Solar Usb Charger




This instructable will teach you how to make a device that will charge your usb devices with solar power. This can be very handy on vacation or at school.

This is my first instructable. I am Dutch, so I'm sorry for the crappy grammar^^

I was looking all over the web and I found a lot of people how did make an usb charger with batteries and some people how made a solar usb charger without batteries. But I wanted to make an usb charger with both. So that it can charge itself when lying in the sun and charge my usb devices (mobile phone, Ipod touch) when I want to. I couldn't find anything like it on the web, so I made this instructable so you guys can make one too:)

I forgot to take a lot of pictures during the building process, so I apologize for that too.

Step 1: Materials and Tools

A list of the materials I used to make this usb charger:
- 4x solar garden lanterns (I used the one you can see on the picture)
- 4x rechargeable AA batteries
- a double usb port
- 4x 150k ohm resistor
- 4x 560k ohm resistor
- 1x diode (no LED)
- a little bit of plywood
- a little bit of some kind of strong wood
- some isolation tape
- a little bit of wire
- solder
- some green spray paint
- some white paint
- some hot glue

And here's a list of the tools I used:
- drill
- wood saw
- hacksaw
- soldering iron
- screwdrivers
- pincers
- a really small brush
- sanding paper/sander
- a hot glue gun

Step 2: Taking Apart the Solar Garden Lanterns

When you open up your solar garden lantern, you will probably see a circuit board with at least one LED, one solar panel (probably glued into the plastic case), one switch, two battery connectors and one battery. If you're lucky, this battery is an AA battery. I was not that lucky. I had 4 rechargeable AAA batteries. My circuit will not work with these batteries. The batteries that you will find in there, will always be rechargeable, so if you can't use theme with this project, put them is some kind of other device that uses AAA batteries.
From all this, you will need all 4 solar panel, one switch and all 8 battery connectors. You could also use some wires from here.

Step 3: The Circuit (usb)

First, I do only have a drawing of the resistors soldered to the usb port and a picture of the finished circuit:)

The double usb port has 8 pins. 4 in a row for each usb port. The one to the left is the one through which the electricity will flow to the usb device. Then, from left to right, there's the data- pin, then the data+ and then ground. Maybe yours has no pins, but wires. Than the red one is the 5V, the white one is the data-, the green wire is the data+ and the black wire is ground.

You will need to solder some resistors to the pins/wires to make your usb device recognize the solar usb charger as a charging device. You will need to solder one 150k ohm resistor to the data- pin/wire of port 1, as well as to the data+ pin/wire and also to both data pins/wires of port 2. So you will need 4 150k ohm resistors. Then you need to solder a 560k ohm resistor to both ground pins/wires and both 5V pins/wires. So here you will need 4 560k ohms resistors. Then solder the other sides of all resistors connected to port one together, and do the same with port 2. 
Now you solder 1 wire to both 5V pins/wires an 1 wire to both ground pins/wires. Now you take one switch from one of your solar garden lanterns and solder it to one of the wires. Then you solder the battery connectors including wire from one of your solar garden lanterns onto the switch and onto the other extending wire.

Step 4: Preparing the Solar Panels (part 1)

Probably the solar panels will have some kind of protection sheet on top of it. Make sure these sheets stay there during the building process. 
If you have solar garden lanterns with easy to take out solar panels, you can skip the rest of this step. If you don't, like me, you will have to saw the plastic around the solar panels.
My solar panels looked like you can see on the picture after taking off all loose parts. As you can see there is a peas of blue tape at the end of the red wire of one of the solar panels. Inside this peas of tape is a diode. I will explain that to you in step 6:)

To do so, I used a hacksaw. First I sawed all the plastic parts I didn't need. Then I used sanding paper and a sander to smooth the sides.
After you have sawn the solar panels, they will look like those on the picture. Like this, they are much smaller and much easier to work with.

Step 5: Preparing the Solar Panels (part 2)

Now we only need to glue the solar panels together before soldering. Be sure you glue them in the right way. You need to make sure the side at which a red wire is connected, is attached to a side with a yellow wire. You probably don't have the same colour wires as I do, so to compare, the red wire is the + and the yellow wire is the -. If you have really thin solar panels which can be placed on top of the box (step 7), do not glue the solar panels together.

