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Question about multiple power source for project

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I bought a nice and very inexpensive little fm radio. I built a case for it and have power input terminals on the outside of the case. I put a 5 volt voltage regulator chip inside the case to allow correct voltage fed into radio using various feed power sources such as a solar panel, battery pack, or both. Question: using the solar cell connected along with the (alk) batteries, is it correct to say the solar panel reduces the drain on the batteries? Is this OK? The solar cell has a blocking diode. If I used 4 ni-cad AA batteries, could I hook them in so the solar panel will charge them? Where-- after the 5 volt regulator? Hope this makes some sense. It is a learning adventure. I've tried it and nothing has smoked or failed so far. My goal is to have a solar source powered radio, but what I'm doing seems a little strange.


You need a blocking diode for alkaline batteries.

The solar panel will only save battery life, if the output voltage is one diode drop greater than the battery voltage.

For Nicad, you need something to limit the current.

4 batteries won't be enough, you'll need six or more to get anywhere near decent battery life out of it. Alkaline cells quickly drop to 1.2V each and should ideally, it should be able to work down to <1V per cell.
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