Starting the compressor is the most critical moment in the operation of any refrigeration equipment. It is in this fraction of a second, when the motor rotor begins to rotate, that there is a sharp jump in current consumption, which can be several times higher than the rated values. Many owners, when installing new equipment or choosing an autonomous power source, forget to take this factor into account, which leads to knocked out plugs or failure of inverters.
Understanding the nature of this phenomenon is necessary not only for engineers, but also for ordinary users planning to connect a refrigerator via voltage stabilizer or generator. If the calculated power is insufficient, the equipment simply will not start, and the protection system will de-energize the line. Let's figure out where these numbers come from and how to use them correctly.
In this article we will take a detailed look at the calculation methodology, the influence of the type of compressor and safety factors. You will learn to distinguish real power consumption from peak loads and will be able to independently select equipment that will ensure stable operation of your in any conditions refrigerator
Physics of the process: why consumption increases during startup
At the moment the compressor electric motor is turned on, the rotor is in a stationary state. To move it from its place and overcome the inertia, as well as the refrigerant pressure in the system, considerable force is required. Electrically, this is expressed in a sharp increase in the current flowing through the motor windings, which creates the so-called starting power starting power.
The duration of this process is extremely short - usually from 0.5 to 3 seconds, but it is during this period of time that the load on the network is maximum. If the wiring or power supply is not designed to withstand such short-term overloads, the circuit breaker will trip. This is a protective reaction that prevents overheating of the wires and fire.
It is important to understand the difference between the active and reactive components of the current. Refrigerator motors are inductive loads, which means there is a phase shift between current and voltage. This reduces power factor (cos φ), due to which the total power consumed from the network is higher than the useful operation of the engine.
⚠️ Attention: Old models of refrigerators with starting-protective relays can create higher and longer-lasting starting currents compared to modern analogues. If you have equipment that is more than 10-15 years old, consider an increased safety margin when making calculations.
It is also worth considering the temperature factor. When first turned on after defrosting or a long period of inactivity, the compressor may run longer at high load until the set temperature is reached. During this period, starting cycles may be more frequent, which requires stability from the network.
Basic formula and starting current coefficient
For the initial calculation, you can use a simplified formula that gives an approximate, but quite accurate value for domestic needs. The basis is the rated power of the device, indicated on the technical sticker or in the instructions. Typically it is in the range from 100 to 300 W for standard models.
The key parameter here is starting current coefficient. For refrigeration compressors, it varies from 3 to 7. This means that at the start, consumption can increase by 3–7 times. The formula is as follows:
Starting power = Rated power × Starting coefficient
For example, if your nameplate refrigerator indicates a power of 150 W, and the coefficient we take it equal to 5 (average value), then the peak load will be 750 W. It is this figure that you need to focus on when choosing protective automation.
However, blind multiplication can give an unnecessarily inflated result. Modern inverter models have a soft start, where the coefficient can be 1.5–2. Therefore, it is important to know the type of compressor you have. If you are not sure of the exact ratio, it is better to play it safe and take the maximum value from the range.
The influence of compressor type on the calculations
Not all refrigerators are created equal, and this directly affects the calculations. There are two main types of compressors: conventional (linear) and inverter. The difference in their operation radically changes the approach to choosing a power source.
Conventional compressors operate on the principle of “turn on - work - turn off”. They are the ones who create those very powerful inrush currents that we talked about above. Each cooling cycle begins with a jerk that loads the network. In such systems, a a starting relayis used, which switches the motor windings.
Inverter models, such as Samsung Digital Inverter or LG Linear Compressor, work differently. They do not turn off completely, but only reduce the speed to a minimum. When it is necessary to cool the chamber, the rotation speed gradually increases. Thanks to this, sharp current surges are eliminated, and the starting power is almost equal to the rated power.
How to distinguish an inverter refrigerator?
Look at the sticker with the characteristics. If it says “Inverter” or a power range (for example, 70-300 W), this is an inverter model. They also work much quieter and do not have characteristic clicks when turned on.
When calculating the power for inverter refrigerators, it is enough to add the standard 20-30% reserve. This makes them more friendly to weak power grids and autonomous low-power generators.
Table of approximate values for different classes of equipment
So that you do not have to look for a calculator for each calculation, we have prepared a summary table with average data. Remember that actual indicators may vary depending on the year of manufacture, chamber volume and energy efficiency of the model.
| Refrigerator type | Rated power (W) | Coefficient. start-up (average) | Starting power (W) |
|---|---|---|---|
| Single-chamber (small) | 100 - 150 | 4 - 5 | 400 - 750 |
| Double-chamber (standard) | 200 - 300 | 5 - 6 | 1000 - 1800 |
| Side-by-Side (large) | 400 - 600 | 6 - 7 | 2400 - 4200 |
| Inverter (any) | 150 - 400 | 1.5 - 2 | 300 - 800 |
Using these data, you can quickly estimate the required power stabilizer or generator. For example, for a large two-chamber refrigerator of an old model, it is better not to take a stabilizer with a power of less than 2 kW, even if it consumes only 250 W in normal mode.
