Victron Multiplus keeps switching to passthrough overnight - anyone seen this?

Had this exact issue with my Multiplus-II last summer. Drove me mad for about two weeks before I tracked it down.

In my case it turned out to be the DC input low shutdown voltage set too conservatively. The Multiplus was deciding the battery was "too low" and dropping to passthrough to protect it — even though the SOC on my Cerbo was showing 40%+. The voltage sag under load was triggering it.

A few things worth checking:

• Battery type configuration — if it's set to AGM but you're running lithium (Fogstar Drift in my case), the voltage thresholds will be completely wrong
• DC input low restart/shutdown settings in VEConfigure — these are separate from your MPPT settings and often get overlooked
• ESS assistant if you're running it — there's a "minimum SOC" setting that can cause passthrough behaviour that looks identical to a fault

What's your battery chemistry and what does the DVCC screen show when it switches over? Also worth checking the VRM logs if you've got a GX device — the passthrough events should show up clearly and you can see exactly what voltage/SOC triggered it.

Is this happening at a consistent time each night or seemingly random? Consistent usually points to a threshold being hit, random could be a communication issue between the BMS and the Multiplus.

Worth posting your VEConfigure screenshot if you can — someone here will spot it quickly.

@HO_Marine glad you tracked yours down — worth also checking the AC input current limit in VEConfig if anyone's still troubleshooting this.

On my narrowboat setup I had passthrough happening because the shore power sensing threshold was set oddly — the Multiplus was seeing weak grid voltage from a dodgy marina hookup and deciding to "help" by passing through rather than inverting, then flipping back. Looked random but was entirely load-dependent.

Few things worth ruling out:

• Grid frequency tolerance — marinas can be noisy
• Dynamic current limiter enabled/disabled (check your ESS assistant config if running one)
• Shore line cable length/voltage drop under load

VRM logs are your friend here if you've got a Cerbo or Venus GX — the passthrough events will show up clearly and you can correlate with input voltage dips.

Yeah this has happened to me on the narrowboat! 🙄

Turned out my battery temperature sensor had fallen off — so the Multiplus was getting dodgy temp readings and being overly cautious overnight when it got cold.

Also worth checking your VEBus state in VRM (if you've got a Cerbo or Venus GX) — you can actually see the exact moment it drops to passthrough and what triggered it. Saved me hours of head-scratching.

@PennineNomad good shout on the AC input current limit too — I had mine set way too low initially and it was basically forcing passthrough whenever the shore power fluctuated slightly.

Interesting thread — I'm dealing with something similar on my boat and it's been a nightmare to diagnose.

Quick question for anyone who's been through this: could a dodgy shore power connection cause the Multiplus to behave erratically overnight? I'm wondering if the unit is seeing the AC input drop below threshold intermittently rather than it being a DC-side issue.

I've got a Victron Multiplus-II 24/3000 and my batteries are Fogstar Drift 100Ah cells. SOC looks perfectly healthy in VRM when I check the next morning, so I'm fairly convinced it's not the DC input low voltage causing mine.

@PanelKate did yours also show any alarms in VRM history, or did it just silently switch over? Trying to work out whether to dig into the logs or focus on the physical connections first.

Had something similar last year with my Multiplus-II 48/3000. Worth checking your ESS assistant settings if you're running one — mine was set to "optimised with battery life" which causes the unit to deliberately switch to passthrough when SOC drops below a threshold, even if your actual battery can handle more discharge.

Also, what BMS are you using? If your BMS is sending a DVCC signal via the VE.Bus or canbus that doesn't match what VEConfig expects, it can trigger passthrough unexpectedly. Took me ages to realise my Fogstar batteries weren't communicating the SOC correctly after a firmware update.

@WelshVanLifer — what's your battery bank setup? LFP or lead acid? Makes a big difference in which settings to look at first.

Great thread — a few things not yet mentioned worth checking:

AC input current limit is one I see trip people up regularly. If VEConfigure has it set very low (say 6A), the Multiplus can decide it's more efficient to stop charging and drop to passthrough rather than invert, especially if your shore power is marginal.

Also worth checking your grid code settings — in VEConfigure under the inverter tab, confirm "accept wide input frequency range" is ticked. Some marina hookups and campsite posts have slightly wobbly frequency, and the unit will bail to passthrough if it detects out-of-spec AC.

@WelshVanLifer narrowboats particularly suffer this at some canal-side electric points — older installations with poor earthing can look "wrong" to the Multiplus.

Run a VRM log overnight and check the "reason for state" field — it'll tell you exactly why it switched. Takes the guesswork out completely.