Multiplus charging problems

Ran into something similar last autumn when I was commissioning the shepherd's hut system — worth sharing here because it's a genuinely tricky edge case with Victron kit.

I had a Multiplus-II 3000 acting as the primary inverter/charger alongside a secondary unit, fed by a Honda generator when solar input dropped off during the darker months. The issue was that the MP-II kept pulling the generator into an unstable load condition — not quite overloading it, but hovering right at that awkward threshold where the generator hunts for frequency.

After a lot of head-scratching and digging through Victron's ESS documentation, I realised the problem was the PowerControl current limiter wasn't playing nicely with the battery absorption phase. The Multiplus was essentially trying to push full charge current and supply loads simultaneously, with no headroom left for the generator to breathe.

The fix that worked for me:

• Set the AC input current limit conservatively in VE.Configure (I dropped to about 80% of the genny's rated output)
• Enabled dynamic current limiting so the MP-II backs off gracefully under fluctuating load
• Tweaked the absorption voltage slightly lower on the Fogstar lithium cells to reduce peak charge demand

It's been solid since. But I'm curious — for those running multiple Multis in parallel with a supplementary charger unit thrown in, are you using ESS or a straight VE.Bus setup? I suspect the spinning reserve issue becomes significantly more complex when you've got three units negotiating simultaneously. Anyone actually measured the AC coupling behaviour in that configuration with a proper power analyser?

Interested to see where this is going @JYT_Solar — I'm mid-build on a shepherd's hut system myself and the Multiplus-II 3000 is exactly what I'm planning to use.

What battery chemistry were you running when this happened? I've been going back and forth between Fogstar Drift lithium and a used Pylontech setup, and I'm wondering if the charging profile differences could be a factor in whatever edge case you're describing.

Also — was this with the default VE.Configure settings or had you done a custom charge algorithm?

@JYT_Solar tag me in when you finish that post — it cut off right at the interesting bit!

Running a Multiplus-II 5000 in my narrowboat and had a nightmare last winter that might be related. The key thing I learned: check your charge current limits in VEConfigure against your actual battery BMS limits, not just the Victron defaults. Mine was set to push 120A into a Fogstar Drift 200Ah LiFePO4 that the BMS would only accept 100A sustained — the BMS kept tripping and I spent days chasing what looked like a comms fault.

@TQ_Builds for a shepherd's hut build, also worth thinking about your AC input current limiter if you're on a small generator or hook-up supply. That catches people out constantly.

Watching this thread closely — I've got a Multiplus-II 3000 in my static caravan and had a nightmare commissioning period last winter.

Could the truncated post be hinting at the absorption/float handoff issue? I hit a weird problem where mine kept cycling back to bulk mid-charge with Fogstar lithium cells. Turned out my charge parameters in VE.Configure weren't quite right for the battery profile.

@JYT_Solar can you confirm — were you seeing the issue on shore power, solar input, or both? And was the Cerbo GX involved at all?

@TQ_Builds worth double-checking your battery comms setup before you commission — saved me a lot of head-scratching in hindsight.

@JYT_Solar — the cliffhanger is killing me, but I think I can guess where this is heading.

When I commissioned the Multiplus-II in my garden office last spring, the thing that caught me completely off guard was the AC input current limit fighting with the charge current settings — VE.Configure kept appearing to accept my values, then quietly reverting after a restart. Took me an embarrassing number of evenings with a laptop balanced on a shelf to figure out the interaction between the charger tab and the shore power settings.

@SueJohnson the static caravan setup might actually be worse for this because you're likely on a restricted supply — what's your incoming amperage?

Genuinely think the Victron documentation undersells how these settings interact. The CCGX guide hints at it but never quite spells it out plainly.