Hi there,
And Welcome here…
So, On XIAO boards, the EN pin typically uses a weak pull-up (100 kΩ–1 MΩ) with a small C (~0.1–1 µF). When VBUS ramps slowly (e.g., from a spinning turbine), this:
- Causes partial EN activation,
- Powers the chip partially (warm to touch),
- But fails to start properly.
Unfortunetly you can’t have it both ways as built.
Use a Soft Power-Up Supply (e.g. Supercap + Fast Diode + LDO)
Design your power circuit so that:
- A Schottky diode charges a supercapacitor or large ceramic cap from the turbine.
- Then feed that into a low dropout regulator (LDO) with a Power-Good (PG) pin.
- Use PG to gate the LDO or control a switch to 3.3 V rail or USB port.
This ensures the LDO doesn’t output until it sees steady voltage is one way to do it that I know works.
I have used a small power bank in between the Charge cable and powered it with a solar panel power mc4 input, for example.
HTH
GL 
PJ 
When you insert a USB power bank or regulated USB device between your turbine and the XIAO, it:
- Buffers the input voltage from the turbine’s ramp-up (slow/dirty 5V).
- Provides a clean, regulated 5V USB output to the XIAO.
- Holds enough internal charge to avoid brownouts on minor dips.
- Effectively delays VBUS rise seen by the Xiao until it’s stable.
This “virtualizes” the power-up curve and mimics the stable power expected by the ESP32’s internal EN circuitry.