We have an off-grid setup with a MultiPlus 24/5000 and an AC-coupled Fronius inverter. Our Victron MultiPlus 24/5000 failed, so while it is out for repair, we purchased a second-hand 24/3000 unit to tide us over. So then we will have 2 multiplus. Since our battery bank consisted of two different models with slightly mismatched voltages, we can now connect the large 24V battery bank to the MultiPlus 24/5000 and the small battery bank to the 24/3000. Because the MultiPlus units are not of the same rating, I assume they cannot operate in synchronized parallel mode via VE.Bus. However, is there a way to keep the secondary MultiPlus operational? I would be interested in using it like an emergency generator or connecting it to critical loads via an AC transfer switch. Ideally, I would like the secondary MultiPlus to behave like the Fronius—AC-coupled to the main AC line—so I can recover the system after a complete battery discharge.
More details: I have a Color Control GX, and Home assistant
I’d look for another MP3000, or MP5000 to match your existing equipment. 2x3000 can be run in parallel, but should be on the same battery. However, you could use the MP3000 off the small battery to feed the AC in of the MP5, as long as the max AC current is properly limited.
Yeah, that’s the setup I ended up landing on too. Two scenarios, one contactor pair:
Scenario 1 — 3000 feeds the 5000 (like a generator)
The 3000 idles always-on. On the 5000, I use the built-in “Generator start/stop” Assistant — same feature meant for a real genset, just pointed at the 3000. When the 5000 needs more power than Battery A alone can give (or based on SOC/schedule), its relay closes a contactor between the 3000’s AC-out and the 5000’s AC-in. AC-in current limit on the 5000 is set to what the 3000 can actually sustain, so the rest still comes from Battery A via PowerAssist.
Scenario 2 — 5000 feeds the 3000 (to recover Battery B / use curtailed PV)
Reverse direction: a second contactor connects the 5000’s AC-out to the 3000’s AC-in. Diverting AC-coupled PV that’s being frequency-curtailed once Battery A is full. This one I’m driving with my own logic (Node-RED/HA/etc with GX data, watching AC-out frequency and/or PV AC-coupled power).
The catch, and why two contactors + an interlock, not just one:
These two paths must never be closed at the same time — if both contactors close together, you get an unsynchronized loop between two Multis that aren’t paralleled, with real risk of circulating current and a fault/trip on one or both units.
Fix: on each contactor, use its normally-closed auxiliary contact wired in series with the other contactor’s coil. So if Contactor A is closed, Contactor B’s coil circuit is physically broken — can’t close no matter what your automation says. It’s a har interlock.
Started with a MultiPlus 24/2000 and 200Ah lead-acid.
Upgraded to a MultiPlus 24/5000 with 500Ah lead-acid.
Then upgraded again to a 600Ah LiFePO₄ bank on the 24/5000.
Rather than scrapping the 500Ah lead-acid bank, I brought the 24/2000 back into service as a backup to the lithium system.
The lithium bank is my primary power source.
During periods of surplus PV, a Cerbo relay enables the MultiPlus 24/2000 to charge the lead-acid bank.
When the lithium bank needs support, the relay is switched off and an Orion 24/24 DC-DC charger transfers energy from the lead-acid bank to the lithium bank.
It’s still a fairly new setup, and I’m no expert, but it has been working well for me so far.