Most people make a simple math error when buying an inverter for a fridge. They look at the sticker inside the door, see “150 watts,” and buy a 300-watt inverter. That inverter will fail immediately. It might even damage your refrigerator.
Refrigerators are inductive loads. This means they use magnetic coils in the motor. These motors require a massive spike of power to start turning. This is called “surge wattage.” If your inverter cannot handle that split-second spike, the fridge won’t start.
To run a standard residential refrigerator, you generally need a pure sine wave inverter rated for at least 1500 to 2000 watts. For smaller RV or dorm-style fridges, a 1000-watt unit usually works. The math requires looking at more than just the running watts.
- Ignore Running Watts: Size your inverter based on the “surge” or startup current, not the running current.
- The 5x Rule: A fridge motor often requires 5 to 7 times its running wattage to start up.
- Waveform Matters: Always use a Pure Sine Wave inverter. Modified sine wave inverters can overheat and destroy compressor motors.
- Battery Bank: A big inverter is useless without enough battery capacity (Amp-hours) to back it up.
The Science of Surge Wattage
A refrigerator is not like a lightbulb. A lightbulb is a resistive load. It draws steady power. A fridge has a compressor motor. When that motor is sitting still, it fights gravity and friction to get moving. This requires a massive jolt of electricity.
We call this “Locked Rotor Amps” (LRA). This number is sometimes listed on the compressor itself, but rarely on the main sticker. The LRA represents the surge current needed for a fraction of a second. If your inverter detects this surge as a “short circuit” and shuts down, your food spoils.
How Big of a Power Inverter to Run a Refrigerator
Determining exactly how big of a power inverter to run a refrigerator depends on the specific size and age of your appliance. Older units are less efficient and have harder starts. Newer Energy Star models have “soft start” technology, but they still spike.
Here is the step-by-step process we use in the shop to size these systems correctly.
1. Find the Electrical Plate
Look inside the door or on the back of the fridge. You are looking for “Amps” (A). You might see 1.5A or 3.0A. If it only lists Watts, divide Watts by Volts (120) to get Amps.
2. Calculate Running Watts
Multiply the Volts (120V) by the Amps.
Example: 120V x 1.5A = 180 Running Watts.
3. Calculate Surge Watts (The Critical Step)
Multiply the Running Watts by roughly 6. This covers the LRA spike.
Example: 180 Watts x 6 = 1080 Surge Watts.
In this scenario, a 1000W inverter is right on the edge. It might work, but it will struggle. A 1500W inverter is the safe choice.
Inverter Sizing Matrix
- Small Dorm Fridge (1-3 cu. ft.): Needs 500W – 800W Inverter.
- Standard RV Fridge (6-10 cu. ft.): Needs 1000W – 1500W Inverter.
- Full-Size Home Fridge (18-22 cu. ft.): Needs 2000W – 3000W Inverter.
- Commercial/Old Chest Freezer: Needs 2000W+ Inverter.
Why Waveform Type is Critical
Size is not the only factor. The “shape” of the electricity matters. There are two main types of inverters: Modified Sine Wave and Pure Sine Wave.
Modified Sine Wave: These are cheap. They create a blocky, stair-step electrical signal. Simple tools like drills or heaters run fine on them. However, sensitive electronics and AC motors hate them. The blocky wave causes the motor to run hot. It buzzes. It wears out the windings inside the compressor.
Pure Sine Wave: These replicate the smooth power you get from a wall outlet at home. You must use a Pure Sine Wave inverter for modern refrigerators. If the fridge has a digital display or a smart control board, a modified sine wave inverter will likely fry the circuit board.
From the Shop: The $1,200 Mistake
Last summer, a customer brought in a camper van. He had installed a cheap 3000W Modified Sine Wave inverter he bought online for $150. He thought he was saving money. He plugged in his new Samsung residential fridge.
It worked for two weeks. Then, the fridge stopped cooling. The “dirty” power from the modified sine wave caused the compressor motor to overheat. The heat melted the insulation on the internal wires, causing a short. He had to replace the entire fridge. We swapped his inverter for a high-quality 2000W Pure Sine Wave unit (Victron), and he hasn’t had an issue since.
Battery Bank Requirements
Your inverter converts DC battery power to AC household power. If your battery bank is too small, the voltage will drop instantly when the fridge tries to start. This voltage drop triggers the inverter’s low-voltage alarm, and it shuts off.
Even if you have a massive 3000W inverter, it cannot run a fridge if it is hooked up to a single, old car battery. For a reliable system, you need deep cycle batteries (Lithium or AGM).
For a standard full-size fridge, we recommend at least 200Ah of Lithium (LiFePO4) or 400Ah of AGM/Lead Acid. This ensures the voltage stays stable during that massive startup surge.
How We Evaluated This
Our recommendations are based on bench testing performed in February 2026. We utilized a clamp meter to measure the “Inrush Current” (startup surge) of three different refrigerator types: a 3.2 cu. ft. dorm fridge, a 10 cu. ft. apartment fridge, and a 20 cu. ft. residential unit.
We tested these against various inverter brands, monitoring for voltage sag and waveform distortion. We referenced Energy.gov standards for appliance energy estimation to ensure our baseline math aligns with federal averages.
Frequently Asked Questions
Can I run a fridge on a 1000 watt inverter?
Yes, but only if it is a small to medium-sized fridge (under 10 cubic feet). For a full-size residential kitchen refrigerator, a 1000-watt inverter will likely trip its overload protection when the compressor kicks on.
Does a fridge run continuously?
No. A refrigerator cycles on and off. It typically runs for 15 to 20 minutes per hour, depending on the ambient temperature and insulation. This is called the “duty cycle.” While it doesn’t use power 100% of the time, the inverter must stay on 24/7 to catch the start of the cycle.
Will a modified sine wave inverter damage my fridge?
Yes, over time it will. The blocky electrical wave causes the motor to run hotter and less efficiently. It can also damage the control boards on modern “smart” fridges. Always choose a Pure Sine Wave model. You can read more about how induction motors react to power quality on Wikipedia.
How many batteries do I need to run a fridge for 24 hours?
An average efficient fridge uses about 100 to 150 amp-hours (at 12V) over a 24-hour period. To run this without damaging lead-acid batteries (which shouldn’t be drained below 50%), you would need roughly 300Ah of battery capacity. If using Lithium batteries, 200Ah is usually sufficient.
Why does my inverter beep when the fridge starts?
That beep is likely a low-voltage alarm. When the fridge surges, it pulls a massive amount of current from the batteries. This causes the battery voltage to dip temporarily. If your cables are too thin or your batteries are weak, the voltage drops below the safety threshold (usually 11.0V or 10.5V), causing the alarm.
