False low voltage shut down, Victron phoenix 24/1200 inverter

Been having a similar head-scratcher with my Phoenix 24/1200 in the shepherd's hut build and wondering if anyone else has hit this wall.

The inverter keeps throwing a low voltage alarm and shutting down, but when I check the battery bank immediately after, the voltage reads completely normal on both the Victron BMV-712 and a separate multimeter — nowhere near the cutoff threshold I've set in VictronConnect.

Bank is 4x 12V Fogstar Drift lithium in series/parallel giving me 24V/200Ah, so capacity shouldn't be the issue. Cables are 70mm² with decent terminations, so I don't think it's a voltage drop problem under load.

A few things I'm considering:

• Could there be a brief spike in load causing a momentary voltage dip that the inverter catches but the BMV smooths over in its readings?
• Is it worth adjusting the dynamic cutoff settings in VictronConnect, or would that just be masking an underlying problem?
• Could the inverter itself be developing a fault after a few years of service?

The loads triggering it seem fairly modest — mainly a small induction hob or occasionally a space heater. Nothing that should be catastrophic for this setup.

Has anyone gone through the Victron troubleshooting flow for false low voltage shutdowns specifically? I've had a look through the Victron community pages but most threads seem to be about lead-acid setups with different behaviour.

Would be really useful to know if anyone has found a definitive fix rather than just tweaking thresholds and hoping for the best.

IslandDweller | Posts: 847

@AlanWard Classic one this! Before anything else, check your battery cable connections and gauge. A 24/1200 can pull some serious current on startup loads, and even a slightly undersized cable or dodgy crimp will cause a genuine voltage sag at the inverter terminals even when your battery is perfectly healthy. The inverter isn't lying - it IS seeing low voltage, just not because your batteries are flat.

Grab a multimeter and measure directly at the inverter's DC terminals under load. Compare that to your battery terminal voltage simultaneously. Any more than 0.5V difference and you've found your culprit.

Also worth checking your cable run length - what gauge are you running and how long is the run from batteries to inverter?

This caught me out with my garden office setup last year. The Phoenix looks like it's seeing low voltage but often it's a voltage sag under load — the battery cables are doing their job poorly under surge current.

Measure your resting voltage, then measure at the inverter terminals the moment it throws the alarm. If there's more than 0.5V difference between your battery terminals and the inverter terminals, your cabling is the culprit — undersized or a dodgy crimp somewhere.

Worth also checking whether your battery BMS is momentarily disconnecting under load spike — the inverter sees that as a low voltage event. I was pulling hair out for weeks before I caught mine on a Victron Cerbo log. What's your battery chemistry and cable run length?

DailySolar | Posts: 2,341

@AlanWard Something both @IslandDweller and @LindaLamb are dancing around — voltage sag under load is almost certainly your culprit.

The Phoenix 24/1200 can pull ~55A peak from a 24V bank. If your battery cables are undersized (anything below 16mm² for runs over a metre), you'll see the bus voltage crater momentarily and trigger the low-voltage cutoff even with a healthy state of charge.

Check this specifically:

• Cable cross-section — go 25mm² minimum ideally
• BMS discharge current limit — some Fogstar/EVE cells ship with conservative defaults
• VRM logs if you've got a Cerbo/CCGX** — the voltage trace will show you exactly when it's dipping

I had identical behaviour on my cabin's 24V system before I swapped to proper busbars. The inverter wasn't lying — it genuinely was seeing low voltage, just for microseconds under surge load.

FormerCop | Posts: 1,203

@AlanWard — everyone's covered the sag angle, so I'll add the thing nobody mentions: check your actual low voltage disconnect setting in VictronConnect.

On 24V systems the factory default LVD can be surprisingly aggressive, and if someone's previously connected it via Bluetooth and fiddled about, it might be set higher than you'd expect. Mine was triggering at 23.2V because a previous owner had it configured for LiFePO4 thresholds on what was clearly a lead-acid setup — took me an embarrassing amount of time to clock that.

Open VictronConnect → Phoenix → settings, check your "DC input low shutdown" voltage is appropriate for your battery chemistry. 🔋