Hi all,
I have a 3-phase, 50 Hz power grid setup with 3 x MultiPlus II 5000/48 units configured in an ESS system, working together with a Fronius Gen 24 inverter, which is AC-coupled on the AC-out side. The battery bank consists of 8 x Pylontech US5000 (4.9 kWh each), set up according to Victron’s integration guidelines. The Pylontech BMS communicates via CAN bus with the Victron system for SoC, voltage, and current data.
Issue: Occasionally — especially during autumn and winter nights — I experience loss of one or two grid phases for several hours or even up to a full day. When this happens, the ESS system goes off-grid and powers the house from batteries, since it requires all three phases to be available to operate in grid-connected (on-grid) mode and to allow grid charging of the batteries.
If the batteries reach 0% during such outages, the system shuts down completely, resulting in a blackout.
Proposed solution: To address this, I use a third-party electronic phase selector that constantly monitors all three grid phases and outputs the best available single phase — automatically switching to a working phase if another fails. This ensures at least one usable phase is always available, even during partial grid outages.
I also have a spare MultiPlus II 5000VA unit and would like to use it in this scenario. The idea is to connect its AC input to the output of the phase selector, and use it only as a charger for the Pylontech batteries during times when the main ESS system is off-grid due to missing phases.
When the grid returns to normal and all three phases are available again — allowing the ESS to reconnect to the grid — I would like this extra MultiPlus to automatically go into standby and stop charging.
My questions:
-
Can this spare MultiPlus II be configured to operate independently as a standalone charger, and still communicate with the Cerbo GX for DVCC-based monitoring and control?
-
Will it be able to dynamically adjust its charging current based on the battery SoC and charge limits reported by the Pylontech BMS via CAN?
-
Are there any known issues, limitations, or best practices when using a MultiPlus like this — outside the main ESS VE.Bus cluster, but still integrated via Cerbo GX with DVCC enabled?
The goal is to maintain safe and intelligent charging of the battery bank during partial grid outages, and to make effective use of a spare MultiPlus II unit that would otherwise be idle.
Thanks in advance for any advice or feedback!