I have ~100 mAh 6 V solar cell that I want to use to charge 18650 lithium-ion battery. Purpose is to use a PIR sensor to turn on light when someone passes by,
I am not very confident about the efficiency of circuits I found online or using something like a TP4056 as I only have limited energy to work with that I don't want to waste as heat while charging so I was looking for a simple solution that cuts off or dumps excessive solar energy to some load when battery is at 4.2 V.
I tried reverse-engineering professional products but they seem to use unlabeled ICs and might have some peak power harnessing magic going on as they work with puny solar cells (50 mAh) yet work without a fail all night, I can reuse such product but
- My solar cell is twice as powerful
- Light is twice as big
- PIR sensor looks different, mine is bigger
- There is no fun in slapping everything on existing circuit without learning anything
What kind of simple circuit can be used here? I don't care about battery health as much as LEDs I have turn off at around 3.3 V anyway.