Starting a refrigeration unit is always the moment of maximum load on the electrical network of an apartment or house. In this split second, when the motor rotor is still stationary and the windings are already energized, a sharp jump in energy consumption occurs. It is this parameter, known as the starting current, that often causes machines to break out, lights to flicker, or weak inverters to fail.
Understanding the nature of this phenomenon is necessary not only for engineers, but also for ordinary users who want to extend the life of their equipment. Rated power, indicated on the nameplate, can be 150-200 W, but at the moment of start the consumption is short-term increases by 3, 5, and sometimes 7 times. If you do not take this factor into account when selecting stabilizers or UPSs, the equipment may simply not start.
In this article we will analyze in detail the physics of the process, consider typical values for different types of motors and find out how to correctly calculate the required power of protective equipment. We will also touch on the question of why starting currents they can increase over time and what this says about the technical condition of your refrigerator.
Physics of the process: why a voltage surge occurs
The operation of the compressor is based on an electric motor, most often an asynchronous type. The moment you hear the relay click and power is applied, the motor rotor is at rest. To move it from its place and overcome the inertia, as well as the freon pressure in the system, a colossal effort is required. The electrical equivalent of this force is current.
According to the laws of electrical engineering, at the initial moment of rotation the resistance of the windings is minimal, since it has not yet arise Self-induction EMFwhich limits the current in operating mode. In fact, in the first milliseconds the motor is almost a short circuit. The voltage in the network may “sag” for a short time, which is visually manifested as blinking of incandescent lamps.
⚠️ Attention: Frequent voltage surges when the compressor starts can negatively affect other sensitive electronics in the house, for example, computer power supplies or audio systems.
The duration of this process is usually from 0.5 to 2 seconds. During this time, the rotor gains operating speed, a back-EMF appears in the system, and consumption drops to nominal values. If this process is delayed, a thermal protection relay comes into play, turning off the motor to avoid overheating of the windings.
The influence of temperature on start-up
At low ambient temperatures, the viscosity of the oil in the compressor increases. This creates additional mechanical resistance, due to which the starting current may be higher than usual, and the engine acceleration time may be longer.
Typical values of starting currents for different models
The magnitude of the jump directly depends on the power of the engine and its design. Middle-class household refrigerators are characterized by certain ranges of values. It is important to distinguish between single-phase motors with a starting winding and more modern inverter models, where the starting processes are smoothed electronically.
The table below shows average data for common types of compressors. Please note that actual indicators may differ depending on the manufacturer and the specific year of manufacture unit.
| Compressor type | Rated power (W) | Starting current (A) | Multiplicity excess |
|---|---|---|---|
| Single-phase (old type) | 100 - 140 | 15 - 25 | 5-7 times |
| Single-phase (modern) | 120 - 180 | 10 - 18 | 4-5 times |
| Inverter | 80 - 150 | 2 - 5 | 1.2-1.5 times |
| Two-compressor (in total) | 200 - 300 | 20 - 35 | Depends on synchronization |
As can be seen from the data, classic models create the greatest load. That is why in old houses with aluminum wiring, the simultaneous start of a refrigerator and, for example, a washing machine could lead to heating of the contacts in the sockets. Modern energy efficient models often do not have this drawback thanks to the use of inverter technologies.
Calculation of power for generators and UPS
If you plan to use the refrigerator in conditions of unstable power supply, in a country house or in a motorhome, the question of selecting an uninterruptible power supply (UPS) or generator becomes critical. Many people make the mistake of summing up only the rated power of devices, forgetting about starting loads.
For a correct calculation, you need to know not only watts, but also amperes. The formula is simple: we multiply the power of the device by the starting current coefficient (usually we take 3 or 4 for reserve). For example, for a 200 W compressor with a factor of 4, the required generator power will be 800 W. However, this is only active power.
It is important to consider the total power in Volt-Amperes (VA), since motors have low power factor (cos φ). For electric motors it is often 0.6–0.8. Therefore, the UPS must be selected with a margin of at least 30-40% of the calculated peak power.
Problems with wiring and automatic protection
High starting current is stressful not only for the compressor itself, but also for the entire home electrical network. Loose contacts in sockets, old circuit breakers and thin wires may not withstand regular surges. Over time, this leads to oxidation of the contacts and heating.
If the circuit breaker trips exactly at the moment the refrigerator relay clicks, this is a sure sign that its rating is incorrectly selected or the wiring is in poor condition. Often in old panels there are 6A or 10A circuit breakers, which physically cannot pass the starting current of a modern powerful compressor without false operation.
It is also worth remembering the phenomenon of “false start”. If the mains voltage drops below a critical level, the engine may try to start, fail to turn the shaft all the way, and stop again. Repeated attempts to start with high current can quickly damage starting relay or burn the winding.
☑️ Checking the condition of the wiring
Diagnostics of faults based on consumption current
Measuring current is one of the most accurate ways to diagnose the condition of the compressor. For this purpose, a clamp meter device is used. It is considered normal if the starting current exceeds the operating current by 3-5 times and drops quickly. If the current remains high or drops very slowly, this is a signal of mechanical problems.
High starting current may indicate a jammed piston group, thickened oil, or problems with the electrical part of the engine, for example, an interturn short circuit. In such cases, the protection relay may not have time to operate, and the windings burn out. It is also worth checking capacitorif it is provided for in the design, since its malfunction changes the phase and increases the load.
⚠️ Attention: Measurements with current clamps should be taken with caution. Do not touch exposed live wires and make sure that the device is designed for the current range being measured.
If you notice that the light in the apartment began to dim more than usual when starting the refrigerator, this may indicate degradation of the motor. Over time, wear of rubbing parts increases resistance, requiring more current to start. In such a situation, it is better to think about replacing the unit before it starts a fire in the panel.
Ways to reduce starting loads
There are technical solutions to soften the blow to the network. The most common method is the use of soft start devices. They gradually increase the voltage on the motor windings, allowing the rotor to spin up without a sudden surge of current.
However, for domestic refrigerators, the installation of such devices requires intervention in the electrical circuit, which may violate the warranty. A simpler way is to stagger the switching on of powerful consumers in time. Some modern Smart Home systems can monitor the startup of the refrigerator and temporarily turn off less important appliances, for example, a boiler.
Also an effective solution is to install a separate wiring line for the refrigerator, coming directly from the panel, using a copper cable with a cross-section of at least 2.5 mm². This minimizes the voltage drop and reduces the risks for the rest of the equipment.
Is it possible to use a stabilizer?
Yes, but its power should be designed specifically for the starting current, and not at the nominal value. A conventional 1 kVA stabilizer may not be able to start up if its peak power is limited.
Frequently asked questions (FAQ)
Why does the refrigerator hum and click, but does not start?
Most likely, the starting current is not enough to turn the shaft due to low voltage in the network or faulty start relay. It is also possible for the compressor to jam.
Is frequent starting and stopping harmful to the compressor?
Yes, every start is mechanical and thermal stress. The optimal work cycle involves working for 10-15 minutes and resting for the same amount of time as working. Frequent switching on indicates problems with the thermostat or a freon leak.
Can the inrush current damage the TV?
If there is a sharp jump in consumption by the refrigerator, a short-term voltage drop may occur in the entire network. If the wiring is weak, this can cause sensitive electronics to overload, but rarely leads to breakdowns unless there are serious network failures.
How can I find out the exact starting current of my model?
The exact data is only available in the manufacturer's technical documentation. In practice, they use the calculation method: they multiply the rated current indicated on the nameplate by a factor of 3-5.