5V/12V UPS with USB charging port, off switch and integrated 5V charger

thingiverse

# 5V/12V UPS with USB charging port, off switch and 5V buck regulator to charge the batteries This is an add-on for https://www.thingiverse.com/thing:4970270 that adds an off switch and integrated battery charger. It requires to modify the UPS PCB ## LTspice simulation I have added a LTspice simulation of the UPS to test the output voltage, and the complete wiring. ## Off Switch To avoid switching the entire current of the batteries, the switch pulls the voltage detection to ground. The battery protection chip sees ~0.9V and goes into under voltage mode. The UPS draws 9µA instead of a couple mA and there is no need to remove the batteries or leave the charger connected. Do not forget to charge the batteries every 3-6 months if not in use. To turn it on again, the charging cable needs to be unplugged to reset the battery protection. The chip is a FM5056. It is possible that it turns on automatically after a couple minutes, but I did not test that. ## 5V Charger I added a buck converter to the 12V input to avoid connecting USB or external 5V. The charging current is less than 1A. https://www.aliexpress.com/item/1005001621804332.html