VanWire

Tell it what you're fitting. It works out the battery, the charging, and every cable and fuse — with the voltage drop shown for each circuit.

1. Your van

Pick your van and VanWire works the cable runs out from its real internal dimensions, instead of you guessing them. The figures come from the manufacturers' own converter drawings.

Got the reg to hand? It'll fill in the make. DVLA records don't carry the model or the body size, so you'll still need to pick those two yourself.

The three short links below sit together near the battery, which is why they default to a metre. Change them if yours are further apart — at 300 amps every extra metre costs real money in copper.

2. What you're fitting

Tick what's going in, adjust the hours to match how you actually use it, and say roughly where each thing sits. The run column fills itself in — type over it only if you've measured the real thing.

ApplianceWattsQty Hours/dayDuty% ? WhereSideHeightRunm ?

Swipe the table sideways to reach the rest of the columns.

3. Battery

4. Charging

5. Inverter

Leave the size at 0 if you're not fitting one. An inverter left switched on all day can use more than the fridge.

Your van

Your van drawn to its real internal size, with every cable run on it. This is the one to take out to the van.

Your wiring diagram

What connects to what, with the size and fuse on every wire.

Circuits

Each cable is sized on voltage drop and on current capacity — whichever needs the thicker wire wins. "Sized by" tells you which one decided it, so you know whether shortening the run would help.

Parts

Runtime budget

How long the bank lasts doing what you actually do, month by month, on a flat roof in the UK.

Read this before you start

VanWire is a design aid, not a certified electrical design. It doesn't replace a qualified auto-electrician signing off your work.