TBE DesignerFree toolAuthorised Victron Energy Installer
Victron system designer
In short: our free designer plans a whole Victron system for a campervan, motorhome or off-grid cabin, from the battery and solar to every cable and fuse, and shows its working. It is a design aid: the 230 V side must be installed, tested and certified to BS 7671. Checked by Tom Alderdice, 18th Edition (BS 7671) plus inspection and testing.
Designer v1.9.6Working shown
- Built from
- Victron datasheets and manuals
- Checked against
- BS 7671:2018+A4:2026 (Amendment 4)
- Informed by
- Anonymised data from 180+ Victron systems on VRM
- Last checked
A whole Victron system for your campervan, motorhome or off-grid cabin, with every cable and fuse sized by our cable size calculator.
How it works
- EnergyWhat you run, and for how long, including the MultiPlus left on all day.
- BatteryEnough lithium for the days you want without charging, using 90% of its capacity.
- SolarSized on UK sun data for your region and the worst month you plan for, then checked against the controller on a cold morning.
- Every circuitCable, fuse and lugs from the same engine as our cable calculator.
A design aid, not a design
Check every rating against your own parts. The 230V side must be checked by a qualified electrician. Want it done properly? We'll fit it for you, or book a free call.
What it runs: appliance power and daily use
These are the average figures our system designer uses for each appliance. Pick the ones you have in the designer and it adds them up, sizes the battery, inverter and solar, and shows its workings.
Swipe the table sideways to see every column.
| Appliance | Power (W) | Full-power hours a day | Wh a day | Ah a day at 12 V | Ah a day at 24 V | Ah a day at 48 V |
|---|---|---|---|---|---|---|
| 12 V things (straight off the battery) | ||||||
| Compressor fridge | 60 | 6 | 360 | 30 | 15 | 7.5 |
| LED lights (6 lights, 3 W each) estimate | 18 | 4 | 72 | 6.0 | 3.0 | 1.5 |
| Water pump | 54 | 0.25 | 14 | 1.1 | 0.6 | 0.3 |
| Diesel heater | 30 | 5.5 | 165 | 14 | 6.9 | 3.4 |
| Roof fan | 45 | 1.5 | 68 | 5.6 | 2.8 | 1.4 |
| Phones and tablets (2 people, 15 W each) estimate | 30 | 1.5 | 45 | 3.8 | 1.9 | 0.9 |
| 4G/5G router | 7 | 12 | 84 | 7.0 | 3.5 | 1.8 |
| TV (12 V) estimate | 40 | 2 | 80 | 6.7 | 3.3 | 1.7 |
| 230 V things (through the inverter) | ||||||
| Laptop (230 V) estimate | 65 | 2 | 130 | 12 | 6.0 | 3.0 |
| Kettle (low-watt) estimate | 1,200 | 0.15 | 180 | 17 | 8.3 | 4.2 |
| Induction hob | 1,800 | 0.5 | 900 | 83 | 42 | 21 |
| Microwave (800 W output) | 1,250 | 0.2 | 250 | 23 | 12 | 5.8 |
| Coffee machine (capsule) | 1,310 | 0.1 | 131 | 12 | 6.1 | 3.0 |
| Hair dryer (low-watt) | 1,200 | 0.1 | 120 | 11 | 5.6 | 2.8 |
| Air fryer | 1,550 | 0.3 | 465 | 43 | 22 | 11 |
| Power tool charging | 310 | 0.25 | 78 | 7.2 | 3.6 | 1.8 |
- Full-power hours are the hours at the rated power that give an average day. A fridge cycles on and off all day; 6 full-power hours is its average.
- 230 V rows: Wh a day is what the appliance uses. Ah a day includes 10% inverter losses, as the designer allows.
- Leaving the inverter/charger on adds its standby draw, from Victron's figures: Victron MultiPlus 12/2000/80, 9 W (216 Wh a day); Victron MultiPlus-II 12/3000/120-32, 13 W (312 Wh a day). Search mode cuts this.
- Same energy, fewer amps: Ah a day is Wh divided by the system voltage, so the same use reads as fewer Ah at 24 V or 48 V. We design 48 V systems with you on a call.
