Campervan electrical system calculator
List what you actually run, and this works the whole 12 V system back from it: daily watt-hours for summer and winter, a battery bank that survives the days you pick with no sun, a solar array sized for where you camp, and the inverter, charge controller, alternator (B2B) and shore chargers to match. Start from a preset, then edit every row.
Edit any row afterwards — the preset just fills the table.
How many rainy days the bank alone must cover. 2 is the usual planning figure.
| Appliance | Watts | h/day summer | h/day winter | Qty | 230 V | |
|---|---|---|---|---|---|---|
Tick 230 V for anything that plugs into a mains socket — it runs through the inverter, which costs ~15 % and sets the inverter size. Watts are running draw; hours are effective run time (a fridge compressor's duty cycle is already folded into its 9 h).
Daily draw, summer
693 Wh
Daily draw, winter
368 Wh
Battery bank
150 Ah @ 12 V
1440 Wh usable at 80 % depth of discharge, sized for the worse season.
Solar array
200 W
5 peak sun-hours/day × 0.75 system derate. Summer ≈ 200 W, winter ≈ 350 W.
Inverter
—
No 230 V loads — a 12 V-only system needs no inverter.
MPPT charge controller
100/20 · 20 A
DC-DC (B2B) charger
50 A
≈ 2.4 h of driving to refill the usable capacity from empty.
Shore charger
30 A
≈ 4.0 h on hook-up to refill from empty.
Rule-of-thumb cross-check: solar W ≈ 2 × battery Ah = 300 W. If the two disagree, the sun-hour figure is the honest one — the rule assumes summer.
Planning sizes, rounded up to what shops sell. In the VanPlot editor the appliance list comes from the parts you place, and the batteries and roof panels you draw are what gets counted.
Planning figures, not certification. Standards are summarised for builders; your inspector, your van's plate and your own measurements always win.
How this is calculated
- Daily energy = Σ (watts × hours × quantity) per appliance, for summer and winter separately; anything on 230 V is divided by the inverter's 0.85 efficiency — the (W ÷ 12 V × h) ÷ 0.85 rule in Wh form.
- Battery Ah = worse-season Wh/day × days without sun ÷ (system volts × usable share). LiFePO4 gives 80 % usable, AGM and flooded lead 50 % — the reason an AGM bank is twice the size for the same job.
- Solar W = Wh/day ÷ (peak sun-hours × 0.75). Peak sun-hours come from the latitude band and season (Central Europe: ~5 h in summer, ~1.5 h in winter); the 0.75 derate covers panel temperature, wiring, controller and dirt losses.
- Inverter = largest simultaneous 230 V load × 1.2, rounded up to a sold size. MPPT tier from array watts ÷ battery volts (100/20 up to ~290 W at 12 V, 100/30 to ~440 W, 100/50 to ~700 W, 150/70 to ~1 000 W).
- DC-DC (B2B) charger = up to 0.3 C for LiFePO4 / 0.2 C for lead (the rate the bank accepts without ageing), capped at 60 A; shore charger ≈ 0.15 C. Hours to full = usable Ah ÷ charger amps.
Sources
- FarOutRide — Electrical System Calculator and five years of measured consumption data
- Explorist.life — inverter and charge-controller sizing guides
- Victron Energy — Wiring Unlimited; SmartSolar MPPT and Orion DC-DC datasheets
- Battle Born Batteries — usable capacity by chemistry
- PVGIS / Global Solar Atlas — peak sun-hour planning figures for Europe
Questions builders ask
How big a battery does a camper van need?
Multiply your daily watt-hours by the number of days you want to survive without sun, then divide by the usable fraction of the bank: 80 % for LiFePO4, 50 % for AGM or flooded lead-acid. A 1,200 Wh/day van that must last two rainy days needs 2,400 Wh usable — 250 Ah of LiFePO4 at 12 V, or 500 Ah of AGM.
How much solar do I need for a campervan?
Divide daily watt-hours by the peak sun-hours where you camp, times a 0.75 loss factor. For 1,200 Wh/day in Central Europe that is ~350 W in summer (5 sun-hours) but ~1,100 W in winter (1.5 sun-hours) — which is why winter vans lean on a B2B charger from the alternator. The rule of thumb 'solar watts ≈ 2 × battery Ah' assumes summer.
What size inverter for a van conversion?
Size it to the largest 230 V load you run at the same time, plus 20 % headroom: an 1,800 W induction hob needs a 2,000 W inverter; a laptop and a kettle together need about 1,500 W. If nothing you own plugs into a mains socket, you don't need one — run everything on 12 V.
LiFePO4 or AGM for a camper — does the chemistry change the sizing?
Yes, by 2×. AGM and flooded lead-acid should only be discharged to 50 % if they are to last, so a 200 Ah AGM bank delivers 100 Ah; a 200 Ah LiFePO4 bank delivers 160 Ah and weighs less than half. That is why most calculators quietly assume lithium — pick your real chemistry here and the battery figure follows.
Keep reading
Plan the whole van, not just this number
VanPlot is a 3D layout planner for camper conversions. Place real components in your real van and watch weight, axle loads, power and cost update live — this calculator is one panel of it.
Who makes this
I'm Vladimir. I'm planning my own conversion, and none of the tools I tried could tell me whether a layout would fit or what it would do to the rear axle, so I made this one. I work on it alone. If something's wrong or missing, write to me — the address goes to my inbox.
Vladimir Šterjoski