I’m new here and have been reading through the forum trying to find a clear answer to my question, but couldn’t find a thread that matches my exact configuration — apologies if this has been covered elsewhere.
I’m planning an off-grid system in the French Pyrenees (1,200m altitude, unheated barn, long winter absences) with the following setup:
Victron MultiPlus-II 48/5000
Victron Cerbo GX MK2
Victron MPPT SmartSolar RS 450/100
BYD Battery-Box Premium LVS 12.0 (3 modules, CAN-bus communication via VE.Can to CAN-bus BMS type A cable)
DVCC will be enabled.
My use case: during long winter absences, I’d like to turn off the MultiPlus-II remotely via VRM to minimise standby consumption (~20-25W idle), while keeping the Cerbo GX and MPPT active — both powered directly from the 48V DC bus. A router and a small DC/DC converter (Orion-Tr 48/12) would also remain permanently powered from the DC bus (I will enable the “Has DC System” setting in Venus OS for proper SOC tracking).
When I return, I’d wake up the MultiPlus remotely via VRM the evening before to heat the place.
My questions:
Is remote On/Off of the MultiPlus-II supported via Cerbo GX / VRM in this configuration (BYD LVS via CAN-bus)? Assuming the physical switch on the unit is left in the ‘ON’ position.
I’ve read that there is a limitation with VE.Bus BMS that prevents remote switching — does this limitation also apply when using a third-party battery (BYD) communicating via CAN-bus rather than VE.Bus BMS?
Is there anything in the BYD CAN-bus communication that requires the MultiPlus to remain permanently on (keep-alive signal, etc.)?
Thanks in advance for your help, really appreciate the expertise in this community!
Thanks for the quick reply! That’s really encouraging and confirms my reading of the Victron & BYD manual.
Since I’m finalizing my system design, I’d love to hear from anyone else currently running a similar “wintering” setup in production. Have you noticed any unexpected quirks or things to watch out for when leaving the Cerbo, MPPT, and DC loads running alone on the bus for months?
Also, one technical follow-up regarding the worst-case scenario: if there’s no sun for weeks and the batteries fully discharge, causing the BYD BMS to physically cut the DC output (taking down the Cerbo GX and everything else)… would the system recover autonomously once the MPPT gets sunlight again, or would it require a manual intervention on-site to wake up the BYD BMS and re-establish CAN-bus communication?
Not necessarily, depends on the BMS, some need manual intervention.
It is never advised to allow this to happen, but to set inverter shutdown voltage thresholds so the batteries are never fully discharged and the system can black-start.
Also, victron BMSs are only for victron batteries, not third party ones.
Regarding the black-start: since the MultiPlus will be off via VRM, its internal VEConfigure threshold won’t stop my active DC loads (the 4G router).
To prevent a total shutdown, I will use a Cerbo GX relay to automatically cut the Orion-Tr/router if the battery drops to 15%. This leaves only the Cerbo running and protects the BYD from reaching its hardware cutoff.
For black start: Some of the smaller MPPT’s CAN operate on “Dead Bus” conditions, providing a start up current of say up to 10A to re-energise a system. However, the correct operation of this is down to the BMS sensing the bus voltage is in the “charging” range (V bus >Vbat; Vbus < Vbat+3-6V). Again this depends on the BMS design.
Far better to design your system to not take the batteries that low: a 12kWh battery can hold a system at idle for a long time, especially if the inverter is in the “off” state. Most PV arrays can produce >5% of their name plate capacity even in really cloudy days, more commonly 20%. so as long as this covers the idle current demand of the system, the low voltage / black start should not be a problem.
Thanks again for your advice. I looked into the Smart BatteryProtect. It’s a great piece of gear, but since I already have the Cerbo GX, I’m going to use its programmable relay (managed via a simple Node-RED flow) to cut off the 12V loads. It saves me from adding another hardware component, while still giving me the exact “watchdog” feature I need to protect the battery.
Thank you Mike for your answer ! That makes perfect sense regarding the PV array’s ability to cover idle loads even on cloudy days. By shutting down the MultiPlus-II via VRM, my total continuous draw on the 48V bus will be around 25-30W max (Cerbo + MPPT + Orion-Tr 48/12 powering the 4G router and a real link PoE camera). The solar array should easily cover this even in deep winter, so the 15% SOC cutoff via the Cerbo relay is really just a “doomsday” failsafe to ensure the BYD BMS never reaches its hardware cutoff.