20 Minutes USB Solar Charger!




I was leaving for my grandfathers ranch this weekend and at the last moment I realize I need something to charge my phone. With only some components I have in my house the idea of a solar charger came to me, and it works!!! :D

The materials you will need:

-A 6V solar cell, you can use a 12v solar cell also.(I use two 6v solar cells to get more current)

- Voltage regulator 7805

-1 female usb connector, or female to female usb adapter

-1 1n4007 diode

-two electrolitic capacitors 10nF 16V

-1 ceramic capacitor 22pF (optional)


-Solder iron and solder

-wire strippers

For the spanish version please enter to my site: http://bioespin.com/cargador-solar-usb-en-20-minut...

Step 1: Pinout, Understanding Connections

First we have to understand how everyting is connected, and what is the function of every pin in every component.

The pinout of the 7805 is in a image here. The first pin counting prom left to right is the voltage In. In here you can connect every voltage source from 6V (7V in some) to 12V to assure you have 5V in the Vout pin. The second pin is the ground, and the third pin is the one that is always 5 Volts.

You just have to connect the solar cell to the Vin and the ground to the ground.

The pinout for the usb is also really simple. If you look it whit the copper looking up and counting from right to left, the first pin is 5 Volts, and the 4th pin is ground. I will upload a image to you to see it clearer.

Step 2: Schematics

to make sure I don't overcharge the battery of my phone I use a voltage regulator (7805). this make sure the voltage I have to charge the battery is always 5 volts. Then I connect the solar cell to the regulator in and the usb adapter to the regulator voltage out. To get a even voltage in all time I add the electrolitic capacitors 100uF 16V, and that it really.

Step 3: Ready to Go

Just connect everything like the schematic and you are ready to go.

If you like this project or want to look at this in spanish, please enter to my web page to see more projects like this. :D




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    13 Discussions


    3 years ago

    I'm running into an issue when I tried to build this. I'm using a 9v solar panel. As soon as I connect the ground from the lm7805 to the ground of the circuit, my multimeter reads 0 volts. I even replaced the lm7805 thinking something was wrong with it. I think I'm not understanding something simple, but I don't know what it is. I'd appreciate some insight into this issue I'm having.

    One possibility that comes to mind is if the current from the solar panel is not high enough, then it runs into some issue with the lm7805. Is that even a possibility?

    this will never work if you are using two 6vdc solar cells connected in parallel due to fact that the LM7805 has a dropout voltage of 2vdc. You also have a diode connected which has a dropout voltage of about 0.5vdc. Which mean for the LM7805 operate, it input must be no less than 7.5vdc.

    1 reply

    Reply 3 years ago

    I was wondering this as well. @Jochefor, does the charger work as expected? I'm trying to use this design without the capacitor and using a Schottky diode instead for the lower voltage drop out. Would be curious to hear if yours work.


    4 years ago

    What will be the current output ? Should I consider open circuit voltage of panel or the regulator output voltage in current output calculation ?


    5 years ago on Introduction

    A couple of quick questions:

    Why do you need the capacitors?

    Do I need 2 capacitors, or will one work just as well?

    What about the voltage and amps -- does it matter how much the solar panels are collecting and pushing into the USB part?

    2 replies

    Reply 5 years ago on Introduction

    Why do you need the capacitors?
    Capacitor work like the a storage. The solar panels are going to generate power but you need something that holds that power and store it. In that way if your solar panels don't generate electricity in a moment( because sunlight goes away or a cloud is passing by) the capacitor can give all the power they have stored in them. In that way your cellphone is not going to think that the power is going on an off quickly.

    Do I need 2 capacitors, or will one work just as well?
    You need one ceramic capacitor and one electrolytic, because the ceramic capacitor works well with high frequencies filtering and the electrolytic works with low frequencies. You can place only the electrolytic capacitor, but I recommend you get the ceramic too.

    What about the voltage and amps -- does it matter how much the solar panels are collecting and pushing into the USB part?
    The 7805 work in a range between 7V and 12V. If your solar panels are between this range the circuit is going to be ok. Just make sure all your capacitors before the 7805 are 16V or higher. The rule with capacitor is: "more than the voltage you are using multriply by 2.3 and you are safe". :)

    Talking about amps, if your solar panels can produce 1amp and you need 0.20 amps your are good. But if you need 1amp and you can produce 0.20amp the charger is not going to work. It doesn't matter if you can produce more amps that you need because your charger is going to get just the amps he need and nothing more, but if your solar cells can't produce the current necessary to charge the voltage will drop and it's not going to work at all.

    I hope I help :), if you need more help or have doubts please ask.

    diode helps prevent battery drain, if you leave it plugged in when thee's not enough sun to produce power.
    Nothing says disappointment to find your phone battery "lighting up" your solar panel.

    If you always remember to unplug, and only use it in good strong lighting, then yes. you can leave the diode out. For the rest of us, that extra 5 cents is well worth the time and trouble.

    phones don't put power out over there usb port only recive the charging circuit built into the phone wont allow back feed

    may have been true at one time, but the galaxy s3, note 2, and galaxy s4 all CAN put out power over their usb port. It's part of the USB-on-the-go specifications for those phones. And since those phones are very popular, and the s4 currently has some battery issues for some people ... :-)
    Just saying.

    90% of people would probably be just fine without the diode, but the solar energy is "free" so why fret. just add the safety like Jochefor says to.