Using a Dc motor as a generator

https://youtu.be/0PG55ZWxkSI

It might come as a surprise to some readers, but there is absolutely no need for any conversion, for while many DC motors are operating as motors, THEY ARE AT THE VERY SAME TIME ACTING AS GENERATORS while their conductors in their armatures are cutting the magnetic field. This is all explained by the relations Force = BI(length) while Volts = Bl(velocity) which are both occurring at the same time in any DC motor.

Anyway to obtain some relevant voltage you need speed for this you can use a large flywheel. In this project I used a 10 kg weight. All you have to do is to attach the Dc motor to the flywheel.

I used in the test C9050-6003 brushed electric motor series. You can test diferent Dc motors and diferent flywheels.

The complete project you can find it here : https://www.instructables.com/DC-Motor-Generator-2/

Using a larger flywheel is better.
ST.