I have a doubt about my new setup here. I am off grid with 5KWp of solar panels, MPPT 85/250, cerbogx, Lynx Distribution (no shunt), a multiplus2 and a BasenGreen 16Kwh LiFePo4 16Cells battery.
Mostly the communication between the BMS and the GX seem to work but I have noticed recently that at the end of my charging cycle, the BMS screen on the battery shows 92%SOC 53,5V 0Amps and the Cerbogx shows a 100% SOC.
I am not sure why the charging stops there and if it should be like that but my main question is : Where is that 100% SOC information coming from ? Why does the GX not display whatever the BMS says ?
Charging is set to be controlled by BMS and I use CAN with Pylontech protocole.
It would definitely be better and more advisable to use a shunt, as the Multi Plus can only estimate the SOC approximately. The Multi cannot measure the tail current and merely ‘calculates’ the approximate current that has flowed into the battery based on its settings. The ‘Enable Battery Monitor’ settings only include the ‘State of Charge after completion of the constant-current phase’ … plus the capacity and efficiency … . But even so, the difference between 92 per cent and 100 per cent isn’t that great … there have been worse cases … so you can only experiment with the three values mentioned.
A shunt would be better … that’s what it’s designed for.
As Steffen has already noted, the only way to get a reasonably accurate SOC measurement is via a shunt. Determining SOC via the BMS is at least as inaccurate as calculating it using the Multiplus. I have no intention of getting into endless debates about this; I’m just sharing the information. BMS units fail to detect small currents, whether during charging or discharging.
