ESS dischagers

Been down a similar rabbit hole recently with my boat setup, so this one caught my attention.

Running a Victron Multiplus-II with a Fogstar Drift 48V bank and a modest 1.2kW of panels — nothing as beefy as a 3-phase 64kWh monster — but the ESS behaviour when you start nudging grid interaction settings is surprisingly fiddly regardless of scale.

My particular headache was getting the system to discharge to grid in a sensible, controlled way rather than just sitting there hoarding electrons like a digital squirrel. The Cerbo GX gives you all the knobs to turn, but the interaction between:

• Minimum SOC limits
• Feed-in excess solar toggle
• Scheduled charging windows
• Grid set-point values

...is not exactly intuitive. Change one thing and something else behaves oddly downstream.

On a boat it matters less because I'm mostly island mode anyway, but I know folks with hybrid home setups are pulling their hair out trying to get smart export working properly with their DNO, especially on G98/G99 installs where the inverter behaviour has to be locked down.

Anyone here running ESS with active grid feed-in on a UK install? Curious whether you've cracked the logic around keep-batteries-charged mode vs proper ESS, and whether your installer had to do anything special for the grid code compliance side.

Feels like there's a gap between what Victron's system can do and what UK grid regs allow it to do without someone professional signing it off.

@FZ_Builds what grid connection are you using on the boat — shore power hookup at a marina? Curious because on my narrowboat the Multiplus-II is brilliant but I've been wrestling with whether ESS mode even makes sense when you're moving between moorings and frequently off-grid entirely.

I ended up running Optimum without battery life rather than Keep Batteries Charged because the latter just hammers the inverter as soon as shore power appears.

One thing worth checking — have you set your minimum SOC correctly in VictronConnect? I had mine far too low initially and was confused why the system kept discharging past what I'd expected. The Fogstar Drift's BMS should protect it but better not to rely on that as your primary cutoff.

@FZ_Builds similar setup on my narrowboat — Multiplus-II, Fogstar 48V (two 206Ah in parallel), around 800W of panels. ESS works well when you're on a marina shoreline but the behaviour changes noticeably when you're moored off-grid and running the inverter in island mode.

Worth checking your ESS Assistant configuration — specifically the "minimum SOC" and whether you've got "keep batteries charged" toggling unexpectedly. I had a phase where mine was discharging past my floor limit because the AC input voltage from a dodgy marina hookup was dipping below the acceptance threshold, so Victron kept cutting the grid connection and draining the bank instead.

@MultiPlus_Queen the shore power question is spot on — the ESS logic behaves completely differently depending on whether AC-in is present or absent. That distinction matters a lot in a marina context.

@FZ_Builds one thing worth flagging with ESS on a boat (or anywhere with a wobbly grid connection) — Victron's ESS assistant is very particular about grid quality. If shore power at the marina is even slightly dodgy in frequency or voltage, the Multiplus-II will keep dropping out of ESS mode and reverting to inverter-only. Drove me absolutely crackers before I found the GridSetpoint and weak AC input tolerance settings buried in VEConfigure.

Also worth checking your MinimumSOC under ESS — boats notoriously over-discharge through the night on 12V systems fed from the 48V bank. The Fogstar Drift BMS will protect you ultimately, but better not to rely on that as your first line of defence.

What firmware are you running on the Multiplus-II? There were some ESS stability fixes in the 5xx series that made a noticeable difference.

@TracyAllen that's a really useful point about wobbly connections — what actually triggers the assistant to drop out in that scenario? Is it a voltage threshold, frequency deviation, or both?

Asking because I'm on a tidal mooring and shore power via the pontoon can be genuinely grim at times. Wondering whether I'd be better off running PowerAssist rather than full ESS given the unreliable feed, or whether there's a middle ground in the Victron config that handles both cases without constantly tripping.

@DorsetSolar did you end up adjusting any of the AC input current limits to compensate for your marina's supply quality?

Jumping in here because I had exactly this with my shepherd's hut setup before I moved it fully off-grid.

When I was still connected to a long cable run from the farmhouse — effectively a "wobbly grid" situation — the ESS assistant was dropping out constantly. Turned out the voltage at the Multiplus input was sagging just enough under load to confuse it.

What sorted it for me was adjusting the AC input current limit down slightly, which stopped the unit chasing a connection it couldn't reliably hold. Counterintuitive, but it gave the system breathing room.

Worth checking your input voltage range settings in VE.Configure too — there's a tolerance window you can widen carefully without causing other headaches. @VE_Boats this might be part of what's triggering your dropouts.