Build Your Own Hand-Cranked Powerbank to Charge Your Phone in Emergencies

Like most people, you probably rely very heavily on your smart phone. And we’ve all experienced the inconvenience of a dead phone battery, which is a hassle even when you’re just out running errands. However, that inconvenience can easily turn into a legitimately dangerous situation if your phone dies during an emergency. In this tutorial, GreatScott! will walk you through how to build an emergency hand-cranked powerbank generator to charge your phone in a situation like that.

In the YouTube video below, GreatScott! spends a lot of time thoroughly explaining how this hand-cranked generator works, and why his initial designs failed. Originally he was planning on using a BLDC (brushless direct current) motor like you’d use for a drone. But those are designed to run at a high RPM, which means they have to be turned at a high RPM to produce a sufficient amount of power to charge a powerbank. He was able to improve the low RPM performance a bit by rewinding the motor, but ultimately it just wasn’t enough.

Switching to a geared DC motor dramatically improved the performance. Geared motors take the high RPM output of a DC motor and gear it down, reducing the speed and increasing the torque. The opposite is also true: turning the output shaft at a hand-crank speed spins the motor itself quickly and generates enough power to charge the powerbank’s battery. With that in mind, it’s a simple matter of connecting the motor leads to the battery. A 3D-printed case holds everything together, and a printed hand crank is used to turn the shaft. It would take several hours to fully charge your phone with this, but a few minutes should be enough to place a call in an emergency.