When you turn on any electrical device with an electric motor, a short-term but powerful jump in energy consumption occurs, which is called inrush current. For owners of household appliances, this parameter often remains a mystery until the need arises to choose a voltage stabilizer or buy a generator for the cottage. Understanding the nature of this phenomenon allows you to avoid frequent knockouts of machines and extend the service life of the compressor.
Unlike a light bulb or heater, refrigerator is a complex inductive load that requires significant effort to initially spin up the motor rotor. It is in the first fractions of a second after voltage is applied to the windings that the maximum energy consumption occurs, which can be several times higher than the rated operating values. Let's figure out what these numbers depend on and how they affect your home electrical network.
Physics of the process: why a power surge occurs
The main reason for the occurrence of high starting current lies in the nature of the asynchronous motor, which is the heart of most household refrigerators. At the moment of rest, the engine rotor is motionless, and to move it from its place it is necessary to overcome the force of inertia and friction in the mechanical components of the compressor. The electrical resistance of the windings at this moment is minimal, which leads to a sharp surge of current.
After the rotor begins to rotate, a back-EMF electromotive force arises in the motor, which effectively limits further growth of the current. This process takes a fraction of a second, usually from 0.1 to 0.5 seconds, but it is during this period of time that the load on the network is maximum. Compressors Modern models may have soft start systems, but classic units work according to the described principle.
It is important to note that the magnitude of the jump is direct depends on the position of the piston group at the moment of stopping. If the refrigerator shuts down when the refrigerant pressure in the system is at its maximum, the next start will require more energy to overcome this pressure. This phenomenon is known as back pressure, and it significantly increases the load on the starting windings.
⚠️ Attention: Frequently turning the refrigerator on and off at short intervals can lead to overheating of the starting relay and failure of the compressor due to the inability to relieve pressure in the system.
Ratio of rated and starting current
Rated current is the value that the refrigerator consumes in normal operation, when the compressor has already spun up and is cooling the chamber. The starting current, as a rule, exceeds the rated current by 3, 5, and sometimes 7-9 times. The exact figure depends on the engine power, the type of refrigerant and the design features of the specific model.
For household refrigerators with an average power of 100-200 Watts, the rated current is usually from 0.5 to 1.0 Amperes. Consequently, the peak value at startup can reach 7.5 Amps or higher. Such surges are short-lived, but they must be taken into account when calculating the wiring cross-section and choosing protective automation.
Below is a table with approximate values for various types of compressors so that you can estimate the load on your network:
| Refrigerator type | Power (W) | Rated current (A) | Starting current (A) |
|---|---|---|---|
| Small-capacity (single-chamber) | 80 - 120 | 0.4 - 0.6 | 2.5 - 4.0 |
| Standard two-chamber | 150 - 250 | 0.7 - 1.1 | 4.5 - 7.5 |
| Freezer compartment (No Frost) | 200 - 300 | 0.9 - 1.4 | 6.0 - 9.0 |
| Industrial / Large volume | 400+ | 1.8+ | 12.0+ |
It is worth considering that the data in the table are averaged. Actual performance may vary depending on the line voltage: at lower voltages, the starting current may be even higher, since the motor takes longer to accelerate.
The influence of compressor type on peak loads
Compressor manufacturing technologies are evolving, and today there are different types of motors on the market, each of which behaves differently when starting. Classic linear compressors, which can be found in most budget and mid-range models, start sharply, creating a characteristic click and a noticeable jump in the network.
Inverter models, which are gaining popularity in the segment premium refrigerators, work on a different principle. They do not turn off completely, but only reduce the speed to a minimum, maintaining the temperature. Due to this, starting currents are either absent or significantly smoothed out by the soft start system. This makes them more friendly to weak wiring.
Linear inverter compressors used by some major brands also demonstrate reduced starting characteristics compared to traditional piston counterparts. However, even in such systems, when initially turned on after a long period of inactivity, a surge of current is observed, although less pronounced.
⚠️ Attention: When using inverter refrigerators with electricity generators, it is important to choose sine-wave models, since a modified sine wave can damage the control electronics.
