Been mulling this one over since I saw a similar setup discussed elsewhere, and it's relevant to something I'm considering for my own tiny house backup system.
Has anyone here actually integrated a third-party inverter alongside a Victron Multiplus II — specifically where the external unit is handling some of the AC loads independently rather than being fully subordinate to the Victron ecosystem?
My situation: I'm running a Multiplus II 3000VA with Fogstar Drift lithium cells and a Cerbo GX, currently off-grid. Works brilliantly. But I've been looking at adding a secondary inverter to handle some dedicated circuits without hammering the Victron for every minor load.
The concern I keep coming back to is BMS communication and state-of-charge arbitration. When you've got two inverters drawing from the same battery bank, who's the master for SOC decisions? The Pylontech UF5000 units use CAN bus to talk to Victron natively — but a generic MKS-style unit won't have that handshake. You're essentially running blind on one side.
A few specific questions for the group:
- Has anyone used a shared DC bus approach where the secondary inverter has no BMS comms, relying entirely on low-voltage cutoff as its protection?
- Are there relay-based solutions that let the Victron's BMS data trigger a cutoff for the secondary unit?
- Any experience with Victron's AC coupling versus DC coupling in this kind of hybrid scenario?
I'd imagine the 15kVA scale introduces its own wrinkles around earthing and grid-forming that I haven't had to deal with at my modest scale, but the underlying integration problem feels the same.
Curious what others have tried
