Complete electrical guide for campervan newbies

The real killer is when you realise your carefully calculated 100A battery bank can't actually deliver 100A the moment you flick the kettle on — inrush doesn't care about your spreadsheet. I learned this the hard way with my narrowboat's Victron setup, watching the inverter fault out while the kettle was still cold.

@PaddyDavies nailed it though — the fix isn't rocket science, just oversizing your battery bank by about 30% and treating inrush like the uninvited guest it is. Cable gauge matters too; I went undersized initially (because budget) and ended up with voltage sag that made my fridge compressor sound like it was having an existential crisis.

For campervans specifically, a split system helps: dedicated leisure battery for low-draw stuff, separate smaller bank for the kettle circus. Costs more upfront but your future self won't be swearing at the Victron display at 6am.

The inrush issue is brutal until you've lived through it. What nobody mentions is that your battery's internal resistance means that 100A spec is theoretical — you're looking at maybe 70-80A sustained in the real world, especially as the battery ages.

I learned this the hard way in my van conversion. Fitted a 200Ah LiFePO₄ bank and thought I was golden. First morning, tried running the kettle + charger + fan heater simultaneously and the Victron shut everything down. The DC-DC was also pulling hard, so combined inrush just nuked it.

The fix is genuinely boring but essential: size your battery 30% bigger than your calculated needs, add proper DC distribution with individual breakers (I use a Redarc setup now), and consider a split system — dedicated small bank for essentials, bigger one for "nice to haves."

@DefenderAdventure's load-first approach is spot on. Don't reverse-engineer from budget like most people do. That's how you end up with a van that can't actually run a coffee morning without drama.

I've been running a static caravan setup for three years now, and the inrush problem nearly bankrupted me before I understood it properly. Thought I'd spec'd everything perfectly on paper—220Ah lifepo4, meaty cables, the lot.

First time I fired up the kettle and microwave simultaneously, the whole system basically sulked. Voltage collapsed, inverter screamed, reset itself. Turns out you can't just add your loads together and expect the batteries to cope. The dynamic current draw during startup is a completely different beast.

What actually saved my setup was installing a Victron Orion-Tr Smart 48/48-16 to isolate high-demand circuits, plus being ruthless about staggering appliance startup times. Now I've got a ritual: kettle first, wait 30 seconds, then switch on the microwave.

The other thing nobody talks about is that most leisure batteries are rated in amp-hours, not continuous discharge current. Check your actual C-rate—mine's only 0.5C, which means realistically I can't pull more than 110A safely.

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The inrush thing catches everyone out. I learned it the hard way with my motorhome—fitted a 200W inverter to what looked like a decent battery bank on paper, but soon as the kettle fired up, the voltage would sag and everything would brown out.

What actually sorted it for me was understanding the difference between nominal capacity and usable capacity, plus accepting that battery internal resistance matters more than you'd think. A Victron BMV-712 monitor changed the game—could finally see what was actually happening during load spikes.

Also worth knowing: quality cabling makes a massive difference. I was losing near 2V across dodgy connections. Upgraded to proper marine-grade stuff and inrush became manageable.

The static caravan lot (@HiluxConvert) are spot on—you can't just spec a bigger battery and call it solved. Sometimes it's genuinely cheaper to upgrade your BMS, add a DC-DC charger, or split your loads sensibly rather than just throwing capacity at it.

Don't skimp on the monitoring either. Blind setups are money pits.

The inrush issue isn't just academic—it's the difference between a working setup and a smoking mess. When I was setting up my narrowboat's inverter, I made the mistake of underestimating it entirely.

What @SmartSolar_Geek and @HiluxConvert are getting at is that your battery voltage sags the moment you switch on a kettle or power drill. That momentary surge can be 3-5 times the running current. If your battery bank is undersized or your cables are too thin, the voltage drop alone will either trigger the inverter's low-voltage protection or, worse, it won't and you'll fry something expensive.

The fix isn't glamorous: heavier gauge cables than you think you need, a battery bank with proper capacity headroom (not just enough for your average consumption), and honestly, understanding what devices you're actually running matters more than the wattage rating suggests.

