Some preliminary information:
I have several systems but only one with this issue.The affected system consists of a multiplus, bmv-712, two 100/30 charge controllers, and a cerbo gx. The battery is a custom 11kwh lithium iron phosphate battery. The BMS on that battery maintains normal charge level indications. There are no loads or chargers that do not go through the bmv. Peukert exponent is set to 1.
The issue:
In VRM the consumption kwh always shows about 10-20% more than the solar production. Day after day. If this were the case the battery would be slowly depleting, which is what the BMV shows, but that is not the case. The BMS on the battery shows that it is returning to 100% every morning. But the BMV will show it only returning to 99.8%. The next day will be 99.7%. The day after will be 99.6% and so on until I get irritated and reset the SOC in the bmv back to 100%
The system mostly sits idle and there is plenty of excess solar capacity that is not being used. I have tried disconnecting all charging and loads and resetting the current calibration on the bmv.
The more power I use, the higher the difference becomes. On idle days it's usually a difference of .5kwh. On days where I use 5-6 kwh the difference can be as much as 1.5kwh. If I use power after dark the discrepancy will show up the next day.
All of this leads me to believe that one or both charge controllers are actually delivering more power than they report. Is this possible? Is there a way to calibrate them? Shouldn't the bmv be counting the actual incomimg charge anyway? Or am I possibly missing something in the battery setup?
The problem isn't when it's grid connected. It'almost never connected to the grid anyway. Maybe 3-4 days a year. Either the solar chargers are reporting less than they actually produce, or the BMV is overestimating the loads. Day after day the consumption shows more than the solar has produced which is impossible. The battery would deplete. But the battery reaches charged voltage every day and then the solar chargers back down to only cover the loads and stop charging the battery. There is plenty of excess solar so l know it's being fully charged every day. The battery soc always shows higher at the end of the day than the morning so if anything the solar production should show MORE than the consumption due to inherent system losses! I know I could have the BMV set to reset the soc to 100 every time the charged voltage is reached but that would only fix half the problem. I still want the VRM to show a more realistic balance between the power produced and the power used as it is impossible to use more power than is produced, which is what it currently shows.
