Starting the compressor is the most energy-intensive moment in the operating cycle of the refrigeration unit. It is in this split second that maximum electricity consumption occurs, which often raises questions among owners of household appliances when trying to connect a refrigerator through a generator, UPS or weak voltage stabilizer. Understanding the nature of this phenomenon is necessary for the correct selection of protective equipment that can withstand a short-term but powerful load without shutting down.
Many users mistakenly focus only on the rated power indicated on the nameplate, forgetting that at the moment of starting the engine requires significantly more energy to overcome inertia and create pressure in the system. If you ignore this factor, you may encounter constant knockouts or, worse, failure of the compressor itself due to a voltage drop. In this article we will analyze the physical basis of the process, methods for calculating the necessary parameters and methods for accurately measuring them.
Physics of the process and the difference from rated power
The operation of the refrigerator is based on an asynchronous motor, which has a unique characteristic: at the moment of switching on, the rotor is at rest. To move it and start compression of the refrigerant, it is necessary to create a powerful magnetic field that consumes colossal current. This value, known as inrush current, can exceed the rated operating indicators by 3, 5, and sometimes 7 times.
The duration of this peak is extremely short and usually ranges from 0.3 to 1.5 seconds. During this time, the power grid experiences a short-term shock. If the equipment used (for example, a generator) does not have a power reserve or a system for compensating inrush currents, the voltage in the network drops sharply. For the compressor itself, low voltage at startup is dangerous because it may not pick up speed and burn out due to overheating of the windings.
⚠️ Attention: Constant unsuccessful startup attempts due to lack of power from the current source lead to rapid destruction of the starting relay and melting of the contacts, which is a common cause of breakdown of refrigerators when operating from autonomous power sources.
It is important to distinguish between the active and reactive components of power. The passport data of the refrigerator most often indicates the active power in Watts, which characterizes the useful cooling work. However, to calculate the network load, the total power must be taken into account, especially if an inductive load is used, which includes electric motors. The power factor (cos φ) of compressors is usually in the range of 0.6–0.8, which requires an increase in the calculated power of the power source.
Calculation methods starting current according to passport data
The most accessible way to find out the approximate value of the starting current is to use the data indicated on the factory tag or in the technical documentation of the device. There is always a sticker with markings on the back wall of the refrigerator or inside the chamber. We are interested in the parameter rated current or power (Power/Rated Power).
If only the current is indicated on the nameplate (for example, 1.0 A), then an empirical coefficient is used to obtain the starting value. For middle-class household compressors, a multiplicity factor of 5 is accepted. Thus, with an operating current of 1 Ampere, the starting current will be about 5 Amperes. If the power is indicated in Watts, the calculation is made using the formula: Current = Power / Mains voltage (220V), and the resulting result is also multiplied by 5.
However, it is worth considering that modern inverter models LG or Samsung work on a different principle. Their starting current is smoothed out electronically and can exceed the operating current by only 1.2–1.5 times. Therefore, for an accurate calculation, it is critical to know the type of compressor: classic piston or inverter.
Let's consider approximate values for different classes of equipment:
- 🧊 Small refrigerators (volume up to 150 l): operating current 0.5–0.8 A, starting current up to 4 A.
- ❄️ Medium two-chamber models: operating current 1.0–1.5 A, starting current up to 7.5 A.
- 🏭 Powerful units No Frost: operating current 1.8–2.5 A, starting current can reach 12–15 A.
Accurate measurements using current clamps
Calculated data are often averaged, since wear of the mechanism, ambient temperature and network voltage make their own adjustments. The only way to obtain reliable information is to carry out instrumental measurements. For this, they use current clamps a device that allows you to measure the current strength without breaking the circuit.
The measurement process requires caution, since the work is carried out with high voltage. The clamps are closed around one of the power wires (phase or neutral) immediately when the refrigerator is turned on to the network. It is important to catch exactly the starting moment, so it is better to carry out measurements together: one person plugs the plug into the socket, and the second records the maximum value on the device screen.
Sequence of actions:1. Set the clamp switch to ACA (alternating current) mode.
2. Select the maximum range (usually 20A or 100A).
3. Open the “sponges” of the pliers and grasp one wire of the power cord.
4. Connect the refrigerator to the network and record the peak value.
The resulting value will be the real starting current for a specific piece of equipment. If the clamp readings go off scale or the device does not have time to detect the peak, you can use an oscilloscope with a current shunt, but this is the domain of professional service centers. It is also worth remembering that old analog clamps can give an error on short pulses, so digital models with the function Inrush Current are preferable.
☑️ Checking readiness for measurements
The influence of the type of compressor on starting characteristics
The type of installed engine radically changes the approach to calculating loads. Classic piston compressors, which can be found in models Indesit, Atlant or old Bosch, have a rigid mechanical connection and require instantaneous application of force. It is they that produce the highest starting currents and the characteristic click of the starting relay.
