How long does your cellphone's battery keep the charge? I guess not for long time... and your GPS? Do you have a spare battery to not lose yourself in the woods? A solution is to buy a solar charger, they're cheap nowadays, but not many of them allow you to power your device during the charging process. Indeed this is an effective solution in many cases, and saves you from using a specific battery. Therefore, what are we waiting? Let's build it!

Step 1: solar cells

You can buy different types of solar cells: very cheap 2V tiny or huge and more expensive 5V 700 mAh panels. Also halfway choices are good. You need to obtain about 4-5V output voltage from them (a voltage up to 6V doesn't hurt), so if you choose the tiny cells you can connect two of them in series, with sun light they will provide 5V, although the amperage will remain very low. Scissors are there only as size comparison, don't cut the bigger solar cell to obtain many little ones!!

[UPDATE NOTE: as I said you can choose between different sizes and prices of solar panels, and if you want a charger which charges the battery in few hours in direct sunlight, or that charges in shadow too even though slower, you have to spend more and having a bigger surface and weight]

Step 2: charger modules

As charger circuit you also have multiple choices. You can find circuits to charge one or more cells, with or without charge indicators (leds), and with many shapes and dimensions. Some modules only charge the battery, but others also provide +5V output voltage from the battery (usually 3.7V), pay attention to buy one this last type.
In this instructable you see two similar PCB, one has two leds to show charging process (red led) and full charge (green led), other one has no leds and is a bit cheaper. Both are meant to charge a single cell, although you can in theory connect two cells in parallel, but I don't suggest it because that will reduce their life. They also both provide +5V output.

These battery charger modules usually have three pairs of pads for connections, for all three couples of wires beware to respect the polarity (don't follow my example, try to use black and red wires):
  • DC input (also marked as "charge", "charging port", "P+ and P-", "3.7V+ and 3.7V-") where you have to connect your solar cell(s), this usually accepts from 3.7 to 6V or more.
  • 5V DC output (also marked as "increasing output" or "V+ and V-") where you will connect your device, through an USB or another power female plug, as you see in picture this voltage is very precise.
  • Battery connections (usually marked as "B+ and B-"), here connect your battery (or better your battery holder), you can also try to connect two or more batteries in parallel, but I don't suggest it.

Step 3: batteries

As battery I suggest an 18650 Li-ion cell. These are very handy, powerful, cheap and common. Also buy a clip holder. Anyway you can chose to buy a flat Li-ion 3.7V battery for cellphones, although those are not powerful as 18650 cells.

Step 4: soft-power

To start the circuit you have to soft-power it. That means to provide +5V to DC input with battery connected. Then you can disconnect +5V and check that the output provides +5V. To soft-power the device the solar cell can be already connected or not (to the same DC input pads), it doesn't matter.

Step 5: prototypes

Here I tested my two prototypes. The bigger solar cell is able to charge the battery with no direct sun light, day light is enough, even in a cloudy day. With little cells you need exposing them directly at the sun. My GPS is here connected to the solar PSU and it has no internal batteries, this is pretty useful when you otherwise have buy expensive specific Li-ion cells for a device equipped with USB plug (as a modern phone or a digital camera).

Step 6: the hub

Now let’s find a proper, easy, and cheap of course, way to connect devices to the charger. As you already saw I used an USB female socket to connect an USB cable to the bigger solar cell, but that was a prototype, now I want something more elegant and maybe with more than a single connection.
This is an USB hub with four USB 2.0 (you don't need 3.0 for this project, actually 1.0 is good enough) ports, each one with switch and blue led, all this for only 4$. That’s perfect! I see that there is also a +5V DC-IN socket to receive an external power source. That would be fantastic, we neither need to open it! But I want to put my tiny pcb inside it, so let’s open it to see if there is enough space.

Step 7: some desoldering and salvage

It probably will fit, so we can begin adapting our bus. Let’s cut out the USB cable and unsolder the DC-IN socket and the power blue led, which otherwise would slowly discharge our battery. We now also have obtained a few free useful components ;-)
Before cutting the cable look where the black wire is soldered, that is the ground (-), and it’s connected with the ground pin of the DC-IN socket, we need to know where to solder the wires from the charger.

Step 8: avoiding power dissipation

Then cut the trace which bring electricity to the hub's IC, since it consumes power and we don't want that. As you see in the picture, the big trace I cut is the only positive power supply to the black plastic drop which contains the hub's brain, interrupting it you'll avoid any power waste.
Beside I've discovered it's better interrupting the signal traces that come out from the black IC (the plastic drop) and arrive at second and third USB pins. I had some difficulty to power some device before doing that.
You can also decide to replace blue leds with similar red ones (which use less current) or to remove them completely to save energy from the battery, after all this solar psu has to be as much efficient as possible.

