6F22 9V Ni-MH Charger - Ninecraft nano

6F22 9V Ni-MH Charger on DC-DC step UP module.

Inside the battery(6F22), there are 7 cells connected in series, each with 1.2V, totaling 8.4V. As is known, Ni-MH batteries should be charged to about 1.5V, hence the calculation: ( 1.5 x 7 = 10.5V ).
For charging a 6F22 Ni-MH battery, it must be charged to a voltage of 10.5V and a current not exceeding 45mA. To do this, we will make a converter from 5V to 12V because 1V drops on the LM317 and 0.5V on SS14 and there will be exactly 10.5V left. The charging current will be limited to 35mA; at the end of charging, the current will be about 2mA. The end of charging will be indicated by an LED indicator when the voltage on the battery reaches about ~9.88V.

This project was based on Multi-function Mini Boost Module Step Up Board 5V/8V/9V/12V 1.5A LED Indicator.

It's a small module, very popular in many markets. We need to set up a resistor divider on this board to output 11.8V~12V. From the datasheet (SDB628), for 11.8V~12V just need to replace one resistor 15K to 16K.

the divider must be set up to output strong 11.8~12V. With this, we got a perfect small charger for 6F22 Ni-MH battery, working from any 5V USB charger, with an LED indicator, indicating when charging is complete. We don't need to implement charge termination, as at the end of the charge cycle, the current to the battery will be very low, around 1mA. In such a mode, the battery can remain connected for quite a long time, up to several days.