What Size Generator to Run a Refrigerator and Freezer?

Sizing Your Generator: Surge Power, Running Power and Reactive Loads

When you pressurize a gas, it heats up, and when you depressurize it, it cools down. Refrigeration uses this to cool air. An electric motor runs the compressor, which compresses the gas. Next, this hot, compressed gas passes through a set of coils, cooling it down. This cooled gas goes into larger passages, dropping the pressure and lowering the gas’s temperature even more.

At this point, it’s well below ambient temperature. This cold refrigerant passes through the heat exchanger, which cools down the surrounding air. Air conditioners blow air past the exchanger and out through the vents. Refrigerators and freezers circulate the air inside them through the exchanger, keeping their contents cool. A thermostat cycles the compressor on and off, maintaining the desired temperature.

What Does this Have to do with Generators?

Electric motors are reactive loads. It takes more electricity to get an electric motor to spin than it takes to keep it spinning, even when under load. Once the engine is spinning, the electrical load drops by around 50%. While these spikes are easy to plan for when you’re using most motor-driven appliances, you don’t control when a refrigeration unit turns on and off. That’s up to the thermostat. That means you always need enough power on hand to operate any refrigeration units connected to your generator.

Generators have two load ratings: surge power and running power. Surge power is the maximum power the generator can make for a short period, typically 60 seconds. This is useful for covering load spikes when electric motors start up. Running power is the amount of power it can maintain the entire time it’s running. This is the power you need to keep your refrigeration unit running.

When you’re shopping for a generator, you need to have enough sustained power to keep everything running, and enough surge power to cover all of your appliances, plus the largest reactive load. If you’re using an air conditioner, it’s going to be your biggest reactive load. If you aren’t powering an air conditioner, your refrigerator or freezer is usually your biggest reactive load.

Keep in mind that you don’t want to use it at 100% power all of the time. This increases wear and tear, as well as fuel consumption and noise. If you can afford it, look for a generator that is only running at 50% or less of its rated sustained power while your appliances are running. If you can’t, plan to have at least 10% more power than you need to cut down on wear.

How Long Can You Run a Refrigerator and Freezer on a Generator?

You can run a refrigeration unit from generator power indefinitely. However, you need to minimize downtime, so your refrigerator or freezer’s temperature doesn’t reach unsafe levels. An unopened freezer will reach unsafe temperatures for food storage after about four hours. A partially-full chest freezer will reach these temperatures in 24 hours, and a full freezer can keep food safe up to 48 hours.

Do I Need to Use an Inverter Generator to Power a Refrigerator or Freezer?

It depends on the amount of electronics in your refrigerator or freezer. Inverter generators use a rectifier and an inverter to turn the AC power from the generator’s alternator into DC power, then back into AC power. This filters out distortion, so the power coming from the plugs is nearly identical to what you get from your home electric sockets. This clean power won’t burn out electronics. This is important for smart fridges and refrigeration equipment that uses digital controls.

Can You Use a Solar Generator to Power a Refrigerator and Freezer?

Yes, as long as it has a sine wave inverter and you have enough power to keep it charged.

Why do you need a sine wave inverter? A solar generator doesn’t generate power. Instead, it’s a battery that stores power from other sources. While you can hook one up to solar panels, you can also charge it from a household electric outlet or a gas generator.

Batteries provide direct current power. This is converted into alternating current by an inverter. The AC power from the grid gradually changes between positive and negative polarity. If you measured this electricity using an oscilloscope, you would see a sine wave. Alternating current motors use this gradual change to create rotating magnetic fields. This pulls the motor shaft toward sections on the stator, then pushes them away. Low end solar generators use a simple switch to go between 100% negative to 100% positive current flow. If you measured this with an oscilloscope, you’d see a square wave. Since the magnetic field is always at full strength, the stator can’t spin the motor shaft.

