What Size Generator do I Need to Run a Refrigerator?
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The nameplate on your refrigerator and freezer will give you an idea of what size of generator you need to run it. It will give you a “rated” current and voltage. If you multiply them, you will get the running (or continuous) watts that your refrigerator needs. To get a complete picture, you will also need a “startup” or “surge” rating.
The rating label that is placed on the back or side of your refrigerator can be used to determine the required watts to run it. The current that the refrigerator draws is measured in amps (example below, 2.4A). Standard voltage in the USA is 110-120 volts but for calculation, use the number on the refrigerator plate itself (example below, 127V).
The needed information on the nameplate generally looks like this:
Once you know amps and volts, wattage is calculated by multiplying amperage (rated current) by voltage (on the nameplate). The formula for calculating watts goes as follows:
Watts = Volts x Amps
This number is a draw with a working compressor, but it is constantly turning on and off. The compressor will be operational about 25% of the time, though this varies by model type.
However, you should be aware that all motors, including those in refrigerator compressors, use a lot of electricity in the initial few seconds of operation. It’s possible that it’ll be three to five times as much.
When you get your generator and plan to use it for the refrigerator, make sure it can handle the required surge wattage. So, this is how refrigerators are rated:
- Startup watts (or surge rating). The power draw peak that occurs when an appliance is functioning in its most demanding condition or cycle is known as startup current. This usually occurs during a start-up of a compressor. The amperage draw will restore to normal once the internal compressor components have reached the running state (typically less than a few seconds).
- Running wattage (or continuous rating). The rated current is the maximum continuous current at which the unit can run. Continuously drawing more current than the rated current can cause generator failure.
Even though the “running wattage” is important, you should also look at surge (or startup watts) as well before purchasing a generator. These surges also have to be long enough for your refrigerator to start the compressor any time it needs to.
How many seconds does the generator offer peak power? In generators, surge watts last only a few seconds, but that is usually enough to give your refrigerator a boost in power when needed.
To get information on starting wattage, you can also look at generator specifications (source):
When the motor achieves full speed, the inrush (or surge current) begins off strong and quickly fades away. The average current is three to five times higher during this brief startup period than at full speed under load.
As current grows, so does the amount of heat produced by the current flow. A generator could burn out or catch fire if it doesn’t include a device to avoid overload.
A circuit breaker rated near to the continuous power capacity (running watts) avoids overloads while allowing greater current levels (surge watts) to flow for a very short time. Within the generator’s restrictions, this permits the generator to start motors.
Refrigerator energy consumption
It is important to know what factors influence how much electricity your refrigerator or freezer uses.
- Type of refrigerator or freezer. A business display fridge, for example, can consume 10 times as much energy as your home bar fridge.
- Size of refrigerator or freezer. Larger refrigerators require more power since they have a bigger capacity.
- Location of refrigerator or freezer. The fridge will consume more electricity in a warm and poorly ventilated area.
- Consider the seasonality. Is it summer or winter? Because the ambient temperature is greater in the summer than in the winter, your refrigerator or freezer will require more power.
- How are you using your fridge? The compressor will have to work harder to keep items cold if the fridge door is opened or left open regularly.
- Is your fridge full or almost empty? Since more the cold air is replaced with the warm air each time the door is opened, an empty fridge may have to work harder than a well-stocked fridge.
- When was the last time you’ve checked the refrigerator factory setting? It’s possible that the factory setting keeps the fridge colder than you really need, therefore you are using more energy than necessary.
- How old is your refrigerator or freezer? Old refrigerators are often less energy-efficient than modern refrigerators with high star ratings. Also, your refrigerator will be less efficient if the seals are damaged.
There are three basic ways to determine your generator power needs and we will go over them in detail below:
- Reading nameplates
- Energy Star rating
- Energy KWA meter
The amount of electrical current used by a refrigerator’s compressor to chill its compartment is measured in amps. When the voltage is 120, the amperage for typical domestic freezers ranges from 3 to 5 amps.
Since the compressor isn’t working all of the time, the average continuous amperage is lower and this is frequently expressed in kilowatt-hours (or KWh). So what does the refrigerator nameplate tell us?
First of all, we need to look at two different nameplates! The first one is the nameplate of the actual refrigerator or freezer:
This will give us an idea of what the continuous wattage of the refrigerator may be. In our example above we need:
Multiply VOLTAGE (115V) by AMPERAGE (1.4 amps)
With this type of refrigerator, our generator needs to be able to handle:
161-watts of continuous power
In that particular model (see example above), they do mention “max amps”, so you don’t have to look for a second nameplate (of compressor). Not all refrigerator models are so generous, and offer only running wattage rating:
In the given example 1.4A x 115V = 161-watts, which means that for normal use, continuous use, 161 operating watts will be required. As previously stated, there are instances when starting or surge power is 2-3 times the number of operating watts.
As a rule of thumb, and as a precaution, assume that up to 6 times the rated current may be necessary for the appliance’s initial starting. Now let’s find out our surge rating!
