Victron Multiplus 2 kept tripping at 80% load — turned out to be a dodgy battery connection, not the inverter

Spent three weeks convinced my Multiplus 2 (48V/3000VA) was faulty. It kept cutting out under load — washing machine mid-cycle, angle grinder, anything that pulled over 2kW for more than a few minutes. The fault log just showed "overload" but I was nowhere near the rated limit. Nearly sent the unit back to the supplier.

Turned out one of the busbars connecting my 16-cell 280Ah EVE LiFePO4 pack had a loose bolt. Resistance crept up enough that under load the voltage sag triggered the Multiplus's protection before the BMS even blinked. Tightened everything to spec with a torque wrench, cleaned the contacts, problem gone overnight.

What I've learnt: before you blame the inverter, check every connection between the battery and the unit. I'm talking busbars, fuse holders, Anderson connectors, all of it. A cheap clamp meter won't catch this — I only found it by measuring voltage at the Multiplus terminals under load and comparing it to voltage directly at the battery. The drop told the whole story.

Anyone else been down this rabbit hole? Curious whether this is more common with DIY packs than with something like a Fogstar Drift where the terminals are a bit more engineered.

@VanJim This is a classic one. High-resistance connections are brutal on inverter diagnostics because the fault signature looks exactly like an overtemperature or overcurrent protection trip rather than a supply-side issue.

Worth noting for anyone else chasing similar ghosts: the voltage drop across a dodgy terminal can be surprisingly small at idle — measure under load. I use a proper clamp meter across each connection point when drawing 2kW+ from my Fogstar 48V bank. Anything over 0.2V drop across a single lug joint is suspect.

Also check the busbars and inter-cell links if you're running a DIY pack. Torque matters enormously — I've seen "finger-tight" bolts read fine on a multimeter but fail catastrophically under sustained draw. My Multiplus-II setup is now on a quarterly connection inspection schedule precisely because of experiences like yours.