Choosing the right size and type of inverter is crucial for reliable refrigerator performance. In this article, I will guide you through the process of selecting the appropriate inverter to power your refrigerator effectively.
First, we’ll explore the manufacturer specifications that determine the power capabilities and type of inverter required. Understanding these specifications is essential before making any decision.
Once we’ve covered these key inverter characteristics, I will then explain the important specifications of your refrigerator that need to be considered and matched with the inverter’s specifications. By following these steps, you’ll have the knowledge you need to find the perfect inverter for your fridge.
So, let’s dive in and find the perfect inverter for your refrigerator.
What are the inverter specifications to consider when sizing one for your refrigerator?
In general, off-grid inverters have 4 ratings that characterize them and that you should pay attention to:
- The Continuous Power of the inverter, rated in Watts (W).
- The Surge Power of the inverter, rated in Watts (W).
- The Input Voltage of the inverter, rated in Volts (V).
- The Output Waveform of the inverter
Let’s see what each of these ratings represents.
Continuous Power (Watts):
The Continous Power (Watts) rating of the inverter is its most important rating, as it represents 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 rating of the inverter.
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.
One of the main criteria when sizing an inverter is that the Continuous Power rating of the inverter should always be greater than the combined Power usage (Wattage) of the appliances you’re trying to run on the inverter.
In this particular case, the Continuous Power rating of the inverter should be greater than the Power usage (Wattage) of your refrigerator. More on that in the next section.
Surge Power (Watts):
The Surge Power (Watts) rating of an inverter represents the maximum amount of overloading power that an inverter can handle for a very short period of time (usually less than a second).
In general, the surge power rating of an inverter is 2 times its continuous power rating. For example, If we look at this 1000W Renogy inverter, for example, we can see that manufacturer specifies 2000W as its surge power rating.
The Surge Power 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 only need between 1000 and 2000 watts to start.
In any case, the Surge Power rating of the inverter should be greater than the surge power requirements of the refrigerator, or else, the fridge will be unable to start. More on that in the next section.
Input Voltage (Volts):
Inverters not only turn DC (Direct Current) power to AC (Alternating Current) power, but also convert the low voltage (usually 12 Volts) supplied by the batteries into a higher voltage (110-120 volts) that the refrigerator requires.
The manufacturer specifies the DC voltage that can be connected to the DC input of the inverter.
For example, this Renogy inverter has a nominal Input Voltage rating of 12V (Volts). In comparison, this 1200W Giandel inverter is rated at 24V for its Input Voltage.
For 12V inverters, the acceptable Input Voltage is usually between 9.5 Volts and 16 Volts, meaning that if the battery voltage goes below 9.5 Volts, or exceeds 16 Volts, the inverter will automatically turn off, and will stop supplying power to your refrigerator.
For 24V inverters, the acceptable Input Voltage typically ranges between 19 and 32 volts.
When sizing an inverter for your refrigerator, make sure the Input Voltage that it’s rated for is compatible with the voltage of your battery bank.
If you haven’t yet sized the battery bank that can run your refrigerator, feel free to read more about the topic here.
The Output Waveform:
Inverters convert DC (Direct Current) Power into an AC (Alternating Current) Power. What that means is that they essentially take the constant voltage supplied by a DC source such as a battery or a solar panel, and convert it into an alternating voltage that appliances such as refrigerators can use.
However, the quality of the AC signal at the inverter’s output will depend on the type of the inverter you’re using.
For example, while a Pure Sine Wave (PSW) inverter will generally produce a smooth-looking AC signal at its output, like the one illustrated in the image above, a Modified Sine Wave (MSW) inverter will output an AC waveform that resembles a square wave:
This is important because refrigerators, and any appliance that operates on a motor, typically require a high-quality AC power source to function optimally and efficiently. A pure sine wave inverter provides a clean and stable AC waveform, similar to what is supplied by the utility grid, which will ensure the smooth operation of a refrigerator.
So, when sizing an inverter for your refrigerator, make sure that it is a Pure Sine Wave inverter.
Now that we know what to look for in an inverter, let’s shift our focus to what to look at in your refrigerator.
What size inverter do I need to run a refrigerator?
In general, you could run most refrigerators using a 1500 Watt pure sine wave inverter, as inverters of this size and type are able to supply 1500 Watts of smooth AC power continuously, and up to 3000 Watts of power for a brief moment if required.
However, depending on the size of your refrigerator and its power usage, you’ll probably be able to run the fridge on a smaller inverter, as long as it’s a Pure Sine Wave inverter.
For example, 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|
|Continuous Power Rating||Surge Power Rating|
|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.
Now, the estimates provided in the table are pretty accurate, however, it is recommended to do your own due diligence before making a purchase.
In order to determine the size of the inverter needed to run your refrigerator as accurately as possible, you’ll first need to determine the continuous power and surge power usage of your refrigerator and look for an inverter that can work with both.