Step 6: The Circuit (solar)

This circuit is much easier than the first part we made. You will have to make the long wires from the solar panels a little bit shorter. Then you solder three red wires to three yellow wires, so the will be in series and you have one red and one yellow wire left. Only do this if you have thick solar panels, like I have. If you have really thin solar panels which can be placed on top of the box (step 7), it's better to not solder the solar panels yet.
Solder a diode to the + wire, for me that's the red one. Make sure you solder it in the right way. This means you will need to solder it with the grey tip away from the solar panels. This way the electricity can flow from the solar panels to the batteries, but not the other direction.
You can also solder the diode to the other wire, but if you do so, make sure you solder it with the grey tip towards the solar panels.

I already attached the diode to one of the solar panels before I sawed the plastic, because I didn't really thought that one through...

Step 7: The Box

You can begin to make the box. First you'll make the bottom and cover. To do so, you take your peas of plywood and saw 2 rectangles. Both the same size: 10 x 11 cm. The you'll have to make the sides. You take the strong wood and saw 2 pieces of 3,5 cm high, 10 cm long and 1 cm thick. Then you saw 2 pieces of 3,5 cm high, 9 cm long and 1 cm thick. Be sure all sides fit the bottom. You will also need a 'battery holder'. By this I mean a piece of wood inside the box to keep the batteries on place. I made this form the same wood as the sides. This time you need a rectangle sized 2 cm high, 7 cm long and 1 cm thick.
Now the hard part. If you have a fretsaw, this part ain't that hard. I did not have that kind of luxury, so I had to do it the hard way. To saw the hole in one of the sides, you will have to measure the size of your usb ports and switch and saw a hole at the right size. I did this with a normal handsaw by sawing vertical lines through the place of the hole, so the really thin pieces of wood will break. Then when the hole is a little bit to small, you need to use sanding paper to make the hole the right size. 

When you have all pieces at the right size, it's time to smooth them. Just use some sanding paper or a sander. The 'battery holder' you don't have to sand, because these won't be visible then your solar usb charger is finished.
Then you can glue everything on place. First glue the sides to the bottom. Don't yet glue the cover onto the box, nor the circuit into the box! Place the 'battery holder' by measuring the right place with the batteries. Place the batteries against one side of the box and put the 'battery holder' not directly against the batteries, but about 1 cm off them. 

Now your box is finished:)

Step 8: The Cover

First draw a square on top of your cover of exactly the size of your solar panels. Then take out your drill and drill two holes inside this square. Next you use your fretsaw to saw the square. Be sure your solar panels fit the gap.
If you have really thin solar panels which can be placed on top of your box, drill eight little holes, for the wires to get into the box. 
Before you glue your solar panels in place, be sure your cover is smooth, because after you've glued them on place, you won't be able so sand it again.
When your cover is smooth, you can glue your solar panels on place.
If you have really thin solar panels you placed on top of your box, you can now solder the wires together.

Step 9: Finishing the Circuit

Now solder the solar circuit to the usb circuit by soldering the + wire from the solar panels to the flat battery connector and the - wire to the spring. 
Then take all the battery connectors from your solar garden lanterns and solder three times one flat battery connector to one with a spring.

Now your circuit is officially finished.

Step 10: Glue Everything in Place

Now it's time to glue everything in place. The best way to do this is to first glue the battery connectors in place, then the batteries, then the switch and the usb ports, and then the cover. 

Step 11: Embellish Everything

Now your solar usb charger is in fact finished, but it's not really beautiful. That's why I took out my sander and rounded all corners, took off the protection sheets from the solar panels and gave it a paint job.
You need to make sure you do not paint the solar panels and usb ports, so put some tape over it, before spraying. Also do not place the tape on top of the protection sheets, because the protection sheets won't stick to the solar panels.
To finish everything, I've painted a little 0 and 1 beneath the switch, so I could see if the solar usb charger is on, without having to plug in my usb device. 

