How to Size a Campervan Electrical System

Q: Does Starlink really change the calculation?

Yes. A Starlink Standard dish averages 45 to 60 W, which is 750 to 1,000 Wh over a 16-hour working day, roughly twice a 12 V fridge and the largest continuous load in most modern vans. Starlink Mini roughly halves it. Budget for it explicitly rather than discovering it after the batteries are installed.

Q: Where does the fuse go on a lithium battery?

Within 7 inches of the battery terminal, per ABYC E-11, extended to 40 inches only if the conductor runs inside a sheath or enclosure. Use a Class T fuse on the main battery conductor, because LFP can deliver several thousand amps into a short, beyond the interrupt rating of common ANL and MRBF fuses.

September 8, 2026

How to Size a Campervan Electrical System

The short answer: add up what you use in a day in watt-hours, multiply by two so you can survive a cloudy day without driving, and buy that much usable battery. For most builds the number lands between 1 and 3 kWh per day, which means a 5 kWh bank for a weekender, 10 kWh for a full-timer with Starlink and an induction cooktop, and 15 kWh the moment you add air conditioning. Solar is the smallest of your three charging sources — the alternator does most of the work. And if your peak load is above about 2,000 W, do it at 48 volts, because at 12 volts the cable stops being cable and starts being plumbing.

The rest of this guide shows the arithmetic so you can run it against your own build instead of trusting ours.

Last updated 8 September 2026 by the build team at Noke Van Co., Roanoke, Virginia.

Step 1: Build a load budget in watt-hours per day

Amp-hours are a trap in a mixed 12 V / 48 V / 120 V system, because an amp-hour means nothing until you say at what voltage. Work in watt-hours (Wh). Watts times hours. That is it.

For each appliance you need three numbers: its running wattage, its hours per day, and its duty cycle — the fraction of those hours it is actually drawing power. A fridge is not a 45 W load for 24 hours; it is a 45 W load for the 40% of the day its compressor runs.

Here is a realistic table for a four-season van in summer conditions. These are the numbers we use when we spec a system in our shop, not nameplate maximums.

Load	Running power	Hours/day	Duty	Wh/day
12V compressor fridge, 45–65 L, 85 °F ambient	45–65 W	24	35–45%	380–600
LED interior lighting, 8 fixtures	24 W total	4	100%	~100
Roof fan on low, overnight (ProBreeze brushless)	12–18 W	8	100%	100–150
Water pump	60 W	0.3	100%	~20
Diesel or gas air heater, running draw	4–27 W	12	cycling	~150
Same heater, glow-plug starts (30 A × 12 V ≈ 360 W, ~90 s)	360 W	6 starts	—	~55
Phones and one laptop, charged through the inverter	—	—	—	150–200
Starlink Standard, actuated dish	45–60 W avg	16	100%	750–1,000
Starlink Mini	20–40 W avg	16	100%	350–650
Induction cooktop, one real meal	~1,200 W avg	0.35	100%	420 + inverter loss
Electric kettle, two boils	1,500 W	0.13	100%	~200
Hot water: Pundmann Therm 6L from 60 °F to 140 °F	—	—	—	~350
12V rooftop A/C (RTAC12, up to 58 A)	~700 W max	8	40–55%	2,200–3,100
48V rooftop A/C (RTAC48, up to 15 A)	~720 W max	8	40–55%	2,300–3,200
Inverter standby, left switched on	15–40 W	24	100%	360–960

Two rows in that table are worth staring at.

Starlink. A satellite dish is the largest continuous load most modern vans carry, and it is the single most common reason a system that was sized in 2021 is undersized now. At 50 W average over a 16-hour day it eats 800 Wh — roughly twice the fridge. If you work from the van, budget for it explicitly, and consider the Mini, which roughly halves the number.

Inverter standby. A 3,000–5,000 W inverter idles at 15–40 W just being switched on. Leave it on around the clock and it can consume more than your refrigerator while doing nothing at all. This is why every well-built van has a way to switch the inverter off from the panel or the app, and why we tell customers to run the fridge, lights, fan, pump and heater on DC rather than through the inverter.

