YouTuber "GreatScott!" has come up with four solutions for a common problem when powering microcontroller projects from commercial USB power banks: their tendency to power down under low load conditions.
"It is no secret that I do love power banks," GreatScott says in the introduction to his latest video. "They are not only super handy when it comes to charging up your phone, or nowadays even your laptop, but they are also a perfect fit to power your portable electronics projects. They pretty much only come with one major flaw that I just recently noticed again. And that flaw is that all power banks turn off automatically if you are only drawing very little current on the output, which sadly for me though is quite often with my projects."
While there are commercial power banks which can be switched on and stay on regardless of load, they're less common — and it can be a little late when you discover that your particular project draws just under the power required to keep the more common types of power banks from trying to conserve their power by automatically shutting down. The most obvious solution, short of replacing the power bank, is to increase the power draw above the cut-off limit — but that's only one of the solutions offered in GreatScott's video.
"[The] most simple solution that everyone can use [is] simply using a power bank with a USB [Type-]C output [with] a Power Delivery trigger board, that you can get for cheap," GreatScott explains, referring to the USB Power Delivery (USB PD) standard. Another solution solves the problem of a deliberate constant load draining the battery too quickly: a pulsed load. "All components in total cost maybe around $2," the YouTuber says, "while only drawing current spikes around every eight seconds."
The final solution: hacking the power bank itself. This, however, proved a lot more challenging — with several approaches proving their potential but falling short of full usability, including in making the output voltage unstable and thus badly-suited for use with precision electronics. GreatScott does note, however, that even with this unstable output his low-power projects continued to work.
The full video is embedded above and available on GreatScott's YouTube channel.