…. I should have known better than to raise this in an existing thread. At OP's request, I would be glad to move it all to a separate thread, if she prefers.
In an indirect way, all this could actually be germane to the issue of
lithium life loss (we need to name this emerging phenomenon and I’m considering L-cubed or L3).
Not discussed thus far is the extent to which L3 wreaks havoc on the reliability of the output displayed by the BMS that was calibrated to the original nominal capacity. Or perhaps just some BMSs, depending on their programming - I don’t understand the scope of what I’m trying to express just yet, but let me introduce this aspect anyway.
To make a long story short, I don’t want to turn my van into an academic hobby. The whole point is to USE THE VAN, and aside from cursory monitoring, the electrical system is supposed to take care of itself without a lot of mental gymnastics required of me. A good electrical system is mostly “set it and forget it”.
That being the case, I have largely ignored the individual cell voltage measurements and the other avalanche of data that the Electrodacus generates in favor of that one magic number displayed in the biggest, most convenient font - the percent SOC.
L3 destroys the accuracy of the percent SOC readout, and recalibrating it to the reduced effective battery capacity is not as easy as theory suggests. The drift is somehow far larger than what my intuition says it should be, leading to the following maddening result: Right at the point where my reduced battery capacity requires me to monitor the SOC more closely than ever, my ability to do so is thwarted.
So, OK, life sucks and then you die, but until that time, you develop workarounds.
Initially, I stuck a piece of masking tape on the control panel reminding myself to charge to 13.6 irrespective of what SOC the BMS says the battery is at, which I found reminiscent of what astronaut Jack Swigert did during Apollo 13 - a $2 billion spacecraft that, analogous to my battery, did not survive first contact with the enemy that nobody comprehended until it manifested. And so he used a note taped onto his control panel in partial compensation for the failures he was coping with.
But even with that alternate administrative control, I still wasn’t able to recalibrate my feel for SOC because guess what?? There is not a linear correlation between voltage and SOC. I told my husband that a “charge to” reminder was not enough - if the BMS itself cannot give me a feel for the degraded-battery SOC in real time, then I need a cheat sheet, an XY graph that plots voltage against actual SOC to the best of our ability to determine it, because it will be awhile before we can replace this battery to the effect that we will no longer need to worry about eking out power at the margins. He’s in the process of making individual measurements for that right now, and it’s clearly not linear.
All this is to say - HOW SHOULD these things be designed to account for the inevitable L3? Amp hours, watt hours, voltages,… some of these power-related claims reflect marketing obscurations on top of the technical obscurations that every LFP owner is probably going to face sooner or later. I don’t have a feel for any of this yet, for what should happen or how things should be designed to make things easier for the end user. I’m just throwing this bit onto the thread.