Hot-water arithmetic, since nobody publishes it: heating 6 litres of water by 80 °F (44.4 K) takes 6 kg × 4.186 kJ/kg·K × 44.4 K ≈ 1,115 kJ ≈ 0.31 kWh, plus standby losses. On the Pundmann's 200 W DC element that is about 1.7 hours of heating. On its 1,000 W AC element it is roughly 20 minutes — but those 20 minutes pull 1,000 W through your inverter. Same energy, very different peak. Browse the full range in water heaters.

Step 2: Turn daily watt-hours into a battery size

Three multipliers stand between your daily load and the bank you should buy.

1. Days of autonomy. How long must the van run with no driving and no sun? For most people the honest answer is two days. One day is brittle: a single overcast morning in a shaded campsite puts you at zero. Three days is expensive and rarely used. Multiply your daily load by 2.

2. Usable capacity. Lithium iron phosphate (LFP) will happily deliver 100% of its rated capacity, but designing to 100% means arriving at 0% state of charge, which is where the BMS starts disconnecting things and where cycle life suffers. Design to 85–90% usable. A 5 kWh LFP battery is 5,120 Wh nameplate; call it 4,400 Wh of design capacity.

3. Cold. LFP cannot be charged below freezing without damage. Batteries with built-in self-heating — such as the EcoFlow 2 kWh and 5 kWh LFP packs, rated for use down to −4 °F — solve this, but the heater itself draws from the pack. If you ski out of the van, add 5–10% to the bank for winter heating overhead.

So the formula is:

Bank (Wh) = daily load × days of autonomy ÷ 0.875

A 1.2 kWh/day build with two days of autonomy needs 1,200 × 2 ÷ 0.875 ≈ 2,740 Wh. A 5 kWh battery is the right size, with genuine headroom for the winter heater and the year you buy an induction hob.

Step 3: Be honest about charging

This is where most van electrical plans fall apart. People buy an enormous battery and 200 W of solar, then wonder why the bank never comes back up.

Solar: smaller than the brochure says

A flat-mounted van roof panel does not produce its nameplate rating. It is horizontal rather than tilted to latitude, it runs hot (silicon loses roughly 0.4% of output per °C above 25 °C, so a panel at 65 °C is down about 15%), it gets dirty, and one shaded corner drags a whole string down.

Use this instead of nameplate watts:

Daily solar (Wh) ≈ nameplate W × peak-sun-hours × 0.7 to 0.8

Season, mid-latitude US	Peak-sun-hours (flat)	200 W array	400 W array	600 W array
June, clear, unshaded	4.5–5.0	650–800 Wh	1,300–1,600 Wh	1,900–2,400 Wh
April / September	3.5–4.0	500–640 Wh	1,000–1,280 Wh	1,500–1,900 Wh
December, 40 °N	1.5–2.5	210–400 Wh	420–800 Wh	630–1,200 Wh
Any season, forested campsite	0.5–1.5	70–240 Wh	140–480 Wh	210–720 Wh

A 400 W roof in December in Virginia is a 500–800 Wh appliance. That is a fridge and some lights. It is not a Starlink and an induction cooktop.

Mount it without turning the roof into a colander: flush-mount stainless solar brackets, top-mount brackets in sets of four, or dedicated solar bars for the Transit. The whole range is in solar mounting.

The alternator does the heavy lifting

A DC-DC alternator charger running at 600–800 W puts 0.6–0.8 kWh into the bank per hour of driving. Two hours on the interstate beats a whole clear summer day of 400 W solar, and it works at night, in rain, and under trees.

Practical consequence: if you move the van every second or third day — which most people do — the alternator is your primary charger and solar is the top-up that keeps you level while parked. If you genuinely park for a week at a time, invert that, and buy roof area accordingly. Check the current alternator-charging rating for your specific power hub revision before you size around it; the number has changed between hardware generations.

Shore power

Shore power is the cheapest kilowatt-hour you will ever put in the van and it is worth wiring for even if you plan to boondock. A 30 A / 120 V pedestal is 3,600 W: it refills a 10 kWh bank in about four hours. The AC side of a van — shore inlet, transfer switching, bonding, GFCI protection — is the part we tell DIY builders to have inspected by a licensed electrician or an RV tech. DC mistakes start fires slowly; AC mistakes are immediate.

Step 4: 12 volts or 48 volts?

