CAMPING / KNOWLEDGE / FRIDGE SIZING
Camping fridge sizing: why duty cycle beats inverter wattage
A portable refrigerator is the most common reason people buy a power station for camping, and the most commonly mis-sized. The mistake is almost always the same: comparing inverter wattage instead of energy over time.
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Why inverter wattage is the wrong number
A 2,000W inverter is not better at running a 50W fridge than a 1,800W one. The fridge never approaches either ceiling, so the rating that looks like the headline specification is irrelevant to this job.
What actually decides fridge runtime is energy over time. A compressor cycles: it draws its rated power for a while, then rests. A fridge labelled 60W therefore does not consume 60W continuously for 24 hours. Judge it by measured daily energy, or by a duty-cycle assumption you are honest about — not by its peak draw.
The four things that decide fridge runtime
- Battery capacity. The tank size. Everything else modifies how fast you drain it.
- DC versus AC operation. If the fridge can run from the station's 12V DC output rather than through the AC inverter, you avoid a double conversion and keep more of the stored energy.
- Idle consumption. Some coolers draw meaningful power even when the compressor is off. That load runs 24 hours a day.
- Solar replenishment. On a trip longer than two nights, how you refill matters more than how much you started with.
Portability matters last. The fridge is the load that keeps you near the vehicle anyway, so the station's weight is rarely the binding constraint on a fridge trip.
A worked estimate you can change
Take a compressor cooler rated 60W while running, cycling at roughly 50% duty across a day. Average draw is therefore about 30W. Add a constant 10W overhead for the inverter and standby draw, and the planning load is 40W.
Using the same transparent formula we apply across this site:
Illustrative runtime = (1,024Wh × 0.80) ÷ (average load + 10W)
At a 30W average that gives roughly 20 hours. If the same cooler runs harder and averages 60W, the figure falls to about 11.7 hours. That gap — not the inverter rating — is what you should plan around.
The 0.80 is an assumption about usable energy, not a measured efficiency figure. It is applied identically to every station on this site, which makes it fair for comparison and useless as a prediction.
Sizing by trip length
| Trip | Typical fridge energy | Roughly what you need |
|---|---|---|
| One night, car camping | ~350Wh | A 500–800Wh station, or overnight on 1kWh |
| Two nights, no recharge | ~700Wh | Around 1kWh, used carefully |
| Three nights or more | ~1,050Wh+ | 1kWh plus a reliable recharge plan |
Startup surge, not average draw, is what rules out the smaller stations. Check the cooler's documented startup requirement against the station's rated output, not its surge mode.
What this cannot tell you
Real duty cycle varies enormously with ambient temperature, how full the fridge is, how often it is opened, and whether it sits in direct sun. A cooler in a hot car can run near-continuously; the same unit in a shaded tent at night barely cycles. We have not measured any of these products, and none of the figures here are appliance test results.
Where to go next
This page is the reasoning. The product shortlist — which station, and why — is on the camping guide, which now covers only the buying decision.