Step 4: Choose Your Solar

If we use two rechargeable AAs that put out a total of 2.4Vs we're going to need a solar panel that is at least 3 - 4Vs just to meet basic levels of charging. The higher the voltage of our solar cell (or cells) the less light we need to charge up our batteries.

Now we're also trying to fit this into an Altoids Tin, so we're limited in space. I have found some great 4V solar cells that perfectly fit into Altoids Tins. They're the same ones I use with my Solar AA Altoids Charger.

Sure, a bigger and better solar cell would give us added power, but it wouldn't fit into our tin. (Something that has annoyed me with nearly every Altoids Solar Guide out there.)

You could also use a combination of several smaller cells to get your four volts. For example, 2V cells are very cheap and small on ebay. You could easily connect two of those in a series to get your 4Vs.

Just remember that when charging NiMh batteries we don't want to throw more than 10% of their capacity at them at any one time. For instance if your battery has a capacity of 2000 ma we can only use a solar cell that puts out 200 ma or less of current. This isn't usually a problem unless you're using a massive solar cell or a big combination of cells. None the less, keep this in mind.

<p>Hey so I've made my first solar usb charger, but I'm having strange issues. I'm starting to wonder whether these usb circuit boards are crap, because, when I check for continuity on the board, touches the leads of my multimeter to the positive and negative all I get is an OL and silence (yes I'm in the right mode on the MM). Whenever I try to charge my phone, my battery drains if I'm charging off the battery. Or, if I'm trying to only use the solar panel, I get this weird pulsing of a few volts. It's really weird. I'm only a novice, but I'm very interested in troubleshooting this problem. I think I'd learn a lot if anyone had ideas on what was going on. I'm about to stick some non-rechargeable batteries in and get some reading so I at least have a control here. Anyway, please some advice or help would be greatly appreciated. I want to solve this puzzle!!! Thanks. </p>
Also could i use solar cells out of landscape lights and the batteries
Could i cannibalise part of a wall charger minus the transformer
<p>Does this work for apple lightning charger such as those used with the newer iPhones? </p>
Oh ur made version is a way too costly.......
<p>By 'USB charger' do you mean the cable or a wall adapter?</p>
<p><a href="http://www.browndoggadgets.com/products/usb-charging-circuit" rel="nofollow">http://www.browndoggadgets.com/products/usb-chargi...</a></p><p>It would be more like a wall adapter</p>
<p>Could this be done using an 18650 battery? I am thinking this way I could set it in a window to charge all day and get a full charge or 2 to my cell phone off it.</p>
use 3 18650s and a 3.7 to 5v boost circut and charger in one in an altoids tin, if you get really good 18650s then you can have 10400 mah in an altoids tin, enough to charge your phone many times
<p>Whenever we get the charger to work the batteries start smoking, the battery pack melts, and the charger breaks. My teacher was wondering if we could get your phone number or email to ask further questions. Please get back to me as soon as possible. Thank you!</p>
Is there a way of adding a led power indicator into the the circuit to monitor how full the rechargeables are?
<p>Nice project...!! Useful one......... But what is the alternative of regular batteries ? </p>
<p>sorry, where have u find the usb charging circuit</p>
<p>The DC-DC charge circuit for this project costs 57c on AliExpress with free shipping.</p><p><a href="http://www.aliexpress.com/item/1Pcs-Mini-DC-DC-USB-0-9V-5V-to-5V-Boost-Step-up-Power-Supply-Module/32383087922.html" rel="nofollow">http://www.aliexpress.com/item/1Pcs-Mini-DC-DC-USB...</a></p>
<p>My website, browndoggadgets.com</p>
<p>I purchased a cell phone battery pack extender and was not impressed so I'm looking into making my own. I first tried connecting one of those cigarette lighter USB converters into a 12V power point adapter connected to a 9V battery but the phone would not constantly charge. If that makes sense. </p><p>But charges perfectly fine off the 6V car battery on my Trabant. The only thing I can think of is the milliamp per hour rating of the 9V battery I was using was too low to support charging.</p>
<p>i love it</p>
the OP mentioned that you can take the circuit out of a phone charger and use it for this project. what I'm wondering, though, is that the project calls for a DC to USB circuit, whereas the wall chargers would be AC to USB circuits, right? if this is correct, do I need to do anything to alter the chip I take out of the charger in any way to fit with the project, or can I use it as is and just insert it into the new circuit?
Nice build. Do you think if you placed a mirror in the lid you could use it to refract more light onto the solar panel? <br><br>Have a great day! :-)
<p>Nah, it would be a super duper tight fit then, and you're better off just angling the panel at 45 degrees.</p>
<p>justForFun's idea [ i think ] was to have direct sun on the panel PLUS reflected light from a mirror to increase output LOL i think you misunderstood the idea trying to be conveyed. JustForFun did not mean for the mirror's light to be the only light applied to the solar panel. personally i thought it was a fantastic idea!!!!!! be well my friends</p>
<p>have you thought about using super capacitors? they charge in seconds</p>
<p>Super caps are nice, but they hold very very very very very very very little amperage compared to even the cheapest AA. Sure, you could get giant soda bottle sized super caps (and spend hundreds of dollars per cap), but thats a bit above and beyond the scope of this. With current technology it's not financially or practically a good solution.</p>
<p>nice and simple, i like it. a question: why don't you add a switch for solar charging? just because when there is no sunlight, the panel will slowly drain the batteries. better to open the circuit when you don't use the panel.</p>
<p>Thats why there is a diode, to prevent drain. A lot of people add switches to this project, no reason why you couldn't. Just not necessary. </p>
ah well okay a diode is a lot better of course :)
I got this circuit board off an LG travel charger . Trying to figure out where I would put the negative and positive wires. I also wanted to add a switch I'm not sure if that would makes things more complicated. Wondering if any of you could help
<p>those looks like a step-down? If they are they will work if you have a big solar panel to step the voltage down to 5vdc. You can get the battery powered usb charge at the Dollarama if you live in Ontario, they are like three bucks!</p>
<p>What the guy above me said. You have a STEP DOWN. You want a STEP UP. Two completely different things.</p>
<p>Does this work with 18650 battery cells?</p>
<p>No, you'd need a charge controller in the mix. At the start of the write up I link to my Lithium Heavy Duty 2.0 project, which uses 18650 lithium battery cells. It's not too much different from this write up.</p>
<p>this instructable was posted in 2011, so this guy made it about 4 years ago.</p>
These look awesome!
<p>What was the problem with this kit? what batteries did you use?</p>
<strong>aa batteries</strong>
<p>Lithium aa?</p>
<p>Those would explode.</p><p>Lithium batteries are NOT rechargable. Lithium-Ion batteries are, but with special controlling hardware. He used Nickel Metal Hydride batteries (Ni-Mh), your standard rechargable ones.</p>
<p>use NiCads if you are not concerned about their self-discharge rate, they have a much higher mAh than their cousin NiMh.</p>
<p>Rechargeable 1.2V AA batteries. Nothing special.</p>
<p>what happens when the battery is fully charged, nothing is connected but the panel is left out in the sun?</p>
<p>given the cell panel's low amperage, it should be safe to leave them in the sun once they are fully charged.</p>
<p>Nothing. It just kind of tops off. Thats why we keep the amperage low enough as to not harm the batteries.</p>

About This Instructable




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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