The answer is set by your peak load, not your daily energy. Power equals volts times amps, so the same 3,000 W draws:

250 A at 12 V
62.5 A at 48 V

Current is what sizes cable, lugs, fuses, busbars and switches — and resistive loss scales with the square of current.

Take a 10-foot run (20 feet of conductor there and back) of 2 AWG copper, which is 0.156 milliohms per foot, so 3.13 mΩ round trip:

	12 V at 250 A	48 V at 62.5 A
I²R loss in that cable	62,500 × 0.00313 = 195 W	3,906 × 0.00313 = 12 W
As a share of 3,000 W	6.5% burned as heat	0.4%
Voltage drop	0.78 V (6.5% of 12 V)	0.20 V (0.4% of 48 V)

Now size properly for a 3% drop:

12 V, 250 A, 10 ft: allowed drop 0.36 V, so total resistance must be under 1.44 mΩ, or 0.072 mΩ/ft. That is 3/0 or 4/0 cable — thumb-thick, expensive, brutal to route around a wheel arch, and needing a hydraulic crimper.
48 V, 62.5 A, 10 ft: allowed drop 1.44 V, so 1.15 mΩ/ft, which even 10 AWG satisfies. Here ampacity governs, not voltage drop: you use 6 AWG because 62.5 A demands it, not because of drop.

Copper resistance for the sizes you will actually use (milliohms per foot, at 25 °C):

AWG	mΩ/ft	AWG	mΩ/ft
10	0.999	2	0.156
8	0.628	1/0	0.098
6	0.395	2/0	0.078
4	0.249	4/0	0.049

The rule we use: under about 2,000 W of peak load, 12 V is simpler and every accessory you will ever buy speaks it natively. Above 2,000 W — which in practice means air conditioning, induction cooking, or a 3 kW-plus inverter — go 48 V and step down to 12 V for the DC loads. That is exactly how the EcoFlow Power Kits are architected: a 48 V battery bus with 12 V and 120 V taken off the hub.

The clearest illustration is air conditioning. The RTAC12 pulls up to 58 A for 10,000 BTU. The RTAC48 pulls up to 15 A for 12,000 BTU. More cooling, a quarter of the current, ordinary cable. On an EcoFlow system you feed it from a battery port with the 48-volt air conditioner cable, which frees the distribution panel's DC circuits for everything else. The full comparison lives in 12V vs. 48V van air conditioning.

Step 5: Protect the wire, not the appliance

Two rules cover most of what goes wrong in van DC systems.

A fuse protects the conductor. Size the wire for the load and the run, then fuse at or below that wire's ampacity. A 60 A fuse on 10 AWG is not "extra safety margin," it is a wire that will glow before the fuse opens.

Fuse at the source. ABYC E-11 requires overcurrent protection within 7 inches of the point where a conductor connects to its power source, extended to 40 inches only if the conductor is in a sheath or enclosure. The battery-positive to power-hub cable is the one people leave unfused because "it's short." That short cable is the one carrying enough current to vaporise a wrench.

Use the right fuse class on lithium. An LFP bank can deliver several thousand amps into a dead short. Common ANL and MRBF fuses are rated to interrupt roughly 2,700–6,000 A. Class T fuses interrupt around 20,000 A. On the main battery conductor of any serious LFP bank, use Class T.

Also worth doing: a shunt-based battery monitor so state of charge is measured rather than guessed from voltage — LFP's flat discharge curve makes voltage a nearly useless fuel gauge. The EcoFlow Power Link brings tank levels and sensor data into the same console, and the Power Dock lets you hang up to nine batteries off a single hub when you outgrow the three battery ports.

Three worked builds

Build A — the weekender

Fridge 450 + lights 100 + fan 120 + pump 20 + heater 205 + devices 175 + occasional inverter use 60 = ~1,130 Wh/day.

Two days of autonomy, 87.5% usable → 2.6 kWh required.

Buy: the 3.6 kW EcoFlow Power Kit, 5 kWh at $7,239, plus 200–400 W of solar. You will spend most weekends never dropping below 60%.

Build B — the full-timer

Build A + Starlink 800 + induction 450 + kettle 200 + inverter standby 400 = ~2,980 Wh/day.

Two days → 6.8 kWh required.

