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Picture of Solar Powered USB Power Supply and Charger
0 - 2 - Solar Panel.JPG
I've always wanted to go green and use solar energy to charge my power hungry devices. I recently found and purchased a new United Solar US-21 12 Volt 21 Watt solar panel at a garage sale for $20.  What a deal!  So, I decided to construct the necessary components so I can use it to power and charge my gadgets.  This instructables shows how to construct a solar powered USB power supply and charger that can used with a solar panel or large solar cell.

I made it at TechShop.
 
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Step 1: Parts

The following parts are needed to construct for the Solar Powered USB Power Converter (pictures in this step).  Parts can be obtained at Jameco, Digikey, Radio Shack, etc.
  • 1 LM7805 5 volt 2.2 amp voltage regulator (Jameco 786138)
  • 1 Heat sink for LM7805 (Jameco 158051)
  • 1 Heat sink mounting kit for TO-220 heat sinks (Jameco 34121)
  • 1 47 uF 50 volt Electrolytic capacitor (Jameco 31114)
  • 1 100 uF 50 volt Electrolytic capacitor (Jameco 158394)
  • 2 0.1uF 50 volt Ceramic capacitors (Jameco 544921)
  • 1 1N4001 50 volt 1 amp Diode (Jameco 35975)
  • 1 2 volt 20 mA LED with chrome bezel (Jameco 141129)
  • 1 150 ohm 1/4 watt Resistor
  • 1 2 position Dual barrier strip (Radio Shack 274-656)
  • 1 Single Pole Single Throw (SPST) Switch (Radio Shack 275-602 or similar).  I had a switch with a red safety cover so I used that - the safety cover is optional but it makes it look really cool!
  • 1 tube Heat sink compound (Radio Shack 276-1372)
  • 1 Plastic case (Velleman G311 or similar) - no smaller than 4.5" x 3.5" x 2.2"
  • 1 Printed circuit board (Adafruit Perma-Proto Quarter-sized Breadboard PCB part # 589)
  • 4 Rubber feet (available at hardware stores - also called rubber bumpers)
  • 2 #6-32 x 1/2" Machine bolts with rounded heads
  • 2 #6-32 Nuts
  • 2 #4-40 x 3/4" Machine bolts with rounded heads
  • 2 #6/6 Nylon washers
  • 2 1/4" #4 Nylon spacers (#6 can also be used)
  • 2 #4-40 Nuts
  • 12" Red wire
  • 12" Black wire
  • Solar Panel or large solar cell
The following parts are needed to construct the USB charging cable (photos of parts are shown in Step 7):
  • 1 USB cable with a male type A connector and a female type A connector
  • Electrical tape
  • Heat shrink tubing (optional)
The following parts are needed to construct the Apple charging adapter (photos of parts are shown in Step 8):
  • 1 USB cable with a male type A connector and a female type A connector
  • 1 Printed circuit board for the Apple charging circuit (Radio Shack 276-159)
  • 1 Small plastic case no smaller than 3 1/8" long, 2" wide, and 1 3/8" deep
  • 1 Small piece of insulating material
  • 6" Thin insulated wire
  • 2 75K ohm 1/4 watt Resistors
  • 2 51K ohm 1/4 watt Resistors
The following parts are needed to construct the test cable used in steps 9, 10, and 11:
  • 1 USB cable with a male type A connector
  • 1 Four position barrier strip (Radio Shack 274-658)
  • 1 Nine volt battery
The following tools are needed:
  • Soldering iron and solder
  • Wire strippers and cutters
  • Small knife
  • Small screwdrivers (Philips head and flat head)
  • Electric drill and assorted sized drill bits
  • Heat gun (optional if heat shrink tubing is used)

Step 2: How It Works

Picture of How It Works
2 - 3 - Schematic.png
2 - 2 - Breadboard.png
The Solar Powered USB Power Supply and Charger consists of a Solar panel, a power converter, a standard USB cable, a USB charging cable, and an Apple Charging Adapter as shown in the first diagram.
  • The Power Converter connects to the Solar Panel and reduces the voltage to a regulated 5 volt output suitable for powering and charging USB devices.  The Power Converter will accept up to 35 volts as input if you use the specified voltage regulator.
  • The standard USB cable connects the Power Converter to the USB device and is used to power the device and for older USB devices it may be used to charge them.
  • The USB Charging cable is a standard USB cable modified to implement the USB charging standard that allows the device to "know" that it can draw enough current to charge the device.  More details on this can be found in Step 7.
  • The Apple Charging Adapter contains a circuit that allows newer Apple devices to "know" that they can draw enough current to charge the device.  More details on this can be found in Step 8.
The schematic for the Power Converter is shown in the second diagram.  It's a simple and standard circuit that uses a voltage regulator to convert the input voltage to a regulated 5 volts.  Note that there is a diode in the circuit (next to the switch) that will protect the circuit if the input power leads from the solar panel are connected incorrectly.

