A modern refrigerator is not just a box with cold, but a complex electrical appliance that is sensitive to the quality of the power supply. In conditions of unstable power supply, when the voltage fluctuates and the light can go out at the most inopportune moment, uninterruptible power supply becomes not a luxury, but a necessity. Turning off the compressor even for a few minutes can lead to defrosting of food and loss of an expensive supply of food.
However, you won’t be able to simply buy the first device you come across to protect your computer. Refrigeration equipment has a unique feature - the starting current of the compressor can exceed the rated current by 5-7 times, which requires the UPS to be able to withstand short-term overloads. If you choose a device with insufficient power reserve, it will go into protection or burn out along with the refrigerator electronics when you first start the engine.
In this article we will look at how to correctly calculate the required power, why the shape of the output signal is important and what type of UPS will ensure maximum safety of your equipment. You will learn how different device topologies differ and what characteristics you need to look at first when purchasing.
Why is a refrigerator sensitive to voltage surges
The electronics of modern refrigerators, including inverter models, are extremely sensitive to the quality of electric current. Power surges in the network can lead to failure control unit, which is the “brain” of the device. Repairing such a module often costs more than the cost of a high-quality uninterruptible power supply.
In addition, low voltage in the network forces the compressor to work with increased load, trying to gain the required power. This leads to overheating of the motor windings and a reduction in the service life of the unit. Inverter compressors, which smoothly regulate the rotation speed, are especially demanding on the stability of the frequency and shape of the sinusoid.
Another critical point is frequent power outages. If there is a short-term loss of voltage, the compressor turns off, but the pressure in the system does not yet have time to equalize. If the light turns on at this moment, the engine will try to start under load, which can lead to jamming of the piston group or burnout of the start relay.
⚠️ Attention: After a power outage, do not immediately plug in the refrigerator. Let it sit unplugged for 5-10 minutes to allow the pressure in the refrigerant system to equalize. A UPS with a turn-on delay function solves this problem automatically.
Using a UPS allows you to smooth out all these negative factors. The device not only gives time to preserve the cold, but also acts as a stabilizer, filtering interference and equalizing the voltage to standard values.
Calculation of power: rated and starting
The most common mistake when choosing equipment is focusing only on the rated power indicated in the refrigerator's passport. On the sticker on the back of the device you can see a value, for example, 150-200 W. However, this is only the energy consumed in the temperature maintenance mode.
At the moment the compressor electric motor starts, a sharp jump in energy consumption occurs. Starting current can be several times higher than the operating one. For older models with piston compressors, this coefficient can reach 7, and for modern ones - 3-5. It is this short-term peak that the selected UPS must withstand.
How to find out the starting current?
If the documentation does not indicate the starting current, use the average factor of 5. Multiply the rated power of the refrigerator by 5 - this will be the minimum peak power that the UPS must withstand without going into overload.
To calculate the required power of the UPS, use the following formula: the rated power of the refrigerator is multiplied by the starting current coefficient. For example, for a 200 W refrigerator, the calculation would look like this: 200 W × 5 = 1000 W. This means that you need a UPS with a short-term overload capability of up to 1 kW.
It is also worth considering the active and reactive components of power. Refrigerator motors are inductive loads, so total power is measured in Volt Amperes (VA) rather than Watts. The power factor (cos φ) is usually 0.6-0.7. To obtain the required power in VA, divide the calculated active power by this coefficient.
Below is a table with an approximate calculation of power for various types of refrigerators:
| Refrigerator type | Rated power (W) | Coefficient. starting current | Required peak power (W) | Recommended UPS power (VA) |
|---|---|---|---|---|
| Single chamber (old) | 150 | 7 | 1050 | 1500-2000 |
| Double chamber (modern) | 200 | 5 | 1000 | 1500 |
| Side-by-Side | 300 | 4 | 1200 | 2000 |
| Inverter | 100 | 2 | 200 | 600-800 |
UPS types: which one to choose for a refrigerator
There are three main types of uninterruptible power supplies on the market, and each of them interacts differently with refrigeration equipment. Understanding the difference between them will help you avoid buying the wrong device.
Off-line (backup) UPS - the cheapest and simplest. They pass mains voltage directly to the consumer and switch to batteries only when the current completely disappears. They are not suitable for refrigerators, as they do not stabilize the voltage and have a long switching time, which can lead to a reboot of the electronics.
Line-interactive (line-interactive) models are equipped with a built-in voltage stabilizer. They adjust the voltage within a certain range without switching to batteries, which saves battery life. This is the optimal choice for most household refrigerators in conditions of an unstable, but not critically poor network.