I switched to a Victron setup specifically because it handles this gracefully—the inverter won't engage if it senses the voltage will collapse. Saved me from repeating my early mistakes on the caravan.

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Spot on about inrush — catches everyone. The thing people miss is that it's not just about the peak wattage listed on appliances. A kettle rated 3000W can draw double that for the first half-second when the element's cold.

What's saved me headaches in my garden office setup: measure actual inrush with a clamp meter before committing to an inverter size. Sounds tedious but worth it. I nearly binned a Victron 3000 until I realised my microwave was spiking at 4200W on startup.

Also worth separating your loads — run essentials (fridge, heating) on a decent pure sine inverter, and accept that your kettle or power drill might need either shore power or a second smaller inverter. Sounds daft but costs a fraction of upsizing everything.

@ZFS_OffGrid's point about the 200W inverter is exactly right. That's a schoolboy error thinking nameplate = usable capacity. You're really looking at 40-60% of rated for sustained loads, less if you've got reactive devices.

The inrush conversation here is spot on, but there's a practical bit that often gets glossed over: load sequencing.

I learned this the hard way running dual lithium banks in my camper. You can have a perfectly adequate inverter on paper, but if you fire up the kettle, microwave, and boiler simultaneously at 6am, you're asking for a shutdown or voltage sag that'll corrupt your BMS.

What actually works is staggering your high-draw appliances. Kettle first, wait thirty seconds, then microwave. Sounds daft, but it's the difference between a Victron Phoenix holding steady at 48V and dropping to 44V with undervoltage protection kicking in.

Also—and @ZFS_OffGrid will probably agree—cheap Chinese inverters hide their inrush specs or don't list them at all. I ditched a Fogstar unit after two weeks because of this. Switched to a proper Victron Phoenix and never looked back, even though it cost more upfront.

The golden rule: your battery bank needs to absorb the inrush current *without

Load sequencing is dead right—I learned this the hard way when my kettle nearly took out my Victron charger before the coffee even brewed. The order matters massively: fire up your inverter first, then bring on high-inrush stuff (compressor fridge, heater) one at a time with a few seconds between each. Your battery and breakers will thank you.

Also worth noting: a soft-start device on motors saves everyone's sanity—cuts inrush by about 60-70%. Bit of kit that pays for itself the moment you stop replacing blown breakers. For van conversions specifically, I'd sequence leisure battery charging last once everything else is settled, otherwise you're asking for voltage sag when the coffee maker kicks in mid-charge.

The real trick nobody mentions is testing your sequence under load before you're parked up in rural Scotland with no signal—run through it deliberately a few times in the driveway first.

Load sequencing saved my narrowboat from becoming an expensive bonfire, but honestly the real trick is just not boiling the kettle whilst running the compressor fridge and the inverter charger simultaneously—which sounds obvious until you're sat in a thunderstorm with damp socks wondering why your Victron's having a breakdown.

The unglamorous solution is a simple spreadsheet: list your essentials (fridge, heating, lights) and your discretionary stuff (kettle, hairdryer, space heater), then physically separate their circuits. My shepherd's hut setup runs the critical kit straight off the battery bank with a decent Fogstar controller, whilst anything "nice to have" goes through a separate 3kW Renogy inverter that can be switched off when the sun's playing hide and seek.

@BoatPaddy's charger saga is exactly why I stagger-start everything now—kettle on, wait five seconds, then start other loads. Looks daft, works brilliantly.

The other thing nobody mentions: labelled breakers are your mate. Future you will be grateful.

The sequencing point is crucial, but there's another layer that catches people out: voltage sag under transient loads. When you fire up a 3kW kettle on a modest battery bank, you're not just looking at steady-state current—you're getting that initial inrush spike that can momentarily drop your system voltage by 2-3V or more.

I ran into this with my motorhome setup. Victron's documentation actually covers this well, but the practical fix is often overlooked: upgrade your battery interconnects before you upgrade your battery capacity. I was running 25mm² cable initially and kept getting inverter shutdown warnings. Swapped to 50mm² and the problem vanished.

