Anyone else running EV charging off solar in a tiny house without burning the place down?

Finally bit the bullet and wired up a Zappi to my 5kW Victron MultiPlus on the tiny house — been sweating bullets every time the Fogstar 48V battery hits absorption wondering if today's the day I find out what my insurance excess is.

Running about 16 x 200W panels on a south-facing pitched roof, decent yield even up here in Scotland, but the Zappi's appetite is something else. Set it to eco mode so it only draws surplus, but on a cloudy day it just sits there sulking at 1.4kW like a teenager told to tidy their room.

Main question: has anyone managed to get the Victron/Zappi combo to properly communicate so the Zappi knows actual battery state rather than just watching CT clamp figures? Mine feels like it's guessing, and not confidently.

@Jock90 running a Zappi off a Victron is actually a decent combo — the eco mode plays nicely with surplus solar so it's not hammering your battery constantly.

Main thing I'd watch is your DC cabling between the Multiplus and the battery bank. EV charging pulls hard and any dodgy terminations get warm fast.

Got a similar setup on my garden office — not EV but heavy loads — and I keep a Victron Cerbo GX logging everything so I can spot thermal creep before it becomes a problem.

What's your BMS set to cut off at? If your Fogstar cells are hitting absorption regularly that might just mean your array is undersized for the load rather than anything actually dangerous.

IanWhite | Posts: 847

@Jock90 the anxiety is real! One thing worth checking if you haven't already — make sure your MultiPlus is properly configured with the AC input current limit set conservatively. The Zappi in Eco+ mode is brilliant for surplus diversion but it can occasionally get a bit greedy during cloud edge events when irradiance spikes suddenly.

Also worth logging your Fogstar's charge cycles through VRM if you're on a Cerbo — you'll quickly spot any patterns that correlate with those nervous moments near absorption.

What's your array size feeding that 5kW? I ran a similar setup for about eighteen months and the weak link turned out to be my DC cabling rather than anything the Victron or Zappi were doing. Proper cable sizing saved my sanity more than any settings tweak. 🔌

SuffolkDweller | Posts: 312

@Jock90 I've been running something similar for about 18 months now — 4.8kW of panels into a Multiplus-II with a DIY 48V lithium pack. The thing that gave me genuine peace of mind was setting a hard SOC limit in VenusOS so the Zappi only gets enabled once the battery clears 85% and cuts off before it dips below 40%. Took the guesswork out completely.

Also worth having a look at your cable ratings between the inverter and consumer unit — tiny houses often have surprisingly long runs tucked behind cladding that people sized for 240V appliances, not EV charging sustained over hours. That's where I'd be focusing my anxiety rather than the Fogstar itself, honestly. Those cells are pretty well-regarded.

How are you triggering the Zappi — Node-RED or straight DVCC?