Right, I saw your posts on ESS continous switching between charge/discharge when battery full and negative grid power - #21 by owenb79
which is discussing a very similar issue.
I did run for a while using the Multiplus SOC estimation and it is very innacurate, fairly quickly getting more than 10% off, although I take your point that what really matters is battery voltage so the MPII SOC estimation is not that important (and you can still display the CAN-bus reported SOC level, even if the MPII is using its own estimated one). And it did seem to work fine in terms of charge-termination.
I do prefer to have charge termination controlled by the BMS as that will turn down when any cell gets near termination voltage, not just when the whole pack gets high enough. For a new, balanced, pack this doesn’t make any difference, but over time it seems that using DVCC should give better results. (Optimum charge-termination algorithms is a big subject - see massive, but fascinating, thread here, for example: GUIDE to properly Top-Balance and Charge a LFP Battery: Part 1 | DIY Solar Power Forum ) But I’m not totally averse to not using DVCC if there are advantages to doing it the other way.
Last time I switched DVCC off the MPII had to reset which resulted in a power cut (and some corresponding device reprogramming) which was tiresome. Switching it on was fine. I’m not sure if it always does that, but it’s a disincentive to just testing. Should I be able to turn it on/off normally without a reset?
I was struggling a little to interpret your charts on that thread. Are you saying that if one isn’t using DVCC, but charging/discharging controlled by the Multiplus/GX instead, then the ‘DC coupled PV - feed in excess’ works as as expected, and just automatically switches over? Then, of course, the question is ‘why’?