Many owners of household appliances wonder about the real consumption of electricity, but rarely think about what happens in the first seconds after plugging the plug into the socket. It is at this short-term moment that starting current reaches maximum values, significantly exceeding the average values stated in the passport. Understanding these processes is necessary not only for the competent selection of voltage stabilizers, but also for assessing the condition of the wiring in old houses.
Unlike incandescent lamps or heating devices, the compressor motor requires enormous energy to overcome the inertia of the resting mechanical parts and create initial pressure in the system. If the standard consumption can be 100-200 watts, then at the moment of start the power instantly jumps 3-7 times. This is a critical parameter for those who use autonomous power supplies or UPS.
In this article we will analyze in detail the physics of the startup process, look at the difference between different types of compressors and explain why a short-term surge in energy does not lead to the meter burning out, but can become a problem for a weak electrical network. You will learn how to correctly calculate the required power of protective equipment.
Physics of the starting process and inertia of the compressor
The operation of any refrigeration unit is based on an electric motor that drives the piston or rotor of the compressor. At rest, all metal parts of the system are in a static position, and the refrigerant is distributed along the circuit according to the laws of thermodynamics. In order to move the piston from a dead point and begin to pump freon, the engine needs to overcome significant pressure in the system. Mechanical resistance The electric current flowing through the stator windings at this moment is called starting. Its value depends on the design of the engine and the current pressure in the circuit. If the refrigerator has just defrosted or has been turned off for a long time, the pressure in the system is equalized and it is easier to start the unit. However, during a short-term blackout, when the pressure has not yet stabilized, the load on the motor increases many times over. mechanical resistance and system pressure.
The electric current flowing through the stator windings at this moment is called starting current. Its value depends on the design of the engine and the current pressure in the circuit. If the refrigerator has just defrosted or has been turned off for a long time, the pressure in the system is equalized and it is easier to start the unit. However, during a short-term blackout, when the pressure has not yet stabilized, the load on the motor increases many times over.
The duration of this process usually ranges from 0.5 to 2 seconds. Despite the short duration, it is in these fractions of a second that the main heating of the windings occurs and the maximum load on the relay contacts is created. Modern models are equipped with protective systems that prevent the compressor from restarting ahead of time, waiting for the pressure to equalize.
⚠️ Attention: Frequent on-off cycles (less than 3-5 minutes after shutdown) can lead to failure of the starting relay or burnout of the windings due to high starting current when the pressure is not released.
It is worth noting that classic asynchronous motors consume a current at the moment of start that can be 5-7 times higher than the rated operating current. This phenomenon is called inrush current. For a household refrigerator with a power of 200 Watts, the peak value can reach 1000-1200 Watts or more. It is this figure that you need to focus on when choosing a generator or stabilizer.
Differences in consumption: Inverter versus Linear
Technology does not stand still, and today two main types of compressors dominate the market: classic (linear or stepped) and inverter. The principle of their operation is radically different, which directly affects the nature of electricity consumption, especially at the time of start. The classic compressor works on the principle of “turned on - cooled - turned off.”
In linear models, each start is accompanied by full acceleration of the engine to maximum speed. This means that starting current occurs regularly, every time the temperature in the chamber rises above the set one. The frequency of such starts depends on thermal insulation, product load and ambient temperature. On average, an ordinary refrigerator turns on 10-20 times a day.
Inverter models, such as the popular series LG Linear Inverter or Samsung Digital Inverter, work differently. After the initial cooling, they do not turn off completely, but only reduce engine speed, maintaining the temperature. In this mode, the starting current occurs only once - when it is first connected to the network. Subsequently, energy consumption occurs smoothly, without sudden jumps.
- 🚀 Linear compressor: High starting current with each cycle, a characteristic click of the relay, noticeable vibration at start.
- 📉 Inverter compressor: Smooth start without current surges, quiet operation, no characteristic clicks, saving up to 30% energy.
- ⚙️ Hybrid systems: Some models use a combination of technologies where soft start is implemented electronically, but the mechanics remain classic.
The difference in consumption at start-up between these types colossal. If a linear motor is characterized by a sharp jump to 1000 W and higher, then the inverter power supply allows you to accelerate the motor shaft smoothly, starting from minimal currents. This reduces the wear of mechanical parts and allows the use of less powerful wiring.
Calculation of peak power and impact on the network
For correct selection equipment, such as voltage stabilizers or uninterruptible power supplies (UPS), must be able to calculate peak load. Simply summing up the rated power of all appliances in the house will not give the real picture. It is important to take into account the inrush current factor.
The formula for calculating the approximate peak power is as follows: P_start = P_nom * Kwhere P_nom is the rated power indicated on the nameplate, and K is the inrush current factor. For refrigerators, this coefficient is usually taken to be 3.5–5, but for older models it can reach 7.
Let's consider an example. On the back wall of the refrigerator the power is indicated at 150 watts. When starting, it may briefly consume: 150 W * 5 = 750 W. If at the same moment you turn on the microwave oven (1000 W) and the electric kettle (2000 W), the total load may exceed the permissible wiring, especially if it is aluminum and old.
| Equipment type | Rated power (W) | Fact. start (K) | Peak power (W) |
|---|---|---|---|
| Refrigerator (old) | 200 | 6.0 | 1200 |
| Refrigerator (inverter) | 180 | 1.5 | 270 |
| Freezer | 250 | 5.0 | 1250 |
| Showcase trading | 400 | 4.5 | 1800 |
It is important to understand that electricity meters installed in apartments usually have a safety margin and do not respond to such short-term surges. However circuit breakers (automatic machines) in the panel may operate if their characteristics do not correspond to the type of load. For motors, circuit breakers with characteristic “C” or “D” are used, which can withstand short-term overloads.
