Lithium Battery Solar USB/ iPhone/ Arduino Charger

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One of the most fun and useful projects on instructables is to create your very own solar USB/ iPhone charger.  They're not overly difficult to make, nor are the parts overly expensive or hard to find.  For the most part they do a rather good job of charging up small gadgets.  Mostly.

The big flaw in the DIY solar charger world are the batteries.  Nearly all the designs on instructables (including all of my designs) use standard NiMh rechargeable batteries.  They're cheap, easy to find, and very safe to use.  The problem is that their capacity and voltage are both low, and the gadgets we keep wanting to charge are getting bigger and better batteries.

For instance an iPhone 4 has a 2,000mAh battery inside of it.  Now that isn't too tough to charge up decently with a well made solar charger using 2 or 4 AA batteries.  On the other hand an iPad 2 has a 6,000mAh battery pack on it.  Not so easy to charge up.

The solution for these problems is to ditch NiMh batteries and turn to Lithium batteries.  

In this guide I will show you how to make your very own Lithium battery charger.  One that is cheap to make, easy to build, and most importantly safe to use.

(Oh and help me win the Instructables Green Tech Contest by voting for this project!  An iPad would be great for my classroom!  Even better, I'll build a massive Lithium powered charger to run the iPad.  It'll be 100% green in my classroom.)

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Cats Science Club made it!23 days ago

Joshua does an amazing job explaining everything he does. Thanks to him we found a love for instructables. Take a look at what we made with a great instructable showing us how.


taylorjr1 month ago

Thank you for the detailed project. I've zero interest or knowledge of electronics prior to finding this site, now i'm stoked about building this and I have all the pieces to make my first least I think so, we'll see. Thanks again for peaking my interest in something I think I can really use and will benefit me to have.

But please help, Can I use double AA batteries with the lithium charging board, if I use 3 aa batteries i'll be at 4.5V, shouldn't that work? I already own many rechargeable AA's and zero lithium batteries.

My reason in wanting to try this is for the lighting indications. I'll know when fully charged and they wont be over charged, etc.


callega2 months ago

Thanks for this great project! I'm going to try it!

I have two questions:

1. There is a problem if you have connect the USB input and the solar panel at the same time?

2. It's possible to have connected any input source and charging a device at the same time?

Thanks again

steviemontana9 months ago
I followed your project but I am having a problem with the phone battery not charging even with phone off. I wired this as to the specs and double checked....Do I need to put another blocking diode to the USB controller?

By the way, I like this solar charger.
We have used usb circuits that worked find for everything but Apple products. Could it be your usb circuit? Like it was for us. Is the battery on the charger fully charged to start with? Good luck!
"In this guide I'm using a 5.5V 320mA solar cell which is encased in a hard plastic. Any large solar cell will do, but ideally for the Charge Controller you want your solar cell between 5-6V in power."

What if my 6.3V solar cell only has 30mAh. Will that still work?

Anyone with knowledge, feel free to answer.
bobert6105 months ago
The small black component that runs length wise along one side of the lithium charging board popped off and i lost it. Its the one that is directly in line with the negative inputs and reads "322" if i am correct....i bridged over the two spots with solder and it still charged the battery...does it need this component to function properly?
miszcz_tcz7 months ago
Can this circuit charge AA batteries as well? Can add switch that will cut off Lithium charging circuit, and than AA bateeries will be charged directly from solar cell/boosting circuit?
LazerPaul9 months ago
Hi, I recently saw your tutorials on solar usb chargers. They seem pretty straightforward and cool. I'd really like to get into it. I just had a quick question.
Is it a bad idea to not have a battery in the solar charger? Essentially just the solar panel, no case, no batteries, just plug and charger.

I'd be mainly using the charger when I go camping.

Thanks for the help!
Schmidty1610 months ago
How much is this if i bought everything from scratch
Schmidty1610 months ago
How much is this if i bought everything from scratch
libelluleft10 months ago
Hi and thank you for this great tutorial, being a newbie in the electrical world I truly appreciate this. I have a few questions:
1) Can i make this charger for anything else than an iphone i.e. a cheap cellphone which I use only for texting? (can i use the same materials)
2) I bought the "single USB boost + controller " from your website instead of the 2 of them separate and i was wondering How i should solder the panel mount and lithium battery since there seem to be only 2 soldering hole on the board.
3)finally, how efficient do you think this charger would be if im using a 6v/ 50 mA solar and a 3.7V/110mAh (tiny) lithium battery. (i.e. How long would it take to charge the phone,and how long would it the charge last me for.)
Im sorry for such a long question, but i would really appreciate your help. THANK YOU AGAIN :)
wuttheheeck11 months ago
built one very similar. using a 4000ma battery. experiencing phone battery draining when plugged in, even when phone is off. what type of blocking diode should i use that has the least resistance
wuttheheeck11 months ago
thanks for the tutorial. I do have several questions. I appreciate any knowledge provided!

