The moment any compressor equipment is turned on, a sharp jump in energy consumption occurs in the electrical circuit, which engineers call inrush current. For a household refrigerator, this parameter is critical, since it determines whether the wiring, circuit breaker or backup power source (generator/UPS) will withstand the moment the engine starts.
Many owners of household appliances mistakenly focus only on the rated power indicated in the device passport, forgetting that in the first fractions of a second the refrigerator consumes 3-7 times more energy. Understanding the nature of this phenomenon is necessary for the correct organization of power supply, especially in the conditions of holiday villages with unstable voltage or when using autonomous generators.
In this article we will analyze in detail the physical causes of inrush currents, learn how to calculate them and select protective equipment. Ignoring starting characteristics often leads to knocked out plugs, failure of the voltage relay and, in the worst case, to overheating of the compressor windings.
Physical nature of the occurrence of starting current
The main consumer of energy in the refrigerator is the compressor electric motor. The moment you insert the plug into the socket or the thermal relay closes the circuit, the motor rotor is at rest. To move it from its place, overcome inertia and create the necessary refrigerant pressure in the system, a colossal force is required, which is provided by a powerful magnetic field.
From the point of view of electrical engineering, at this moment the resistance of the stator windings is minimal, which leads to a sharp increase in current strength. Induction motorused in most modern refrigerators, consumes maximum current until the rotor will gain working momentum. This process lasts only a few milliseconds, but it is during this time interval that the load on the network reaches peak values.
In addition, there may already be residual freon pressure in the system, which the piston group also needs to overcome. If the refrigerator has been turned off recently, the pressure in the circuits has not yet equalized, and the compressor has to work with increased load. Starting current under such conditions it may even be higher than calculated, which creates a stressful situation for all electrical wiring.
⚠️ Attention: Frequent switching on and off of the refrigerator (for example, due to a faulty thermostat) do not allow the pressure in the system to equalize. This leads to repeated starts under load, which greatly increases the wear of the compressor and the risk of its combustion.
Why do old refrigerators hum louder when starting?
In older models with mechanical-type start-protective relays, the startup process was accompanied by a characteristic click and a longer humming. This is due to the fact that the starting winding was turned on for a longer time, creating more noise and heat than in modern inverter systems.
The difference between rated and peak power
On the information sticker, usually located on the back wall or inside the camera, you will find the power consumption value. Most often for a household refrigerator it ranges from 100 to 200 watts. However, this nominal power, that is, the average value required to maintain the operation of a compressor that has already started.
Starting (or peak) power is a short-term value that can reach 1000-1500 Watts and even higher, depending on the model and state of the equipment. The difference between these two indicators can be tenfold. It is for the peak value that your protective equipment should be designed: circuit breakers, RCDs, stabilizers and generators.
For clarity, let’s consider the dependence of the type of compressor on the magnitude of the starting current. Modern inverter models do not have the classic inrush current, as they start smoothly, but classic linear compressors show a pronounced peak.
Below is a table showing the approximate ratio of rated and starting power for various types of refrigeration equipment:
| Equipment type | Rated power (W) | Starting power (W) | Excess factor |
|---|---|---|---|
| Small refrigerator (up to 200 l) | 120 | 600 - 800 | 5-6 times |
| Medium two-chamber refrigerator | 180 | 900 - 1200 | 5-7 times |
| Freezer (chest) | 200 | 1000 - 1400 | 5-7 times |
| Industrial refrigerator | 500+ | 2500 - 3500 | 5-6 times |
Methodology for calculating starting power
To accurately select a generator or stabilizer, you need to know how to correctly calculate the required power. Simply multiplying the power rating by the safety factor is a basic but not always accurate method. A more professional approach requires taking into account the power factor (cos φ) and the efficiency of the motor.
The formula for calculating the total starting power is as follows: it is necessary to divide the rated power in Watts by the power factor and multiply by the multiple of the starting current. For household refrigerators, the cosine phi is usually 0.6–0.8, and the multiplicity is taken to be 5, unless otherwise indicated in the documentation.
Consider an example: a refrigerator consumes 150 W. cos φ = 0.7. Multiplicity = 5.
Calculation: (150 / 0.7) * 5 ≈ 1071 W.
Thus, your power supply must withstand a short-term load of more than 1 kW, although only 150 W are consumed in normal mode.
☑️ Check before calculation
It is important to consider that aging of equipment affects these indicators. Over time, rubbing parts wear out, the oil thickens, and starting an old compressor may require more current than a new analogue of the same model.