The physical layout and wiring for the circuit is shown in the third diagram.

Step 3: Prepare the Case

Picture of Prepare the Case
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3 - 3 - Prepare the Case.JPG
3 - 4 - Prepare the Case.JPG
3 - 5 - Prepare the Case.JPG
Prepare the case as follows:
  1. Drill two mounting holes for the Adafruit printed circuit board in the bottom of the case as shown in the first photo.
  2. Drill holes for the switch and the LED in the top of the case as shown in the second photo.
  3. Drill a hole in the side of the side of the case for the USB cable as shown in the third photo.
  4. Drill the four holes in the other side of the case as shown in the fourth photo. The upper holes are for the barrier strip.  The lower holes are for the power wires coming from the circuit board.
  5. Mount the barrier strip as shown in the fifth photo using the #6-32 machine screws and nuts.

Step 4: Build the Circuit

Picture of Build the Circuit
2 - 2- Prepare the Heat Shrink.JPG
2 - 3 - Prepare the Heat Shrink.JPG
2 - 4 - Prepare the Heat Shrink.JPG
2 - 5 - Construct the Circuit.JPG
The first diagram on this step shows the circuit wiring on a breadboard. I usually breadboard all my circuits before soldering them to a printed circuit board so I can verify the circuit works properly and that none of the components are defective.  If you use the Adafruit Perma-Proto Breadboard printed circuit board, you can use the breadboard diagram as a guide on how to place and solder all the components.
  1. Attach the heat sink to the voltage regulator as shown in the second, third, and fourth photos.  Use a dab of heat sink compound between the voltage regulator and the heat sink.
  2. Solder the components to the board using the breadboard diagram as a guide as shown in the fifth diagram.

Step 5: Assemble the External Components

Picture of Assemble the External Components
5 - 2 - Solder the LED.JPG
5 - 3 - Solder the LED.JPG
5 - 4 - Prepare the USB Cable.JPG
Prepare the external components as follows:
  1. Solder the wires to the switch and to the circuit board as shown in first photo.
  2. Solder wires to the LED as shown in the second photo.
  3. Insulate the exposed connections using heat shrink tubing or electrical tape as shown in the third photo.
  4. Cut a female USB type A connector and strip the ends off the power leads as shown in the fourth photo.  Just cut off the data lines (green and white wires).  They will not be used.

Step 6: Final Assembly

Complete the assembly as follows:
  1. Attach the LED to the top of the case as shown in the first and second photos.
  2. Insert the USB cable through the hole in the side of the case and solder the switch wires, the LED wires, and the USB wires as shown in the third and fourth photos.  Use the breadboard diagram as a guide.
  3. Slide the power wires through the holes below the barrier strip on the side of the case and mount the circuit board in the case using the #4-40 machine screws, nuts, nylon spacers, and washers as shown in the fifth and sixth photos.
  4. Gently push all the wires into the case, close the case, and screw it shut as shown in the seventh and eighth photos.
  5. Strip the power wires and attach them to the barrier strip screws and shown in the ninth and tenth photos.
  6. Attach the rubber feet to the bottom of the case as shown in the last photo.
Voila! The Power Converter is now complete!

Step 7: Assemble USB Charging Cable

According to the USB specifications, the technique a USB charger should use to indicate to a device that it can draw full current for charging is by shorting (connecting) the two data lines together.  This works for most devices except Apple devices which are covered in the next step.  The power converter constructed in the previous steps can provide power to a USB device but the data lines are left unconnected so newer devices will not charge with just the power converter and a standard USB cable.  This step describes how to modify a USB cable for charging.

The following parts are needed for this step:
  • USB cable with a male type A connector and a female type A connector (shown in the first photo).
  • Electrical tape.
  • Heat shrink tubing (optional)
Follow these steps to construct the charging cable:
  1. Cut the cable in half.  Optionally slide a piece of heat shrink tubing down one end of the cable.  See the second diagram.
  2. Using a knife, carefully remove the outer shielding from the USB cables.  Using wire strippers, strip the wires as shown in the third diagram.
  3. Connect and solder the various leads together as shown in the fourth diagram.  Note that the data lines are connected on USB cable with the female connector.
  4. Insulate the exposed connections with electrical tape as shown in the fifth diagram.
  5. Wrap electrical tape over the wires or use the heat shrink tubing to hold the individual wires together as shown in the sixth diagram.
Voila! The finished cable is shown in the last two photos.