Step 9: wire them all

I then made two couples of holes in the plastic container to let wires passing through. Use soft narrow short wires, because they have to stay inside with everything else, mine are a bit too long. After inserting wires in the holes solder  each wire’s end to the right pad.

Step 10: attach solar panels

Using double side tape, attach the pair of solar cells to the plastic surface on the side of the USB bus.

Step 11: accommodate the pcb

Now search a place where to put the pcb… I thought it was simpler, I had to change three different positions. Closing the cover the pcb pushed against the components. Finally I found the best position, between switches and USB sockets. A double face tape avoid the pcb touches the metal of the sockets. Before closing remember to soft-power the device as I explained before.

Step 12: complete with battery (holder)

Closing the cover we keep the battery wires out. Now a 18650 clip holder is needed… mine is travelling from China to Italy together with his nine mates. So you will find here an update in a month or a bit more. For now let’s use a rubber band (from a bicycle tire) to keep wires connected and let’s attach battery with a piece of double face tape.
Maybe that pcb will reset when you take off or disconnect the battery. In that case you have to soft-power it again, notice that DC input wires are accessible from the narrow slot between solar cells and container, try to keep an easy accessibility to them, otherwise you have to open the case. Also remember to mark the wires so to know which one is positive and which is negative. Yes I know, much better to use red and black wires... :-P

Step 13: enjoy the sun

Blue LEDs appear violet… maybe I’m color-blind and my camera has the right sense… anyway, to see if the solar charger works, measure the voltage of the battery with your multimeter, expose the solar cells to the sun light, wait a few hours, then check the voltage again, it should reach about 4.1V to be full charged. For more skeptical persons I added an image showing the GPS powered and three more devices being charged (two databanks and a GPS tracker).
Now enjoy and be sure to not enter a too dark wood ;-)

Step 14: [UPDATE]

