In this Instructable I will guide you through the process of creating your own solar panel phone charger that is capable of charging your phone should you find yourself out of battery. This charger is perfect for go kits and emergencies and will allow you to tap into some of the (practically) limitless power of the sun!
I believe in teaching while explaining, so you will find me explain things like buck converts in this Instructable. If you're not interested in learning about the details and simply want to make the solar panel phone charger skip the sections delineated by asterisks. Like this *-------*.
Ok, lets get started!
Step 1: Watch the Video
Watch this video to see the build process and to see a demonstration of the final product.
Step 2: Assemble the Supplies
For this project you will need the following supplies:
(shortened links are NOT affiliate links)
1 5w Solar Panel Buy: http://goo.gl/zvYnDp (Exact panel I got has been out of stock for ~a year, this will be a suitable replacement.)
1 DC/DC Buck Converter Buy: http://goo.gl/Z672Tz
Some Perfboard/Protoboard Buy: http://goo.gl/3Yc1kt
2 47k ohm Resistors Buy: http://goo.gl/rmqCgw
2 51k ohm Resistors Buy: http://goo.gl/rmqCgw
1 220 ohm Resister Buy: http://goo.gl/rmqCgw
1 Green or Red LED (optional)
USB A Port
Heat Shrink Tubing
Spade Connectors (optional)
You will also need the following tools:
Wire Strippers or Wire Cutters
Step 3: Solder Wires to the DC/DC Converter
*Let me explain the purpose of the DC/DC converter. A DC/DC buck converter like the one we will be using takes a high(er) voltage and lowers it to a lower voltage. We need this because our solar panel puts out 12-18v and we need to lower it to 5.2v to charge the phone. If we directly connected the solar panel to the phone we would more than likely cause damage to the phone. There are other methods of lowering voltage, including linear voltage regulators, but they become increasingly inefficient as the difference between input and output voltage increases.*
Therefore, we need to make it so that we can connect things to the DC/DC converter. Get 4 wires and solder them to the four corner pads, making sure that you leave them long enough to connect to other things.
Step 4: Build and Test the Circuit on a Breadboard
*This circuit is designed to fool Apple iPhones into thinking that they are connected to a genuine Apple charger. Apple iPhones require a 2v bias on their D+ and D- pins. These are the two center pins on the USB plug. If you have an Android phone, you technically can skip this step. This will, however, render the charger useless for iPhones and by adding it you increase compatibility of your charger.
If you have an Android and don't care about supporting iPhone charging you can directly connect the output of the DC/DC converter to the USB connector. Be sure to check and make sure the polarity is correct though.*
Follow the schematic that I have provided above and build the circuit on a breadboard for testing. The circuit is fairly simple so you hopefully won't have any issues. One you have built the circuit, hook the input of the DC/DC converter to a test power supply and set the voltage between 10v and 18v. Move on to the next step to calibrate the DC/DC Converter.
Step 5: Set the DC/DC Converter's Output
To calibrate the DC/DC converter, hook the input leads of the converter to your power supply. Set the voltage between 10 and 18v and turn on the power supply. The blue onboard LED should illuminate. Grab your multimeter and a common screwdriver and turn the brass screw on the blue trim potentiometer until the output reads 5.2v!The picture shows 5.011v and after extensive testing, I have found that to be too low a voltage to get the phone to charge. The small apple cube charger charges at 5.2v as well so it is perfectly safe.
After you have fixed the output to 5.2v, check with your multimeter the voltage between the center of the resistor dividers. In the schematic, that is the junction between R4 and R5 to ground, and the junction between R3 and R6 to ground. You should read ~2.0v. If not, reverse the order of the resistors.
At this point I decided to conserve power and remove the small SMD blue LED. I just used my soldering iron, heated the pads and pushed it off.
Step 6: Build the USB Board
Snap a piece of perfboard off of the sheet that is the width of the USB port you are using. Make sure to keep it longer then the USB port so that you will have room to add the resistors.
For simplicities sake, I opted with through hole resistors. This will make it easier for other people to emulate the project. You can, however, if you (like me) believe that surface mount is the way to go, replace the through hole resistors with surface mount variants.
Follow the schematic and don't forget to sand down the rough edges of the perfboard. You should have already prototyped the circuit on a breadboard so it will be a piece of cake to transfer it all to the perfboard.
In the event that you do not have a breadboard or decided to skip that step you can go right to the perfboard. Keep in mind that you have to follow the schematic exactly so you don't make any mistakes and have to correct them later.
Step 7: Add an LED Indicator (optional)
This step is optional, but if you want a way to see when the DC/DC converter is active and providing a 5v output to the phone you can add an indicator LED. Follow the schematic and solder the LED in being sure not to forget the 220 ohm resister that is needed.
*LED's require current limiting. If you were to directly connect an LED to a voltage source it would draw excess current and would be consequently destroyed. We use a resistor to limit the maximum current flow to 20 mA. Do not forget it.*
Get a drill and drill a ~5mm hole in the solar panel's aluminum edging. Solder the LED to the circuit board you made earlier. Anode to anode, cathode to cathode. If you accidentally reverse the polarity the LED will not light and it won't be harmed. Push the LED with circuit board through the hole you drilled and make sure it fits. Once the two boards have been connected in the next step we can glue the LED in place.
Step 8: Wire the Converter and USB Board Together
Now it's time to hook the DC/DC converter to the USB board that we made in another step. Wire the converters output to the input of the USB board making sure the polarity is correct. See the attached image and use that to wire the polarity correctly. I added heat shrink tubing between by connections but that is optional.
Step 9: Connect Everything to Solar Panel
This is the part were we finalize everything. Glue the indicator LED into the hole if you chose to do that step. Glue down the DC/DC converter and connect its inputs to the solar panel's outputs making sure to get the polarity correct.
Once the glue dries, plug in your USB cable of choice and put the panel out into the light and you're golden. If for some reason you don't get indicator LED to light see the next section on troubleshooting.
Step 10: Testing and Troubleshooting
If you put the solar panel in the sun and the phone starts charging, congratulations! You're done!
If not, there are some simple things you can check.
The golden rule of troubleshooting is when in doubt, thou shalt test voltages.
Check to see that the solar panel is outputting voltage. Check the polarity between the panel and the converter. Check the converter output. Are you getting 5.2v? Are the resistors putting 2v on the D+ and D- pins of the USB? Are all of the solder joints solid and shiny? Did you glue the boards to anything metallic? Are any pins shorted? Most importantly, did you follow the schematic exactly?
Hopefully this helps!
Thanks for watching and reading along! Happy making!
- Ben KM4GPL