⚠️ Attention: Technical characteristics of electrical networks and requirements for electrical equipment may change. Always check the permissible load on your wiring with the current data in the house electrical supply project or consult with an electrician.
The role of the starting relay and protective automatics
The key element that controls engine starting is the starting relay. In older models it can be electromechanical (current), in new ones it can be electronic. The relay's task is to supply current to the starting winding only for the duration of the rotor acceleration, and then turn it off. If this mechanism is faulty, the engine will hum, but will not start, consuming huge current.
When the power is turned on, voltage is applied to the main winding. The current passing through the relay coil creates a magnetic field that closes the contacts of the starting winding. The engine starts to rotate. As soon as the speed reaches 75% of the rated speed, the current drops, the magnetic field weakens, and the contacts open under the influence of gravity or a spring.
Modern control systems such as Soft Start, avoid the use of bulky mechanical relays. The electronics smoothly increases the voltage on the windings, simulating a frequency converter. This reduces the starting current to a minimum and extends the life of the compressor.
What happens when the relay contacts stick?
If the starting relay contacts stick and do not open, the starting winding remains on. Since it is not designed for long-term operation, it quickly overheats and burns out, which can lead to a short circuit and failure of the entire compressor.
A protective thermal relay, often combined with a starting one in one housing (tablet), plays the role of a fuse. It monitors the current passing through the motor. If the start is delayed or the current exceeds the norm due to jamming, the bimetallic plate inside the relay heats up and opens the circuit, turning off the power to the unit.
Factors that increase consumption at start
There are a number of external and internal factors that can cause the refrigerator to consume more energy at start-up than is intended by the design. One of the main enemies is low voltage in the network. If instead of 220 Volts in the outlet there are 180-190 Volts, the motor requires more time and current to accelerate, which leads to overheating.
The ambient temperature also plays a role. In a hot room, heat exchange occurs worse, the compressor is forced to work longer and more often. In addition, the viscosity of the oil in the compressor at low temperatures (for example, when transporting in winter) can temporarily increase the resistance at the first start.
- 🌡️ High temperature: Increases the frequency of switching on and the load on the capacitor.
- 📉 Low voltage: Causes an increase in the starting current and engine humming.
- 🧊 Excess ice: A thick coat on the evaporator impairs heat transfer, causing the motor to wear out.
Improper installation also affects efficiency. If the refrigerator is located close to a wall or in a niche without ventilation, heat is not removed from the condenser. The pressure in the system increases, and the compressor requires more effort (and current) to pump freon the next time it starts.
☑️ Diagnosis of problematic startup
The influence of the condition of the refrigerant and oil
The internal state of the refrigeration system directly dictates how difficult it will be to start compressor. The refrigerant (freon) and compressor oil are in a closed circuit under pressure. If the system is sealed, the pressure equalizes within 3-5 minutes after stopping. Starting up with equalized pressure proceeds normally.
However, if there is a freon leak or, conversely, the system was refilled in violation of the standards, the balance is upset. If there is a lack of refrigerant, the compressor may run “idle”, but at the same time it will cool worse, since oil circulation is often associated with freon circulation. This leads to overheating and increased currents.
Particular attention should be paid to the condition of the oil. Over time, it can oxidize, especially if moisture gets into the system. Thick oil that has lost its properties creates high hydraulic resistance. At the time of startup, it is difficult for the piston group to push through this mass, which sharply increases the load on the electric motor.
If the refrigerator was turned off for a long time, the oil could drain into the lower part of the system (into the evaporator). When turned on abruptly, a so-called “hydraulic hammer” is possible when liquid oil enters the compressor cylinder. The liquid is not compressed, and this can lead to mechanical damage to the valves or piston.
Recommendations for protection and savings
To extend the life of the refrigerator and protect your home network from overloads, it is recommended to follow a few simple rules. First of all, this concerns the organization of power supply. Using a high-quality surge protector with overload protection is the required minimum.
If you live in an area with unstable voltage, installation voltage stabilizer is mandatory. It will not only equalize the voltage, but also provide a start delay (timer), preventing the compressor from restarting before the pressure in the system has equalized. This will save the engine from running on “back pressure.”
It is also important to keep the condenser clean (the grill at the back of the refrigerator). Dust and animal hair act as a heat insulator, increasing system pressure and causing the compressor to consume more energy each time it starts. Regular cleaning behind the refrigerator is not only a matter of hygiene, but also saving electricity.
How often can you turn the refrigerator on and off?
The optimal interval between turning it off and turning it on again is at least 5-10 minutes. This time is necessary to completely equalize the freon pressure in the system. Frequent switching on (every 30-60 seconds) indicates a malfunction of the thermostat or a freon leak.
Why does the refrigerator hum when starting up?
A hum lasting 1-2 seconds is normal operation of the engine when overcoming inertia. If the humming continues longer or is accompanied by clicking sounds, the starting relay may be faulty or the engine is running at current limits due to low voltage.
Does the fullness of the refrigerator affect the starting current?
The fullness does not directly affect the value of the starting current. However, a full chamber holds the cold better, which reduces the frequency of compressor starts. An empty refrigerator will turn on more often, in total consuming more energy per day, although each individual start will be standard.
Is it necessary to defrost the refrigerator before a long shutdown?
Yes, this is necessary. Remaining moisture and food may cause mold and corrosion of internal components. In addition, before transportation, compressor pipes are often sealed so that the oil does not leak out, which also requires preparation.