After the right concern of many readers about the very low power (about 150 mA if I'm not wrong) of these tiny solar panels, I decided to improve my solar psu doubling the solar cells. Indeed now two more cells are connected in parallel with the first two. Output is still 4-5V but currend is double than before, so charging time (referring to the Li-ion battery under the solar cells) is half than before.
I also glued pivots between panels and case, so that the solar charger is foldable.
I've still to add the battery socket, but unfortunately shipping time is very long.
Could I use this pcb for the build ?
Hi , where can you buy the Charging modules from ?
go to link in step 2
<p>ive been trying to find the pcb board, but I cant find the board anywhere. also id rather have the parts sooner than later, some of these dates are saying march 2016</p>
<p>I love this idea. But i am having trouble finding the charging/regulating pcb with a 5 volt output ,do you know any other sources or descriptions to find and purchase this pcb?</p>
<p>Try Amazon. That's where I got all my stuff.</p>
<p>cant find it on amazon. could you send me a link to the one you found?</p>
<p>can i get those things in INDIA.........</p><p>I searched at EBAY.in but i didn't find the PCBs....</p>
<p>can i get those things in INDIA.........</p><p>I searched at EBAY.in but i didn't find the PCBs....</p>
<p>where do i find one of those pcbs?</p>
try links in step 2! :)
<p>I got the same battery as in the picture, but it only puts out 3.7v. I couldn't find any that put out 5v, only 3.7v. Where am I doing wrong? </p><p>I tried an <u>old</u> cellphone battery, it worked, but it didn't last long(battery died). </p>
3.7 Volt for battery is right, the circuit will raise voltage to 5v
<p>My <br>charger module is different than yours can you tell me which parts are which?</p>
Been trying to work on this still. I have the usb hub it's insides look a smidge different (need to get it out of storage someone accidentally put it there.) i have two decent sized solar panels think are 5v i don't remember the amps or milliamps. I accidentally used wrong gauge wire (didn't realize different wire sizes could cause resistance or what not so power doesn't get threw.) so i need to desolder the solar panels. I am also still working on getting proper 18650 batteries and a pcb charger. I've been super excited at this instructable.
<p>Any website where I can purchase all these components at once? I live in Sweden and some of these items are hard to get so if you could give me a website to order everything i'd greatly appreciate it :) I am thinking of making my own usb solar charger as my highschool exam work :P</p><p>Thanks in advance!</p>
<p>yeah, you can buy all of them on eBay, I did so</p>
<p>I purchased a diode, solar panel, 2 AA rechargeable batteries, battery holder, and an usb hub with 4 ports (with a cord for the wires). You got a charger module in there aswell but I need to order one from e-bay or something to get hold on one of those. Are there any other options, for me to make this happen? Please, i'd like to finish this for my project :(</p><p>I'd really appreciate a quick answer. I heard that you could use an usb circuit but I am not sure if any usb-circuit will do.</p>
<p>I made this with some modifications ...</p><p>I kept the USB cord. This allows me to charge the battery from any USB outlet, and plug into solar panels that have been customised with a female USB outlet.</p><p>I didn't see any reason to keep the switches, so I used one of them as a disconnect for the battery. This is to eliminate any current drain when not in use.</p><p>I also rigged one of the switches and original HUB LED to the output. This is to confirm that the unit is outputting power, while being able to turn the light off to reduce battery drain.</p><p>Next, I attached the Charge complete LED on the charging board to one of the HUB LEDs - This is finicky soldering! No I know when I've got a full charge. My thinking is that if it is fully charged, the little power lost to the LED is 'extra' anyway. As soon as it is no longer charging, the LED turns off, preventing power loss.</p>
Awesome improvements! Thanks for sharing, I will probably add your suggestions to the ible!
ok ma il mio dubbio persiste! Il circuito di carica che suggerisco nell'instructables fornisce 5V nei piedini per la carica della batteria. Ma come puoi vedere nella foto sotto aulla batteria c'&egrave; scritto che i volt massimo che supporta in input sono al massimo 4,2. La mia domanda &egrave;: posso attaccare la batteria direttamente al circuito da te consigliato fregandosene dei 4,2 e sperando che la batteria non si Frigga oppure faccio un partitore di tensione per collegarla al tuo circuito in modo da abbassare la tensione a circa 4V per non rischiare? perch&eacute; avevo gi&agrave; provato a collegarci direttamente un'altra batteria A ioni tempo fa ma si &egrave; rotta e non capisco se si &egrave; fritta per i 5V in voltaggio o se sono rimasto troppo con il saldatore sui suoi pannelli di rame
<p>Please refer to notes on pictures of step 2: you can see that +5V is different from &quot;battery connections&quot;. So the battery has to be connected to &quot;battery connections&quot;, not to &quot;+5V&quot;... easy, isn't it?</p><p>Devi connettere la batteria a &quot;battery connections&quot;, i 5V sono DC-OUT, puoi connetterci ci&ograve; che devi alimentare.</p>
<p>si ma nel &quot;battery connection&quot; sono presenti 5 volts misurati con il multimetro che provengono dal pannello solare, per questo dicevo</p>
<p>Ah ok, non lo sapevo. Sar&agrave; perch&egrave; non c'&egrave; collegato alcun carico...</p>
quindo secondo te posso collegare la batteria direttamente anche se il suo limite di carica &egrave; 4,2V? haha scusa se ti rompo le palle ma non ho voglia di brucare la batteria, ci ha messo due mesi e mezzo ad arrivare
<p>prima devi dirci perch&egrave; odi la fra! ;-)</p>
