After successful tests with the 72V battery pack's PCM branded as Signalab, I was expecting similar behaviour from the 12V battery pack PCM. I do not know the manufacturer of this board which is shown in the picture, but it is still available in eBay.
When I first connected the batteries to the 12V PCM I had my multimeter connected to measure the resistance between the P- and B- terminals. I was expecting the resistance to drop close to zero when the last cell was connected. To my disappointment the resistance dropped before the last cell was connected to the B+ terminated. My first assumption was that the board was faulty. A new PCM board would take weeks to arrive so I though that I would examine this one a bit more before giving up with it.
I disconnected the PCM and took it to my lab room to examine it with a laboratory power supply. I found out that the PCM worked as it should with the cell over- and under voltages, but what was left undocumented is that if any cell voltage would be less than about 0,7V the under voltage situation is no longer detected and the P- terminal is enabled again (if the other cell's do have a valid voltage between 2.0 to 3.85V). This happened to me during the first test of the PCM when the last cell was disconnected and still the P- was enabled.
Now that I know how this circuit works I decided to install it anyway although the circuit can not be expected to disconnect the load if for example a wire gets disconnected between the PCM and the battery pack.
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