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hello everyone!

in my last instructable i have shared with you how to put together a simple plant arm; https://www.instructables.com/id/LED-plant-light-ba... which runs on batteries. I have a battery charger but that means paying for electricity. luckily I had a box of unused solar path lights just sitting around collecting dust.

in this instructable, I will share with you how to make a simple solar panel that can charge 2 x AA batteries in 6-8hrs. which is really not bad at all. I plug this thing in before I go to work and when I get back my batteries are fully charged..!

since the plant light is not on for long periods of time, it actually lasts 2-3 days before going out. i keep them on for 3 extra hours a day usually if i don't forget. remember, my plant gets direct sunlight but only for a short period of time during the day. so this battery charger is actually perfect for my needs and it was all for free on my end..!

let's have a look...

Step 1: Parts

-- the only thing you will need to find really is a simple diode; http://www.dx.com/p/jtron-in4007-smd-rectifier-dio...

the rest,

1. solar path lights. I have used 12 in this design.

2. we need a 2xAA battery holder pack. go to your local dollar store (or thrift) and buy an LED desk light of some sort that runs on 2 x AA batteries, that is what I always do, because you get lots and lots of parts for just 1 dollar :)

3. multimeter. this is not needed to build the solar panel, just to test it..!

4. cardboard or styrofoam for the body. notice my panels are cut into the cardboard so they sit flat on the surface, this improved durability and looks much better.

5. clear plastic wrap for kitchen use, i'm sure you have this at home. this will protect the solar panels.

6. 22" wire. radioshack or you can use old power cables from your local thrift store - reuse always !!!

7. solder/soldering iron

8. USB female and male connectors. this is completely optional. i like converting all my connections to usb ports. it's just way easier and universal..

next..>

Step 2: Assembly

sadly i put this thing together very fast and didn't take picture until it was soldered and wired up, so follow my drawings on the back image of the panel.

(for the body of the solar panel, i carved out a piece of styrofoam i had. you can use cardboard as well, just be careful not to break or scratch your panels while working with them!)

ok now. we need to make 6 sets of 2 in series solar panels. before I soldered anything anywhere, I checked how much electricity a single cell created in full sun. it was upto 2.2V sometimes but steady around 1.7Vish. anyways, connecting 2 of them in series gave me a steady 4.5 per set. then I decided to add more mA to my setup, the remaning I soldered in parallel. giving me about 120mA in total. so maximum this solar panel gets 4.7V as you can see from the multimeter reading. not bad at all right ?!

one thing to watch out here is to add a simple diode on the positive (+) wire in the direction that you want the electricity to flow, to the batteries, not back to the solar panel. apparently solar panels suck back energy in the dark which can kill them. with this diode, the little different colored part being the direction of the electricity can save your panels !

the battery pack i chose is connected in series. i personally do not know what would happen if it was connected in parallel. but it works this way. maybe it would charge faster or slower - anyone know the answer to this?

UPDATE: here is the answer to this question thanks to user " ironsmiter "

quoting his comment;if pitch black, and you supply voltage to a solar cell, you can sometimes SEE the light it produces. the same applies in reverse, if you shine an extremely bright light onto an led, you can Measure minute voltages. Not suggesting either works efficiently or even well That way.As to your serial vs parallel battery... if you had them in parallel instead, charge time would be nearly identical but you would want your solar panels wired in a 1 × 12 configuration instead of 6 × 2. you would have half the voltage and double the mAh on both the battery pack and solar panel

Step 3: Conclusion

it works. the multimeter reads 4.7Volts. from what I have learned, as long as the voltage coming out of the solar panels are higher than the charging batteries, they will charge. otherwhise nothing will happen. on the other hand the mA coming out of the solar panels decide how fast the batteries charge.

i was never able to measure the mA reading from the solar panel with my multimeter, i actually have no clue on how to use them :) I did get a very good reading for the voltage tho and the charged batteries, while dead and charged. so overall the system works and it is perfect for my needs. i don't even use my AC wall charger anymore !

please message or comment with questions/answers..

also make sure to check out my other designs; https://www.instructables.com/member/0bios0/