I find that the DC side become quite unstable when the MPPT charges about the same amount of power that the MPII's are generating to the grid and load, and the batteries are full, in "Optimized with or without Batt. Life" mode. In "Keep batt. charged" mode, DC stable. The DC are fluctuating between 48 and 62 V ( see pic. ), and huge amount of alarms are generated. Sometimes also "Voltage Sensor error" on MPII.
When the MPPT power are constant more than the load, system are stable ( about 55 V ).
It feels that the MPII's has a stable voltage ( 54-56V ), start to generate power to the grid, ( are increases the power export too fast ), gets a dip at about 49V, MPII#1 generates "Low voltage", the MPII's does a restart, the MPPT does not respond to that fast enough and the DC arises to 61-62V.
Cable length about 1 - 1,5m, 140 mm2 to MPPT, 70 mm2 to the MPII's
System:
1 pcs. MPPT 450/200
3 pcs. MPII 48/5000/70-50
1 pcs. Smartshunt 500A
1 pcs. Cerbo GX
9 pcs. Lithuim batt. with internal BMS, 100 Ah. each
This generates poor efficiency on the system in this situation, and could in the long therm reduce the system life.
I can put an Agilent 34970A logger on the system if you want more detailed info.
/BR
Erling Anderberg
