ESP8266 Community Forum

The 5V on the NodeMCU is your positive input, not an output, and the 3V3 is generally an output not an input.

If you check the D1 circuit, there's an ME6211 LDO supplied by the 5V pin that outputs up to 500mA on the 3V3 line - this is used to power the ESP and also for any external sensors that need power. The dropout voltage on the LDO is about 300-500mV so you can supply as low as 3.6-3.8V on the 5V pin and it will still work.

What Voltage is your LiPo charger circuit supplying? Can it be hooked up to the 5V pin? As it is the diode on your circuit is going to protect the LiPo so put one on the 5V side as well and you should be fine

That is interesting @davydnorris but I may not have explained my problem very well:
Back feeding through the 3V3 works but at some point I need to get my data file off the device and onto my PC. What I intended on doing was pluging the Nodemcu into my computer; again not a problem if I isolate the battery. But I know at some point I will forget to turn off the battery. In this case I will have both the Nodemcu USB and battery powering the same circuit. I feel thing will not go well for the device in this case.


My options seem to be:
Put some sort of automatic switch in before the battery to isolate it if the Nodemcu USB is plugged in.
Put a mechanical shutter in front of the Nodemcu USB port which isolates the battery when it is opened.
Send the data file to my PC or a website and blank off the Noemcu USB connector. This does not seem as easy as it sounds. I have sent a string to a Pi in the past without a problem but am unsure how to send a file and the same goes for a website.

No that should be fine - I have the exact same situation with my board and as long as you protect the forward voltage from both it should be fine