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How can I set-up my small solar panel to charge AA solar-rechargeable btteries?
My set-up looks like this...
Solar panel
Rated power: 5w (per hour)
Rated voltage: 12.5 V
rated current: .40 A
Open circuit voltage: 15.6 V
Short circuit voltage: .45 A
10 - AA batteries
1.2 volt
900 mAh
I have the batteries wired in series so i can come up with the desired 12 volts I am looking for. But I am not sure if I this will charge the batteries at the same time? I'm hoping to set a small light or two to run off the batteries after dark and was planning on running that on a switch in parallel to the system. Will this work? Or do I need to change it to get a charge from the batteries?
No, you need to keep the voltage at the batteries somewhat lower than the solar cell output so current will flow.
The batteries when under charge will be at about 1.4-1.5 volts, so 10 would add up to 15 volts, much more than your array will put out.
But more important is the actual output of the array, not the specified output, which is at peak sun, with the array at exactly right angles to the sun's rays.
Get a voltmeter and check it's output voltage under your conditions. It may be as low as 6 volts. Then calculate a resistor value to draw 400ma and put that on the output and measure the voltage again. You could also measure at lower current, say 200ma.
Once you get the array characterized, then pick how many cells you can charge in series. You will need to monitor the current to be sure you don't exceed the max charging current of the cells. And you need to monitor the voltage to be sure you don't overcharge them, which can cause them to explode.
You may want to buy or build a charge controller that will do all this automatically. Some of the better models use a DC-DC converter so the correct voltage is always available.
it gets more complicated. contact me if you need to.
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