Will a portable power station run my refrigerator? Watts, surge and hours, explained

The short answer

Most US household appliances run on 120 volts, which is what a power station's AC outlets supply. A refrigerator is one of the easier large appliances to back up, because it spends most of the day idle. The two things that trip people up are the short burst of power when the compressor starts, and how many hours the battery lasts. Both are worked out from numbers you can read off your own appliance.

How much power a refrigerator uses

The Department of Energy says the wattage of most appliances "is usually stamped on the bottom or back of the appliance, or on its nameplate," and that "the wattage listed is the maximum power drawn by the appliance." Look on the fridge itself or in its owner's manual. DOE says that if the wattage is not listed, you can estimate it by finding the electrical current draw in amperes and multiplying by the voltage, and most US appliances use 120 volts.

DOE also explains that "refrigerators, although turned 'on' all the time, actually cycle on and off as needed to maintain interior temperatures," and to estimate the hours a refrigerator actually operates at its maximum wattage, you "divide the total time the refrigerator is plugged in by three." So a fridge plugged in for 24 hours runs at its listed wattage for about 8. DOE adds that wattage values vary with product age and features.

Starting surge: the number people forget

A compressor needs more power for a moment when it starts than while it runs. The Department of Energy's Grid Deployment Office notes that a home will often need more capacity than its peak load "to accommodate the starting wattage required for household appliances." The Red Cross says some machines draw "up to 3 times as much power when starting up."

There is no official surge-watt table for refrigerators, so use the maker's figure if your fridge manual or a service label has one. Then compare it with the surge (peak) rating on the power station, not just its continuous AC watts. Our what will it run pages and the runtime tool use cautious surge figures for refrigerators, drawn from generator charts, and say so.

How many hours to expect

Power is watts; a battery's capacity is watt-hours. DOE's example 18.1 cubic-foot, top-freezer refrigerator with automatic defrost lists annual energy use of 363.5 kWh for an ENERGY STAR model and 404 kWh for a less efficient one. Divided by 365 days, that is about 1.0 kWh and about 1.1 kWh a day. That arithmetic is ours, not DOE's, and a larger or older fridge, or one with its door opened often, uses more.

Batteries do not deliver their full rating through the inverter that makes 120V AC. Applying our runtime tool's formula (90% usable capacity, 85% inverter efficiency and about 10 watts for the unit itself) to DOE's figure of about 41.5 watts on average, a 1,000 watt-hour station runs roughly 15 hours and a 2,000 watt-hour station roughly 30. That is our arithmetic, not an agency figure. The runtime tool itself uses Energy Star's range of 34 to 84 watts for a full-size fridge and shows about 8 to 17 hours per 1,000 watt-hours. For your own fridge, a plug-in energy meter reading kWh over a day gives the best number, as DOE notes for devices that do not run constantly.

Read the arithmetic as a guide, not a promise: ice in the freezer, keeping the door shut and unplugging the fridge between runs all change it.

You may not need power for the fridge at all

Ready.gov: "Keep freezers and refrigerators closed. The refrigerator will keep food cold for about four hours. A full freezer will keep the temperature for about 48 hours. Use coolers with ice if necessary. Monitor temperatures with a thermometer. Throw out food if the temperature is 40 degrees or higher." The Red Cross adds that a freezer holds for about 24 hours if it is half full and the door stays closed.

USDA's FoodSafety.gov says to discard refrigerated perishable food such as meat, poultry, fish, eggs and leftovers after 4 hours without power, and its chart lists perishable foods to throw out after more than 2 hours at 40°F or above. For an outage of a few hours, a closed door and a thermometer cost nothing. A station mainly helps when an outage is likely to last longer than about 4 hours. Our food safety in a power outage guide has the full chart.

Using the station safely

Keep the cords and the equipment safe. The Red Cross says to "plug appliances directly into the generator, or use a heavy duty, outdoor-rated extension cord that is rated (in watts or amps) at least equal to the sum of the connected appliance loads." Ready.gov says: "Always connect the generator to appliances with heavy-duty extension cords" and "Keep the generator dry and protected from rain or flooding. Touching a wet generator or devices connected to one can cause electrical shock."

Fuel-burning generators are the carbon monoxide risk. CPSC: "Never use portable generators inside homes or garages, even if doors and windows are open. Use generators outside only, at least 20 feet away from homes with exhaust facing away." CDC: "When using a generator, use a battery-powered or battery backup CO detector in your home." We found no federal guidance specific to battery power stations, so follow its manual for placement and ventilation, and see generator safety if you are comparing the two.