If the inverter you’re using to run your refrigerator is undersized, the refrigerator may not work at all. Or it might work, but at the expense of the inverter, which will fail prematurely.
Since no one likes to waste money, there are a few details worth looking at when shopping for an inverter.
In this article, I’ll show you how to determine the size and specifications of the inverter that you need to run your refrigerator.
Inverter specifications to consider
In general, off-grid inverters have 3 ratings that characterize them and that you should pay attention to:
- The Continuous Power rating: in Watts (W).
- The Surge Power rating: in Watts (W).
- The Input Voltage Rating: in Volts (V).
Let’s see what each of these ratings represents.
This is the amount of electrical power (in Watts) that the inverter is designed to continuously deliver at its output. When an inverter is rated at a certain wattage, that wattage usually refers to the continuous power.
For example, this Renogy inverter is designed to output 1000W of power.
This means that if an energy source is provided (Battery, solar panels, etc…), this inverter can run anything that consumes 1000 watts or less.
The surge power rating represents the maximum amount of overloading power that an inverter can handle for a very short period of time (usually less than a second).
This rating is especially useful when the inverter is for a refrigerator or an air conditioner. This is because these appliances can require as much as 10 times their running wattage to startup (usually 3 to 7 times).
For example, a refrigerator that requires 300W to run may require up to 3000W to start. Usually, such a refrigerator will need between 1000 and 2000 watts to start. More on that below.
In general, the surge power rating of an inverter is 2 times its continuous power rating. However, this is not always the case.
Some inverters have a very low surge capacity and are not designed to run refrigerators. So make sure to look for this value in the specifications before making any decisions.
If we look at this 1000W Renogy inverter, for example, we can see that manufacturer specifies 2000W as the surge power.
Inverters not only turn DC power to AC power but also convert low voltage (usually 12 Volts) into higher voltage (110-120 volts).
The manufacturer specifies the DC voltage that can be connected to the DC input of the inverter.
For example, this Renogy inverter has an input voltage of 12V.
On the other hand, this 1200W Giandel inverter is rated at 24V for its input voltage.
For 12V inverters, the acceptable input voltage is usually between 9.5V and 16V. For 24V inverters, the input voltage can range between 19 and 32 volts.
So before buying an inverter, make sure that its input voltage will match the battery’s voltage.
Now, let’s see how we can use these ratings and compare them to the specifications of your refrigerator
What size inverter do I need to run a refrigerator?
Short answer: it mainly depends on the surge wattage of the refrigerator.
Refrigerators are not really ON all the time, the compressor in a refrigerator turns ON and OFF in a way that maintains a low internal temperature.
When a refrigerator starts, it draws a huge amount of current which causes a spike in power usage. The surge power can be 3 to 10 times the running wattage.
Although it usually only lasts for a fraction of a second, the inverter needs to be able to handle it.
When trying to choose the right inverter for your refrigerator, make sure that the inverter can handle both the running wattage and the surge wattage of the fridge.
As a general rule of thumb, the inverter you choose needs to be rated at 5 times the running wattage of your refrigerator. In most cases, this will make sure the inverter can handle the running power of the refrigerator, and the surge power required to start.
The following table gives you an idea about refrigerator sizes, their power usage, and the inverter sizes needed to run them:
|Refrigerator type||Refrigerator Size||Power Usage (Watts)||Inverter Size|
|Mini-fridge||4 Cu. ft.||75W||400W||800W|
|RV fridge||10 Cu. ft.||150W||750W||1500W|
|Full-size fridge 1||16 Cu. ft||200W||1000W||2000W|
|Full-size fridge 2||22 Cu. ft.||300W||1500W||3000W|
For example, a 1000W/2000W (continuous/surge) inverter can run a 200W refrigerator.
However, the best way to size an inverter for your refrigerator is to determine its running and surge wattage and look for an inverter that can work with both.
The first step is to determine the power usage of your fridge.
What is the running power of your refrigerator?
To determine the running wattage of your refrigerator, find the voltage and the current specified by the manufacturer, and multiply them together.
Running Wattage (Watts) = Rated Voltage (V) x Rated Current (A)
For example, the following image is of a specification sheet stuck to the side of a refrigerator:
Running Wattage (Watts) = Rated Voltage (V) x Rated Current (A)
Running Wattage (Watts) = 127 V x 2.4 A
Running Wattage (Watts) = 305 W
For this particular refrigerator, the inverter needs to have a Continuous Power rating of more than 305 watts.
Now for the Surge Power rating.
What is the surge power of your refrigerator?
Manufacturers don’t usually specify the surge wattage or current on the refrigerator’s specification sheet, but there are 2 ways you can go about this:
- The first way is to estimate the surge power of the refrigerator using its running power.
- The 2nd and more precise way is to look for the Locked Rotor Amps (LRA for short) specified on the compressor.
Estimate the surge power of your refrigerator:
As mentioned above, the surge power of a refrigerator can be up to 10 times its running power.
So if you know the running wattage of your refrigerator, multiply that by 10 and you’ll get a safe estimation of the surge power.
For instance, the estimated surge power of the refrigerator from the example above is:
Estimated Surge Wattage (Watts) = Running Wattage (W) x 10
Estimated Surge Wattage (Watts) = 305 W x 10
Estimated Surge Wattage (Watts) = 3050 W
The surge power will probably be lower than that, but this would make sure the inverter you choose will comfortably operate, and therefore last longer.
If we round this number down to 3000W, an inverter such as the Aims power 1500W inverter would be a good choice. It’s rated at 1500W continuous and 3000W surge.
A more precise way of determining the surge power would be to use the specified locked rotor amps.
Locked Rotor Amps:
Locked Rotor Amps – or LRA for short – refers to the amount of current the motor in a compressor requires to start. This value is not usually printed on the refrigerator’s specification label, but on the specification label on the compressor itself.
The compressor can be found on the back of the refrigerator.
The LRA can be used to calculate the Surge Power of the refrigerator. For example, the surge power of the compressor from the image above is calculated as such:
Surge Wattage (Watts) = LRA (A) x Voltage (V)
Surge Wattage (Watts) = 6.6 A x 120 V
Surge Wattage (Watts) = 792 W
Assuming the running wattage of this fridge is less than 500W (which is surely the case), an inverter such as the BESTEK 500W Power Inverter would be a perfect match.
It’s rated at 500W and has a 1000W peak power capacity.
Once you know how much power your refrigerator requires to start and run, you can easily find a matching inverter.
A very important thing to add is that the inverter you choose should be a Pure Sine Wave inverter (as opposed to a Modified Sine Wave one). Otherwise, your refrigerator would consume more energy and its compressor would sustain permanent damage.