So you are going on a camping trip and have a 12-volt battery and a refrigerator.
In this article, I’m going to break down what you need to know and answer your question:
How long will a 12 volt battery run a refrigerator?
Step 1: Estimate the Energy consumption of the fridge
There are many types of fridges. Big, small, top loader, front loader, 12 volts DC, 110 volts AC, …
They will all have a different power consumption. Their power consumption will also depend on environmental factors like heat, ability to vent, sun exposure, and efficiency, … Just to name a few.
If we look at the CFX-40W (40 quarts or 20 liters), an efficient top-loading fridge on Amazon.com, we can see that they will consume about 0.74 Ah on 12 Volts. This means that the fridge will consume 9 Watts per hour or 216 Watts per day. This includes running and idling time.
You need to figure out how much power your fridge consumes. Be careful; the rating of a fridge will not be an accurate measure of its total power consumption. The compressor will not always run because it shuts off once the temperature has been reached. This can be seen in the following image:
If you want to take a fridge with you that you already have at home, it can be helpful to plug it in a Kill A Watt meter to measure daily consumption before you hit the road.
Step 2: Size your Battery Bank
In the next step, we will determine how big your battery needs to be to supply the fridge with electricity.
You need to ask yourself, how long do I want to run my fridge on the battery?
Your answer can be one day or even a week. The longer it needs to run on the batteries, the bigger your battery needs to be.
The following is best explained with an example.
I’m going to camp for the weekend, and I will bring the CFX-40W with me. The fridge consumes 9 watts per hour and will run for 24 hours daily. This means that the fridge will consume 216 watt hours per day. Let’s assume this is tested in a laboratory where the outer temperature is 90°F or 32°C. Let’s use a little safe space to account for opening and closing the fridge, assuming 250 watt-hours per day.
We need to know the number of amp-hours we need for our battery. You need to divide the number of watt-hours by the battery voltage.
250 watt-hours / 12 volts = 20.8 Amp-hours
If you are using a lead-acid battery, you can only use 50% of its capacity.
20.8 amp-hours x (100%/50%) = 41.6 Ah
If you are using a lithium battery, you can use 80% of its capacity.
20.8 watt-hours x (100%/80%) = 26 Ah
Days of Running
Next, you decide the number of days you need to run the fridge. Our example was a weekend trip, so it’s two days.
41.6 Ah x 2 = 83.2 Ah
26 Ah x 2 = 52 Ah
Next, we need to consider the efficiency of the battery. For a lead-acid battery, the efficiency is 80%. For lithium, this is 99%.
83.2 Ah x 1.25 = 104 Ah
52 Ah x 1.01 = 52.52 Ah
You need a lead-acid battery of 104 Ah to run an efficient top-loading fridge for two days.
If you use a lithium battery, you need a 52.52 Ah battery to run the same fridge for two days.
If you want to include a solar panel, then read my post on how to connect a solar panel to a battery.