I am trying to build 18650 solar light. I would like the lights to come on when it gets dark and go off when the batteries reach a set voltage or when it gets light out.
You can use a small photoresistor to get the lights to turn on when it gets dark and turn off when it's not.
The TP4056 module has a discharge cutoff function that stops the battery from providing power when it's charge is too low to prevent any damage to the battery.
LED = 12V * 50mA = 0.6W
I have a few cheap 18650s, and I hope to have some Panasonic 3400s fairly soon.
Well, why didn't you say this before. You don't really need 3 batteries for that.
A single 2600mAH 18650 has about 9.3WH so it can power you 0.6W LED for about 13-15 hours = more than enough to power your light from for a dusk to dawn.
Them Panasonic 3400s will give you well above a 20 hour runtime.
You just have to boost your battery voltage to attain 12V
I have 3 solar panels to choose from:
Solar Panel 2.5W 5V/500mAh (x2)
Solar Panel 12V 3W
Just use 1x 5V (2.5W) solar panel for the setup I suggested. 500mA is more than enough to charge a single 18650 cell. At optimum conditions your panel will fully charge a 2600mAH cell within 6 hours.
I have some p-channel mosfets (9v gate) and I have some logic level P channels on the way
You don't really need MOSFETs for a 0.6W LED, Transistors will do the job. Just connect that photoresistor to the Transistor.
Watch this example --> https://www.youtube.com/watch?v=eEBMTpxdPiE