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Your 12V fridge is the single biggest continuous load in a van — it never turns off. A compressor fridge draws 30-50Ah per day depending on ambient temperature and how often you open the door. On a 200Ah LiFePO4, that's 3-5 days of fridge-only runtime before you hit 20%.
The math: a Dometic CFX-35 draws 35Ah/day at 25°C ambient (manufacturer spec, confirmed by my own measurements). On a 200Ah LiFePO4 with 80% usable capacity = 160Ah available. 160 / 35 = 4.6 days of just the fridge. Add lights (5Ah), phones (3Ah), and a MaxxFan at night (8Ah) = 51Ah/day total. That drops to 3.1 days.
⚡ Expert tip
Set your fridge to 5°C instead of 3°C. That 2-degree difference reduces compressor runtime by 15-20% and you won't notice any difference in food safety. Also: pre-cool everything in your house fridge before loading the van — the compressor doesn't have to work as hard to maintain temperature vs cooling warm items.
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)
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
Ambient temperature is the biggest variable nobody accounts for. That 35Ah/day figure is at 25°C. Park in direct sun in Spain at 35°C and the compressor runs almost continuously — 55-65Ah/day. Park in a shaded forest at 18°C and it drops to 22-28Ah/day. That's nearly a 3x difference. I've measured my own Dometic at both extremes. The other factor: how full the fridge is. A full fridge holds temperature better than an empty one — the thermal mass of the food acts as a buffer. I fill empty space with frozen water bottles. They keep the fridge cold during defrost cycles and provide cold drinking water. Free efficiency hack. If you're concerned about fridge autonomy, the single biggest improvement is adding 200W of solar. Even in winter, 200W produces enough to cover the fridge most days. In summer, it covers the fridge AND everything else with energy to spare.
Frequently asked questions
How many Ah does a van fridge use per day?▼
25-55Ah depending on model and temperature. Dometic CFX-35: 28-38Ah. Engel MT35: 20-28Ah. Cheap 12V cooler: 40-60Ah (less efficient). At 25°C ambient, expect 30-40Ah/day for a quality compressor fridge.
How long will a 100Ah battery run a fridge?▼
A 100Ah LiFePO4 gives 80Ah usable. At 35Ah/day fridge draw: about 2.3 days. With other loads (lights, phones, fan): 1.5-2 days. A 200Ah battery doubles this to 3-4 days.
Does ambient temperature affect fridge battery drain?▼
Massively. At 18°C ambient: 22-28Ah/day. At 25°C: 30-38Ah/day. At 35°C: 50-65Ah/day. The compressor runs more to maintain the 4°C setpoint against higher ambient. Parking in shade vs sun can double your fridge autonomy.
Should I turn off my fridge at night to save battery?▼
No. Turning it off lets interior temperature rise, then the compressor works extra hard to cool back down — using more energy overall than continuous operation. Keep it running 24/7.
What's the most efficient van fridge?▼
Engel MT35 (Swing motor compressor): 20-28Ah/day, the most efficient on the market. Dometic CFX series: 28-38Ah/day, good balance of price and efficiency. Avoid Peltier/thermoelectric coolers — they draw 4-6A continuously and barely cool.