A project log for Coin Cell Challenge...

Lithium coin cells are convenient energy stores for projects. Not safe if swallowed though. Can we do better?

Simon MerrettSimon Merrett 04/06/2019 at 20:050 Comments

This is just a short run-down of the thought process going into selecting alternative energy stores

Candidate requirements for an alternative store:

  1. Must be removable/replaceable OR rechargeable (and firmly fitted if removable/replaceable).
  2. Must aim to be low volume (so as to fit on the back/front of a blinky badge).
  3. Should not require superhuman skills to implement (SMD - yes if the pitch is >= 1mm, BGA - no!).
  4. If rechargeable, charging should not take so long as to put people off doing so (for the limited expected gain in pleasure of running the device again)
  5. Must allow the device to run for a reasonable duration. Requirements 4. and 5. are somewhat intertwined - if the charge time is low enough, I'd expect people would tolerate lower run-times.
  6. If removable, be harder/less attractive to put in mouth/swallow from a child's perspective, than a coin cell.
  7. If replaceable, be available to purchase from outlets the general public would use (such as AA cells).
  8. If rechargeable, be so from electrical supplies that are common in most homes (e.g. DC 5V phone charger)

I'm sure there are probably more requirements (other aspects of safety). From these, I assessed the following alternatives to lithium primary CR2032:

Next time...

...maybe the modified CR2032. And perhaps a supercap experiment too.