The influence of the type of compressor on starting currents
Not all refrigerators start the same. The type of compressor installed radically changes the energy consumption picture. Traditional linear compressors operate on an “on-off” principle, which generates high starting currents each time they cycle.
Inverter compressors, which are becoming standard in modern models from brands like LG, Samsung, Bosch, work differently. They do not turn off completely, but only reduce the speed to maintain the temperature. Thanks to this, there is practically no sharp current jump at start, since the engine is already in rotation or starts smoothly through the frequency converter.
However, if the inverter refrigerator was completely de-energized, when it is turned on for the first time, its electronics should also start the motor. Although the peak will be smoothed out by electronics, the load on the network in the first seconds will still be higher than nominal, although not as critical as that of linear models.
It is worth noting that the electronics of inverter systems are more sensitive to voltage quality. Power surges can damage the starting module (inverter board), the repair of which will cost much more than replacing a conventional starting relay.
Choosing a generator and voltage stabilizer
When choosing a backup power source for a refrigerator, the key parameter is the overload capacity of the device. The generator must have a power reserve that covers the starting current, otherwise when starting the compressor the voltage will drop and the engine may not start or the winding may burn out.
For gasoline and diesel generators, the maximum and rated power are important. If the generator says 2 kW (maximum), its rated continuous power will be about 1.8 kW. The starting current of the refrigerator should not exceed the short-term maximum of the generator.
⚠️ Attention: When using voltage stabilizers with a small power reserve (for example, 500 VA), connecting a refrigerator is impossible. The stabilizer will go into overload protection, as it will not be able to provide the required starting current. The minimum stabilizer power for one refrigerator is 1.5–2 kVA.
The type of generator should also be taken into account. Synchronous generators can withstand starting loads better than asynchronous ones. Inverter generators, despite the high quality of the current, may have a strict limitation on peak power and will simply turn off when trying to start a powerful compressor.
To organize reliable power, it is recommended to use the following sequence of actions:
- 🔌 Calculate the total starting power of all consumers.
- ⚡ Select a generator with a margin of 20-30% above the calculated starting power.
- 🛡️ Install a voltage control relay to protect against surges in the main network.
- 🔋 Consider using a UPS (uninterruptible power supply) with a pure sine wave for critical inverter models.
Problems and protection of electrical wiring
High starting current creates a danger not only for the refrigerator itself, but also for the home electrical network. If the wiring is old (aluminum) or has twists, a short-term surge of current can cause heating of the contacts and even fire of the insulation in places of poor connection.
Circuit breakers (automatic circuit breakers) have two protections: thermal and electromagnetic. Thermal protection responds to prolonged overcurrent, and electromagnetic protection to short circuits. The starting current of the refrigerator may be mistakenly perceived by the electromagnetic release as a short circuit if the circuit breaker is selected incorrectly (too low power or with characteristic “B” instead of “C”).
For refrigerators, especially with powerful compressors, it is recommended to use circuit breakers with characteristic "C", which allow short-term excess of the nominal value of 5-10 times without turning off. This allows the compressor to start quietly without knocking out the plugs.
⚠️ Attention: If the machine breaks right when the refrigerator is turned on, under no circumstances replace it with a more powerful one without checking the condition of the wiring. This can lead to a fire if the wires cannot withstand the increased load.
Regular maintenance of contacts in sockets and distribution panels will help avoid problems associated with heating during inrush currents. A weakened contact is a place of increased resistance, which at high current begins to spark and heat up.
Frequent questions and answers (FAQ)
Why does the refrigerator knock out the machine when turned on?
This happens if the starting current of the compressor exceeds the operating threshold of the electromagnetic release of the machine. Also, the cause may be a malfunction of the compressor itself (turn-to-turn short circuit) or a too weak circuit breaker (less than 10A type C).
Is it possible to connect a refrigerator through a regular extension cord?
It is possible, but only if the cross-section of the extension cord wire is at least 1.5 mm² (preferably 2.5 mm²) and it is completely unwound from a reel. Thin wires of Chinese extension cords can melt when starting current.
Does starting current affect the service life of the refrigerator?
Yes, every start is stress for the motor windings and mechanics. That is why it is not recommended to turn off and immediately turn on the refrigerator. You need to wait 5-10 minutes for the pressure to equalize and the starting winding to cool.
What kind of UPS is needed for a refrigerator?
You need a UPS with a pure sine wave output and a power exceeding the starting power of the refrigerator. Conventional computer UPSs with an approximated sine wave can damage the compressor or will not be able to start it.