Since I can’t seem to comment on your article of the 3.0A battery teardown, I’m starting a new thread for my question.
I see from the teardown that there really isn’t any over discharge protection, but all the inter-battery connections are exposed. If I wanted to 3D print a power-tap that I can, for example, run my TS100 soldering iron from my existing stock of 20V MAX (damn marketing department, these are really 18V (well 18.5V) battery packs) batteries I realize that I should include into the design a protection circuit. I’m thinking that this pre-fabbed board might work:
But I’m just now dipping my toes into battery technology. Would that board work, or would the balancing network built into the DeWalt batteries just confuse this protection circuit module that I found?
Yes, I know I can tell my TS100 that I’m connecting it to a 5S battery and it’ll properly shut down at the correct low voltage, but what if I decide to plug it into something dumb like a LED strip that’s been hacked to take up to 24V(two 12V LED strips in series)?
It would have been nice if I’d remembered to open the “comments” category up for general posting… theoretically fixed now if you’d be so kind to try replying there at some point.
That board should work fine. As I understand the 20V Max system, there’s no balancing at all in the pack, just during charging - and what seems to be a midpoint tap that will catch a badly damaged pack and prevent you from fully draining a cell group. That BMS should do more than the DeWalt system and be just fine.
For a well behaved pack, you could probably get away with just a low voltage cutoff circuit at about 15.0V (3.0V/cell), but I’m not sure you can find one of those for much less money than a 5S BMS, and the BMS will (should?) also cut output if any single cell group gets below the cutoff voltage for the groups.
I have a Milwaukee m18 setup through a buck converter to power the baby swing - and unfortunately it seems to run the battery completely dry. Perhaps something like the above would prevent it from doing a full discharge (the battery came back to life but was a bit finicky before it came live and charged).