A few days ago I was asked by a former student how to size the battery backup for a refrigerator. My answer was that you need to consider two things before purchasing the battery.
The two things you need to consider when buying the battery backup for your refrigerator are the amount of power the refrigerator consumes while it is working and the amount of power needed to start the refrigerator, I am going to explain this below.
How much power does a refrigerator use?
The first thing you need to figure out is how much power your refrigerator consumes, you can find this by checking the power consumption label on your refrigerator.
Most refrigerator manufacturers have the power consumption rating data for their products. Depending on where your refrigerator was manufactured the power unit can be different, just make sure you convert them to the units that a familiar to you.
The power consumption units can be listed in BTUs (British Thermal Unit) per hour, average WH (watt-hours), or KWH (kilowatt-hours).
Common household refrigerators are labeled to consume between 250watts and 300 watts, but the real power consumption can be even lower, this is because the refrigerator works on cycles, it can work 30% of the time and be Off 70% of the time (this number can be changed depending fast do you want it to cool things).
How much is the start-up power?
Refrigerators contain compressors/motors that will help with air circulations, and these motors will require a high start-up power in order to overcome the inertia when they are completely stopped.
The startup amps are usually referred to as the LRA (Locked Rotor Amps). The locked rotor amps are the amount of power/amperage it takes to start the compressor/motor of the fridge from being completely stopped.
This power is usually 5 to 10 times the nominal power of the refrigerator, this is the reason why sometimes people buy a battery with enough power to run the refrigerator but yet the refrigerator will never start.
For example: if you had a refrigerator that according to the manufacturer can consume 300 watts, you will need a battery with an output of 1500 – 3000 watts. If the battery surge watts output is not high enough, it will never get the motor started and not be able to run the refrigerator once the power is lost.
That is it, this is how you can size the battery backup for the refrigerator, you need to consider the nominal power your refrigerator will consume and also the power surge needed to power the refrigerator when it is not working.
The failure to do that will result in you buying a battery and finding out that it can not power your refrigerator.