Step 8: Assemble Apple Charging Adapter

Apple devices require that a specific voltage be present on the two data lines in order for the device to "know" that it can draw sufficient current on the power leads in order to charge the device.  An excellent write-up on the mysteries of Apple device charging can be found at http://www.ladyada.net/make/mintyboost/icharge.html.  The circuit used in this step comes from that write-up.

For this step the following parts are required:
  • USB cable with a male type A connector and a female type A connector as shown in the first photo.
  • Printed circuit board for the Apple charging circuit.  I used the Radio Shack PC board 276-159 as shown in the second photo.  Only one half of the board is used in this project.
  • A small plastic case to hold the circuit board as shown in the third and fourth photos. The case I used was 3 1/8" long, 2" wide, and 1 3/8" deep.  I would not recommend using anything smaller as this was a tight squeeze to get everything inside the case.
  • A small piece of insulating material - I used a piece of stiff plastic.  See fifth photo.  You only need this if your case has a metal bottom.
  • 6" thin insulated wire
  • 2 75K ohm 1/4 watt resistors
  • 2 51K ohm 1/4 watt resistors
To construct the Apple charging adapter:
  1. Drill a hole in each end of the case for the USB cables as shown in the sixth photo.
  2. Cut the USB cable in half (if it's a long cable you can cut the leads to a shorter length but I'd recommend not shorter than 5 inches. See the seventh photo.
  3. Using a knife, carefully remove the outer shielding from the USB cables and strip the wires.
  4. Using the schematic (eighth diagram) as a guide, solder the circuit on the PCB as shown in the ninth photo.  Important: pull the ends of the USB cables through the holes in the case before soldering the USB wires to the circuit board.
  5. Push the circuit board and USB wires down into the case as shown in the tenth photo.
  6. Place the non-conductive material on top of the circuit board as shown in the eleventh photo.
  7. Screw the cover onto the case and attach the rubber feet as shown in the twelfth photo.
Voila! The Apple charging adapter is now complete as shown in the last photo!

Step 9: Test the Power Converter

Before using the USB power converter, it's important to test it to make sure everything is connected properly so you will not damage your USB device. A simple test cable can be constructed to make testing easy.  This cable will come in handy for your future USB projects.

To construct the test cable, you will need a four position barrier strip (Radio Shack 274-658) and a USB cable with a male type A connector. 
  1. Cut the USB cable, remove the outer layer and shielding.
  2. Connect the wires to the barrier strip as shown in the first two photos.  I used some heat shrink tubing to protect the wires; electrical tape would also work.
Testing the USB Power Converter:
  1. Attach a power source to the power converter using the barrier strip on the side of the case.  For testing purposes, I used a 9 volt battery.
  2. Connect the USB test cable to the USB female connector on the power converter as shown in the third diagram.
  3. Turn the power switch on the power converter to the "On" position.
  4. Using a multimeter, set it to test for DC volts and touch the test probes to the positive (red) and ground (black) leads as shown in the fourth photo.  The voltage should read very close to 5 volts as shown in the fifth photo.
  5. Turn off the power using the switch on the case and verify that no voltage is present - the meter should read zero.
  6. Set the multimeter to measure resistance and touch the test probes to the two data lines (white and green) as shown in the sixth photo.  The meter should indicate that the resistance is infinite (i.e. not connected) as shown in the seventh photo.

Step 10: Test the Charging Cable

Picture of Test the Charging Cable
10 - 2 - Testing the Charging Cable.JPG
10 - 3 - Testing the Charging Cable.JPG
10 - 4 - Verify Data Lines Connected.JPG
10 - 5 - Verify Data Lines Connected.JPG
Now that the power converter is working correctly, it's time to test the charging cable.
  1. Connect the charging cable to the power converter and the test cable to the charging cable as shown in the first diagram.
  2. Turn the power switch on the power converter to the "On" position.
  3. Using a multimeter, set it to test for DC volts and touch the test probes to the positive (red) and ground (black) leads as shown in the second photo.  The voltage should read very close to 5 volts as shown in the third photo.
  4. Turn off the power using the switch on the case and verify that no voltage is present - the meter should read zero.
  5. Set the multimeter to measure resistance and touch the test probes to the two data lines (white and green) as shown in the fourth photo.  The meter should indicate that the resistance as zero ohms (i.e. connected) as shown in the fifth photo.

