Organizing uninterrupted power supply for kitchen appliances is not just a whim, but a necessity that extends the life of expensive equipment. When two refrigeration units are installed in a house or apartment, the issue of protection against power surges becomes critical, since the simultaneous failure of two compressors will cause a serious financial blow. Many owners mistakenly believe that a conventional surge filter is sufficient for protection, but reality dictates different operating conditions for electrical networks.
In modern conditions of unstable energy supply, especially in the private sector or old apartment buildings, voltage fluctuations can reach dangerous values. Starting currentsthat occur when the motor-compressor is started are several times higher than the nominal values, which requires significant safety margin. Correct calculation of power will avoid false shutdowns and ensure smooth operation of equipment.
In this article we will analyze the technical nuances of choosing equipment that will help you choose the optimal solution for your food storage system. We will not rely on general phrases, but will consider specific formulas and physical processes occurring inside the electric motor at start. Understanding these processes will save you from buying an overly expensive or, conversely, weak device.
Features of operation of a refrigeration compressor
A refrigeration compressor is an electric motor with a special design that experiences maximum load at the time of startup. Unlike incandescent lamps or heating elements, an inductive load requires consideration power factor (cos φ), which can be quite low in older models. This means that the actual power consumption at the time of start-up differs significantly from the rating data indicated on the nameplate.
When starting, the engine rotor must overcome the inertia of rest and the refrigerant pressure in the system, which causes a short-term but powerful jump in energy consumption. Asynchronous motorsused in most household models can consume 3-7 times more energy at this moment than in normal operation. Ignoring this fact when choosing a stabilizer will lead to the fact that the device will go into protection every time the compressor is turned on.
⚠️ Attention: Using a stabilizer with a power equal to the sum of the rated powers of the refrigerators will lead to overload and failure of the stabilizer itself at the time the compressors start.
Modern inverter models behave differently: they start smoothly, without sudden surges of current, but the sensitivity of their electronics to the quality of the voltage sinusoid is extremely high. For such units, not only the ability to withstand the starting current is important, but also the shape of the output signal, which is provided by the stabilizer. Pure sine wave at the output is required for the correct operation of inverter control boards.
Why does the refrigerator hum at low voltage?
When the network voltage drops below 190 Volts, the engine torque drops. The compressor tries to start or rev up, but cannot overcome the pressure in the system, which causes a characteristic hum and overheating of the windings.
Calculation of the total power for two devices
To determine the required stabilizer power, it is not enough to simply add up the numbers indicated in the refrigerator passports. It is necessary to calculate the total power, measured in Volt-Amps (VA), taking into account the reactive component of the load. The calculation formula is as follows: total power is equal to active power divided by power factor.
Consider a practical example: if you have two refrigerators with a power consumption of 200 W each, and the power factor is 0.6, then the calculation will not start from 400 W. The total active power will be 400 W, but taking into account cos φ = 0.6, the total power will increase to 666 VA. This is only the operating mode, without taking into account inrush currents.
A reserve for inrush currents must be added to the resulting value. If the inrush current factor is 5, then when the compressors are turned on, the load will briefly jump to 3330 VA. However, since compressors rarely turn on at the same time with millisecond precision, a simultaneity factor can be used, but for reliability it is better to count on the worst-case scenario.
It is also important to consider that when the mains voltage is low (e.g. 150-160 Volts) the power that the stabilizer can produce drops. The electronics must compensate for the drawdown by increasing the input current, which limits the actual power delivered. Therefore, in case of strong drawdowns in the network, the power reserve should be even more significant.
Types of stabilizers: relay, electromechanical and inverter
The choice of stabilizer type directly affects the durability of your refrigerators. There are three main types of devices on the market, each of which has its own advantages and disadvantages in the context of working with compressor equipment. Understanding the principle of operation will help you avoid purchasing equipment that can harm equipment.
Relay stabilizers they work on the principle of switching transformer windings using electromagnetic relays. They differ in speed, but have stepwise voltage regulation. When switching stages, short-term breaks in the circuit occur, which can be critical for the electronics of modern refrigerators. In addition, relay clicks can be annoying at night.
Electromechanical (servo-drive) models provide smooth voltage regulation without sinusoid distortion. However, their performance leaves much to be desired: the mechanics simply do not have time to handle sudden voltage surges that are often found in networks. For refrigerators with sensitive electronics, a slow response can be fatal.
- 🔌 Inverter models: Convert the voltage to direct and then back to alternating, providing an ideal sine wave and instant response to changes in the network.
- ⚙️ Thyristor/triac: Quiet operation and high performance, but higher cost and complexity of repair.
- 📉 Ferroresonant: Outdated type, creating strong interference and having low efficiency, not recommended for household appliances.
The best choice for a pair of refrigerators, especially if one of them is inverter, would be thyristor or inverter stabilizers. They guarantee no surges during switching and provide high-quality current. Double energy conversion in inverter models, completely isolates equipment from external network problems.
The influence of starting currents on the choice of equipment
Starting current is the most important parameter that is often ignored when purchasing. When the compressor is turned on, the resistance of the windings is minimal, and the current can reach values 5-8 times higher than the nominal value. For two refrigerators, this creates a situation where the total peak current can be comparable to the short circuit current for weak wiring.
If the stabilizer does not have sufficient overload capacity, it will perceive the inrush current as an emergency and turn off the load. As a result, the refrigerator will not start and the food will begin to defrost. Moreover, frequent attempts to start at low voltage (when the stabilizer tries to compensate for the drawdown) can lead to burnout of the motor starting winding.
⚠️ Attention: It is strictly not recommended to use stabilizers with current protection, which operates faster than the duration of the compressor starting pulse (usually 0.5-1 second).
