Inverter kept cutting out during last night's storm — glad I tested it before winter

Had a similar scare a few weeks back on my boat when the weather turned nasty. My Victron MultiPlus started throwing low voltage warnings even though my Fogstar lithium bank showed plenty of charge on the BMS display.

Turned out the issue was the cable run from the battery to the inverter — the terminations had started corroding from the damp marine environment and the voltage drop under load was enough to trigger the cutoff. Completely invisible until I actually stress-tested it.

A few things I'd suggest checking if anyone else is troubleshooting similar:

• Voltage at the inverter terminals under actual load, not just at the battery
• All fuse holders and busbars for corrosion or loose connections
• Whether your BMS is cutting out before the inverter even gets a chance to respond
• The inverter's low voltage disconnect threshold — worth reviewing in VictronConnect if you haven't already

What was the actual cause in your case — was it the inverter itself or something upstream? Did it throw any fault codes you could read back?

Also curious whether anyone has a good routine for pre-winter load testing. I've been doing a rough test with a kettle and a 1kW fan heater simultaneously but I'm not sure that's really pushing things hard enough to surface marginal connections before they become a real problem in January.

CraftyWanderer | 847 posts | Midlands

@SmartSolar_Queen ah, the classic "battery says it's fine but the inverter disagrees" situation! Worth checking your BMS discharge current limits — when temperatures drop sharply during a storm, lithium cells can temporarily struggle to deliver high current even if the state of charge looks healthy on paper.

Also, have a close look at your cable connections and bus bar joints. Vibration on a boat is relentless, and even a slightly loose terminal creates enough resistance to cause voltage sag under load, which then triggers the low voltage cutoff.

Victron's app usually logs the exact moment of the warning — dig through those graphs and you'll likely spot a sudden voltage dip rather than a gradual decline, which points firmly toward a connection issue rather than actual battery capacity. Glad you caught it before the worst of winter hits! 🔧

DodgyRoamer | 1,203 posts | Array

@SmartSolar_Queen worth checking your BMS discharge rate settings — Fogstar cells are brilliant but the default BMS parameters on some units are quite conservative. Under heavy storm loads (heating, pumps, lighting all simultaneously) you can hit the BMS current limit even with healthy state-of-charge, which the MultiPlus interprets as low voltage.

Specifically look at:

• Peak discharge current threshold
• Short-duration overload tolerance

On my garden office setup I had identical behaviour until I reconfigured the BMS via the app and adjusted the MultiPlus Low Battery Restart Voltage in VictronConnect. The two systems weren't communicating their limits properly.

If you're running VE.Bus between them, also verify your DVCC settings — incorrect charge current limits there caused me no end of grief last winter before I properly read Victron's DVCC documentation.

SarahFrost | 312 posts | Scottish Highlands

@SmartSolar_Queen I had almost identical issues with my MultiPlus last winter — turned out the problem wasn't the battery or BMS at all, but the cable run between the battery and inverter. Under heavy load during a storm (heating, lighting, the lot running simultaneously) the voltage drop across undersized cables was enough to trip the low voltage cutoff, even though the cells themselves were perfectly healthy.

Worth grabbing a multimeter and measuring voltage directly at the inverter terminals while it's under load, then comparing that to what the BMS is reporting. If there's more than 0.3–0.5V difference, your cabling is likely the culprit. Upgrading to proper 70mm² welding cable made a massive difference for me. Boats are especially prone to this given the longer runs involved.

BayTim | 284 posts | Array

@SmartSolar_Queen had exactly this on my static caravan setup last winter. Turned out to be the cable run between the battery and inverter — looked fine visually but under load the voltage drop was enough to trigger the low voltage cutoff even with a decent state of charge.

Worth sticking a multimeter directly across the inverter terminals while it's under load rather than measuring at the battery. Surprised how many people skip that step.

What gauge cabling are you running and how long's the run? On the boat I went up to 70mm² and the nuisance trips stopped immediately. Victron's own cable sizing guidance is worth a look if you haven't already — they're quite conservative with their recommendations, which in this case is no bad thing.

OddJobBob17 | 847 posts | Yorkshire

@SmartSolar_Queen one thing nobody's mentioned yet — check the cable runs between your battery bank and the MultiPlus. I had almost identical symptoms last year and it turned out my negative busbar connection had developed a dodgy joint. Looked absolutely fine visually but under load during a storm (heater, lights, bilge pump all running simultaneously) the resistance was enough to cause voltage sag at the inverter terminals even though the batteries themselves were reading fine. Crimped the lot properly and used some decent 70mm² tinned marine cable and the problem vanished completely. Worth doing a voltage drop test under full load across every connection point before the really grim weather arrives. Takes twenty minutes and could save you a nasty surprise.