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I do a lot of camping in the summer and like to travel light. I also love taking photos and hate it when my batteries die right before I take an awesome photo.

Thus I decided to design a little battery recharger that was small, light weight, and cute. Ok, the cute part wasn't the original idea but who can argue with cute?

Cost: $5
Time: 20 Minutes
Difficulty: Very Easy

Step 1: What You Need

Supplies:
4V or greater solar cell
AA or AAA battery holder
1N914 Blocking Diode
Altoids Tin to house it in (or whatever)
Tape

Tools:
Soldering Iron

All the supplies for this project can be found at my website, BrownDogGadgets. 90% of the money goes to me making more projects, the other 10% goes for dog treats and the occasional stuffed frog toy.

Step 2: Cells and Charging

Almost all rechargeable batteries you buy in the store are NiMh batteries. Usually people use a wall adapter to quick charge them in an hour or so, but we're not going to be that fancy. We're going to use the "trickle" method to slowly charge them up over time. This also prevents them from overcharging or getting destroyed.

To be safe we need to be sure that we're not throwing more than 10% of their capacity at them when charging. For example my AA batteries have a capacity of 2,000 mah. The max I can charge them at is 200 ma.

When you decide what solar cell to use make sure you're not going over the 10%.

At the same time be sure that you're getting at least 3.5 volts out of your solar cell otherwise the batteries won't charge. Remember, the more voltage your cells put out the less sunlight you'll need to reach your minimum voltage requirement. (Higher voltage cells = more charge time, even in low light.)

For this project I've chosen some 4V cells that put out 50 ma. I picked it because it's just the right size to fit into the Aloids tin. If you pick a bigger sized cell you can always glue it onto the outside of the tin.

You could also use a combination of smaller cells. I've used combinations of little 1.5V and 2V cells in series to get my desired voltage levels, while still fitting inside the tin.

Step 3: Hook Up the Diode


We need a blocking diode. This prevents the solar cell from sucking power out of the batteries when in darkness.

The 1N914 is a good diode as it has a very low voltage drop and is very common.

You want to connect the red wire from your battery holder to the black bar leg of the diode.

BLACK BAR LEG.

Otherwise you won't get any power from the solar cells.

Step 4: Solder the Solar Cell

Now heat up your soldering iron.

Solder the other leg of your diode to the positive solar point.

Solder the black wire from your battery pack to the negative point on your solar panel.

Don't forget to solder the red wire to the diode.

Snip off the extra bits of the diode.

Lastly you can use some tape to keep it all together. Hot glue/ melt glue also works. We'd hate to rip out the wires by mistake.

Step 5: The Battery Pack

I find it helpful to snip off the tops of the battery holders. All the ones you find in stores have these horrible plastic "guards" on them. they're great at keeping batteries in, and a pain to get batteries out. As we're wanting to do a lot of battery switching, removing them isn't a bad idea.

I like to use double sided foam tape to keep my battery packs down. You can use hot glue/ melt glue if you want. Heck you might not even need to use anything as the battery pack is nearly a perfect fit inside the tin.

Well just put it in and see how it works.

Step 6: Enjoy

And that is it. We're done. The best part is that the solar cell fits perfectly inside the tin so we can shut the top. No one would ever know that we've got a solar charger inside.

If you really wanted to be crazy you could put a little charge indicator light in there, or a test LED.

I hope you found this helpful. These are easy to make and are also really fun to give away as gifts, especially to people who are always on the road.

If you'd like parts or a fully made charger you can grab one at my website BrownDogGadgets.

