Victron Multiplus keeps switching to passthrough during the night - anyone seen this?

Had almost exactly this on my Multiplus-II 48/3000 back in February. Turned out to be the low battery voltage threshold kicking in earlier than expected because my Fogstar Drift 48V pack was voltage-sagging under overnight loads more than the resting voltage suggested.

The Multiplus was seeing a momentary dip below the configured "DC input low shut-down" voltage and switching to passthrough to protect the battery. Problem was the threshold was set at Victron's defaults, which didn't account for the internal resistance characteristics of my specific cells under load.

Things worth checking in VE.Configure:

• DC input low shut-down and DC input low restart values — are they sensible for your battery chemistry?
• DC input low pre-alarm — if this is triggering, you'll see it in VRM history
• Whether you've got Dynamic Current Limiter enabled, which can cause odd behaviour with certain loads

Also worth pulling the VRM logs if you're connected — the 15-minute interval data won't always catch a brief switchover, but the alarm history usually will. If you haven't got remote monitoring set up, connecting a Raspberry Pi with Venus OS is worth the effort just for the diagnostics alone.

What battery chemistry are you running and what's your typical overnight load? LFP and lead-acid behave very differently under sustained discharge, and the default Victron profiles don't always match real-world cell behaviour.

Also — is this every night or intermittent? Intermittent points more towards a transient load spike rather than a steady state voltage issue.

@KangooNomad interesting one — worth checking whether it's actually a voltage sag issue rather than a true low-battery cutoff.

On my shepherd's hut setup I had the Multiplus dropping to passthrough during high-load moments (induction hob spike) even with decent SOC remaining, purely because the instantaneous voltage dip crossed the threshold.

A few things worth investigating:

• DC ripple on the battery terminals under load — Victron's own monitoring can mask this
• Check assistantlowbatteryshutdown voltage settings in VEConfigure — defaults are sometimes too conservative for LiFePO4
• BMS communication — if your Fogstar's BMS is sending a DVCC signal, that overrides your manual thresholds entirely

Connect a cheap USB oscilloscope or at minimum watch the VRM portal's minimum voltage graph overnight rather than the averaged readings. The averaged data hides the sags completely.

What's your cable cross-section between battery and inverter?

@BordersExplorer that's a really useful distinction to draw — do you know if there's a straightforward way to tell the difference in the VRM logs? I'm asking partly for my own cabin setup where I've got a Multiplus-II paired with a Fogstar Drift pack, and I'd love to understand what I'm actually looking at when voltage dips appear overnight.

Specifically — is there a minimum log interval in VRM that actually captures those momentary sags, or does the default sampling rate smooth them out? I've wondered whether I'm missing transient events entirely.

Also curious whether adjusting the DC input low shut-down threshold in VEConfigure makes a meaningful difference here, or whether that just masks an underlying cell-balance issue. Happy to share my logs if that helps anyone diagnose the pattern.

@PartnerNomad the clearest way I've found is to pull up VRM portal and look at the DC voltage graph overlaid against the passthrough events. If you see a sharp dip just before the switch — we're talking a momentary plunge of maybe 3–4V — that's almost certainly voltage sag under load rather than genuine depletion.

What caught me out on my own cabin setup was a undersized cable run between the battery and the Multiplus. The resistance was enough to cause a sag spike whenever the fridge compressor kicked in at 2am. Tightened up the cable gauge and the problem vanished overnight — literally.

In VictronConnect you can also temporarily nudge the DC input low shut-down voltage down a fraction to confirm whether the threshold is the culprit before committing to any wiring changes.

@CaddyCamper nailed the VRM approach, but worth adding — if you don't have VRM set up yet, the GX device console shows a live DC bus voltage you can watch in real time. What I'd specifically look for is whether the voltage recovers immediately once load drops. Genuine low SOC means slow recovery; voltage sag from high-draw appliances (kettle, inverter surge) means near-instant bounce-back. On my van setup I saw exactly this pattern — Multiplus tripping out around 3am when the compressor fridge cycled. Fixed it by tightening the DC cable connections (resistance was causing localised voltage drop) and bumping the low-voltage cutoff down 0.5V in VEConfigure. Check your cable terminations first before changing any thresholds — loose lugs on a Fogstar pack will cause this repeatedly.