So, let’s first discuss the continuous power usage of your refrigerator.
What is the continuous power usage of your refrigerator?
The continuous power usage of your refrigerator is the maximum amount of electrical power (in Watts) that your refrigerator is likely to use for an extensive period of time. The inverter you choose should be able to provide this amount of power continuously.
The continuous power usage of a refrigerator will vary depending on factors such as its size, age, and efficiency, but it can be determined using the information provided in the user manual, or in the specifications label/sticker that comes with the refrigerator.
To determine the continuous power usage of your refrigerator, find the Voltage (in Volts) and the Current (in Amps) specified by the manufacturer, and multiply them together.
Running Wattage (Watts) = Rated Voltage (V) x Rated Current (A)
As mentioned above, these specifications (Current and Voltage) can be found on the specifications label that came with the fridge.
For example, the following image is of a specification label stuck to the side of a refrigerator:
You can see that the manufacturer specifies 127 Volts as the voltage of this fridge and 2.4 Amps as its rated current. Using these 2 ratings, we can then calculate the power usage of the refrigerator as follows:
Continuous Power Usage (Watts) = Rated Voltage (V) x Rated Current (A)
Continuous Power Usage (Watts) = 127 V x 2.4 A
Continuous Power Usage (Watts) = 305 W
For this particular refrigerator, the inverter needs to have a Continuous Power rating of more than 305 watts.
Now, as previously explained, determining the continuous power usage of your refrigerator is just the initial step when selecting the appropriate inverter. It is equally important to consider the inverter’s capacity to handle the intermittent spikes in power consumption that occur during the refrigerator’s operation.
Let me explain.
What is the surge power of your 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. And sometimes, when the refrigerator turns ON, it draws a huge amount of current which causes a spike in its power usage. The surge power can be 3 to 10 times the running wattage.
Although this spike in power usually only lasts for a fraction of a second, the inverter needs to be able to handle it.
For instance, the following graph illustrates the power usage of a refrigerator:
In the image above, you can see that the refrigerator uses between 130 to 150 Watts of power continuously but can briefly use over 400 Watts of power.
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. For example, a 300W/600W (Continuous/Surge) inverter will be a good fit for this particular fridge.
But, how do you determine the surge power usage of YOUR fridge?
Well, manufacturers don’t usually specify the surge wattage (or current) on the refrigerator’s specification label/sticker, but there are 2 ways you can go about this:
- The first way is to estimate the surge power of the refrigerator using its Continuous Power usage.
- The 2nd and more precise way is to look for the Locked Rotor Amps (LRA for short) specified on the compressor.
1- 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, let’s say you’ve determined that the continuous power usage of the refrigerator is 300 Watts. The surge power usage of this fridge can be estimated as such:
Estimated Surge Wattage (Watts) = Running Wattage (W) x 10
Estimated Surge Wattage (Watts) = 300 W x 10
Estimated Surge Wattage (Watts) = 3000 W
The surge power will probably be lower than that, but this would make sure the inverter you choose will comfortably operate your refrigerator.
An inverter such as the Aims power 1500W inverter would be a good fit. 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.
2- Use the Locked Rotor Amps rating:
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 sticker but on the specification sticker 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 500 Watts and has a 1000W peak power capacity, and it’s a Pure Sine Wave inverter.
Once you know how much power your refrigerator requires to start and run, you can easily find a matching inverter.
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What a great explanation thank you. Clear and precise.
Thanks for the explanation, it really helps me alot.
Thanx for the explanation Younes
I just added this site to my google reader, great stuff. Can not get enough!
Thank you Younes. Simple and straightforward!
Nice and clear right up, which was very helpful.
Are fridge freezers less efficient on 120v than 240v? As my “A” rating, Beko FR uses 75w when running and 165w defrosting, and it’s 460lt (16.24CF) but i’m glad I saw this, so I tested a full start up, by fully defrosting it overnight and for the first minute when turning it back on it used 950w, I was planing to buy a 600/1200w SW inverter, but now I know I need to go much bigger.
Thanks again Aaron.
Very helpful. Thank you!!!
Unfortunately this didn’t help because I can’t get the numbers off of the compressor and my label is not as detail oriented as the example that you gave. For novice the explanation needs to be simplified.
All the explanation did was make me afraid to now get anything to keep my refrigerator running in case of a power outage
As mentioned above, a 1500W should be able to power most refrigerators. However, if you want to be 100% sure and can’t locate the LRA on your compressor, you can use an electricity monitoring device, such as the kill-A-Watt meter.
Plug the electricity meter into the outlet, plug your fridge into the meter, turn on the fridge, and look at the maximum amount of watts it uses when it kicks off.
Hope this helps.
Thank You so much!
Hi, thank you very mjch for the clear and understandable explanation and information.