Complete electrical guide for campervan newbies

Right, I'll break down what I've learned retrofitting a narrowboat and then applying it to a campervan setup, since the principles are identical.

Start with your loads
Before touching a single wire, calculate your daily consumption in amp-hours. Everything from your fridge (typically 30-40Ah daily) to your heater, lights, and laptop charger. Be honest—most people underestimate by 50%. I use a simple spreadsheet: device wattage ÷ 12V = amps, then multiply by hours used daily.

Battery sizing
Your battery bank should handle 3-5 days without sun (useable capacity, not total). Lithium LiFePO₄ gives you roughly double the useable capacity versus lead-acid, though the upfront cost stings. I run 200Ah lithium and honestly wouldn't go back—the space savings alone on a van are worth it.

Solar and charging
A quality 200W+ solar array is realistic for UK conditions. Don't assume peak output; plan for 60-70% efficiency in winter. Pair it with an MPPT controller (Victron or Renogy are solid). Most vans also benefit from a split charger to top up from the engine alternator whilst driving.

The inverter question
2000W pure sine is the sweet spot for campervans—enough for kettles and power tools without massive battery drain or installation headaches.

Cabling matters
Seriously, don't cheap out here. Undersized cables = fire risk. Calculate your longest cable run and use appropriate gauges. Victron's sizing guide is worth reading properly.

Start small, monitor everything for a month, then expand. That's how you learn what actually works for your lifestyle.

@DefenderAdventure spot on with loads-first thinking. Most people reverse-engineer this and wonder why their 100W solar panel doesn't cut it.

One thing worth emphasising for van-specific setups: your parasitic draw is brutal in a vehicle. I've seen folks lose 40-50% of battery capacity overnight just from leisure battery management systems, habitation relays, and fridge draw. On my setup I've got everything on a master kill switch – sounds daft but it genuinely extends autonomy by days.

Also, narrowboat and van differ on one critical point: you can't rely on shore power between sites. So your battery sizing needs to account for consecutive poor weather days, not just the daily average. I'd budget for 5 days minimum in winter.

The other gotcha is thermal load. Fridges absolutely hammer lithium setups if you're not careful with insulation and positioning. Worth a separate thread really.

@DefenderAdventure and @Titch are spot on. I'd add that once you've got your daily consumption figured out, you need to account for seasonal variation — this catches everyone out.

My shepherd's hut setup runs about 3kWh/day in summer but balloons to 5kWh once heating kicks in. A 400W solar array handles summer comfortably, but November through January I'm barely scraping 60% of nominal output due to angle and cloud cover. That's when your battery bank and either a backup genset or grid connection becomes essential.

The other thing nobody mentions: parasitic draw. Fridge, router, chargers left plugged in — easily 40-50W continuous in my experience. Size your system accounting for this vampire load running 24/7, not just your active-use consumption.

Calculate everything twice before ordering components. It's far cheaper to spec correctly upfront than retrofit larger batteries and panels later.

Worth pointing out the often-missed bit: battery chemistry changes everything. LiFePO4 vs lead-acid completely alters how you calculate your usable capacity—you'll get maybe 80-90% usable from LiFe but only 50% from lead-acid if you want it lasting more than a season.

I've got a shepherd's hut setup with a Victron 48V LiFe system and the difference between what the nameplate says and what you can actually draw is massive. Took me three months of trial and error to stop oversizing components.

Also, don't forget phantom loads. Phone chargers, control boards, that little fan you thought was off—they add up. A cheap energy monitor on your leisure battery for a week will genuinely shock you.

The loads-first approach @DefenderAdventure mentions is absolutely right, but run the numbers twice. Most people get it wrong first time.

@DefenderAdventure's methodology is sound, but I'd hammer home one practical point that catches most people out: peaking vs sustained draw.

Your kettle might pull 1500W for three minutes, but your battery bank needs to handle that instantaneous demand, not just daily watt-hours. Lead-acid especially suffers here — you'll flatten a 200Ah bank trying to run high-draw appliances even if your daily consumption suggests you've got plenty.

On narrowboats and vans alike, I've found Victron's MPPT controllers genuinely worth the outlay because they handle mismatched arrays better than budget units, particularly when you're working with limited roof space and variable solar angles. Pair that with a decent shunt monitor (Victron BMV or similar) and you'll actually see what's happening rather than guessing.

@MarshLover's right about chemistry too — LiFePO4 changes the entire calculation around usable capacity and charge rates. Different beast entirely.

The load calculation is spot on, but I'd flag something that caught me out retrofitting my static caravan: thermal management during charging cycles. Most newcomers spec their battery bank and charger independently, then wonder why their Victron MPPT throttles back mid-summer.

You need to calculate your peak input alongside peak loads. Solar + mains charger running simultaneously generates serious heat in confined spaces. I'm running a 100A Orion-Tr in my setup and had to add forced ventilation behind the battery enclosure—would've melted the connections otherwise.

Also worth noting: if you're retrofitting existing leisure batteries first, do the sums on usable capacity. Most people assume 100Ah = 100Ah, then run lead-acid down to 20% and wonder why their lifespan is rubbish. LiFePO4 changes the game entirely, but that's a separate outlay.

The order matters: loads → battery chemistry → then charging infrastructure.

The chemistry point @MarshLover raises is crucial — I've got LiFePO4 in my shepherds hut and it's transformed how I approach system design. You can pull far higher continuous discharge rates safely, which means smaller battery banks for equivalent usable capacity.

What I'd add though: don't overlook your BMS (Battery Management System) settings. Most off-the-shelf LiFePO4 packs come with conservative factory settings. I spent months scratching my head at poor performance until I realised my Victron system wasn't communicating properly with the battery's CAN bus protocol.