***Several people asked me to put together a kit with a bit of a discount, so here is that kit!

Hi Josh I am needing some help with something... I have a small set of lights powered by a 2aa battery pack... I want to throw a solar charger into the process. How do I connect a charger to them. Or easier question, how would I hook a set of AA powered lights to the battery pack.<br>
Hi josh. I have a switch in my battery charger do I turn it on to charge it or off to charge it?<br>
<p>I have a 5v solar panal. Should i use the same diode described above or is there any other i should go far ??</p>
so my issue was trying to also attach a crank charger to the battery unit provided in my kit.<br>the question is: Is it possible to just splice in a secondary power source into the battery compartment, or would I need a resistor for that?<br>oh I bought your 3d printed case kit.
<p>where can you get the solar panel?</p>
<p>Hi Josh, </p><p>I am a beginner in electronics and for my school project I am making this really cool Altoids Solar Charger based off the instructable. The whole reason I am doing it is to make it based off a schematic. Is there any way you have a schematic for this project because I really need one, so I can order the kit and make it. Get back to me as soon as possible. </p><p>Thanks </p>
<p>Forgot to add that in the schematic that is it possible to add a usb port to charge phones?</p>
I built this for my science fair project and now I'm going to the county fair.
Hi, is there a way this could work as a charger for a Macbook??
<p>You could charge a chromebook, though, I believe those are 5v. You would need a long time and lots of batteries, though.</p>
You'd need a lot more voltage and amperage for that to happen. <br><br>That's a &quot;big scale&quot; solar project, unlike this small scale solar project.
I am not very good with circuits, as I don't know much at all about it, but could you just make 2 parallel circuits, one for AA, and one for AAA, hook both of them to the same panel, and have a switch to go from charging your AA to your AAA instantly? <br>I would do this, but I haven't gotten my solar panel collection yet. <br>
<p>Yes, you could. A couple of things to keep in mind:</p><p>The AAA batteries AND AA batteries must be the same voltage, and both rechargeable. The switch should be a three way toggle.</p><p>Here's a schematic:</p><p>http://snag.gy/2eEbo.jpg</p>
How could you add a switch
put a switch between solar panel +, and battery + that will cut the solar panel from the battery
<p>I have made on of these kits but when I plug my phone in, the battery from my phone drains instead of charging the phone. Any help would be nice. THank you</p>
<p>Is there a simple way to install an LED so I can know if the battery is charged? I'm sure there is, but not sure how! Any suggestions? Love the AA charger in the sealable tupperware box! Works great!</p>
I got your kit in the mail today and I'll be soldering it up this weekend. I just read through the instructable and at the end you have that aside about getting crazy and adding a charge indicator or test light. I'm new to electronics. How would I go about doing that?
Add an LED into the mix so that it's parallel with the solar cell, but also wire a button in so that the LED isn't always on. Use a blue LED which requires 3.6V power. As your batteries can't power it it would have to run off the solar cell.<br><br>Push the button and see if there is enough power coming in.<br><br>I'm sure there is a better way, like using some sort of voltage trigger, but I like keeping things very uncomplicated.
<p>How would you make the button?</p>
Can I put normal batteries in, and make sure the solar panel isn't getting light
Thanks, my 12 yo daughter was able to do this project, so she learned the basics of soldiering and how to use some other tools.
Im working on a charger using a 9 volt 42 mA solar panel. I want to set it up so that I can charge AA or AAA batteries ( will probably use a connector so that I can swap out battery holders. I plan on charging around 4AA at a time around 6v. What do I need to do to keep my batteries from overcharging?
Forgot to add that I also want to be able to use this as a usb charger for a phone. Can I use one system for this or do I need 2 diff systems?
Instead of using the blocking diode, do you think it would be just as efficient to use an LED and a resistor? That way we could visible see if there is enough voltage going through the circuit?
An LED would drop the voltage way too much. Good idea, but not in this situation.
excuse me for my ignorance, but is this the correct type of diode?<br><br>100V 200mA High Conductance Fast Diode:<br>http://uk.rs-online.com/web/p/rectifier/7044013/<br><br>
If we wanted to decrease the time it takes to charge our batteries, would be be better off increasing the voltage or current output of our solar cells?
