Running NodeMCU ESP8266 on 3s 18650 battery pack powered by solar panel

Question

I am making a circuit which controls a 12V analog mechanical device using microcontroller (NodeMCU ESP) GPIO.

The Node MCU uses AMS 1117 to step down voltage to 5V (& another one to 3.3V), but since they are clones, the AMS 1117 (for 5V) used allows for a max of 12 Volts. A lot of literature on net is amass with references to how people burnt their circuit due to 12.5 volt input.

I'm using 3s 18650 battery pack with BMS to power the circuit (The battery pack itself is charged by solar panels). The max voltage is capped at 12.6 Volt, which is enough to kill the chip.

So I've some 'alternatives' in my mind, which I'm not sure what their fallacy be:

1. Take out power between 2 of 11860 batteries, which would give voltage range of 6-8.4 Volts. Good enough to power up the NodeMCU
2. Put a diode to reduce the voltage by 0.7 volts, good enough to keep the input voltage to NodeMCU to 12V max.

I don't understand the implications to any of these from battery's charge perspective. Since this entire thing will work on battery pack, I'd want minimum wastage of energy ideally.

Can someone please suggest if I'm on the right track, OR what may be the right way to go about this?

Answer 1

Get a proper DC-DC converter that accepts the full battery voltage input and outputs 5V. With a suitable "buck" converter this can be very efficient.

(Possibly 3.3V directly? It's not entirely clear that the board needs 5V and if you can just take it directly to 3.3V that would be more efficient.)

Or alternatively just use the two batteries and remove the third entirely. Having it charged but never discharged will cause problems as the pack becomes unbalanced.