I have finished the design of the lid for the case for the mini-power bank which can be used in small projects, where regulated voltage is not required. I have also tested out a concept of having the indication with LEDs through a thinned plastic. A near cut-out has 0.2mm thickness, while the rest of the lid has thickness of 2 mm. When there is no light source inside of the enclosure, the near cut-out is not visible from outside.
I have used Fusion 360 to make a quick enclosure for the charger and a 500mAh LiPo battery. Have made some renderings to show the progress. The outside dimensions of the enclosure are 55 x 35 x 10 mm. The design is prepared for a cover on the top, which will be held by two latches and two M3 screws, screwed directly in the plastic.
I have soldered the wires from a brand new 500 mAh LiPo battery to the charger to make a first serious test. The internal resistance and high SoC put the charger in a constant voltage mode in about 10 minutes. I have measured the voltage across the battery (4.192V) to verify that it is not a thermal throttling. The reason for using USB-A to USB-C cable is because I don’t have a USB power meter with USB-C connector. It is more handy to use USB power meter rather than measure the battery current with the multimeter. However, I have tested it with USB-C to USB-C cable as well, and it seems to work, since the charger gets warm. The next step is to make a simple enclosure, which integrates charger with the battery.
The USB-C has been around for quite awhile, but there is still a lack of a miniature basic USB-C chargers for LiPo battery. I decided to make my own with as minimal footprint as possible, which resulted in being 13.5mm x 16mm. A well known MCP73831 is used as a battery charger in DFN package, to minimize the risk of thermal throttling. Today I have manually assembled the first prototype, which has survived a smoke test!