Instructables

Turn a playing card into a solar charger for AA batteries

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I own loads of rechargeable NiMH AA and AAA batteries, but most always seem to be dead when I need them.  So, I wanted a cheap and fast way to make battery chargers that I can keep on my desk, so that I could have an armada of charged batteries at all times.  I didn't want to take up more outlets and have more wire spaghetti with plug-in chargers, so I settled on a solar charger.  I'm in the solar business so I had stacks of small pieces of raw lasercut PV silicon cells (solettes) laying around, and I first made a simple battery charger with a few business cards as a backing.  Then I found that playing cards were a more stable backing -- and besides, they looked neat.

This instructable details my efforts to make a simple solar battery charger made out of a playing card, some solettes, some magnets and super glue -- if anyone has ideas on how to make this simpler and more effective, please let me know in the comments.

No soldering is required for this project.  It should take about 10-15 minutes.

First, check out this video.  There are two playing-card solar projects detailed in here -- one for a AA charger, and another for an arduino charge card (described in more detail here:  http://www.instructables.com/id/Solar-powered-arduino-on-the-back-of-a-playing-car/ )

 


p.s.  Where can you get the small bits of solar cells -- the solettes -- needed for these Instructables?  Well, it's a pain right now.  You can track these puppies down from suppliers in China, but they aren't easy to pin down:  http://manilamantis.wordpress.com/2012/04/25/the-dark-side-2/ 

So, to make this easier, my buddies and I are launching a Kickstarter campaign (Aug 15 - Sept 14) for all your solar DIY needs:  http://www.kickstarter.com/projects/alex9000/the-solar-pocket-factory-an-invention-adventure   Bangorang!

 
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Step 1: Materials

++ Copper tape with adhesive backing (this should be available at most well-stocked electronic component stores
++ Super glue (the thin stuff, also known as cyanoacrylate)
++ A couple playing cards
++ 4 NdFeB magnets between 1/4" - 1/2" diameter, 1/32"  - 1/8" thick, any grade N42 - N52 (available lots of places, including www.kjmagnetics.com)
++ 4-8 solettes, depending on what type of additional indicators or dark-current blocking diodes you add to the basic charger
++ A few AA rechargeable batteries.  This will work best with NiMH AA and AAA batteries, but can also work with NiCads (which are not the most environmentally benign battery in the world, so best to avoid buying  these if you don't own them already)
++ [Optional] Schottky diode
++ [Optional] Indicator LED
++ [Optional] Rigid backing, like a scrap piece of 1/8" thick acrylic that's a big smaller than a playing card

Step 2: Bend the card and add copper tape

Picture of Bend the card and add copper tape
Bend the playing card so that you end up with two flaps that can touch the contacts of a AA battery. 

Then add a couple pieces of copper tape, taking care to wrap the copper around the entire width of each flap.  These will be your wires that connect the output of a string of solar cells (the solettes) with your AA battery (via some magnets).  I've also added an extra copper tape trace, for an indicator LED on the underside of the card, so that I know the charger is operating properly -- but this is not essential for a functioning battery charger.  

Step 3: Add the magnets

Picture of Add the magnets
The magnets are the terminals that will connect your SunJack charging card to a AA battery.  A rechargeable AA battery has a ferrous shell, which means a magnet can stick to it.  We can pass a small amount of electricity (enough to charge the battery) around the nickel-coating of the NdFeB magnets, which means that when the magnets grab onto a AA battery, current can flow through the copper tape, through/on the surface of the magnets, and then into the AA battery.  This same technique could be used to make a very simple playing card LED lamp, in which the battery is discharging into an LED instead of being charged.

I used two magnets for each copper terminal of the SunJack, just to hold the magnets in place without adhesive.  A single magnet on the underside of the card on each copper terminal could be used instead.


Step 4: Stack the solettes

Picture of Stack the solettes
Theory:

This step is the key to getting the whole enchilada to work properly -- combine solettes in series with a superglued shingling technique.  Each solette, or any chunk of mono or polycrystalline PV silicon for that matter, outputs around 0.5 - 0.6VDC, which is not enough voltage to do very many useful things.  So, we need to combine enough of these solettes together in series so that their voltage outputs add up.

In order to recharge a NiMH rechargeable battery, we will need a minimum of 3 solettes in series (or, 1.5V).  The solettes we are using output Im (or, the max current at the maximum power point of the cells - about max power point here: http://en.wikipedia.org/wiki/Maximum_power_point_tracking) of around 100 mA per solette.  So, since we are combining the solettes in series, the voltages add up, but the current does not.  Or, to put it another way, 3 of our solettes in series will output 1.5VDC and 100mA.  

100mA output at max sun (more or less) is just right for trickle charging a 2000mA battery safely, without worrying about damaging the battery.  You can find 2000mA+ batteries at most stores -- Energizer, Eneloop, etc...

Truth be told, you could even safely use a much lower capacity battery if you are charging inside, near a window for instance.  As long as your maximum current delivered is less than 1/20th the mAh capacity of your battery, all is well.

