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.

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>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>Solar panel $2.00ea</p><p><a href="http://www.ebay.com/itm/2pcs-x-4V-60mA-0-25W-Mini-solar-Panel-small-solar-cell-PV-module-for-Solar-DIY-/261875624221?hash=item3cf900e91d" rel="nofollow">http://www.ebay.com/itm/2pcs-x-4V-60mA-0-25W-Mini-solar-Panel-small-solar-cell-PV-module-for-Solar-DIY-/261875624221?hash=item3cf900e91d</a></p><p>2 X AA Holder 74c</p><p><a href="http://www.aliexpress.com/item/1pc-2AA-Battery-Hoder-Case-2X-AA-2-AA-3V-Battery-Case-Box-Holder-With-Wire/32430582602.html?spm=2114.01020208.3.2.vkJXNb&ws_ab_test=201526_1,201527_4_71_72_73_74_75,201409_4" rel="nofollow">http://www.aliexpress.com/item/1pc-2AA-Battery-Hoder-Case-2X-AA-2-AA-3V-Battery-Case-Box-Holder-With-Wire/32430582602.html?spm=2114.01020208.3.2.vkJXNb&amp;ws_ab_test=201526_1,201527_4_71_72_73_74_75,201409_4</a></p><p></p><p>2 X AA NiMh 76c ea $1.52</p><p><a href="http://www.ebay.com/itm/BTY-Ni-MH-AA-3000mAh-1-2V-Rechargeable-Battery-For-MP3-RC-Toys-S3-/221862248861?hash=item33a805419d" rel="nofollow">http://www.ebay.com/itm/BTY-Ni-MH-AA-3000mAh-1-2V-Rechargeable-Battery-For-MP3-RC-Toys-S3-/221862248861?hash=item33a805419d</a></p><p>It seems like you're making over $20 profit on a $25 kit mate..</p><p>Comments ??</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>Duh the diode prevents the powerfrom the batterys circling backthrough the solar panels fricken idiots</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>It will not work. Your charger is made to convert AC or alternating current, to a specific DC output, being a set voltage and current. .</p><p>.</p><p>Solar panels only put out DC or direct current..</p><p>.</p><p>You NEED to pull your finger out of your arse, and EXAMINE the components.</p><p>.</p><p>On the back of the panel are little white pictures - this is the circuit components and their orientation. The copper tracks are the connecting wires, AND all components have markings on them, to identify the type of component, it's manufacturer, and either the part number or the value (i.e. resistance) of the component.</p><p>.</p><p>You have to start doing your own home work on your own projects, BEFORE you start asking questions, that show that you don't have a clue about how any of this works, because you have made no effort to go and learn by figuring it out yourself. </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>
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It's a good idea and all but kipkay made the same thing looks the same and everything. he. made it about a year ago?
<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>The batteries go supernova, and detonate - blasting the planet to atoms - across the entire galaxy.</p><p>.</p><p>Naaa seriously almost all battery types, if matched to a power supply that is only marginally higher in voltage and at a amperage rate that could be described as marginal, than the peak charged voltage, nothing much will ever happen.</p><p>.</p><p>Making this up to illustrate the point: From the panel, through the blocking diode to the battery. At the blocking diode - your getting say 5V and 100ma, and the battery / battery packs maximum charged voltage is 4.8V (or 4 x 1.2V AA batteries) - that is only a 0.2V difference and 100ma - well if each battery has say 2000ma capacity, then that x 4 is about 80 hours of charge time, to top up a totally flat set of batteries. As the batteries fill up and their internal voltage increases, then rate of charge slows to a veritable crawl. </p><p>.</p><p>Assuming a voltage resistance of say 1V on a blocking diode to stop the power flowing back through the panel, then if you match the peak voltage of the panel, to be a little higher than the peak battery voltage, then the unit will &quot;level off&quot; and ultra slow / low rates of charge are basically inconsequential.</p><p>.</p><p>It's when the voltage of the battery pack is say 4.8V charged, and the charging circuit is running at say 7V, and or the current is say 300ma, over the 4 a 1.2V 2000ma batteries...</p><p>.</p><p>Like the old lead acid car batteries - if you slowly fed power into them, at say 15V, they would charge up, and then develop a chemical &quot;surface&quot; charge - bringing the voltage up to about 13.5V. Well car battery chargers are set to a maximum of 13.8V - which is just enough to creep a little bit of power into a fully charged battery, as a very low rate. </p><p>.</p><p>Same thing.</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>
<p>What was the problem with this kit? what batteries did you use?</p>
<p>Not enough battery power, not enough solar power. Newer gadgets require more amperage and 2 AAs just doesn't do it any more.</p>
<p>will energizer rechargeable batteries work they are 1400 mAh</p>
<p>they would work, but it will give your device about a 10-15% charge before they drain.</p>

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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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