This solar battery charger makes a great emergency AA or AAA battery charger as well as a off the grid, self sufficient battery charger. The bonus is it can be made for about $6-$12 dollars depending on the amount of power and batteries you want it to charge.
Step 1: The Supplies
. Dollar store solar garden lights ($1.50 for small solar cells or $3 for large solar cells) You may chose how many of these you use, I would recomend using four small if you have those or two large. If you plan on using more or you need to reduce the voltage, you may have to use a resistor or a voltage regulator.
. Electrical wire (Positive and negative wire)
. Batteries that are rechargeable (AA or AAA)
. Heat shrinker
. Electrical tape
. Soldering iron
. Solder rosin 60/40 core
. Wire cutters
. (You might need other tools for the solar light disassembly ie screwdrivers or pliers)
Step 2: Solar Garden Light Disassembly
Once you have all the parts, you can start by dissembling the solar garden lights, they will contain a basic circuit board with a voltage regulator, a resistor, solar cells (size depending on the one bought) and a few wires that are connected to a rechargeable battery. We will only be needing the the solar cells, the resistor and the positive and negative battery connecters.
Step 3: The Circuit
The image shown is a diagram of the circuit schematic we will be building. The diagram shows two large solar garden light solar cells being used in series. If you use four smaller ones, it will look similar except for there being four cells in series instead of two.
A diode will be used to prevent the current from flowing backwards when the sun is out of view. Once we check our output of the cells, we may need to implement a resistor or voltage regulator, in my case I didn't. If you plan on adding a charge controller to the circuit then you won't have to check on the batteries every so often, which can be convenient.
I will use a voltmeter to check on the condition of my batteries and their charging rate, this will allow me to make sure they won't overcharge and are fully charged. If some of the materials in the circuit you might be using are bit different from mine, so if you use different batteries, solar cells, resistors, etc expect different results.
Step 4: Plan Before Soldering
Before you plan to solder everything make sure that you have everything laid out, as if you were going to solder it. You can hook up the wires by twisting them together before you solder them, this will make sure everything is in the right location. If you plan on using heat shrinker make sure it is on the wire away from the wire connection so it doesn't by accidently get heated. If using electrical tape to cover the soldering connections wait until it has fully cooled.
Let your soldering iron heat up and have your rosin core ready. Make sure the area your working in is well ventilated and try not breath in the fumes. Some advise would be to use a fan and have the windows open in your work space to allow air flow. Allow the fan to blow towards the were you are soldering and in the direction of an open window or door.
Step 5: Soldering
(I didn't solder on my table and you shouldn't either, just using it for a demonstration, use a work space that will be dedicated to soldering or use third hand clips to hold the wires)
Once your ready to go begin to solder the connections from wire to wire. Make sure your soldering technique is good or you may not get the best connection from the circuit. Once everything is soldered use your volt meter to check the connect of the circuit, current and voltage. If it looks like the batteries will need protection add a voltage regulator or resistor to the circuit.
Step 6: Mounting the Charger (Optional)
Once the charger is fully assembled, it can be used as it is or can be mounted to an object or placed in a clear container, I used my as it was. The charger is not water proof so be carefully where you place it.
Step 7: Test Results
To test the accuracy of this charging device, I would recommend using rechargeable batteries that are either dead or have fifty percent power left in them. Also to accurately test it, place the charging device in the middle of an open place to fully take in the suns rays.
It may take a few days to charge your batteries depending on how many solar cells are in your circuit or the conditions of the sun brightness. You will need to check the status of your batteries by using a voltmeter. I got a reading of about 3.0 volts and an output of about 10 mah (I might be wrong but about the output since I tested it under a lamp at night). Since the batteries are 1.5 volts I had to use a resistor to slow down the voltage. The output depends on the brightness of the sun.
Thank you for reading my Instructable, if you have any questions or ideas on how to improve this project please let me know in the comments, I look forward to from hearing you. If you enjoyed it please favorite it and vote for me in the solar contest, every ballot counts. :)
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Step 8: Improvements to the Circuit
Some improvements that could be added to the circuit to make it charge the battery charge faster, be left for longer durations of time without being checked on and increase charging time.
Here are some possible mods or improvements that I have come up with, if someone wanted to improve the circuit:
. Charge controller (To limit and control the output of the cells and not keep having to check on them with a voltmeter)
. More battery holders (Able to charge more batteries)
. More solar cells (would need a charge controller or voltage regulator)