Back to the solettes:  The (+) output is the grey underbelly of the first solette in your shingled fan-stack.  The (-) output of the series connected fan can ba accessed either at the bus bar or white silver ink runners on the blue top surface of the final solette in your stack, or by using a "false" solette that doesn't produce electricity but just serves to bring do the top surface connections to a solette underbelly. Watch the video for more info.

What to do:

A few dabs of superglue (again, the very thin clear liquid stuff -- also known as cyanoacrylate), a few seconds of pressure, and you've got yourself a solar series connection!

Step 5: Encapsulate with 5-minute epoxy - and you're done!

Picture of Encapsulate with 5-minute epoxy - and you're done!
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Check the output of your SunJack at the inside/underside magnets -- in noonday sun on a sunny day in, say, San Diego, you should read an open voltage of around 1.5VDC - 1.7VDC (if you used 3 solettes in series, or 4 solettes in series where one solette is just a dummy electricity carrier) and a closed current of, well, whatever the closed current of a single solette is.  For solettes of the area I am using in this project, the closed current is around 175mA, whereas the max current deliverable to a load like a rechargeable battery is around 100mA.  

Now, mix up a bit of 5-minute, two part epoxy.  Then, simply pour it onto the top of your SunJack card, over the solettes, magnets, and everything really -- everything on the top side (the side with the solettes), that is.  Take care not to get any epoxy on the inside magnets, since these need to freely carry current to your battery, and epoxy is highly insulating.  

I also like to add a rigid backing on the underside of the card, to stiffen the whole structure.  Solettes are very fragile, and even an epoxy coat is not rigid enough to keep them from fracturing in many cases.  I used a 1/8" thick piece of scrap acrylic just in the middle section of the bent card in this particular model.

One more note:  It's best to put your SunJack on some popsickle sticks or some other stand so that the epoxy can drip off the sides of the card.  

After 5 minutes of curing time, you have yourself a solar battery charger!  Repeat 52 times and be popular.  


Check out the video at the beginning on this instructable -- also here http://www.youtube.com/watch?v=nsX6r-_Nn6Y -- for more details and for dark-current protection diodes and charging indicator lights.  These aren't necessary if you are just charging your batteries during the day and have a multimeter to check that your system is working properly, but they are nice add-ons for the second or third SunJack you might make.

If anyone has neat add-ons (like better LED indicators for charging), or better ways to make a simple solar battery charger from scratch, please let me know and post in the comments...
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sniffrumble1 month ago

For sure. You can just slice the tape down the length to get the right width for this project.

For sure. You can just slice the tape down the length to get the right width for this project.

sheepbars3 months ago

hi i'm back, i was also wondering if i could use a solar panel instead of those solutes! i couldn't find any! it has wires with it that has + and - polarities. I'm doing this as a science fair project and was wondering if my ill-equipped self could still pull this off.

cheshirecorn3 months ago

Thats fascinating...

For sure. You can just slice the tape down the length to get the right width for this project.

clawsgoal3 months ago

For sure. You can just slice the tape down the length to get the right width for this project.

chimplost6 months ago

For sure. You can just slice the tape down the length to get the right width for this project.

steveazhocar7 months ago
Hey i was wondering if I could use about 1/2 of a cm copper tape? i have over 15 ft. of it and i was wondering if i could use somehow.
regaltaxlaw7 months ago
For sure. You can just slice the tape down the length to get the right width for this project.
sfrayne (author)  gamebadly9 months ago
For sure. You can just slice the tape down the length to get the right width for this project.
sfrayne (author)  keithentwhistle11 months ago
Yup, for sure. You can just put the shorter pieces of tape at both ends of the card.
clickworried11 months ago
Yes, you definitely could just use a straight-up already-assembled solar panel.
JensonBut1 year ago
Love this! Will try it out myself! Very smart and practical!
hi i'm back, i was also wondering if i could use a solar panel instead of those solutes! i couldn't find any! it has wires with it that has + and - polarities. I'm doing this as a science fair project and was wondering if my ill-equipped self could still pull this off.
sfrayne (author)  TheSciencebro1 year ago
Yes, you definitely could just use a straight-up already-assembled solar panel. That said, we've made some solettes available in a kit here:

http://solarpocketpages.com/kits/

Good luck!
Hey i was wondering if I could use about 1/2 of a cm copper tape? i have over 15 ft. of it and i was wondering if i could use somehow. i need this project dow almost now! plz answer soon!
Great Instructable! I just received my solettes and I want to adapt your idea to make a cell phone charger. The question I have is the use of your dummy or your "false" solette. How does it bring the top surface connections to a solette underbelly? Do you flip the last solette upside down? If not, why wouldn't you just make the copper tape longer on both sides so as not to waste any solette?

Cheers, and thanks!

