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Author Topic: Anyone playing with solar cells to power their devices?  (Read 473 times)
Maets
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« on: March 26, 2016, 07:06:04 pm »

I would like to use some small solar cells to power a small SD card viewer.  The voltages are the same, but the solar voltage actually varies  with amount of light.  Putting a battery in the system would seem to be a good idea, but what about over charging?

Any thoughts?

Thanks!
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Hektor Plasm
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« Reply #1 on: March 26, 2016, 08:00:34 pm »

You could put a voltage regulator in series with the input, but would need a couple of extra volts for it to play with- eg 5v output, min 7.5v input, and so on. Or you could go old-school and use a zener diode and resistor...

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« Reply #2 on: March 26, 2016, 10:36:48 pm »

If the solar cell current (mA) output is small enough, and the battery capacity (mAh) is high enough, then overcharging shouldn't be much of an issue. Just use a Nickel–metal hydride battery as they can handle a small constant charge input  / mild overcharge better than other types.

Or an easier and perhaps more usefull method is to use a small "super capacitor" and solar panel directly connected - no worries about overcharge. To regulate the power output you will need to use a small voltage regulator, or better, a mini switchmode supply to drop the higher voltage of the capacitor (cap will charge up to the voltage output of the solar cell). The cheap and easy method is a small low-dropout (LDO) regulator, which can continue to regulate the output voltage even when the supply voltage is very close to the output voltage (the cap voltage will drop as the power is drained).
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Maets
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« Reply #3 on: March 28, 2016, 02:41:23 pm »

thanks for the info.  Hope to get a chance to play with this soon.
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