Hi guys, I am building my battery pack out of samsung 18650 30Q cells that I got from my chinese boss for free, I proceeded to test them and found out that they sag pretty hard at 1A load.
The tested capacity from 4.05V down to 3.1V (resting voltage)was 2542mAh at 1A load, which seems reasonable. They do not get hot at all though, even after 2 hours of discharge.
The first test I run was a Li-ion discharge program at 1A… and it couldn’t even start correctly as the cell voltage would fall from 4.05V (at rest) down to 2.5V (in load), which would trigger the low voltage cutoff and stop the discharge.
Then, after a little bit of research, I used the 1A discharge function in NiMH mode and set a very low cutoff voltage of 1.3V. I found out that they can sag down to 1.3V and go back up to 3.1V at rest (that’s when I got a cell capacity of 2542 mAh).
When I see you guys talk about a voltage sag of 20-30% at 5C I kind of understand, and my cells getting a 40% to 60% sag at 0.4C… that worries me a bit since I plan on using my battery at 15A per cell
I mean, they seem like they have the right capacity but the discharge tolerance is clearly not there. Are they fake cells ? Or am I doing something wrong ?