Wiring problems and knocking out plugs
One of the most common problems that users encounter is knocking out the circuit breaker (machine) exactly when the refrigerator is turned on. This occurs when the starting current exceeds the threshold of the thermal or electromagnetic protection of the machine. This is especially true for old houses with aluminum wiring.
Automatic circuit breakers have an operation characteristic designated by the letters B, C or D. For household appliances, automatic circuit breakers of the type Care most often used, which can withstand short-term overloads of up to 5-10 ratings. If you have an automatic machine like B, it may react to the starting current of the refrigerator as a short circuit.
Also the cause may be poor contact in the outlet or distribution box, which leads to local heating and voltage drop, causing the motor to consume even more current to start. Checking the condition of the contacts is the first place to start diagnostics.
☑️ Diagnosis of machine knockout
If the refrigerator alone triggers the protection, this is a signal that either the machine was selected incorrectly (the rating is too small), or the wiring is in an emergency condition and requires replacement. Ignoring this symptom can lead to melting of the insulation and a fire.
Calculation of generator power for a refrigerator
The issue of autonomous power supply is becoming increasingly relevant for summer residents and owners of country houses. When choosing a generator, many people make the mistake of summing up only the rated power of the devices, forgetting about the inrush currents. As a result, the generator stalls when trying to start the refrigerator.
For a correct calculation, you need to take the rated power of the refrigerator, multiply it by the starting current coefficient (usually take 3-5 for reserve) and add the power of other simultaneously operating devices. For example, for a 200 W refrigerator, the peak load will be about 1000 W (1 kW).
If you plan to run the refrigerator from a generator, make sure that its maximum (peak) power exceeds the calculated value. It is best to have a power reserve of about 20-30% of the calculated amount so that the unit does not operate at its maximum capacity.
Why does the generator stall when starting?
The generator may stall due to a sharp drop in engine speed when connecting a large inductive load. The generator engine control system does not have time to react to the surge in consumption, the speed drops, and the protection is triggered or the engine stalls. Solution: use a generator with an AVR system and a large power reserve or a soft starter.
It is also worth considering that at low ambient temperatures the oil in the compressor thickens, which increases resistance at startup. Therefore, winter operation requires even more careful selection of the power of the energy source.
Protection and soft start devices
There are special devices to protect equipment and wiring from the negative influence of inrush currents. A voltage control relay (VCR) does not reduce the starting current, but protects against power surges in the network, which often accompany the moments when neighbors turn on powerful consumers.
Soft start devices (SPDs) allow you to gradually increase the voltage on the motor windings, reducing the peak current to 2-3 times the nominal value. However, such devices are rarely used for household refrigerators and require professional installation inside the case or in a circuit break.
Voltage stabilizers also help smooth out surges, but it is important to choose models with a speed of no more than 10-20 ms. Slow electromechanical stabilizers may not have time to react to a sharp surge, although transformer models have a certain inertia, which is useful in some cases.
⚠️ Attention: Installation of any additional devices in the refrigerator power circuit should be done taking into account their own power consumption and ability to switch an inductive load.
Frequently asked questions (FAQ)
Can the starting current damage the electronics of the refrigerator?
The starting current itself is normal operation and should not damage a working device. However, if there are additional power surges or frequent interruptions in the network, this may adversely affect the control board. For protection, it is better to use a voltage relay.
Why does the refrigerator hum when starting?
Humming at the moment of starting is a normal phenomenon caused by the passage of maximum current through the windings and the start of movement of the piston group. If the humming becomes a loud knocking sound or lasts more than a few seconds, this may indicate a compressor malfunction.
Does room temperature affect the starting current?
Yes, it does. In a cold room, the oil in the compressor becomes more viscous, which increases mechanical resistance. This causes the motor to draw more current to start. In a hot room, the load may be lower, but the risk of overheating during prolonged operation increases.
Do you need a separate RCD for the refrigerator?
Installing a separate RCD (residual current device) for the refrigerator is recommended, especially if it is installed in the kitchen or garage, where humidity is possible. This will protect you from current leakage in the event of an insulation breakdown, but will not save you from voltage surges.
How can I find out the exact starting current of my model?
The exact data is rarely indicated on the sticker on the back. They can be found in the technical documentation (user's manual) in the "Electrical characteristics" section or measured using special current clamps with a function for recording peak values (Inrush current).