Also worth knowing — if you're running 12V in a van, voltage drop becomes genuinely problematic over longer cable runs. Calculate it properly using the formula, or you'll find your "3kW" inverter throttles itself in practice. I learnt that one the hard way with a Renogy setup before upgrading to proper marine-grade cabling.

What chemistry are you leaning towards?

Real talk — load calculation is dead right, but don't sleep on your inverter sizing. I made the mistake of undersizing mine for the garden office setup. Thought 2kW would handle everything, but the moment you're running kettle + laptop + charging batteries, you're maxed out. Now running a Victron 3kW and it's night and day.

Also worth noting: peaks matter more than averages. Microwave or power drill will spike way higher than your continuous draw. That's where folk come unstuck.

@DefenderAdventure's approach is solid though — work backwards from what you actually use, not what you think you'll use. I logged mine for a month before ordering anything. Saved me buying a massive battery bank I'd never fill.

@GlenDoug's inverter sizing point is chef's kiss — I learned that the hard way with my caravan when the kettle nearly took out a Victron 3000. Your peak surge matters more than average load; a basic kettle or compressor can spike to double its rated watts for a split second.

Quick add: cable sizing gets criminally overlooked. I've seen people run 1000W inverters through 2.5mm² cable and wonder why voltage sag makes everything run like it's underwater. Properly sized battery-to-inverter cable is genuinely the difference between a system that works and one that sulks.

And thermal management — yes @VanGill — lithium hates heat. Keep those batteries shaded and ventilated or they'll throttle themselves in summer faster than you can say "battery BMS".

The inverter thing is spot on — I've been there too. What most people miss is the inrush current when things like compressor fridges kick in. On paper your kettle draws 3kW, but the actual peak can be 4–5kW for a split second.

I run a 5kW Victron inverter in my array setup and it's been bulletproof, but I've seen folks get caught out with cheap 3kW units that just shut down under load. Worth spending the extra quid upfront rather than learning it the hard way at 6am when you want a cuppa.

Also worth noting — @DefenderAdventure's load calculation is the real foundation. Get that wrong and you'll either overspec (wasting money) or underspec (wasting sanity). A spreadsheet with realistic usage patterns beats guessing every time.

Spot on about inrush current, @LiFePO4Nerd. I've got a Victron 3000VA in my setup and it handles it fine, but I've seen people use undersized pure sine units and wonder why their compressor fridge trips everything.

Worth noting: if you're planning to run anything with a motor — fridge, water pump, even a small drill — you need your inverter rated for at least 3x the running wattage. Sounds mental but it's the peak draw that matters.

Also, don't cheap out on the DC wiring between battery and inverter. I made that mistake on the narrowboat initially. Proper 4mm² cable minimum, proper crimps, not spade connectors. Voltage drop kills efficiency and causes all sorts of phantom issues.

Mate, the inrush current thing is proper brutal. I learned this the hard way with my garden office setup — threw a £400 inverter at the problem and it lasted about three weeks before the relay started clicking like an angry woodpecker every time the kettle fired up.

Ended up going Victron (yes, more expensive, yes worth it) and now

The inrush spike is exactly why I went for a larger inverter than my peak draw actually needed. Running a 3kW Victron in my static caravan when I could technically get away with 2kW — but that extra headroom absorbs the inrush without the charger throttling back.

Worth noting though: if you're stacking loads (kettle + microwave + compressor fridge all at once), you're asking for trouble regardless. The real solution is load management, not just buying bigger kit. I use a simple relay setup to stagger my boiler and water pump so they never fire simultaneously.

Also consider your battery's ability to deliver current spikes. A LiFePO₄ with a decent BMS will handle it better than lead-acid, but your cable gauge matters more than people realise. I've seen folks cheap out on battery cables and wonder why their 100A system keeps tripping at 60A.

The Fogstar or Renogy battery monitors help here — you can actually see what your peaks are doing before you size everything else. Prevents expensive mistakes down the line.

The inrush thing absolutely caught me out in my van conversion. I'd calculated everything meticulously — kettle draws 2.8kW, microwave 1.2kW, never running together — so I thought a 3kVA would be bulletproof.

First time I switched on the water heater and fridge compressor simultaneously, the inverter just tripped. Turns out that compressor kicks in at nearly double its running current for a split second. I was gutted because I'd already mounted everything.

What actually solved it for me was being ruthless about staggered switching. Sounds mad, but I literally keep a schedule on my phone now — fridge powers on at 6am, water heater only comes on after coffee. Not ideal, but it bought me time to save for the upgrade to a Victron 5000VA, which handles those spikes without breaking a sweat.

The other thing nobody mentions is your battery's ability to supply that surge. You can have the best inverter in the world, but if your LiFePO4 has rubbish BMS settings, it'll cut out before the

The inrush problem cascades worse on boats than vans because you're often running everything off a single battery bank with limited cable diameter. I've had my narrowboat's 200Ah LiFePO4 drop to 10.5V when the immersion heater kicked in — absolutely flattened the house bank in seconds despite having what should've been adequate capacity.

What @VanGill's done with the oversized Victron is spot on, but there's another layer: the battery's internal resistance matters enormously. A cheap leisure battery with high internal resistance will sag harder under inrush than a quality one. Lithium helps because the IR is typically half that of lead-acid, but you're still vulnerable if your cable runs are dodgy.

My solution was fitting a relay-switched soft-start on the immersion circuit — delays the heating element by 500ms so the inverter doesn't take a full hammer blow. Cost about £35 and eliminated the voltage sag completely. Worth considering if you're on a tight budget and don't want to upgrade your inverter.

Also watch AC distribution — undersized shower cable can add enough resistance that