Anyone else built a proper emergency backup into their motorhome for home use during power cuts?

After the storms last winter knocked our power out for nearly 14 hours, I finally got serious about having a proper backup setup rather than just hoping the grid stays up. My motorhome's already running a 200Ah Fogstar Drift LiFePO4 bank with a Victron MultiPlus 12/3000, so I started thinking — why not use it as a proper emergency UPS for the house?

What I've ended up doing is running a 16A hook-up lead from the van (parked on the drive) through the garage wall into a small consumer unit feeding just the essentials — fridge/freezer, a few sockets, and the router. The MultiPlus handles the inversion and the van's 400W of Renogy panels keep the bank topped up during daylight. In a 14-hour outage I reckon I could sustain those loads comfortably, especially if I'm not running the compressor fridge flat out.

The bit I'm still wrestling with is safe changeover — I've got a basic manual changeover switch isolating the house circuits before I connect the van feed, which works but feels a bit agricultural. Has anyone wired in a proper automatic transfer switch (ATS) or a more elegant manual interlock that's fully BS 7671 compliant? Wondering whether Victron's own ATS or something like a Socomec unit would be the cleaner solution, and whether it's something a Part P registered sparky would touch without running a mile.

@SimonKelly done exactly this on my narrowboat and the learnings transfer directly to a motorhome setup.

Key thing most people miss: your motorhome's shore power inlet is already essentially a transfer switch waiting to happen. Run a properly rated extension from the vehicle's output to a small consumer unit feeding your critical circuits — fridges, freezer, a few sockets. Don't try to back-feed your whole house.

Worth checking your inverter's surge capacity before committing. Fridge compressors can pull 3-4x running current on startup. My Victron Multiplus handles it comfortably but a cheap pure sine unit can struggle.

Also consider your battery state when you actually need it. Fogstar Drift LiFePO4 cells hold charge well sitting idle, unlike AGM which sulphates if you leave it at 50% for months.

What's your current inverter/battery spec?

DanFisher89 | 47 posts | West Yorkshire

Great timing on this thread @SimonKelly - did almost identical after the Boxing Day storms a couple of years back left us without power for 11 hours.

One thing worth planning carefully is which circuits you actually need running versus which ones you want running. I made a priority list - boiler, fridge, a couple of sockets and the router - and that kept my motorhome's leisure batteries comfortable for a surprisingly long time without needing to run the engine or hook up the onboard genny.

Also worth fitting a proper changeover switch rather than bodging extension leads between the two systems. Keeps everything safe and honestly makes the whole thing feel much more legitimate than the Heath Robinson setup I started with! 😄

Curious what your current battery bank capacity is?

Great thread @SimonKelly - 14 hours is a proper wake-up call isn't it!

One thing worth flagging that often catches people out: check your motorhome's inverter continuous rating versus peak surge, especially if you're planning to run anything with a compressor start-up draw like a fridge or freezer. A lot of the Renogy inverters rate well for continuous loads but you want decent headroom for those spikes.

Also worth investing in a decent transfer switch setup rather than just swapping leads manually in the dark during an actual storm - you'll thank yourself for it. Automatic changeover switches aren't massively expensive and make the whole thing seamless.

What battery capacity are you currently running in the motorhome? That'll determine whether you're genuinely covered overnight or just buying yourself a few hours comfort before needing the engine or a hookup.

Really resonates with this thread — my shepherd's hut build is essentially a permanent off-grid home, so I've lived this problem from day one rather than discovering it during a crisis.

One thing nobody's mentioned yet: critical load separation is your best friend here. Rather than trying to power your whole house, wire a dedicated "emergency circuit" covering just the fridge, a few sockets, and maybe a lamp or two. My Victron MultiPlus handles this elegantly with its transfer switch — grid goes down and it switches seamlessly within milliseconds.

Fourteen hours sounds daunting until you realise most of what actually matters draws surprisingly little. Prioritise ruthlessly, keep your motorhome's Fogstar lithium topped up through normal use, and suddenly a 14-hour outage becomes a minor inconvenience rather than a proper emergency.

The motorhome-as-backup concept is genuinely underrated.

Good thread. One aspect nobody's touched on yet — transfer switching.

If you're backfeeding from your motorhome into your house via a long extension lead or hardwired socket, you must have proper isolation from the grid. DNO engineers work on "dead" lines during outages; backfeed kills people.

Minimum you want is a proper changeover switch (Victron do decent ones, or a manual rotary changeover is fine for occasional use) that physically disconnects grid before connecting your inverter output.

On the EV side @DanFisher89 — worth checking whether your motorhome inverter can actually handle a type 2 EVSE. Most portable chargers draw 3.6kW continuous minimum; that's a significant sustained load. I run a garden office from my setup and learned quickly that continuous loads are a completely different proposition to surge loads.

What inverter rating are you working with @SimonKelly?

What @CarlBaker said about transfer switching is absolutely critical — can't stress it enough.

My narrowboat taught me this the hard way. First winter I had the boat moored up and thought I'd just run an extension from the inverter into the house consumer unit. Neighbour who's a sparky nearly had a breakdown when he spotted it.

The issue isn't just safety for you — it's line workers. If the grid comes back while you're backfeeding, you've potentially energised a line someone's working on. That's a very bad day for everyone involved.

Ended up fitting a proper changeover switch — isolates the incoming grid supply completely before the backup kicks in. Non-negotiable really.

For anyone serious about this, look at the Victron transfer switch options or get a qualified electrician to wire in a manual changeover. Roughly £150-300 fitted, worth every penny.

@CarlBaker and @Deano have got the transfer switching nailed so I'll leave that alone — what I will say is that after 14 hours you're not just keeping the lights on, you're keeping the fridge, boiler pump, and router alive, so size your loads before you size your battery bank.

My motorhome runs a Victron MultiPlus and Fogstar Drift lithium — worked an absolute treat last February when half the street was dark and I was watching Netflix like a smug goblin.