Buy: the 3.6 kW EcoFlow Power Kit, 10 kWh at $10,639, 400–600 W of solar, and drive-time charging you actually use. If you want the higher-output Gen 2 inverter for heavier AC loads, the EcoFlow 5 kVA Power Kit at $8,296 starts with a single 5 kWh battery and expands.

Build C — the air-conditioned build

Build B (3.0 kWh) + 8 hours of 48 V rooftop A/C at 40–55% duty (2.8 kWh) = ~5.8 kWh/day.

Buy: the 3.6 kW EcoFlow Power Kit, 15 kWh at $14,239 — and understand what it buys you. Fifteen kilowatt-hours at 87.5% usable is 13.1 kWh, which is just over two days at that load. Air conditioning is not a boondocking feature; it is a feature for people who drive most days, or who plug in. Anyone promising you a week of off-grid A/C is selling something.

Two things make Build C work that have nothing to do with batteries: insulation, which directly reduces the compressor's duty cycle, and a roof fan to purge the hot air out of the van before the A/C ever starts. Cooling a 130 °F box down to 75 °F costs far more than holding an 85 °F box at 75 °F.

The eight-step checklist

List every load with running watts, hours, and duty cycle. Sum the watt-hours.
Add inverter standby if the inverter stays on.
Multiply by your days of autonomy — two, unless you have a reason.
Divide by 0.875 for usable capacity.
Check the recharge side: alternator hours per week, real solar yield in your worst month, shore access.
Set the bus voltage from peak load: under 2,000 W, 12 V; over, 48 V.
Size every conductor for 3% drop and ampacity, then fuse the conductor within 7 inches of the source.
Add 20% headroom, because every van build grows.

If you would rather have a second pair of eyes on the spreadsheet, send it to us — we build these vans in Roanoke and we will tell you if your numbers are wrong. Everything referenced here is in van electrical systems, EcoFlow power kits, lithium batteries, and solar mounting.

Frequently asked questions

How many watt-hours per day does a camper van actually use? Most builds land between 1 and 3 kWh per day. A weekender with a fridge, lights, a roof fan, a water pump and a diesel heater uses around 1.1 kWh. Add Starlink, an induction cooktop and an always-on inverter and it rises to roughly 3 kWh. Add rooftop air conditioning for eight hours and it reaches 5–6 kWh.

How many batteries do I need for a camper van? Multiply your daily watt-hours by your days of autonomy (two is the sensible default), then divide by 0.875 to allow for usable capacity. A 1.1 kWh/day build needs about 2.6 kWh, so a 5 kWh bank. A 3 kWh/day build needs about 6.8 kWh, so a 10 kWh bank. Air-conditioned builds need 15 kWh.

How much solar do I need for a van? Estimate real output as nameplate watts times peak-sun-hours times 0.7–0.8, not nameplate alone. A flat-mounted 400 W array yields roughly 1,300–1,600 Wh on a clear June day and only 420–800 Wh in December at 40° north. Solar keeps you level while parked; the alternator does the bulk recharging.

Should my van be 12 volt or 48 volt? Choose by peak load. Below about 2,000 W, 12 V is simpler and every accessory speaks it. Above 2,000 W — air conditioning, induction cooking, a 3 kW-plus inverter — go 48 V and step down for DC loads. At 3,000 W a 12 V system carries 250 A and needs 3/0 or 4/0 cable; a 48 V system carries 62.5 A on 6 AWG.

Does Starlink really change the calculation? Yes. A Starlink Standard dish averages 45–60 W, which is 750–1,000 Wh over a 16-hour working day — roughly twice a 12 V fridge and the largest continuous load in most modern vans. Starlink Mini roughly halves it. Budget for it explicitly rather than discovering it after the batteries are installed.

Where does the fuse go on a lithium battery? Within 7 inches of the battery terminal, per ABYC E-11 (up to 40 inches only if the conductor runs inside a sheath or enclosure). Use a Class T fuse on the main battery conductor: LFP can deliver several thousand amps into a short, beyond the interrupt rating of common ANL and MRBF fuses.

Can I run air conditioning off battery overnight? Yes, but only with a large bank and a plan to recharge. A 48 V rooftop unit draws roughly 290–400 W averaged over an eight-hour night, or 2.3–3.2 kWh. A 15 kWh bank covers about two nights of that plus normal loads, so air conditioning is realistic for people who drive most days or plug in, not for a week parked in one spot.

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