Parkside Team 20V Adapter and Undervoltage protection circuit

thingiverse

The budget Parkside Team 20V batteries contain very good battery cells, so I decided to use it for some mobile applications (soldering iron, power supply, etc.). Only drawback I see: the cells do not contain an undervoltage protection circuit, therefore I added one here too. The adapter itself has 4 holes for M3 screws / nuts for a case which can be mounted on top. For the contact, I used printboard blade terminal flat connectors ("Flachstecker") and warmed it up with the soldering iron to melt it a bit in. Also fixed it with some hot glue. The wires go through two holes also on top. OpenScad files attached - feel free to modify for your own needs! ATTENTION: It is dangerous to deep decharge Li-Ion batteries, since in the worst case they not only het destroyed but can burn/explode when charging after a deep discharge! Therefore I also added an undervoltage protection circuit. See schematics and pictures attached. It usesparts I had laying around (a LM358 as comparator with hysteresis with a MOSFET to cut off the voltage). Justify the potentiometer around 15.3 volts cutoff to protect the batteries (a bit of headroom for safety since the cells are not balanced). Julian Ilett did a stripdown & analysis of the batteries, so you know what you get: https://www.youtube.com/watch?v=CN0q4wZBnBo (Overcurrent fuse seems to be in the battery)