You will need to look at the compressor’s nameplate:
On a label like this, LRA stands for:
“Locked Rotor Amp”
To get the needed surge rating (so you can size your generator appropriately), multiply:
Locked Rotor Amperage (LRA) x Voltage
From our example above, we have:
- 9 LRA – Amp rating
- 115V – Voltage
When we multiply the above numbers, we get:
10.9 x 115 = 1,254 watts
This is how much you need for your generator to be able to handle at least for few seconds and it is called – Starting (or Surge) watts:
For single-phase devices, the basic LRA (Locked Rotor Amps) equation is:
LRA = 1000 x (kVA/HP) / Voltage.
This is the current drawn by a motor at its rated voltage while its rotor is NOT spinning or rotating (the rotor is at rest when we are starting it). It’s important to remember that this is the startup current at full nominal voltage.
Unlike using utility power (which is pretty much stable), when you utilize a generator to power a motor-driven device, the output will drop during the initial load spike. On the bright side, most household appliances will start with a voltage loss of up to 30% and you will probably be ok.
Here is the basic terminology that you may encounter when trying to read the labels (or nameplates):
- LRA – Locked Rotor Amps. A motor draws a very high amperage amount during a startup and it is generally five to six times larger than the operating load. This is a maximum current spike (also called an inrush current) during a motor start.
- RLA – Rated Load Amps. This is the current that a compressor will draw while operating (not startup).
- FLA – Full Load Amperes. Fully loaded motor current.
Here is a code letter breakdown from National Electrical Manufacturers Association (NEMA), which sets the design standards for motors:
with locked rotor
|A||0 – 3.14|
|B||3.15 – 3.55|
|C||3.55 – 3.99|
|D||4.0 – 4.49|
|E||4.5 – 4.99|
|F||5.0 – 5.59|
|G||5.6 – 6.29|
|H||6.3 – 7.09|
|J||7.1 – 7.99|
|K||8.0 – 8.99|
|L||9.0 – 9.99|
|M||10.0 – 11.19|
|N||11.2 – 12.49|
|P||12.5 – 13.99|
|R||14.0 – 15.99|
|S||16.0 – 17.99|
|T||18.0 – 19.99|
|U||20.0 – 22.39|
|V||22.4 – and up|
This is a ratio of locked rotor kVA per horsepower (HP) and you can find it on the nameplate on most modern induction motors:
So, in order to calculate your compressor surge ratings, you basically have three options:
- Multiply running watts by 6 (to be on the safe side) and that will give you an approximate number.
- Find compressors amps on the nameplate and multiply by volts to get watts.
- Find a Code letter (if no amp information is available) and calculate like mentioned here (external link).
It is also important to note that your fridge may not utilize its rated watts and your calculations may be a little bit off. There are many factors that influence your power use, not to mention your old refrigerator may start using a lot more electricity than it once used to…
Energy Guide (star rating)
It is always good to know that you got an Energy Star certified refrigerator:
If your “Estimated Yearly Electricity Use” is:
215 kWh per year = that is 215,000 watts hours (per year)
Now, let’s divide:
215,000 / by 365 (days per year)
And you will get:
215,000 / 365 = 589.04 (watts per day)
Almost there… Now divide daily wattage by 24 hours:
589.04 / 24 = 24.54 (average running watts within an hour)
This number is the closest to your actual refrigerator power consumption. If you need to determine amps that your refrigerator will be consuming, divide this number by local voltage (110-120 volts in the USA):
Amps = Watts / Volts
Or in our example (above), it will be:
24.54 / 120 = 0.20 amps
“Star ratings” is an excellent tool and a good way to determine wattage quickly and easily. However, there are many more elements to keep in mind (as mentioned above), like usage, age of equipment, and the season it’s being used in.
If your refrigerator doesn’t have an energy star rating (and most commercial refrigerators don’t), you’ll need to either contact the refrigerator’s manufacturer (who could have this information) or buy a KWH power meter. KWH meter will provide you with the most accurate and exact measurements.
It is the ONLY way to determine how much electricity your fridge REALLY consumes. Now, let’s get to it!
An energy KWA meter is a simple and effective way to monitor the power usage of your appliances. This is accomplished by first connecting the meter to the power outlet, and then connecting the refrigerator to the meter.
The meter will track how much electricity the gadget consumes over time. These meters are typically affordable and can help you become more aware of how much power your appliances use, perhaps saving you money on your energy bill.
They are also an excellent way to know your power consumption, before running off and buying a generator…
The meter you buy will almost certainly come with instructions, although they are usually fairly simple to operate. Kill-A-Watt is the most popular model (paid link):
And here are some more energy (or power) meeters:
If used properly, they can save you a lot of time by taking the guesswork out of the picture. Not to mention, you don’t have to find and decode labels!
Once you find out exactly how much wattage your fridge or a freezer is using, the rest is quite easy. You will need the following numbers:
- Refrigerator running wattage
- Refrigerator starting wattage (or just multiply running watts by 3-6 times)
- A generator that accommodates starting wattage
Now, let’s take a look at “running time” at 50% load (mentioned in most spec sheets) and determine how long your refrigerator will run before you will need to refill the tank. As a general guideline, you want a generator that can operate for at least 10 hours at half-load (so you can sleep through the night) 😉
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