Can someone give me advise about a solar system?

Hi there,
I'm 17 and i'm studying Industrial Sciences. For my thesis I'm trying to make an energy- and environmentally conscious system. I want to be able to switch between a USB source and a solar-powerd battery. First I tried to make a solar-battery circuit and i made a diagram. But i have absolutely no clue if what I'm doing is actually right. Now I'm also looking for a way to switch between the two sources. Does anyone have some recommendations for me? Can anyone give me some advise or some tips? (I can't put my diagram down here but I will upload it as soon as Arduino gives me permission to do it.)

Already a big thank you to all of you!
New-Project.pdf (73,5 KB)

You will find a great tutorial on making solar powered Arduinos at:

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You can use a double pole double throw switch. Or you can use a double pole double throw relay.

Thanks Paul!
I will look into the double pole double throw relais. I have considered making a power path but I think this will be more useful.

I'm not sure this is a great idea. You might be in danger of re-inventing the wheel and ending up with a square one, but I guess it depends on what you really want Arduino to do.. I understand the normal situation is that Arduino simply takes the most suitable source of power that is available automatically. If you insist on doing this, you might need to look at switches that are make-before-break, which, these days is probably something best done with solid state components.

Thanks for warning me. I actually want to power an Arduino with two sources. But I want to be able to switch between them on certain conditions that I am going to put in my program. An example is that if the battery has a percentage than 20% that I can switch to the USB. Do you have any other recommendations? Can I use two separate relays? (Please let me know if anything that I am saying isn't possible.)


Thanks, this is a actually a great idea!

Schottky diodes. .6 Volt drop across it. allows a little current to trickle backwards. the voltage from each source goes through one of the Schottky diodes. they attach to a common bus bar. that feeds the circuit. either or both sources powers the circuit. if one fails and the other does not the device keeps working. it is wise to put LEDS on the feed sides of the diode so you know if a source has failed.

Why not just let the panel charge the battery and take your power from the battery .

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That's the way I think of solar.

The panel is a current source, the MPW or MPTT Charge controllers is the converter from current source to voltage supply, and the load runs off the battery.

The Charge controller will monitor as the battery is charged. When the battery is charged the charge controller will stop charging the battery. At the moment the charge controller stops charging the battery the project runs off the battery. The charge controller watches the battery until the charge has dropped to a level and then it starts charging the battery.

Assuming there is good reason for doing all this, you might find you need to think outside the box a bit:- where you use two single pole switches and ensure the supply is from source A by having source B turned off.

Well this was also my idea first but I didn't know if it was actually gonna work. I made a diagram and today I have gotten the access to upload it. Can you let me know if I have to change something or if I did something wrong?

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