What Shape Portable USB Powerbank?

Cort and I would like to embed lithium cells in portable projects and want power management that:

  1. steps up the lithium cell’s 3.7 V to a well-regulated 5 V
  2. safely charges the lithium cell from some source
  3. powers the load while charging the cell

I knew it’d be easy finding power management modules that met the first two points, but I wasn’t sure whether the third point (power the load while charging) would be a ubiquitous feature, or even clearly called out in documentation. Fortunately, while browsing power management modules, I quickly found that the HT4928S mobile power management chip supports all three, and found cheap modules both with and without USB connectors on them, and ordered a batch of each style.

18650 lithium cell with power management modules

Now I have them and need to test that they work as described, preferably without burning down my house or pocket. The obvious test is to hook one to a secondhand 18650 cell I have lying around. While I’m at it, I may as well 3D-print an enclosure for it and have a spare USB powerbank.

I know that I want the body of the case to have a square cross section with chamfered corners, because even my hexagonal USB powerbank is a little more rolly than I like. And if I’m printing my own enclosure, I also get to decide the position and orientation of the connectors relative to the 18650 cell. Where should the connectors go, and pointing which direction? On the end pointing out the end is common, but are there reasons other than mere novelty to favor a different position or orientation?

18650 lithium cell with power management module

18650 lithium cell with power management module

18650 lithium cell with power management module

18650 lithium cell with power management module

18650 lithium cell with power management module

3 Responses to “What Shape Portable USB Powerbank?”

  1. Personally, I like the last configuration. It gives you the option of zip-tying the USB cable to the case as a strain relief.

  2. J. Peterson says:

    Since you’re customizing the case, I’d experiment with integrating cable management into it. I.e. make the whole package a convenient place to to neatly wrap up a 3′ USB cable, with clips to hold the connectors in place.

  3. Keith Neufeld says:

    I feel like that’d be a bit tricky starting with an 18650 cell, but I like the idea enough to look for another form factor (like a mini candy bar) that would fit nicely inside a core to wrap cable around!

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