Mini automated solar powered lamp

Thread Starter


Joined May 20, 2022
Hi everyone,
I'm trying to build a solar powered lamp that automatically turns on when it gets dark for my grandfather.

He has already purchased a small solar panel connected with micro USB to a light bulb that has to be switched on, but I wanted to automate this by connecting a photo resistive relay to it.

The bulb itself has its own 600mAh li-on battery where the only real circuitry is a IN4007 MIC diode and an 2000 ohm resistor.

The relay has to be powered with 5v so I thought I'd hook it up to a 2500mAh 3.7v li-on battery and using a voltage booster to boost it to 5v.

I want to try and charge both the 600 and 2500 battery using the single solar panel, but I am not sure if I can charge the 2500 one with only a diode and resistor as is the case with the 600. I have read here that you don't need a charging circuit if the current is quite low.

Given that I live in the Netherlands it is mostly cloudy here and on such a day the solar panel gives a short circuit current of about 0.45A and on sunny days 1.6A.

My question is then: do I need a charging circuit for this setup? Or is a diode and a resistor enough to keep it safe. I will also provide a very crude drawing of the circuit I have in mind, but I'm not the best when it comes to electronic circuits so any changes would be welcome.IMG-20220520-WA0001.jpg

Audioguru again

Joined Oct 21, 2019
A li-Ion battery explodes and catches on fire if it is simply over-charged like you are planning. The battery is also destroyed if the charger does not detect a full charge and disconnect, and if the circuit does not detect a low battery voltage of 3.0V to 3.2V then disconnect the load.

The article you read about using a low charging current talks about a completely different huge 12V lead-acid truck battery.