Step 11: Test the Apple Charger

Picture of Test the Apple Charger
11 - 2 - Testing the Apple Charger.JPG
11 - 3 - Testing the Apple Charger.JPG
11 - 4 - Testing the Apple Charger.JPG
The last testing step is to verify that the Apple charging adapter is working properly.
  1. Connect the Apple charging adapter to the power converter and the test cable to the Apple charging adapter as shown in the first diagram.
  2. Test the power lines (red and black) as you did in the previous two steps to verify that 5 volts are present when the power converter is on and no voltage is present when the power converter is off.
  3. Turn the power switch on the power converter to the "On" position.
  4. Using a multimeter, set it to test for DC volts and touch the test probes to the white data lead and ground (black) lead as shown in the second photo.  The voltage should read very close to 2 volts as shown in the third photo.
  5. Touch the test probes to the green data lead and ground (black) lead as shown in the fourth photo.  The voltage should also read very close to 2 volts.
  6. Turn off the power using the switch on the case and repeat the last two steps and verify that no voltage is present - the meter should read zero.
Voila! The project is now complete. 

One last warning: it is very important to thoroughly test the the power converter, the charging cable, and Apple charging adapter before attempting to power or charge your devices or you may damage them.  Also, while I have tested these with several devices (an Apple iPod Touch, an Apple Nano, and an HTC Incredible 2) to the best of my ability, I can not take responsibility for any damage this may cause to your device.

Step 12: Improved Version

Picture of Improved Version
12 - 2 - Improved Version Schematic.png
After finishing and using the Solar USB Power Supply and Charger, I had some ideas to make it better.  An improved version of the project is shown in the first photo.

There are two improvements:
  1. Rather than require a special cable for charging, a switch has been added to the circuit that, when thrown, will connect the data lines as shown in the circuit schematic (2nd image). 
  2. The LED has been removed from circuit because it is very difficult to see the illuminated LED in bright sunshine.
1337holiday11 months ago

Can this setup be used to power an arduino? I'm trying power an arduino from a remote location so solar is the only option. Thanks!

Charly_ZA1 year ago

Hey, I want to do my own take on this project for a science fair. I'd appreciate your help :)

http://www.instructables.com/community/Help-with-a-school-project-on-solar-power/

cwleveck2 years ago
Have you thought of using a switching regulator? I was reading some comments recently, like REALLY recently that ALL seemed to point to using something called a switching regulator because its supposed to be more efficient and cooler or something.....
HA just kidding. I don't pretend to know too much about it except I've been using a switching regulator made by Demension Engineering. I won't post a link because I think thats some kind of a no no or spam or something? Anyway they fit in the same space as a 7805, three pins and all. You should check them out. I use them in everything....
talk2bruce (author)  JLucas20122 years ago
I'd say anyplace where it will get direct sunlight.
dewsky612 years ago
Does this unit need the 12V panel? Would it work with lower voltages as well? I would like to build this (and add a couple of AA Batteries to it) to make a small portable charger for my cell phone and tablet.
talk2bruce (author)  dewsky612 years ago
Yes it should as long as you supply more than the minimum voltage the 7805 requires which the datasheet states is 7 volts.
PutzMeyer2 years ago
The documentation was well thought out and informative. Have you done any analysis to determine what the cost savings would be, or the length of pay-off time after costing all the parts?
talk2bruce (author)  PutzMeyer2 years ago
I have not done such an analysis.
Hi there and congratulations for winning in the "Off the grid" contest. I'm happy too for that as I just found out about it. Your instructable is very good for people that are not familiar with electronic circuits.

Just to add my two cents here, that 7805 linear regulator is not very efficient. It runs hot ant takes a lot of power. You have enough power from the solar panel to get much more than its 1A max rating (by the way, it's 1 Amp. max, not 2.2). A switching regulator like a LM2576 HVT would put out up to 3A of power in a much more efficient way and without overheating. This way the charging stage will be much shorter. The circuit to make is also very simple.

For people completely unfamiliar with electronics I guess a 5V/2Amps USB car charger directly connected to a 10-15W solar panel will do the same thing. It's important that it has more than 1A output as those are based on the same LM7805 regulator. The 2A versions are switching regulators, much more efficient.
talk2bruce (author)  claudiopolis2 years ago
Thanks for the feedback. A couple of other folks have made similar comments. I agree that the 7805 is not that efficient, so in the next couple of weeks, I'll be publishing an instructable that shows how to do this project with a Texas Instruments 78HT305HC-ND switching regulator. Re: the max rating for the regulator, the 7805 used in this project is rated at a peak current rating of 2.2 amps according to the supplier (Jameco) and the component's data sheet.
manuka2 years ago
OK!    SLA (Sealed Lead Acid) "Gel Cell "batteries are a globally used for standby work, & -although heavy- they're very reliable & convenient. Their 12V 7Amp hour capacity is near ideal for general after dark work.

