Hi all. I am designing a multi-house solar PV system, where multiple (2 to 8) DIY LFP 48V battery banks working in parallel. This multi-string battery will have capacity in the 25-100 kWh and feed multiple 48VDC inverters, even of different type and power. Some of the inverters will have also a PV charger function, but in the plant there are also pure LF inverters (without PV charger) and dedicated PV charger/controllers. I think this is a very common and general layout useful for many offgrid plants whose power exceeds 5-10 kW (a single battery) and wanting a large storage capacity.
From what i read in the forum, some BMS makers, like JoKong, explicitly exclude their BMS working in parallel strings, this is a real pity. Some other BMS, like JBD based on contactors, seems more tolerant to use in parallel string, but I doubt that they are capable to control all the issues (eddy currents, inrush currents from strings, lower max capacity, cascading shutdowns, ...) that could happens in a large multi-strings battery bank, potentially leading to damage of the battery and/or BMS, if not greater damages.
I found this detailed doc from ORION BMS that describes all the problems that must be solved to have a multi-string battery working reliably. I think is a good starting reference to address the design issues of parallel batteries.
I particularly like the solution they describe at page 15 named "Parallel strings with 1 charger per string and single discharge DC bus". Unfortunately this solution does not include PV inverter/chargers, and does not address explicitly the problem of having a different state of charge or capacity in different strings. I think we can work on this simple solution to evolve into a more general and universally applicable one. But this will be the subject of a separate post !
Manfredi
From what i read in the forum, some BMS makers, like JoKong, explicitly exclude their BMS working in parallel strings, this is a real pity. Some other BMS, like JBD based on contactors, seems more tolerant to use in parallel string, but I doubt that they are capable to control all the issues (eddy currents, inrush currents from strings, lower max capacity, cascading shutdowns, ...) that could happens in a large multi-strings battery bank, potentially leading to damage of the battery and/or BMS, if not greater damages.
I found this detailed doc from ORION BMS that describes all the problems that must be solved to have a multi-string battery working reliably. I think is a good starting reference to address the design issues of parallel batteries.
I particularly like the solution they describe at page 15 named "Parallel strings with 1 charger per string and single discharge DC bus". Unfortunately this solution does not include PV inverter/chargers, and does not address explicitly the problem of having a different state of charge or capacity in different strings. I think we can work on this simple solution to evolve into a more general and universally applicable one. But this will be the subject of a separate post !
Manfredi