How Much Power Does a 12 Volt Refrigerator Use?

12 volt refrigerators are becoming extremely popular whether you're going camping or landing van life, or you're just using them around the park.
When we’re shopping for a 12v refrigerator, one of the things that most people really concerned about is how much battery capacity that needs to run. In order to figure that out, we need to know the power consumption on the refrigerator.
I have a 12-volt refrigerator here today, if I'm going to use it on a two-day camping trip. Let's say maybe I use 36 hours of battery run time. If I do a simple calculation of saying 36 hours times 50 watts it yields 1800 watt hours that's a huge number for battery capacity, and it doesn't make sense. So what I decided to do is buy the refrigerator then run some experiments to measure how much power this really does use, I can share the results with you. So you can figure out how much power you need to power your 12 volt refrigerator, so stick around.

What's the main consumer of power on 12v refrigerator?

Let me explain the main consumer of power on 12v refrigerator, it is going to be the compressor. But the compressor is not running all the time, the compressor is only going to be running when it needs to cool the inside of the refrigerator. So it runs until it hits a temperature set point, and it shuts off.
The ratio of time between it running and it not running is called the duty cycle. The duty cycle is also a function of the difference between the outside ambient temperature and the inside temperature inside the refrigerator. So the greater the difference between the outside and inside temperature, the more power this is going to use. For Example, if I use this in a hot desert climate, this is going to use a lot more power than if I used it in a cooler mountain climate.

How much power 12v fridge uses?

To figure out how much power 12v fridge uses in a bunch of different conditions. I used the ac adapter on the refrigerator to power the fridge, so I could use the power meter. Also, I'm more concerned with the steady state on power consumption of this refrigerator rather than the cool down cycle, so before each test I actually cooled it down to that stabilize temperature. Before I started the data collection and I also did all the tests in the shade, so the radiant heat sunlight is not going to have an impact on the data here. I ran all these tests in a really long duration to ensure that I have an excellent, stable average power measurement. 
Let me go into the data now. I took the data from all these experiments, and I plotted them in a graph. On this graph I have an x-axis which is going to be the temperature of delta.


That's the difference between the outside temperature and the temperature set point inside the refrigerator. On the y-axis, I have the actual average power consumption, so this is the rate of power it's actually using at that temperature delta. So given the actual temperature of delta let's say if I know that I have a 50 degree temperature delta is how I want to use it, I can find out how much power the refrigerator is going to use in that situation. Now that we have this data, let's walk through an example of how would we use this data to figure out how much power or battery capacity.  

I'm going to need to run this for a given use, in order to do this you need to know three things. The first thing is you're going to have to know what average ambient temperature you expect to use; the second thing is what's the temperature set point, are you going to be using this as a temp freezer. Those two things combine to give you the temperature delta, and then the third thing that you need to know is how long you need to have this running on the battery? 

Let's come a two-day camping trip again, and I'm going to be running for 36 hours. I expect my average outside temperature to be 85 degrees day, and night average the temperature set point in here is going to be 35.  So 85 minus 35 gives me a 50 degree temperature difference. If I go to the graph, I look at 50 degree temperature differential, and it's going to tell me that that's going to be about 14 watts. So I take my 36 hours times, 14 watts, that gives me just over 500 watt hours of power. So I'm going to need over 500 watt hours of power to power this refrigerator. That's completely different from this example earlier assuming that it uses 50 watts, because that was 1800 watts. If I'm going to use this in the sunlight in the desert in phoenix, it's probably going to be continuously running. It's going to be closer to the 50 watts. I hope you can use this information o to help you calculate how much power you're going to need to run your refrigerator.

What I have is a 55 quart refrigerator,  I think it's going to give you a good ballpark of how much power you're going to use regardless of the different types of Refrigerators. So if it's a smaller refrigerator, maybe it's going to use less power.

Other factors impact?

There are a lot of other factors that are going to impact how much power this uses and how can we make it better. So one of the tips and tricks of being cool down cycle is don't plug this in your car on your battery and then turn it on. It's going to use a lot more power to cool it down to its steady state. I would cool it down before I use it, so I plug it into the wall at home. I load it up, and I let it stabilize the temperature, maybe the night before, and then the day of I can load this back into my car and use it the way I want to. That's going to use a lot less power off your battery. The other thing that you can do is try to keep it in the shade or get some reflective insulation. You'll find that there's a big difference between the insulated and not insulated.

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