Alastair
sfrayne (author)  misobrilliant1 year ago
Hi Alastair,

Thanks! Re: why use the false solette -- using the superglue technique to connect solettes works decently well after a bit of practice, but using it to connect solettes to coppertape is flaky. So, instead of trying to mount the (-) copper tape section to the top of the last solette, I found it easier and more reliable to just do all solette-to-copper tape mountings from the bottoms of the solettes, particularly connecting the bottom silver ink bus bars to the copper tape. This then requires a "false solette" -- no flipping necessary though.

That all said -- you could solder the solettes together with a pre-tinned wire called 'stringing', instead of doing the superglue solderless technique -- and then the false solette isn't really necessary.
Cirdan1 year ago
I had a feeling you were a Beirut fan. Not sure what gave it away.
Excellent instructable...I'm looking forward to trying this myself. Thank you for making these solettes available to us through the Kickstarter campaign, as well!
sfrayne (author)  Cirdan1 year ago
Who's not a Beirut fan?
Cirdan sfrayne1 year ago
Everyone in a 50-mile radius of me, save for my wife. :\
bobwojo1 year ago
I liked your idea of using magnets as part of the battery connector.

I have small 1/4" magnets with a Nickel plating that is conductive. Using a low temperature solder (170 degree F) I soldered wires to the magnets,

Now I have magnetic connectors that stick right to the battery.
Here are photo's, Note that the positive contact on a AA battery is small and not very flat so use very flexible wire so the magnet will stick better and not fall off.
photo2.JPGphoto1.JPG
sfrayne (author)  bobwojo1 year ago
Zing! That's sweet.
sfrayne (author)  bobwojo1 year ago
Zing! Awesome! I found magnets to be the easiest way to make these battery chargers, but also an easy way to connect clips to raw solettes for quick experimentation.

So, you have a photo?
Josh1001001 year ago
What is the size of the solar power does anybody know?
Ok now im hooked !

Excellent instructable and thanks so much for the extra inspiration BUT !!!

Theres no way for us (John-Q-Public, Joe-Bloggs, etc) to CHEAPLY buy these 'Solettes' that are used to make this - they are not even sold on ebay !!!!

AAAAARRRRRRRGGGGGGHHHHH !! !! !! !! !! !! !!

How do we obtain such things if we dont know anyone in the solar-business like yourself ?!?!?!?

Any help would be greatly-appreciated & many thanks in advance !!
I have been buying them at the dollar tree. I get a solar panel,nicad battery led light bulb,diode,battery compartment and switch. But you can just twist off the top of the solar nightlight and all the work is done for you. You would have a hard time buiding this for under a dollar.
thats just Awesome !! many many thanks for the advice, i am most-grateful !
This ebay seller has loads of them for sale in a variety of sizes. http://www.ebay.com/itm/52x19mm-solar-cell-for-DIY-5w-solar-panel-untabbed-poly-solar-cells-/320907099098?pt=LH_DefaultDomain_0&var=&hash=item4ab78dbbda
MAJOR-Thanks !!!

i had been looking for these but so very many months ago that i gave up the pursuit in the end until now, a great many thanks for opening up these doors for me and im very grateful !!

also rated your 'ible 5 stars when i wrote my 1st comment and now another 5 !

thanks again !!!

;-)
ecodad1 year ago
What are the specs on the (optional) LED and Schottky diode shown in the video? Is there a trick to super gluing those to make a solid contact or do you use solder?

p.s. awesome project on Kickstarter
http://www.kickstarter.com/projects/alex9000/the-solar-pocket-factory-an-invention-adventure
kostya2 years ago
Looks great! Solette means a little sun, doesn't it? I wonder what is the amperage of those solettes in the video. Thanks for sharing.
sfrayne (author)  kostya2 years ago
Thanks! Each solette in the video puts out a short circuit current of around 125mA, with a max power point current (Im) in that ballpark as well (around 100-110mA). The shingling technique of stringing the solettes together blocks some of the output from each solette, so if you are getting 80-100mA delivered to your battery, that's right on. (this is also just right for trickle charging a 2000mA NiMH battery safely, even in max sun).
Thanks a lot for the info !
kostya sfrayne2 years ago
Thank you for the informative response. I'm looking forward to your upcoming projects.
I would love to buy Solettes, where can I buy them?
Solettes really aren't that hard to come by...if you search Ebay for solar pieces you get a tons of results. They tend to run only $6 for 40 pieces.
sfrayne (author)  cesar harada1 year ago
Get yer solettes here! http://www.kickstarter.com/projects/alex9000/the-solar-pocket-factory-an-invention-adventure

p.s. More Solar Pocket instructables coming in a few days....stay tuned.
sfrayne (author)  cesar harada2 years ago
Hi -- since solettes are pretty hard to come by , me and a few other folks are launching a solette-laden Kickstarter on Aug 15 -- I'll send a reply once it's up and running.

But for now, you can search on eBay for laser cut or laser scored monocrystalline (or polycrystalline) cells and find a few options. Like this:http://goo.gl/C25he
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