There are special soft starters that can be integrated into the circuit, but modern high-quality stabilizers already have a switch-on delay function. This delay (usually from 3 to 10 minutes) is necessary so that the pressure in the refrigerator system equalizes after shutdown and the compressor does not start under load.
When calculating the power for two units, one should assume that they can turn on simultaneously after a long power outage. At this moment, the load on the network and the stabilizer will be maximum. The total peak power of two average refrigerators can reach 3-4 kW, which requires the installation of a stabilizer with a capacity of at least 5 kW.
Comparative table of characteristics of stabilizers
To simplify the choice, we will provide a comparative analysis of the various types of devices available on the market. These parameters will help you navigate the technical characteristics and choose a model that is suitable specifically for your pair of refrigerators.
| Parameter | Relay | Electromechanical | Inverter | Thyristor |
|---|---|---|---|---|
| Stabilization accuracy | ±8-10% | ±3% | ±1-2% | ±2-3% |
| Response speed | 10-20 ms | 10-50 ms/V | 0 ms (instantly) | 10-20 ms |
| Signal shape | Stepped | Sine wave | Ideal sine wave | Sine wave |
| Noise during operation | Relay clicks | Motor noise | Silent | Silent |
| Working resource | Average | High (mechanics) | Very high | High |
The table shows that relay models are inferior in accuracy and the shape of the output signal, which is undesirable for modern electronics. Electromechanical ones have a good signal shape, but are slow. The leaders are inverter and thyristor devices, which provide the best protection.
When choosing a specific model, pay attention to the input voltage range. If your network experiences severe drops of up to 140 Volts, a narrow-band stabilizer (150-250 V) will protect it, leaving the refrigerators without power. A wide range (100-280 V) will ensure operation even in extreme conditions.
Connection and installation instructions
Proper installation of the voltage stabilizer is the key to its long service and safety. Connection errors can negate all the benefits of the device or even cause a fire. Before starting work, be sure to de-energize the network by turning off the input circuit breaker.
To connect two refrigerators, it is advisable to use a separate socket group or install the stabilizer permanently on a DIN rail in the panel, if the model allows. If a portable version is used, make sure that the cross-section of the wire from the stabilizer to the socket corresponds to the current load.
☑️ Check before turning on
- Connect the input cable of the stabilizer to the network (or plug it into a socket).
- Connect the refrigerators to the output sockets of the stabilizer.
- Turn on the stabilizer and wait for the time delay to complete (usually the "Delay" indicator is on).
- After clicking the turn-on relay, check the output voltage with a multimeter - it should be within 220-230 V.
- Start the refrigerators and check operation during the first hour.
It is important to ensure good contact at the connection points. Poor contact leads to heating and melting of the insulation. If you use an extension cord, its length should be minimal, and the wire cross-section should be at least 1.5 mm² for copper, and preferably 2.5 mm².
Common mistakes when choosing and using
One of the most common mistakes is buying a stabilizer “butt-to-peak” in terms of power. Users look at the 200 W rating and buy a 500 W device, forgetting about inrush currents and power drawdown at low input voltage. Such a stabilizer will work at the limit, get very hot and quickly fail.
Another mistake is ignoring the temperature regime. Stabilizers have an operating temperature range, usually from +5 to +40 degrees. Installation in an unheated garage or on a balcony in winter can lead to condensation inside the case and a short circuit. Condensation is the main enemy of electronics.
⚠️ Attention: Do not cover the operating stabilizer with fabric or interior items. Violation of heat exchange will lead to overheating and automatic shutdown due to thermal protection.
Grounding is also often forgotten. The use of sockets without grounding (Euro) reduces the effectiveness of protection and can be dangerous to humans if the insulation breaks down. Make sure that your wiring complies with modern safety standards.
Is it possible to use one stabilizer for the entire apartment?
Technically, it is possible if its power is enough for all devices. However, to protect refrigerators specifically, it is more profitable and effective to install a separate powerful stabilizer than to buy an expensive industrial device for the whole house.
Conclusion and final recommendations
Choosing a stabilizer for two refrigerators requires a careful approach to calculating peak loads. The main criterion is the ability of the device to withstand a short-term seven-fold inrush current without going into protection. The optimal solution would be thyristor or inverter models with a power reserve of at least 30-50%.
Do not skimp on the quality of protection, since repairing or replacing two compressors will cost much more than buying a good stabilizer. Properly selected equipment will ensure stable operation of the equipment for many years, preserving your products and nerves.
Remember that electrical conditions may change, so periodically check the voltage in the outlet using a multimeter. If you notice an increase in jumps or humming of equipment, this is a signal to diagnose the energy supply system.
How many kilowatts are needed for two refrigerators?
For two medium-sized refrigerators, the total operating power is about 0.4-0.5 kW. However, taking into account the starting currents and reserve, the power of the stabilizer should be at least 3-4 kW (3000-4000 VA).
Is a stabilizer needed for an inverter refrigerator?
Yes, it is. Inverter technology is extremely sensitive to the quality of the voltage and the shape of the sinusoid. Voltage surges can damage an expensive control board, the repair of which is often unprofitable.
Why does the stabilizer click when the refrigerator is running?
Clicks are produced by the relay, switching the transformer windings to adjust the voltage. This is normal for relay models. If the clicks are too frequent, there may be strong surges in the network or the stabilizer is selected incorrectly.
Is it possible to put one stabilizer on a refrigerator and a TV?
Technically, it is possible if the total power allows it. However, TVs create interference and refrigerators cause trigger surges. It is better to separate sensitive electronics and powerful inductive loads for maximum reliability.