pairs of holes so that I can easily sew the base to the fabric. After sewing the base to the fabric I used hot glue to attach the panel in the base. I designed the base as 1mm thick to keep it slim. The 3D design file in .STL format is attached below.
Step 3: Making the Fabric Cover
The main job of the fabric is to hold all the panel together and make it flexible to fold like a stack of the panel. I took a 400cm X 200cm waterproof fabric from an old backpack. I folded it once in 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 a gap, width = 2 * base length) as I arranged the panel as 3 X 2 matrix form.
Step 4: Sewing 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
This is most important any tricky step. I made six holes in the top layer of the fabric in every center of the 3D printed base. Then I insert 2 wires jumper inside the fabric through a hole. 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.
After soldering the wires to the solar panel I placed the panel in the base with some hot glue. Then I bring out the wires through middle hole 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 to the Base
After connecting the wire to each solar panel I added some hot glue to the inner sides of the base and then I placed the panel on the base. Then I put slight pressure on the panel and keep it in place for approximately one minute to tightly attach the panel to the base. Don't add to much glue in 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 panel or base.
Step 7: Testing of Connections
After connecting all the panels and attaching to the base cover it is the right time to test it to check either all connections are 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 a Boost Regulator to USB Connector (Solution of Problem)
The output of the solar panel is 5.5V which is moderately safe to directly charge a mobile phone. But the problem arises in a cloudy weather. Because 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 included a 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 now get a stable 5V output for changing even the generated solar voltage is 0.3. So, now it is a perfect solar charger. The charging current is 600mA so first charging is not possible but more than enough for charging a smartphone in 3-4 hours.
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: The Final Product
If you completed all the steps now you have a 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.
I added some photo of my final product.