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solar charge dual 18650 batteries - best practices

feiticeir0

Hi all !

Again, I'm here with a question regarding the sun.

For a remote project, using a ESP32-CAM, I need it to be powered by batteries and solar panels.

This will be using a ESP32-CAM, a TOF sensor and a LDR sensor.

I have these two solar panels that I will wire in parallel to get 5v and a few more milliamps. I know they are 5v, but the amperage is low, so that's why I'm wiring them in parallel. Don't ask me about the wattage, because I don't know that.

I need them to charge two 18650 batteries and I've seen a few options on the internet.

I would like to use items that I already have, like:

TP4056

image

Solar charger v1.0

image

I have others, but are to big for this project.

The solutions I've seen include - one TP4056 to charge two 18650 batteries in parallel :

image

Although this solution seems sketchy at best - I know that the TP4056 is just to charge 1 battery and not 2.

I've seen using two TP4056, each one connected to one battery, but the output is then connected in parallel to a step-up for the 5v - the input both come from the solar panels.

Or this one:

image

This one seems to be the best and more complete that I've found

What's the best way (and safest way) to accomplish this ?  I'm assuming I need two 18650 batteries to power everything.

The circuit will be using 5v, so a step-up is necessary before connecting to the ESP32-CAM.

Thank you in advance.

  • I have seen 18650  connected in pairs and even by groups of three in parallel in laptop batteries - so it seems that as long as they have similar parameters, even reputable manufacturers do that.

    Don't worry about TP4056 parameters when charging two batteries - panels would provide at most 200mA, so 500mA/1A TP4056 current limit would never be hit.

    In another approach you can connect panels (and batteries) in series, put BMS module to balance cells, and install step-down converter - when battery voltage drops below  5V, both cells will be nearly depleted. Or install step-up/step-down converter to extract all possible energy from cells (to the point when BMS will disconnect the load because of undervoltage: about 2.2V/cell)

    And about converter - MPPT converter would probably extract more power from the panel.

    If you check my project from "experimenting with waterproof connectors", I have used module that is Li-Ion charger integrated with step-up converter (and battery pack of two or three - salvaged from some laptop), unfortunately without under-voltage cut-off, so batteries can be damaged if left too long without charging...