- Where the figures come from: makers' datasheets where one exists, otherwise figures from our customer calls. Rows marked estimate are our own estimate, with no single datasheet behind them. Your own appliances may use more or less.
System designer questions
How do I size a leisure battery for my van?
Take the watt hours you use a day and multiply by the days you want to go with no charging. Divide by the system voltage for amp hours: 1,200 Wh at 12 V is 100 Ah. The designer does this and leaves headroom. Our battery guide compares types.
How much solar do I need for a campervan?
Enough to cover your daily use in the months you travel, within your roof space. Most van roofs take 1,000 to 1,200 W at best. The designer uses PVGIS sun data for your region, so you see what solar covers each month, winter included. Our campervan solar guide goes further.
What size inverter do I need?
Size it on the biggest 230 V load you run at once, in continuous watts. A 1,800 W induction hob needs a MultiPlus-II 12/3000: 2,400 W continuous at 25 °C, less in a hot van. The designer adds loads you'd run together and picks the smallest fit. Our inverter guide explains more.
12 V, 24 V or 48 V: which is right?
Victron's guidance is 12 V up to a 3,000 VA inverter, 24 V up to 5,000 VA and 48 V above that. Higher voltage means lower current for the same power, so thinner cables and less voltage drop. Leave it on Auto and the designer chooses. We design 48 V systems with you.
Does the designer size cables and fuses?
Yes. Every circuit is sized for its current, length and route, then checked against the BS EN 1648-2 voltage drop limits for 12 V vehicle circuits. The main battery fuse is a Class T on the board, or an MRBF beside the terminal for a 12 V battery up to 200 Ah. Cable size calculator.
Can I use it for an off-grid cabin?
Yes: pick Cabin first. The designer sizes solar on the worst month of the season you choose, with panels facing south at 35°; December is the worst month across 50+ off-grid cabins we see on VRM. It adds a background draw from that fleet and swaps hook-up for a mains or generator inlet. Off-grid power costs.
What hook-up supply does the plan allow for?
16 A. In vans and motorhomes we fuse the AC input at 16 A and run 2.5 mm² H07RN-F from the inlet to the inverter/charger AC-in, at every size. BS 7671 Table 721 pairs a 16 A hook-up with 2.5 mm² cable. Need more? PowerAssist tops up the supply from the battery.
Is the plan ready to install?
It's a design aid, not a signed-off design. You get the sizing, working and parts list; your wiring diagram follows within three days of checkout. The 230 V side must be installed, inspected and tested to BS 7671, including Section 721, and certified on an Electrical Installation Certificate. Book a free call.
What customers say
“I wouldn’t work with anybody else, I’ve worked with Tom for my past three van builds.”Rach Harding
“It wasn’t just them trying to sell us something that was off the shelf.”Ben Jones-Gerrard
“They’ve done an absolute grand job writing us a schematic for all this.”Ali Vernett
“Some things are actually just better left to the experts.”Charlie Skinner
Designer FAQs
Is this a finished design I can install from?
No. It is a design aid. It sizes a Victron system from what you run and lists the parts, cables and fuses, but you should check every rating against your own parts and talk it through with us before you buy or install anything.
Does the 230V side need to be checked by a qualified electrician?
Yes. The 230V side must be checked by a qualified electrician and installed to BS 7671. If you'd rather leave that to us, we can fit the system for you, or you can book a free call to talk it through.
Is the designer free?
Yes. It runs in your browser, with no account needed. You can use it as many times as you like and bring the plan to a free call.
Can I buy the parts from you?
Yes. If you want us to supply the kit, book a free call and we'll turn the plan into a quote, a wiring diagram and a build guide matched to what you buy.
What's the difference between this and a free call?
The designer is a first pass you can do on your own. On the free call we go through how you actually use power, check the plan with you and, if you want the kit from us, we take it from there.
Does it work for a motorhome or an off-grid cabin?
Yes. It is built for campervans, motorhomes and off-grid cabins. Tell it what you run and where the system will live, and it will size the battery, charging and solar from that.