USB Fan: Remove battery

I have a simple fan that could either be powered by a battery or through USB. To switch it on or off, I would need to press a button. I wanted to convert the fan to be purely powered by USB and automatically switches on when power is supplied through USB. This will allow me to add the fan to my home automation setup.


Upon prying off the back of the fan, I discovered a simple circuit board with the following connectors.

  1. Connector supplying power to the fan
  2. Connector to 18650 battery
  3. Connector supplying power to an LED
  4. Button to switch on LED
  5. USB-C connector to provide power/charge battery
  6. Button to switch on fan

Since the battery starts charging once power is provided to the USB-C connector (5), I reasoned that if I replaced (2) with (1), the fan will immediately start running once the USB-C connector provides power. Since the battery has been removed from the system, the fan will immediately stop once the USB-C connector stops providing power. This will achieve the desired effect.

The USB-C connector (5) provides an input of 5V, while output (2) is likely to be around 3.7V since it is used to charge the 18650 battery. Could the fan be powered off 3.7V? The chip on the left appears to be a TP4056. I am unsure if the voltage is stepped up before reaching output (1). Nonetheless, it doesn't hurt to try. At most the fan will not spin or spin slower due to lower voltage. After re-assembling the fan, the fan did indeed work as expected.