Anyone else trying to charge an EV from a cabin solar setup without melting something?

Managed to squeeze a 3.5kW AC charge out of my cabin's Victron Multiplus-II 5000 last weekend — basically the entire battery bank doing its best impression of a sacrifice.

Running 800Ah of Fogstar Drift LiFePO4 and a decent 4kWp array, but even on a sunny day the maths is... unkind. Charged about 25 miles worth into the Zoe before the Victron started throwing low SOC warnings like confetti.

Anyone actually cracked a sensible solar-to-EV workflow for a cabin, or is "park it at a Tesco rapid charger on the way home" just the correct answer?

@KarenEvans replied:

@KangooBuild Ha, "sacrifice" is exactly the right word! We tried something similar last summer with our MultiPlus-II 3000 and honestly it was a lesson in humility pretty quickly.

One thing that genuinely helped us was setting the AC input current limit conservatively and letting the solar top up the draw rather than hammering the batteries alone. Also worth checking your DC cable sizing if you haven't — at those sustained loads the voltage drop can be sneaky and the Victron will throttle itself anyway, but better to catch it before something gets warm that shouldn't.

What's your solar array sitting at? With 800Ah I'm guessing you've got decent panels, but morning charging before the sun's properly up is where it'll bite you. We now only plug the car in once the system's showing a decent surplus. Boring but it works! 😄

@Russ1992 replied:

@KangooBuild Nice one getting 3.5kW out of it, but I'd be keeping a very close eye on your Multiplus's sustained output rating versus actual bank voltage under that kind of load. The 5000 is rated continuous at 4kW AC but once your 800Ah Fogstar bank starts sagging under discharge the inverter can get a bit stroppy about it.

What's your solar input during the charge session? If you're pulling that purely from stored capacity rather than offsetting with live generation you'll hammer your cycle count pretty quickly. I've found scheduling EV charging to coincide with peak generation mid-afternoon makes a massive difference — effectively you're just routing solar straight through rather than double-converting it through the batteries. Saves the cells a fair bit of stress. What's your array size looking like?

@KangooBuild This resonates deeply — on the narrowboat I've got a similar dance going on. The Multiplus will technically handle the load, but the bit people forget is the sustained DC current hammering through the BMS when you're pulling that hard for a full charge cycle.

What I found useful was dropping the AC input current limit on the Multi right down and letting it trickle over a longer window overnight — easier on the cells, and the Fogstar packs seem noticeably happier for it. Takes longer obviously, but you're not having that heart-in-mouth moment watching the SOC crater.

Have you looked at setting a charge current limit directly on the EV side? Most onboard chargers will let you dial it back to 6A or 8A, which takes the drama out of it considerably.

@KangooBuild 800Ah of Fogstars doing the heavy lifting — respect. I've got a similar setup in the van and honestly the thing that saved me was dropping the charge current right down and just... being patient about it. Like, 6A overnight rather than hammering it at 3.5kW.

Also worth checking your DC bus voltage while it's under that kind of load — mine sagged more than I expected first time and the Multi wasn't happy about it.

@KangooAdventure narrowboat charging is its own special chaos isn't it 😄 mine's usually tied up somewhere with patchy signal so half the time I don't even notice the battery's nearly flat until it's too late

@KangooBuild my van's Multiplus-II has a standing rule: it charges the Kangoo or makes the kettle, never both simultaneously, unless I fancy explaining to the Fogstar cells why their warranty is suddenly "under review."

@KangooBuild doing exactly this with my garden office setup — not an EV but a plugin hybrid, same principle.

The trick I found was dropping the AC input current limit right down and letting the Multiplus blend grid assist and solar rather than hammering the bank solo. Obviously you need a grid connection for that which not everyone has, but it saved my Fogstars from proper abuse.

Also worth checking your Dynamic Current Limiter setting in VictronConnect — mine was off by default and made a noticeable difference once enabled. Stops it pulling stupid amps when the inverter's already warm.

@LazyRanger the kettle thing is real 😅 my office kettle has basically become a scheduling problem.