ciao! siccome sei italiano ne approfitto haha<br>senti, io avevo intenzione si usare una batteria da telefono, pi&ugrave; precisamente una da 3200 mA 3,7 v cinese, quelle che sono copia di quelle Samsung; pagata 4 dollari au eBay<br>il mio dubbio &egrave; che nel retro della batteria c'&egrave; scritto che il limite di voltaggio per la ricarica &egrave; di 4,2V. Secondo Te posso collegarla direttamente al circuito di ricarica che le fornisce 5v dal pannello solare oppure devo per forza fare un partitore di tensione per abbassare il voltaggio almeno a 4,2?
secondo me devi per forza utilizzare un circuito specifico per la ricarica delle batterie al litio... altrimenti la rovini subito.<br>Ma costano una cavolata quei circuiti, cerca su ebay.<br>Alimenti il circuito di ricarica con i 5V del pannello, e colleghi la batteria al circuito stesso, che magari ha gi&agrave; anche un'uscita a 5V.<br>ps: che ti ha fatto la fra?!
<p>Ah quindi dici che il circuito di ricarica che hai utilizzato tu non va bene per una batteria al litio?</p>
<p>non avevo capito ti riferissi gi&agrave; al circuito di ricarica specifico, certo va benissimo, &egrave; fatto apposta :-)</p>
<p>Thanks for the cool idea and instructions! I made one myself, and it works realy great!</p>
<p>AWESOME! thanks for posting! :-)</p>
<p>Good Instructable.</p><p>There are always issues with just putting two cells in parallel. Firstly, if the voltages aren't the same, one will feed current back into the other until they balance voltages. They will also self discharge through each other if the solar cell isn't charging them, although I'm not sure how long this would take.</p><p>If you are going to use two cells in parallel it's a good idea to use blocking diodes to stop them feeding back into each other when not charging fully or if they are not both starting with the same voltage. However, these diodes will in themselves cause problems due to the voltage drop across them and will stop the diodes providing current back to the USB 5v outputs. Using diodes like this isn't a problem with a mains charger where losing a volt or so isn't an issue, but for solar cells it can be.</p><p>I've also found in the past that there seems to be a minimum current needed to charge a cell and if the current is too low the cell doesn't seem to charge, but this might just be that at low currents it just takes forever. It might be that the circuits are designed to charge one cell because when used with the smaller solar cells this gives a reasonable charging time, which would obviously be doubled using two batteries or because they are checking the current versus voltage to stop overcharging, although I doubt that that's an issue with solar cells.</p>
<p>Trying to figure out how to build this with what I have I didn't want to hunt down the special batteries but looks like might be a good idea. I have usb base (trying to decide if I want to use a 7 plug one instead.) and got some tools but trying to figure out if the charger circuit would work as a current regulator even if I had say 4 of those batteries hooked up to it. Don't really want to blow up any of my gadgets even though I want to keep them charged while out and about.</p>
WHERE DO I FIND THOSE LITTLE TINY HINGES?!?!? I could seriously use those little things
<p>I got a bunch of free solar panel from a VW car dealer, they are used in new cars to keep the battery charge during transport from factory to dealer, output of each panel is about 1000 ma. at 12 volts. I bought USB cigarette lighter adapter from dollar store for $1 and connect the two together. </p><p>Now I have a 5 volt 1 amp USB charger for $1 + my labor... :-)</p>
<p>Oh, that sounds like something I might want to try and get. What should I ask for when I go to a dealership?</p>
<p>Why don't you do an instructable on this?</p>
<p>It should be pretty straight forward if you have gotten these 12 volt solar panels and the 12 volt cigarette lighter USB adapter. Connect one to the other. I doubt if Instructable would help... :-)</p><p>and... by the way, this site used to be gadgets and stuffs, when did it turned into food channels? LOL... sorry got nothing against eating, just could not help it...LOL again falling off my chair this time...</p>
<p>Yup, I need to learn to cook if I wish to post an instructable in each category</p><p>;-) That panel seems great!! I wonder where nearest VW car dealer is... a search is mandatory now!</p>
<p>They were originally OBDII connectors so I changed them to standard barrel plugs, much easier for isolation or diagnostic.</p><p>Go to a dealer that sells import models, locally assembled VW may not have these panels. </p>
<p>cool! if you want to get rid of some of those awesome panels I'm here! ;-) actually I'm sure all Instructables community is available!</p>
Lol... most imports dealers have these panels. You just need a good friend there. Sometimes you can find them in their garbage bin. Those are the non working panels because the wire had lost contact with the back of the solar panel. They can not be soldered, but need to glue back. I don't know what kind of glue needed though so I just insert foam pieces to keep the pressure on
<p>that's interesting! I should follow some of those guys home ;-)</p>
<p>No, I don't meant their home garbage, you might look suspicious there. Its those big metal garbage bin behind the car dealers. You'll be surprised what else they throw away. One time I found a part (US$439 door control) for my neighbor's VW - thrown away because one missing mounting bracket that can easily make with a small piece of Aluminum. Them dealers do not repair, they just replace in order to sell parts - bigger profits paid by customers...</p>
<p>LOL! Ok, but I'll look suspicious behind the car dealer too!</p><p>Anyway you are right, they throw away very expensive and almost new stuff!</p>
<p>Hello, I'm just wondering what type of wire I should use? I'm looking at 26~28 gauge. Is this too thin or too thick? Thank you!</p>
<p>Don't worry too much about that, any thin wire is good, thinner is easier to use. 28 gauge holds more current than needed.</p>
<p>I will try to this in my own.</p>
<p>great, let us know!</p>

About This Instructable


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Bio: I'm an Italian freelance structural engineer, graphic designer and photographer. I'm also investigating electronics, robotics and science in general. I enjoy hacking and ... More »
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