For this second take, I upgraded to a 0.005Ω shunt resistor to eliminate it as a significant current limiter. I also tracked voltages from the 18650 cells’ negative to cell positive, PACK_N and PACK_P to see how far the cell voltage drops, what the absolute current limit actually is, how much quicker the current limit kicks in, and what the current limit is acting on.
Upon contact, the cell voltage drops from 4.2V to 2.5V while PACK_N rises to 2V, telling us that over-current protection is low-side switched. From the ~400mV difference from PACK_P to PACK_N, we can also deduce that about 80A are flowing through the resistor for the first 800µs, going down from there until it cuts off near the 1.4ms mark. This was enough energy to create a weak spot-weld between my resistor and the Q-Cell contacts.
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