Solar Powered USB Power Supply and Charger

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.

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)

Comments

[cwleveck]

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]

I'd say anyplace where it will get direct sunlight.

[dewsky61]

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]

Yes it should as long as you supply more than the minimum voltage the 7805 requires which the datasheet states is 7 volts.

[PutzMeyer]

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]

I have not done such an analysis.

[claudiopolis]

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]

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.

[manuka]

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]

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?

[manuka]

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.

[Orngrimm]

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]

Thanks for the pointer to the PT5101, very cool (no pun intended)!

[legless]

Just in case you're not aware, anti-static bags are not an insulating material. They are conductive.

[talk2bruce]

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!!!

[webby0121]

hi, great build thinking of doing this but what voltage and amps or watts dose YOUR solar panel give out?

[talk2bruce]

The solar panel I'm using is 12 volts, 1.75 amps, 21 watts.

[burningsuntech]

This is a very well built and documented projected. Worthy of "Featured" status. It has my vote! Good Luck! :)

[talk2bruce]

Thanks!

[prenato]

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]

That's a really good idea, thanks!

[billgeo]

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]

Good idea, thanks!

[spu3]

Nicely documented!

[manuka]

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.

[JoshuaZimmerman]

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]

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.

[tutdude98]

I have have Samsung s5230 and i can charge it with normal or apple charging cable ,why?