Stay off hook-up — even through a dark British winter.
A weekend off-grid should not mean a flat leisure battery by Sunday. Wattonomy sizes your leisure battery, solar and B2B charger to how you actually travel, and specs the fused, BS 7671-referenced wiring to match — Victron-friendly throughout.
Built to UK (BS 7671) standards · free · no account
A real Wattonomy output — a UK campervan leisure bank
System
12 V
Battery
2.56 kWh
Solar
2000 W
Inverter
MP 12/1600
SmartSolar 150/1002×
200W solar panel10×
Battery → inverter cable4×
Battery → inverter fuse1×
Wire & fuse sizes follow EN 1648-2 — each conductor carries its fuse and stays under a 3% voltage drop.
Built to UK (BS 7671) standards
Gauge · fuse · volt-drop sized
Every spec sourced
British winter solar barely charges a thing.
From October to March a whole day’s sun might give you a few amps — so the leisure battery and your B2B charger have to carry the van between hook-ups. Wattonomy sizes the bank to your real off-grid days, works in a battery-to-battery charger for lithium, and shows where you will top up on EHU.
What a UK conversion has to get right
Weak winter sun and hook-up culture change how you size a van here.
Leisure battery
Sized to your nights off hook-up on honest lithium depth-of-discharge, kept off the starter battery.
B2B + solar
A battery-to-battery charger tops the bank from the alternator; solar helps spring to autumn, barely in winter.
Winter reality
We size to UK winter sun and flag when you will lean on EHU or the alternator rather than overspend on panels.
Sized wiring
Cable and fusing gauged for current and voltage drop, referenced to BS 7671 / EN 1648-2.
What you walk away with — free
A leisure-battery + solar design sized to your real use
A B2B / alternator charging plan that suits UK winters
A wiring diagram with gauges and fusing
A parts list you can take to any 12V supplier
Building it for real? Unlock the build binder.
Free gets you a safe, correctly-sized design. The build binder gets you the documents to build it right — and prove it's right.
Printable wiring diagram, yours to keep & tape inside the campervan
Full parts list, every line sourced
The volt-drop & fusing calculation trail — the "why" behind every spec
The build binder is a one-time unlock — no subscription, no auto-renew.
Questions
Will solar be enough in winter?
Usually not on its own — UK December sun is very low, so the tool sizes a leisure bank plus B2B/alternator charging and shows when you will need EHU, rather than selling you panels that will not deliver.
Is the wiring to UK standards?
Cable and fusing are sized referencing BS 7671 and EN 1648-2 (12V leisure). The 230V hook-up side should be installed and certified by a registered electrician.
Leisure or starter battery?
The leisure (house) battery powers your 12V kit and is kept separate from the engine starter battery — the tool sizes the leisure bank.
Do I need an account?
No — free, no email wall. Accounts only for saving builds or the build binder.
The standards we build to
Plain version: these are the recognized rulebooks your design is sized against, so the numbers hold up to a surveyor, an inspector or an insurer.
EN 1648-2The European standard for 12 V electrics in leisure vehicles.
BS 7671The UK IET Wiring Regulations for the 230 V side.
Wattonomy applies these standards in its calculations. It is not certified, sponsored or endorsed by ABYC, ISO, NFPA or Victron — it sizes your design to meet what they require, and shows the working.
Sized and checked to BS 7671. Last reviewed June 2026 — see the full methodology for the exact rules behind every number and how each design is validated.
Built by anABYC Certified Master Technician