They're often available cheaply - or FREE- from security firms who've replaced them in critical areas every year or so. This is well before they normally fail, & most are good for at least another 5 years general usage.

Naturally you have to worry about both OVER  charging/discharging  - simple electronic regulators are available (or can be made) however.

EXTRA: Consider adding a circuit diagram/schematic to the steps! Also perhaps some simple current flow indicator. The latter can be an LED - perhaps in the style of my 3 x AA approach =>   www.instructables.com/id/Single-LED-ammeter-FLED-based/ Stan.
talk2bruce (author)  manuka2 years ago
I really like the idea of using SLA's especially since I have a few handy and there's several places I can get new and used ones locally.

Is the LED on your LED ammeter instructable bright enough to be seen in bright sunlight (right now I have the charger mounted behind the solar panel and it's pretty bright there).

On the suggestion about schematics, I have two schematics (one on step 2 and step 8), are you suggesting that I need to include them in the construction steps?
Talk2bruce: The status LED is really best suited to shaded work which is -ahem- where us humans will probably normally be! . For both weather proofing & tinkering I usually have control electronics indoors, with the raw solar DC brought to them via suitably gauged wire.
Orngrimm2 years ago
For a swithcing-mode converter (90%+ efficiency) you can go for http://www.ti.com/lit/ds/symlink/pt5101.pdf or similar devices. As noted by other posters, 7W will get you Linear regulator very got and destry it maybe
talk2bruce (author)  Orngrimm2 years ago
Thanks for the pointer to the PT5101, very cool (no pun intended)!
legless2 years ago
Just in case you're not aware, anti-static bags are not an insulating material. They are conductive.
talk2bruce (author)  legless2 years ago
I was concerned about that when I was writing the instructable so I measured the material I was using with a ohmmeter and it did not show any conductivity. It may be that the material I had was actually not antistatic or it's very slightly conductive. But you make a good point, so to improve the instructable I removed the reference to anti static bags. I appreciate the comment...thanks!!!
webby01212 years ago
hi, great build thinking of doing this but what voltage and amps or watts dose YOUR solar panel give out?
talk2bruce (author)  webby01212 years ago
The solar panel I'm using is 12 volts, 1.75 amps, 21 watts.
This is a very well built and documented projected. Worthy of "Featured" status. It has my vote! Good Luck! :)
talk2bruce (author)  burningsuntech2 years ago
Thanks!
prenato2 years ago
Hi Bruce,

I second the comments from manuka. Your instructable is very well written and you obviously put a lot of work into the graphics/photos. Noticed you are using a linear regulator (78L05) to go from 12V to 5V. One suggestion for improvement would be to use a switching regulator instead. You can actually reuse it from one of those car phone chargers. Pretty much all I've opened use the MC34063 as a step-down buck converter (and already are configured for 12V to 5V conversion). A linear regulator efficiency is roughly Vo/Vi so only 5/12 = 41.6% in this case. The switching regulator will be more like 80% efficient, so less energy will be wasted as heat. Your 78L05 will get very hot for significant loads. If you draw 1A for example, the device will dissipate P= VI = (12-5) * 1 = 7W...

Paulo
talk2bruce (author)  prenato2 years ago
That's a really good idea, thanks!
billgeo2 years ago
Nice project. (and nice price for the panel)
I have a solar iPhone charger in my future, but it'll be much smaller.

One thing to consider though,
next time think about using a switching regulator module
instead of a linear regulator (like the 7805), because its
such a waste of energy (crucial if using the inefficient solar panel technology)
talk2bruce (author)  billgeo2 years ago
Good idea, thanks!
spu32 years ago
Nicely documented!
manuka2 years ago
Top marks for your VERY lucid Instructable & brilliantly lucid parts list! It's often inconvenient to use the energy as it's gathered, so perhaps look to adding a small rechargeable battery as well (maybe a 12V SLA) ? That way the panel can work away for you all day, allowing use of the stored energy after dark.
Yeah, that was the first thing I thought of as well. Even a cheap lead acid battery (though you gotta love those gel ones) would help things out. You can grab a 12V charge controller for under $20 these days.
talk2bruce (author)  manuka2 years ago
Thanks for the compliments! I work hard to make my instructables easy to understand. You have a good point about storing the energy - that would be a very good improvement to this project.
tutdude982 years ago
I have have Samsung s5230 and i can charge it with normal or apple charging cable ,why?