When I’m roaming facebook groups or forums, I see the same question appearing.
What size inverter do I need to run a fridge?
The power rating of a small fridge
When we size an inverter for a fridge we have to know the running power (wattage) of the fridge. Most fridges have a power consumption of 30-100W continuous.
That means that the fridge will use 30 to 100 Watts when it is running. If you already have a fridge and want to know how many watts it consumes, check the label at the back of the fridge.
Alternatively, you can check it in the manual.
We can see that the rated current is 0.5A at 230V. Using ohms law, we can calculate the power needed to run this fridge continuously:
Surge power during startup
Now to power this fridge we cannot just use a 200W inverter. If we do, the inverter will trip because of an overload.
Why is this?
Because the compressor which compresses the cooling liquid inside the fridge requires a higher current for starting.
The normal starting power draw for a fridge will be 6 times the continuous power.
For our example this means:
115W*6 times = 690Watts of peak power
Therefore we need to choose an inverter that can supply 690 Watts of continuous power.
Now you might ask, there are inverters out there that can supply a surge current of up to 2 times the continuous current.
That might be true for low-frequency inverters but not for high-frequency inverters. I have written about these differences in my article: low vs high frequency inverters; read more about it there.
Your additional loads
Remember the 690Watts we needed? Now what if you wanted to charge your laptop or run your TV?
We don’t want the inverter to shut down because of an overload when you are charging your laptop and running the fridge at the same time.
You need to add this to your total AC power.
690W fridge + 30W laptop charger = 720W
Next, we can choose an inverter for our system. But first, let’s talk about the efficiency of an inverter.
Can you add a 2,000 Watt inverter to your system and call it a day?
You could, but it’s not the whole story. You see, inverters have losses. The bigger the inverter the higher the losses. Even when no load is attached to the inverter or the fridge isn’t running, the inverter will consume power. We call this standby power consumption. For a 2,000 Watt inverter, this can even be 50 Watts. If we multiply that by 24 hours, your inverter will consume the following:
50Watts * 24 hours = 1200Wh
This is equal to a 12V, 100Ah battery DAILY!
Therefore I recommend using a smaller, efficient inverter with eco mode.
The ECO mode detects a load and switches on or off accordingly, saving you from idle consumption.
It is important to note that the ECO mode only works when the load is over 25 watts. If the load is below 25 watts, the inverter will not turn on if it’s in ECO mode.
I recommend using a Victron Phoenix inverter. In this case, I would choose the 800W or 1200W Phoenix inverter.
You can get the Victron 800W inverter here.
How long will my battery last with a refrigerator?
Read my article about it here: How long will a 12V battery run a refrigerator