So you are going on a camping trip and have a 12 volt lithium 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
In the next step, we will determine how big your battery needs to be to supply the fridge with electricity. Dont know which battery to get? Read my round-up on the best LifePO4 battery here and read about its lifespan here.
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.
For Lead-acid:
41.6 Ah x 2 = 83.2 Ah
For Lithium:
26 Ah x 2 = 52 Ah
Battery Efficiency
Next, we need to consider the efficiency of the battery. For a lead-acid battery, the efficiency is 80%. For lithium, this is 99%.
For Lead-acid:
83.2 Ah x 1.25 = 104 Ah
For Lithium:
52 Ah x 1.01 = 52.52 Ah
Conclusion
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.
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104 amp hours are you sure about this? 20.8amps a day x2 days=42amps. What am I missing?
Good question. You have missed the efficiency of the battery. If you want to draw 20ah from a lead-acid battery, you need a battery with a capacity of 40Ah. This is because you can only use 50% of a lead-acid battery. If you use more than 50%, you damage the battery. So, 20Ah x 2 x 2days = 80Ah x 1.25 -> heat loss in a lead-acid = 100Ah.
If I have 2 marine cell batteries wired in tandem for my horse trailer to run a refrigerator (120v) 1.4 amps and say a small coffee maker at (120v) 700 watts… I am assuming my small 700 W microwave is best used when plugged into generator. What type of inverter would you say I need?
So your refrigerator is 170Watts, your coffee maker is 700 watts en your microwave is 700 Watts. I assume you won’t be running the coffee maker and the microwave together. So that becomes 170w+700w=870watts. Then a 1000W pure sine wave inverter would be ok. A 12V battery will be sufficient. If you use a 1500watt inverter, then I recommend using 24volts.
The system has to be able to handle the motor start up surge current of the refrigerator. I bought an 845 cold cranking amps deep cycle battery that I figure could handle deeper discharge without ruining the battery. I’ve used it to power motorized floor jacks and even moved fork lifts with two in series.
Yes indeed, the sizing of the inverter is talked about in another article.
the deep cycle marine batteries seem to be less expensive than most regular car batteries.
That can be due to the rise in lifepo4 batteries taking over the market.