Choosing a voltage stabilizer and generator
When the calculations are made, The stage of equipment selection begins. It is important to consider not only watts, but also volt-amperes (VA), since for an inductive load the apparent power is different from the active one. Stabilizers are often marked in VA.
To recalculate, use the formula: Power (VA) = Power (W) / cos φ. If the power factor is not specified, assume it is 0.6–0.7 for older engines. This means that for a refrigerator with a starting power of 1000 W, you need a stabilizer of at least 1500–1700 VA.
When choosing a generator, the situation is even stricter. Gasoline and diesel units do not tolerate sudden load surges if they are more than 30% of their nominal value. Therefore, the reserve should be double. If the starting power of the refrigerator is 1.5 kW, the generator must be at least 3 kW.
⚠️ Attention: Do not connect the refrigerator to the generator without using a high-quality stabilizer or AVR unit. Frequency jumps and sinusoid shapes at the generator output can burn the control board or the compressor motor winding.
Also pay attention to the response speed of the stabilizer. Relay models may switch windings too slowly to protect electronics, it is better to choose electronic or hybrid stabilizers with a response time of up to 10 ms.
Practical instructions for measurements and testing
If you want to get the most accurate data, theoretical calculations can be supplement with practical measurements. To do this, you will need a special device - a wattmeter with the function of measuring peak values (Peak Hold) or a current clamp with memory.
The measurement process is simple, but requires caution, since the work is carried out under a voltage of 220 Volts. Do not touch exposed contacts and use a proper tool. It is better to entrust this procedure to an electrician if you do not have experience.
☑️ Check before connection
Connect the device to the open circuit of the refrigerator. Plug in the refrigerator (preferably after defrosting so that the compressor starts working immediately). Record the maximum value that the device will show in the first seconds. This is your real starting power.
Common errors and operating nuances
One of the main mistakes is ignoring the condition of the wiring. Even if you correctly calculated the power of the stabilizer, old aluminum wiring with oxidized twists may not withstand the inrush current. This will lead to heating of the contacts and a potential fire.
Another nuance is the simultaneous launch of several powerful devices. If the refrigerator starts at the same millisecond as the washing machine or microwave, the total starting current may exceed the rating of the input circuit breaker. Modern systems smart home are able to time the launch of devices.
It is also worth remembering seasonality. In summer, when the room is hot, the compressor works harder, and starting currents may be higher due to diluted oil and high pressure in the circuit. In winter, on the contrary, starting may be difficult due to thickened oil if the refrigerator was in an unheated room.
⚠️ Attention: It is strictly forbidden to plug in the refrigerator immediately after carrying it in a horizontal position. The oil must drain into the compressor crankcase (at least 2-4 hours), otherwise water hammer and destruction of the valves during startup are possible.
Following these simple rules and correct calculation will extend the life of your equipment and protect the electrical network at home. Do not skimp on protection, because repairing a compressor or burnt wiring will cost much more than a high-quality stabilizer.
What to do if the refrigerator hums but does not start?
This may mean a jammed compressor or a faulty start relay. In this case, the inrush current will increase indefinitely until the thermal protection trips. Urgently disconnect the device from the network and call a technician.
Frequently asked questions (FAQ)
Is it possible to connect a refrigerator through a regular surge protector?
No, a regular surge protector (pilot) only protects against power surges and has weak contacts. It is not able to smooth out inrush currents and can melt itself or cause a fire if a powerful compressor is started frequently. Use only specialized stabilizers.
Why does the circuit breaker knock out when you turn on the refrigerator?
Most likely, the rating of your circuit breaker is too small for the motor starting current, or the circuit breaker has a characteristic “B” (for lighting), and not “C” (for motors). Also, the reason may be a malfunction of the compressor itself, which consumes a current higher than normal due to an interturn short circuit.
Does low voltage in the network affect the starting power?
Yes, and very much. At low voltages, the current in the motor windings increases to compensate for the drop in power. This leads to an even higher starting current and overheating of the motor. In such conditions, the use of a stabilizer is mandatory.
Do you need a power reserve for a two-compressor refrigerator?
Yes. In dual-compressor models, the compressors rarely start at the same time, but this is a possibility, especially after a defrost or power surge. Calculate the power of the power source as the sum of the starting powers of both compressors, or use a soft starter.