Of course, available power is also a factor. The smallest generators can’t provide more than 1,000 watts. That may be enough for a mini fridge, but it won’t handle full size appliances. You also need to generate enough power. If you have 200 watts of solar panel capacity, it takes about 8 hours to generate one kWh on a sunny day. On average, a refrigerator uses between one and two kWh of electricity per day, so it’s easy to outpace your solar charging rate.

Do I Need a Surge Protector When I Use a Generator?

No. Surge power has nothing to do with power surges. Instead, it’s a measurement of the maximum amount of power a generator can make over brief periods. This is useful for load spikes caused by the startup of your refrigerator’s compressor.

Can a Generator Damage My Refrigerator, Freezer or Air Conditioner?

In most cases, no. The power from a regular generator is perfectly fine for running the compressor’s electric motor.

However, new smart fridges are packed with electronics that don’t play well with electricity from standard generators. Alternating current gets its name from its constant switching between negative and positive current flow. Electrical interference and power fluctuations affect this polarity switch, causing spikes and drops that can burn out electronics. This can also be a problem with window air conditioners that use electronics to control the thermostat.

How Many Watts Does an Average Refrigerator or Freezer Use?

Power demands vary widely depending on several factors, including the size of the unit, how efficient it is, how old it is, and its operating conditions. These estimates should be close to your refrigerator and freezer’s actual power requirements.

Do you Want to Know Exactly How Much Electricity your Refrigerator or Freezer Uses?

Get an electricity monitor. This plugs in between the appliance and the socket, and tells you exactly how much current is passing through. Be sure to measure load spikes at startup, as well as loads while the compressor is running. This will tell you how much surge and running power you need.

Keep in mind that total power demand will vary depending on the air temperature around your refrigerator or freezer. If you have a chest freezer in a garage, the compressor will cycle more often in the summer than it will in the winter. Likewise, if you have a power outage in the summer, your kitchen will be warmer than normal, since you won’t have working central air conditioning.

Can You Keep a Generator Indoors While it’s Powering a Fridge and Freezer?

You cannot run a gas, propane or diesel generators indoors. These engines produce exhaust that contains carbon monoxide. When you breathe in CO, it enters your blood stream and attaches to red blood cells. These cells have a much stronger attraction to this gas than oxygen.

This keeps them from carrying oxygen through your body, leading to asphyxiation. Inhaling small amounts of CO causes headaches and dizziness, while large amounts can be lethal. The U.S. Consumer Product Safety Commission estimates there are 85 carbon monoxide deaths in America each year caused by people running their generators indoors.

When you buy a generator, you need to plan how you’ll get the power from it to your appliances. There are three ways you can power your refrigerator or freezer:

Solar generators are safe to use indoors, since they’re little more than a battery and some circuitry. You might be able to skip the extension cords entirely, plugging the refrigerator directly into the generator and running solar panel cables through a nearby window. There are also home backup solutions that connect a large solar generator to a transfer switch. These systems cycle on automatically when the power goes out.

Is There Any Way to Lower the Amount of Power My Refrigerator or Freezer Needs?

There isn’t any way to reduce the current draw from your refrigerator or freezer. However, you can keep it from cycling as frequently by making it more efficient. This cuts down on fuel use and noise from internal combustion generators, and helps you keep your solar generator from running out of power.
 
This starts with maintenance. Keeping the condenser coils clean helps the refrigerant reject heat. This makes the refrigerant colder once it reaches the heat exchanger, so you get more cooling power from the energy you put into the unit.
 
Add thermal mass. You may think that removing food that doesn’t have to be chilled will take the load off of your refrigerator, but this actually causes the opposite to happen. Liquids and solids are denser than air, making it harder to change their temperature. Filling empty spaces with ice or water containers helps stabilize the temperature inside the unit.
 
It might be time to buy new appliances. Standard refrigerators that are over 10 years old, as well as freezers and side-by-side refrigerators over 15 years old could be costing you enough in electricity to make a new unit pay for itself. Not only do you get something that has less wear and tear, you also get the benefit of increased insulation and more efficient components. This cuts down on power demand when you’re using a generator and when you’re using power from the grid.