On-line (double conversion) —the most advanced, but also expensive type. They continually convert AC to DC and then back to AC, producing a perfect sine wave output. Such devices are ideal for expensive inverter refrigerators and server cabinets, but have lower efficiency and are noisy due to constantly running fans.
When choosing, also pay attention to the shape of the output signal. For AC motors it is critical pure sine wave. Models that produce an approximate sine wave (stepped) can cause compressor hum, overheating and shortened equipment life.
Battery life and battery capacity
One of the main questions: how long should a refrigerator run on batteries? It is important to understand the physics of the process here. The refrigerator does not consume energy constantly; it turns on cyclically. In normal mode, the compressor works about 30% of the time (coefficient 0.3), the rest of the time it “rests”, maintaining the cold.
This means that an average power UPS can maintain the temperature in the refrigerator much longer than it seems at first glance. For example, a device with batteries designed for 10 minutes of operation under full load will, in reality, provide cold storage for 30-40 minutes of real time.
If your goal is to wait out short-term outages (15-30 minutes) and protect equipment from surges, a standard UPS configuration is sufficient. If the light disappears on the clock, you will need a model with the ability to connect external battery packs.
⚠️ Attention: Increasing the battery capacity proportionally increases the operating time, but also increases the charging time. Make sure that the UPS charging current can handle the capacity of the connected batteries, otherwise they may not have time to charge before the next shutdown.
When calculating the time, take into account the ambient temperature. In the summer, when the room is hot, the refrigerator turns on more often and battery life is reduced. In winter, on the contrary, the intervals between compressor starts increase.
Delay Start function
One of the most useful UPS functions for refrigerators is the load turn-on delay timer. As mentioned earlier, the compressor needs time (usually 5-10 minutes) after stopping for the pressure in the refrigerant system to equalize.
If the electricity blinked and disappeared for 2 seconds, and then appeared again, a conventional UPS will immediately supply voltage to the refrigerator. The compressor will try to start against high pressure, which puts extreme stress on the mechanics. The function Delay Start artificially pauses before applying voltage, simulating manual waiting.
This function should be configured through the control panel or software, if provided. Usually it is enough to set a delay of 180-300 seconds. This is especially true for areas with “flashing” lights, when the voltage either disappears or appears with a high frequency.
Some UPS models have this function by default, in others it may require activation. Check the availability of this option in the specifications before purchasing, especially if you live in a private sector or an area with these networks.
Installation and operating rules
Proper installation of the UPS will extend its service life and ensure safety. The device must be located in a dry, ventilated area. The UPS has lead-acid batteries built into it, which, when overheated (above 25-30°C), sharply lose their capacity and service life.
It is not recommended to place the UPS directly behind the refrigerator, where the heat exchanger emits heat, or in a niche without air access. Also avoid direct sunlight and sources of moisture. The optimal place is on the floor next to the outlet or on a special shelf.
☑️ Check before connecting
The connection must be made into a socket with mandatory grounding. The absence of “ground” can lead to the accumulation of a static charge on the refrigerator body and incorrect operation of the control electronics. If the house has old wiring without grounding, consider organizing a local grounding loop for equipment.
Regularly, at least once every six months, check the functionality of the system. To do this, you can briefly turn off the input circuit breaker in the panel (or unplug the UPS cord from the socket) and make sure that the refrigerator continues to work and the device emits an alarm signal.
Frequently asked questions (FAQ)
Is it possible to use a car battery for a refrigerator UPS?
Technically possible if the UPS supports external batteries and has the appropriate charging current. However, car starter batteries (STarter) are not designed for long-term energy output (Deep Cycle) and will quickly fail in UPS mode. It is better to use specialized gel or AGM batteries.
Will the refrigerator hum when operating from a UPS?
If the UPS produces a pure sine wave, there will be no hum. If the signal shape is approximated (stepped), the engine may produce a characteristic low-frequency hum and heat up. For refrigerators with an inverter compressor, a pure sine wave is required.
Will the UPS work if I also include a TV in it?
Yes, if the total power of the refrigerator and TV (including starting currents) does not exceed the maximum power of the UPS. However, it is worth remembering that adding other appliances will reduce the battery life of the refrigerator. It is better to power the refrigerator separately from the UPS.
How often do you need to change the batteries in the UPS?
The average service life of lead-acid batteries in a UPS is 3-5 years, depending on operating conditions and the number of discharge cycles. If the UPS stops holding the load even for a couple of minutes, it’s time to change the batteries.
Do you need a UPS for a new refrigerator with surge protection?
Built-in protection in modern refrigerators is often represented by a simple varistor or relay, which save electronics from burning out, but do not save food when the lights are turned off. The UPS ensures continuity of operation, which is critical for the safety of food.