In contrast to them, inverter systems, widely used in technology Electrolux and Haierstart smoothly. The electronic control unit gradually increases the shaft rotation speed, so there is practically no current surge as such. This makes them more friendly to weak power grids and autonomous generators.
There are also linear compressors used in premium models. LG. They operate on the principle of linear piston movement without rotating elements. Their starting characteristics occupy an intermediate position: they are softer than those of the classics, but tougher than those of full-fledged inverters with frequency conversion.
⚠️ Attention: Technical characteristics and operating algorithms of compressors may vary depending on the specific series and year of manufacture. Before purchasing expensive equipment for power backup, check the data in the official user manual of your model.
Table: Comparative characteristics of various models
For ease of comparison, we present average data for popular categories of refrigerators. These figures will help you navigate the initial planning of the electrical network.
| Equipment category | Operating current (A) | Starting current (A) | Recommended power reserve |
|---|---|---|---|
| Mini refrigerator (office) | 0.4 - 0.6 | 2.0 - 3.0 | 500 W |
| Standard two-chamber | 1.0 - 1.4 | 5.0 - 7.0 | 1500 W |
| Freezer (chest) | 1.2 - 1.8 | 6.0 - 9.0 | 2000 W |
| Side-by-Side (American) | 2.0 - 2.8 | 10.0 - 14.0 | 3000 W |
| Inverter model (any) | 0.8 - 2.5 | 1.5 - 3.0 | 800 W |
Selection stabilizer and generator, taking into account starting currents
When choosing a backup power source or stabilizer, the key parameter is not so much constant power as the ability to withstand short-term overload. Many cheap stabilizers have protection that operates faster than the compressor can start, turning off the refrigerator.
For generators, it is important to take into account the power reserve. If you plan to run the refrigerator from a gasoline generator, its rated power should be 3-4 times higher than the refrigerator's consumption. For example, for a unit with a consumption of 200 W, a generator of at least 0.8–1 kW is needed. Gas and inverter generators often tolerate sudden load surges worse than their classic gasoline counterparts.
It is also worth paying attention to the shape of the output voltage. A pure sine wave is required for electronically controlled compressors and inverter models. For older engines with a starting winding, an approximated sine wave is allowed, but a pure one is still preferable to extend service life.
Why does the refrigerator hum when operating from a generator?
If, when operating from a generator, the refrigerator makes an unusually loud hum or hum, this may indicate a low quality sinusoid of current or insufficient rotation speed of the generator engine shaft. Under such conditions, the efficiency of the compressor decreases, and the heating of the windings increases.
Frequent problems and ways to solve them
If you are faced with the fact that the refrigerator does not start from an autonomous source, although the calculations seem to be correct, check the condition of the start relay. An old relay may become stuck, increasing the time it takes for the inrush current to flow, causing the generator protection to trip. Replacing the relay is an inexpensive procedure that often solves the problem.
Another reason could be low line voltage before startup. If the voltage drops below 170-180 Volts when the compressor is turned on, the engine will not be able to develop the required torque. In this case, installing stabilizer with a switch-on delay function or using a soft starter will help.
Do not forget about the temperature factor. Starting a “hot” compressor (immediately after defrosting or sitting for a long time in a warm place) requires more energy than starting a cold engine. Allow the equipment to cool to room temperature before connecting to a weak power source.
Is it possible to connect a refrigerator through a regular UPS for a computer?
Conventional computer UPSs produce a square wave or an approximate sinusoid at the output, which is absolutely not suitable for electric motors. This will cause the compressor to overheat and hum. You need a UPS with a pure sine wave (On-Line or Line-Interactive with sine).
Why does the machine knock out when you turn on the refrigerator?
Most likely, the rating of the machine is too low for the starting current. If the machine is type “C” (standard), it can withstand 5-fold overload. If it is set to type “B”, it can even operate on operating current. Try replacing the machine with a type “C” or “D”, but only if the wiring allows it.
Does the length of the extension cord affect the starting current?
Yes, a long and thin wire creates additional resistance, causing a voltage drop at the input to the refrigerator. This forces the motor to consume even more current to compensate for the loss of power, which can lead to protection tripping or burnout of the windings.
How to find out the power without documentation if the nameplate has been erased?
You can use current clamps in operating mode (not starting), measuring the operating current, and multiplying it by 220. Multiply the resulting power by 5 for launch rating. You can also find the compressor model by marking on the unit itself (usually a white barrel on the back) and find its passport on the Internet.
Is the starting current dangerous for wiring in the house?
For serviceable wiring designed for standard loads (16A sockets), the short-term starting current of the refrigerator is absolutely safe. The danger arises only when using low-quality twists, oxidized contacts or too thin extension cords that may not withstand heat.