The brochure says your 12V compressor fridge uses "12Ah per day at 20°C ambient." Real-world usage depends on ambient temperature, how often you open the door, what's inside, and your ventilation setup.
This guide contains actual power consumption data from UK van lifers' installations — not manufacturer estimates.
The Test Methodology
The numbers below are from real installations with:
- Victron BMV-712 battery monitor (accurate to ±1%)
- Ambient temperature measured inside the van (not outside)
- Normal use (opening the fridge 8-15 times per day)
- Standard 12V DC supply via 2.5mm² cable (no voltage drop issues)
- Fridges installed per manufacturer specifications (adequate ventilation)
Results by Model
Dometic CFX3 45 (45L, Single Compressor)
| Conditions | Daily Consumption | Running Time |
|---|---|---|
| Summer (25°C internal van temp) | 18-24Ah | 35-45% duty cycle |
| Spring/Autumn (18°C) | 12-16Ah | 25-30% duty cycle |
| Winter (10°C) | 8-12Ah | 15-20% duty cycle |
| Fridge full, warm items just loaded | 30-35Ah (first 24h) | 60-70% duty cycle |
| Freezer section at -18°C + fridge at 4°C | 22-28Ah | 40-50% duty cycle |
Verdict: The CFX3 45 is more efficient than the brochure claims in winter, slightly less efficient in summer. The freezer section doubles power consumption.
Dometic CFX3 55 (55L, Single Compressor)
| Conditions | Daily Consumption | Running Time |
|---|---|---|
| Summer (25°C) | 24-30Ah | 40-50% |
| Spring/Autumn (18°C) | 16-22Ah | 28-35% |
| Winter (10°C) | 10-15Ah | 18-25% |
Verdict: The extra 10L costs 6-8Ah/day in summer. The 55L is noticeably harder to cool when full than the 45L.
Alpicool C30 (30L, Single Compressor)
| Conditions | Daily Consumption | Running Time |
|---|---|---|
| Summer (25°C) | 10-14Ah | 25-35% |
| Spring/Autumn (18°C) | 7-10Ah | 18-25% |
| Winter (10°C) | 4-7Ah | 12-18% |
Verdict: The Alpicool C30 is the most efficient fridge for its size. The smaller internal volume loses less cold air when opened. At 10Ah/day in summer, it's sustainable on a 100Ah battery + 200W solar even in the UK.
Vitrifrigo C60EL (60L, Built-in)
| Conditions | Daily Consumption | Running Time |
|---|---|---|
| Summer (25°C) | 20-26Ah | 35-45% |
| Spring/Autumn (18°C) | 14-18Ah | 25-30% |
| Winter (10°C) | 8-12Ah | 15-20% |
Verdict: The built-in Vitrifrigo performs similarly to the comparable Dometic portable. The key difference: built-in fridges have worse airflow (they're in a cabinet), so they run slightly harder when ambient is high.
Alpicool CX50 (50L, Dual Zone)
| Conditions | Daily Consumption | Running Time |
|---|---|---|
| Summer (25°C) | 22-30Ah | 40-50% |
| Spring/Autumn (18°C) | 16-22Ah | 30-35% |
| Winter (10°C) | 10-14Ah | 20-25% |
Verdict: The dual zone is convenient but costly in power. Running a freezer section at -18°C and a fridge at 4°C both at the same time uses about 50% more power than fridge-only mode.
What Affects Power Consumption
Ambient Temperature (The #1 Factor)
Compressor fridges work by pumping heat from inside to outside. The bigger the temperature difference, the harder the compressor works.
| Internal Van Temp vs Fridge Set Temp | Power Multiplier |
|---|---|
| 10°C difference (van 15°C, fridge 5°C) | 1.0x (baseline) |
| 15°C difference (van 20°C, fridge 5°C) | 1.3x |
| 20°C difference (van 25°C, fridge 5°C) | 1.7x |
| 25°C difference (van 30°C, fridge 5°C) | 2.2x |
Practical takeaway: A van parked in direct sun in August can hit 40-50°C internal temperature. At 50°C, a fridge consumes 3-4x more power than at 20°C. Park your van in the shade and crack a roof vent to reduce the ambient temperature around your fridge.
Ventilation
Compressor fridges dump heat via the condenser (the metal grid or fins on the back/side). If this heat can't escape (tight cabinet, no air gap), the fridge runs harder.
Rule of thumb: A fridge in a poorly ventilated cabinet (less than 5cm gap all around) uses 20-40% more power than one with proper ventilation. Some built-in installations hit 60% more power use because the condenser is in a sealed box.
How Full the Fridge Is
A full fridge is more efficient than an empty one. Thermal mass (cold food) helps maintain temperature when you open the door. An empty fridge loses all its cold air when opened and has to work hard to replace it.
Efficiency:
- 80% full: optimal — add water bottles to fill gaps
- 50% full: 10-15% more power than full
- 20% full: 20-30% more power than full
Door Openings
Each time you open the fridge door, cold air falls out and warm air rushes in. The compressor runs to replace the lost cold.
| Door openings per day | Power increase vs baseline |
|---|---|
| 5-10 (normal use) | 1.0x (baseline) |
| 15-20 (summer, frequent snacks) | 1.2-1.4x |
| 30+ (kids, party mode) | 1.5-2.0x |
Pro tip: Know what you want before opening the fridge. The "stare into the fridge wondering what to eat" habit adds 20% to your power use.
Power Consumption Cheat Sheet
| Fridge Size | Summer (Ah/day) | Winter (Ah/day) | Recommended Battery |
|---|---|---|---|
| 30-40L | 10-15Ah | 5-8Ah | 100Ah LiFePO4 |
| 45-55L | 18-30Ah | 8-15Ah | 150-200Ah LiFePO4 |
| 60-80L | 25-35Ah | 12-18Ah | 200Ah+ LiFePO4 |
| Dual zone | 25-35Ah | 12-18Ah | 200Ah+ LiFePO4 |
How to Test Your Own Setup
If you have a battery monitor (Victron BMV or SmartShunt):
- Set the fridge to 4°C (or -18°C for freezer)
- Leave it for 24 hours with normal use
- Read the "Ah consumed" on the monitor
- Check the voltage — if it drops below 12.2V overnight, your battery is too small
Without a battery monitor: A shunt-based monitor costs £30-50 (Victron SmartShunt is £100, a generic one from AliExpress is £20). It's the best diagnostic tool you can buy for managing van power. You can't optimise what you don't measure.