I made my charger very similar to this, Im using a 4000ma 14.8wh LIPO
I am using 2 6v 250ma and one 5.5v 320ma solar cells. Can i wire these in parallel to get an ending amperage of 820ma? I know the voltages don't exactly match up, but its close.

my real issue is that my charging circuit wont add power to my phone (android rezound) . I have tried turning it off when i charge and letting it sit for a long time. The charge light on the charge controller and my phone light up acknowledging that it is charging but when i check my phone's battery is lower than when i started. I am using a 1n4001 diode on both the solar input and the usb output to prevent back charging. am i doing this wrong?

i have been charging the lipo from micro usb
ill attach photos for help.
NightLord1 year ago
Could we replace charge controller with simple voltage regulator set to upper charging voltage 4.2V, which would prevent current flow in battery after it is fully charged?
Or is that approach simply too naive? :)
Seafarer1 year ago
I have a 2.1mm female plug. If I solder it with negative to the left and pos in the middle it wont work (negative voltage on the multimeter). Switching sides gives me a positive voltage (normal) on the multimeter and it works...
Seafarer1 year ago
Newb question - I have a 8V 310ma panel, is it ok to hook it up to this charge controller - It says 5v input charge... Thx!
Eristeel1 year ago
or ideal size of battery for an altoids tins*?
Eristeel1 year ago
Is the tin box used in this project the same size as an altoids tin?
also what size is the lithium battery..well what would be the most appropriate size?
MyTopFan1 year ago
Does this possibly work with the iPhone 5?
JoshuaZimmerman (author)  MyTopFan1 year ago
As long as you have the proper cable it won't be a problem.
iPhone 5 cables have a chip inside the cable so you cant charge it without a their own charger *yet* there been some that sells Lightning cable but there is a chance that they are pirate copy and can do more damages to the phone
If i was to connect a USB expansion plug (so that i could connect more than one device), would it charge more than one? Our phone batteries are only 1100mAh and i doubt the mp3 player we use would be very big...
JoshuaZimmerman (author)  Boredandlazy1 year ago
I don't see why not.
Building a couple of these out of your kits... Was wondering, particularly regarding your above comments, do you ever have trouble with these at airports? I was thinking a large sticker labeling it as an IED (improvised electronic device) might be counter-productive....
Nope. I've taken them through a couple, and I've never had anyone email me with issues.
Eilermoon1 year ago
How could I make my Altoid charger more powerful? It works, and i have a bigger solar panel along with a nice big battery but it still charges whatever i plug into it extremely slow to the point where it barely charges at all.
JoshuaZimmerman (author)  Eilermoon1 year ago
Well the output of the USB circuit is around 500mA. The best way to get this out of your charger is to go Lithium.

The problem could be that your gadget is using up more power than what is being put into it. If you're using GPS, listening to music, and have the screen on full brightness you're using up a lot of power really quickly.
Just wondering because I can't seem to find this directly answered anywhere. Is it ok to be charging up your batteries via usb or solar while using them to power whatever you have plugged into them?
Nothing bad will happen if you do both at the same time. It's not going to harm the battery.

Your'e just sucking power away before it even hits the battery.
Does it have to be lithium polymer? I don't want to risk having my batteries crap out on me and everything I've read says if you let them die completely, they're done.
Lithium Ion would work fine as well.
I used a 2000mah 14500 lio on battery. I checked before using it and it was at about 3.9v.
I had everything wired correctly, so I tested it out and it said my phone was fully charged when it really wasn't.
I checked the voltage again and it had dropped to something like 1.7v. I tried a new battery and the same thing happened- fine at first but once it's used, the voltage dropped.
What could have caused this? Thanks.
Lithium batteries have built in circuit that prevent over or under charging, so you shouldn't have any issues.
azanutta1 year ago
i'm interested in this too! i am wondering what happens if i charge (with solar) and discharge (phone charging) the LiPo battery simultaneously.
lizzyyang1 year ago
Okay thankyou for responding! So is there any numerical quantifiable data of the input the battery has in charging an iphone?
äbädrän1 year ago
can this solar charge charge my samsung s3???
please reply to me
my s3 battery is 3.8v 2100 mAh
Just wondering, but could these 2000 mAh Li batteries be run in parallel with this setup, similar to the ones sold at Sparkfun ( Or, would that not be compatible with some part of this circuit?
I am thinking of buying Charge Controller Board from but can I use solder points and the mini USB to charge the battery. I would like to connect solar in one of them and dynamo onto other one to charge the battery.
244 Jake1 year ago
Will this project handle the 2 amps that IPad needs to charge? The other weird issue of 5.1 Volts or something. A regular iPhone changer will not charge a iPad.!


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