A disclaimer before I dive in, I am not working with a battery pack. Anytime I refer to Li-Ion cells or 18650s, I am trying to handle each cell as an individual. I am actually avoiding building a battery pack, that would be a problem.
I am working on an automated 18650 tester for evaluating salvaged cells. To do this I thought I would be able to mux 8 cells so I can have a single calibrated multi-meter (only ever in voltmeter mode) doing all the measurements. I am using a CD74HC4067 analog mux to do this.
The issue I ran into while prototyping is that, when all 8 cells are present, the voltage averages (maybe it just is the highest measured) between them, no matter that the mux is set to. In trying to identify the issue, I can measure continuity between test stalls when no cells are present.
Is this a known and observed behaviour when muxing multiple voltage sources? Or is it more likely that there is a problem with the application rather than the theory (Something like a bad breadboard, circuit assembled incorrectly.)
Is something like 8 analog opto-couplers the right direction for a solution? I have some HCNR200's for this.
My mux circuit is very bare bones as seen here.
These photos are of my prototype, I dont expect it to be obvious in a photo but it provides context.
