Running a chest freezer on a power station in a long blackout

A chest freezer is one of the easier things to keep going in a long blackout, because it does most of the work itself. Queensland Health says a closed freezer won't usually defrost for at least 48 hours if it's full and 24 hours if it's half full. The power station's job is to top the cold back up every so often, and a 1,024Wh station holds roughly one to two days of a typical chest freezer's energy.

The food safety figures here come from Queensland Health, healthdirect, Food Standards Australia New Zealand and NT Health, the surge advice from Energex, and the station specs from EcoFlow and Bluetti's Australian pages. All are linked at the bottom. We haven't run a freezer on a station ourselves, so every runtime below is a sum with the working shown.

Start with the label

Every chest freezer sold here carries an Energy Rating label, and the big number on it is the estimated energy use in kWh a year. Energy Rating says it comes from standard testing, and your own freezer may use more or less depending on how you use it. Divide by 365 for kWh a day, then multiply by 1,000 for watt-hours.

Say your label reads 250 kWh a year. That's about 685Wh a day, or an average of roughly 28W across 24 hours. The compressor draws a good deal more than 28W while it's running and nothing while it's resting. For battery sizing the average is the number that counts.

Label figures vary a lot between chest freezers of different sizes and ages, so read yours rather than borrowing ours. The three in the table below are examples to show the sum, not particular models.

How far a station goes

A station loses some energy turning its battery into 230V AC. We allow 15%, so a 1,024Wh battery gives about 870Wh, and a 2,048Wh setup about 1,741Wh. Divide by the freezer's average watts for hours of running.

The 1,024Wh column fits the EcoFlow DELTA 3 Plus or the Bluetti Elite 100 V2. The 2,048Wh column is the DELTA 3 Plus with a DELTA 3 Smart Extra Battery added. These are arithmetic from the label, which is the best case. A freezer in a hot garage in a Queensland summer will use more, and so will one that's been opened a lot.

If the fridge is on the same station, add its average to the freezer's before you divide. Our fridge blackout guide works out the fridge side, and the runtime calculator adds the two together.

Use the 48 hours, then top up

Because a full freezer coasts for so long, you don't need the station on it from minute one. Note the time the power went out, as Queensland Health suggests, keep the lid shut, and spend the station's battery on the fridge, which only holds about four hours. Bring the freezer in later, in blocks, before it gets near its limit.

How long each block needs is something we can't give you as a fixed figure. A freezer that's warmed a few degrees runs its compressor longer to pull back down, so a block uses more than the average suggests. Put a freezer thermometer in the middle of the load, plug in, and unplug once it's back at -18°C, the temperature healthdirect gives for frozen food. That reading tells you more than any sum on this page.

A half-empty chest freezer is the one to fix before storm season. Fill the gaps with bottles of water and ice bricks and it behaves more like a full one. FSANZ also suggests having ice bricks ready to keep food cold in eskies, and frozen bottles do both jobs.

Check the start-up surge

Energex says appliances with motors use three to four times their running rating while they start. A freezer that runs at 100W might want 300 to 400W for a moment. Both 1,800W stations above handle that easily. A small 300W station may run the freezer and still trip when the compressor kicks in, so check the running watts on the freezer's rating plate, multiply by four, and compare that with the station's rated output.

Refreezing, where the advice differs

Queensland Health's rule is plain: if frozen food has partly thawed, don't refreeze it. Keep it cold and eat it soon, or throw it out. It also says to throw out frozen food after 48 hours without power in a full freezer, or 24 hours in a half-full one. FSANZ says much the same, don't refreeze thawed food.

NT Health is more relaxed. It says food that's at 0°C or lower, or still has ice crystals, can be refrozen or used. That's a real difference between two health departments, and we'd follow Queensland Health if you live here. It's another reason to keep the freezer topped up before anything starts to soften, rather than rescuing it afterwards.

Charging through a long outage

A multi-day outage is where recharging matters more than battery size. A station you can top up from panels each day can keep a freezer going indefinitely if the sun cooperates. Our guide on how much solar a station needs works through panel sizes by city.

Charge the station where you can keep an eye on it. The Queensland Fire Department says not to leave lithium-ion batteries charging unattended, to charge on a hard, non-combustible surface in a ventilated spot, and not to use a battery that's hot, swollen or damaged. A closed garage on a 35°C day is hard on both the freezer and the battery, so open it up or move the station somewhere cooler. The rest of the house is covered in our blackout and cyclone season guide.

Where to buy in Australia

Buying from the brand's Australian store means 230V AU outlets, the local warranty and local support. Prices move around a lot, so check on the day.

• EcoFlow DELTA 3 Plus (1,024Wh, 1,800W)EcoFlow AustraliaSee it at EcoFlow Australia
• EcoFlow DELTA 3 Smart Extra Battery (adds 1,024Wh)EcoFlow AustraliaSee it at EcoFlow Australia
• Bluetti Elite 100 V2 (1,024Wh, 1,800W)Bluetti AustraliaSee it at Bluetti Australia