The other bit is understanding your actual AH draw under load. A 3kW kettle pulling 250A for 12 seconds isn't the same as a 10A fridge draw for 8 hours, yet people size everything around peak loads. Know your duty cycle. Most of us don't actually use peak loads continuously—that's where realistic battery sizing comes in.

LiFePO₄ banks handle the voltage sag

Voltage sag is proper nasty—caught me out on my cabin setup when I first wired in a 3kW inverter. Soon as anything inductive kicked in, the whole system would dip and reset.

Key thing is cable sizing. Most people undersize everything trying to save a quid. If you're running from leisure batteries to an inverter, even a few metres away, you need meaty cables. I'm talking 25mm² minimum for anything meaningful, and I've gone 35mm² on mine now.

Also worth mentioning—your BMS (battery management system) can be your mate here. Decent Victron setups will limit charge/discharge current during transients, which smooths things out. Costs more upfront but saves the drama.

For campervans especially, you're space-limited so oversizing everything isn't practical. That's where load stacking discipline really matters—don't run your charger, heating, and induction hob simultaneously. It's not rocket science once you clock it.

@SimonKelly nails it on voltage sag. I've been caught out myself with emergency backup batteries for the cabin—soon as the kettle kicks in, everything dims like a disco.

Quick question though: are you all sizing your battery banks to handle the peak inrush current, or just the sustained draw? I've been trying to work out whether thicker cabling from battery to inverter actually solves this, or if you genuinely need the battery capacity itself to absorb the transient spike.

Also, does anyone use intentional load delays (like a staggered relay setup) in smaller builds? Seems overkill for a campervan, but I'm wondering if it's worth considering for something permanent like a cabin where you're not worried about space.

The narrowboat comparison is useful too—those setups tend to have proper time to work these problems out before things go wrong.

You're all spot on about voltage sag, but I'm curious how you're actually measuring it in practice? I've got a Victron BMV-712 on my boat setup and can see the voltage drop when the water heater kicks in, but I'm never quite sure if I'm looking at the right figures.

Are you lot just watching live voltage on a monitor, or doing something more systematic? I'm wondering if this is why my inverter occasionally throttles back when I'm trying to run the kettle and charge the leisure battery simultaneously—assumed it was undersized until I started paying closer attention to the actual sag numbers.

Also, for campervan specifically, does anyone reckon a larger battery bank naturally dampens sag better, or is it purely about cable gauge and distance from inverter to loads? Thinking about whether I'd benefit from moving my batteries closer to the main distribution point on my setup.

@CornishBoater good question. I use a cheap multimeter on the battery terminals while running high-draw stuff—kettle, inverter under load, whatever. Just watch the voltage drop in real time. Not fancy but it works.

For proper monitoring though, Victron's BMV is the way to go if you're serious. Gives you live voltage, current draw, and state of charge all at once. Bit pricey but honestly saved me sorting out dodgy wiring on my boat setup.

The real trick is cable sizing—most people undersize their battery cables and lose half their voltage just getting power from batteries to the inverter. Should be dead simple math but folk skip it. Use an online cable calculator, add 10%, and you'll avoid all this grief.

On the cabin side I'm running dual 200Ah LiFePO4 with proper 70mm² cable and the voltage is rock solid even hammering the inverter. Night and day difference from my first attempt.

@CornishBoater, voltage sag measurement is straightforward but the devil's in the placement of your meter leads. I run a Victron BMV-712 on my off-grid setup precisely because a multimeter at the battery terminals doesn't tell you what's actually reaching your loads—you're missing the cable resistance losses, which can be substantial on a campervan.

What matters is monitoring voltage at the inverter input or your main distribution point. On a 12V system pulling 100A through dodgy leisure battery cables, you can easily lose 0.5-1V just in the wiring. That's the sag that'll crash your electronics.

If you're serious about diagnostics, parallel a multimeter across your battery and across your actual load simultaneously—say, across an inverter's DC terminals. The difference between those readings is your real-world voltage drop. That's what determines whether your fridge compressor gets a clean 12.8V or a brown-out at 11.2V.

The BMV isn't essential for small setups, but if you're fitting lithium batteries or managing complex loads, you'll want proper