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There's a correct sequence for wiring a van electrical system, and doing it out of order causes problems. Battery last, solar panels disconnected until MPPT is wired, inverter connections dead until final check. Here's the order I follow on every build.
The sequence: 1) Mount all components (fuse box, MPPT, DC-DC, inverter, battery tray) without any wiring. 2) Run all cables through their routes — don't connect anything yet. 3) Terminate and connect negative/ground bus first. 4) Wire 12V distribution (fuse box to appliances). 5) Connect MPPT output to battery bus. 6) Wire DC-DC charger. 7) Connect battery last. 8) Connect solar panels to MPPT last of all.
⚡ Expert tip
Before connecting the battery, use a multimeter in continuity mode between your positive bus bar and negative bus bar (chassis). If you hear a beep, you have a short somewhere — find it before energizing. This 30-second test has saved me twice from catastrophic shorts.
Example calculation for your setup
Results based on a typical use case
| Appliance | Power | Usage/day | Wh/day |
|---|---|---|---|
| Compression fridge | 45W | 24h | 1080 |
| LED lighting | 20W | 4h | 80 |
| Water pump | 30W | 0.5h | 15 |
| Phone charging | 15W | 2h | 30 |
| Daily consumption | 1205 Wh | ||
Recommended LiFePO4 battery
126 Ah
(80% depth of discharge)
Recommended AGM battery
201 Ah
(50% depth of discharge)
Recommended solar panels
302 Wc
4h average sun hours
Recommended inverter
No 220V appliances — no inverter needed
Adjust these values with the calculator below
VANPOWERCALC PROYOUR ENERGY PROFILE
YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Minimum Daily Consumption
0 WH / DAY
Inventory:
SYSTEM SIZINGPage 2
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
0 AH
LiFePO4 12V
Solar
Minimum power required to recharge your consumption:
0 W
via MPPT
220V AC
Maximum power (with 25% safety margin).
0 W
No Need
Safety & CablingPage 3
12V Cable Sizing Guide
Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.
| Current (A) | Round trip < 2m | Round trip 4m | Round trip 6m |
|---|---|---|---|
| 5A (LEDs, USB) | 1.5 mm² | 2.5 mm² | 4 mm² |
| 10A (Fridge, Pump) | 2.5 mm² | 4 mm² | 6 mm² |
| 20A (Heater) | 4 mm² | 10 mm² | 10 mm² |
| 50A (DC/DC Booster) | 10 mm² | 16 mm² | 25 mm² |
| 100A (Inverter) | 25 mm² | 35 mm² | 50 mm² |
Fuse Sizing
The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).
- Wire 1.5 mm² → Max fuse 10A
- Wire 2.5 mm² → Max fuse 20A
- Wire 4 mm² → Max fuse 30A
- Wire 6 mm² → Max fuse 40A
- Wire 10 mm² → Max fuse 60A
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
REGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
FUSIBLE
FUSIBLE
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
PRO GEARPage 4
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
GENERATED BY VANPOWERCALC PRO - UNLIMITED.
About this tool
Why this order? You want the battery disconnected while you wire everything downstream. This means any accidental short between positive and chassis while routing cables doesn't create a 500A fireball. The solar panels connect last because they're live as soon as there's light — you can't switch them off. Connecting panel to MPPT without a battery attached can damage some controllers (the MPPT needs a battery to sink current into). Once everything is wired and double-checked with a multimeter for shorts and correct polarity, connect the battery. Then walk outside and connect the solar MC4 cables. Your system should come alive: MPPT shows charging, battery monitor shows state of charge, fridge starts cooling. If something trips immediately, disconnect the battery and debug — you likely have a reversed polarity connection or a short somewhere in the distribution wiring.
Frequently asked questions
What do I wire first in a van electrical system?▼
Mount everything, then wire the ground/negative bus bar first. Then 12V distribution circuits. Then MPPT and DC-DC outputs. Connect the battery second-to-last. Solar panels absolute last. This order keeps everything de-energized while you work.
Why connect the battery last?▼
Safety. With the battery disconnected, accidental shorts during wiring don't produce current. A short on a 200Ah LiFePO4 can deliver 500A+ — enough to melt cables and start fires instantly. Keep it disconnected until everything is checked.
Why connect solar panels after the battery?▼
Two reasons. First, solar panels are live whenever there's light — you can't turn them off. Second, connecting panels to an MPPT without a battery connected can damage the controller. Always: battery to MPPT first, then panels to MPPT.
How do I test my wiring before connecting the battery?▼
Multimeter in continuity mode. Touch positive bus to negative bus — no beep means no shorts. Then check each fused circuit: probe from the fuse output to the appliance's positive wire — you should see continuity. Probe positive to ground at each appliance — no beep means no shorts.
What if something trips as soon as I connect the battery?▼
Disconnect the battery immediately. Something is either shorted or reversed polarity. Check the most recent connection you made — that's usually the culprit. Use the multimeter to trace the fault before reconnecting.