And now your solar usb charger is finished:) Have fun with charging:)

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    32 Discussions


    4 years ago on Introduction

    Do you have a circuit diagram for the connection of the double USB port.
    the resistance part, i didn't comprehend that very well.
    Also, additional resources would be great for the electronic circuit :)


    4 years ago on Introduction

    so i have a 4 AA battery holder, and a 7.2V NiMh RC heli battery. which would be more effective with the use of a 6V solar cell?

    My garden lights use Ni-Cd (1.2v rechargeable 2/3 AA 150mAh battery) batteries. Can I use those still? I have 8 garden lights at my disposal.


    4 years ago on Introduction

    Depending on the desired voltage, etc.. buy the solar lights from the "dollar store" and a usb cable, thus spending $3 to $5 and do a little soldering.


    4 years ago

    Hello again. So I've figured out the polarity of the solar panels yesterday so today I decided to try charge the batteries. I had them in the sun for 4 hours and used the battery tester in the picture every now and then. When I put a battery in the tester it shows up as good but then it starts to go back down to replace. I was trying to charge 4 NiMH rechargeable batteries standard charge 16 hours at 170mA. These weren't the ones out of the garden lights. The ones in the garden lights are NiMH 600mAh, will these work better, or have I just got real bad solar cells? What were the batteries you used?

    14 2:20 PM.jpg14 2:20 PM.jpg

    4 years ago

    I don't have a voltmeter but I know people that do so I will test it. I was pretty sure that white is + and black is - but it is always good to know for sure. Thanks for the help. :)


    4 years ago

    The solar panels I pulled apart for this had black and white wires. Does anyone know which is + and which is -

    1 reply

    Reply 4 years ago

    Mostly the black wire is ground, meaning -. This means white should be +. I don't know this for sure, but if you have a voltmeter, you can test it. Yust connect the red wire of your voltmeter to the white wire of the solar panel and the black wire of the voltmeter to the black wire of the solar panel. If the voltmeter gives a positive reaction, this means white is + and black is -. If it gives a negative voltage, this means you 'swaped' + and - and black is + and white is -. But I think black is -.

    Except those solar cells are probably going to only putting out a max if 40mA. MAX.

    So if you do the math on a 2,000mAh battery that would be more than 50 hours.

    (2,000 divided by 40 = 50 hours.)

    I've made chargers with those solar cells before. They really don't put off amperage.

    5 replies

    I'm sorry. I am new to this kind of things, so correct me if I'm wrong. I calculated this using a battery capacity of 700 mA. 2000 mA is more usual indeed, but I am not sure what kind of batteries I used.
    I recalculated it for you, so here is my calculation. Yes, some things could have been measured, but I am not going to break open the box, only to measure the amperage.
    The solar gardenlanterns will fully charge in 8 hours, when using batteries with a battery capacity of 600 mAh (says the manufacture). This means: 8 = 1,2 x 600 / mA, so: mA = 600 x 1,2 / 8 = 90 mA
    This means: hours = 1,2 x 2000 / 90 = 26 hours and 40 minutes.
    With a battery capacity of 700 mAh this will be 1,2 x 700 / 90 = 9,3 hours. So the charging time really depends on what kind of batteries you're using.

    Ahhh true that. I'm glad you know the math! I hate to see really cool projects with huge batteries using very wimpy solar cells.

    Very very cool. (Now how about you try using Lithium batteries? Those pack a huge punch.)

    I am not sure Lithium batteries will work, because they will give of a voltage of 1,5V per unit, so three of them will give 4,5V. A normal usb port gives 5V. Is the usb charging device able to charge on a voltage of 4,5V? Or 6V when using 4 batteries?

    Use a 3.7V lithium battery, a cheap charge controller for the battery, and a boosting circuit to boost up the voltage to 5V. Total cost $10-20 and you'll be able to charge up a phone nearly all the way from a full battery.


    5 years ago on Introduction

    When the battery gives a lower voltage than 5V you can boost the voltage using a voltage-booster...


    6 years ago on Step 3

    a picture would be great :) .... where is it? or should i say where will it be? can u just attach the pic to a reply?

    1 reply

    Reply 5 years ago on Introduction

    That's strange. I uploaded the picture from my ipod to step 3 just before my previous reply... I just added it again, but this time from my laptop. It's at step 3.