Current. Current charged up the amps, you just need a certain minimum level of voltage to get the batteries to charge.<br><br>So adding a second 4V solar cell you could either get 8V 60mA or 4V 120mA. <br><br>To charge in lower light, you'd want to go for 8V 60mA. <br><br>To charge up the batteries faster, you want 4V 120mA.
If I wanted to use this design to charge 4 batteries is it as easy as doubling all the requirements? <br>i.e. need at least 7V <br> <br>also, with the 10% of battery capacity rule: is it only 10% of one battery, or 10% of the sum of the batteries current capacities. <br>i.e. 10% 1 battery @2000 mah = 200 mah <br> 10% 4 batteries @2000 mah = 800 mah or is it still 200 mah? <br> <br>Your Instructables are amazing! keep up the good work!
10% of the capacity of the battery system. <br><br>How you wire them up determines their capacity.<br><br>Hook them up in Parallel and you keep adding capacity. 1 AA is 2,000mA. 2 AA in Parallel is 4,000mA. 3 AA in Parallel is 6,000mA.
What about useability of the mobily charger? What time is it need for full charging of a phone?
As the author says, but 1 more comment: <br><br>use this to charge your AA's...<br>... then use your AA's - with a MintyBoost circuit - to charge your iPhone. <br>As long as you get your AA's charged, this -will- work.
It's a battery charger, not a phone charger. Just AA and AAA batteries. <br><br>Depending on how low your batteries are it can take anywhere from 5 - 10 hours of sunlight. The way I use it is that I have a spare set of batteries stored in the tin, then swap out my &quot;dead&quot; batteries with those spare and then charge the &quot;dead&quot; ones up. By the time my spares are used up my &quot;dead&quot; are all charged.
hi i have an idea if you just use the regulator and then simply connect the battery <br>
The design honestly can't get more simple than this. Trust me.
What about larger batteries such as the batt packs for power tools? I work on a Halloween layout set in the backwoods area where it's kind of difficult to run power.
That depends on the type of battery. Lithium Iron Batteries need &quot;smart&quot; controllers to charge them up. Ni-Cad and NiMh batteries don't, as long as you trickle charge them.<br><br>You could always build a 6V power system using a 9V Solar Panel (say around 3 watt)_, a cheap charge controller, and a big 6V battery.
what are the elements in making solar cell so i can make my own?<br>
Look around instructables, I know I saw someone showing how to make your own solar cells.<br><br>Though if you want to use them in projects I would suggest not doing so. The ones you make are going to be very very poor compared to even the cheapest factory made ones. Shoot, you can get them for free if you can find someone throwing out old garden lights.<br><br>Though I've seen quite a few places selling new solar graden lights for less than $3, which is darned cheap for a solar cell + LED + circuit + rechargeable battery. You might as well buy one and gut it.
Could you charge a Nintendo 3DS with this?
The 3DS doesn't run on AA batteries, so no. What you could use is a AA to USB converter. Like what I use with my <a href="http://www.browndoggadgets.com/tins/altoids/solar-altoids-usb-charger/">Altoids Solar USB Charger.</a>&nbsp;&nbsp;I also have a kit for that as well if you'd rather build it yourself.<br> <br> Then you'd just need a USB cable to hook into your 3DS. &nbsp;I've seen them before, so I know you can find them.
thanks. I'll go buy the USB Charger kit.
Love so far what I've read. However, I'm just curious....type of solar panel would I need to charge a smartphone? Like a Nexus S?
USB runs on 5V of power, so you'd need something bigger than 5V and then use a 5V regulator to keep it at 5V. Always go bigger with solar, so that even in lower light conditions you're getting your minimum voltage.<br> <br> Or you can use a voltage booster which would take a low voltage and boost it up to the 5 you need. If you're interested I have such a kit available on my website, and I'm going to be writing an instructable on it quite soon.<br> <br> <a href="http://www.browndoggadgets.com/kits/solar-usb-kit/">The kit to make the circuit.</a><br> <br> <a href="http://www.browndoggadgets.com/tins/altoids/solar-altoids-usb-charger/">A solar to USB system built into an Altoids tin.</a>
this is great i have been looking for something like this forever but they are usally to complicated or to pricey. great instructable
Building your own solar trickle charger is really easy to do. It's a great project for anyone getting into electrical circuits or solar power. Plus it's darned useful.
Man I've been waiting for this. I think... I think I love you.
Nice.

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Bio: I used to teach middle school science, but now I run my own online educational science website. I spend my days designing new projects for ... More »
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