Uninterruptible power supply: purpose and specifics of operation of a household UPS
To maintain the functionality of devices during network failures, an uninterruptible power supply is used.Depending on the type of consumers served and power parameters, you need to choose different models. These devices are in demand, so purchasing a copy with the required characteristics is not difficult.
But before buying, you need to understand its features yourself, and not trust this issue to managers interested in sales.
In this material we will look at the design and operating features of the UPS, and also talk about the rules for its use.
The content of the article:
AC UPS Circuits
For domestic needs, uninterruptible power supply devices are used, connected to a single-phase 220 V network, which can supply consumers requiring the same voltage for some time in the absence of electricity.
There are also UPSs that are connected to the input to a three-phase network, and the output is either 380 V or 220 V. However, they are expensive, they are used when it is necessary to obtain autonomous power from 10 kVA A, which is not required for domestic needs.
Household AC UPSs are divided into the following types according to their operating scheme:
- backup (offline);
- interactive (linear-interactive);
- double conversion (online).
They differ in the quality of the output voltage and price.The cheapest ones are standby ones, and the most expensive ones are double conversion ones.
To convert alternating current to direct current, a rectifier is used in the charger. And the reverse transformation occurs using an inverter.
In uninterruptible power supply systems, ordinary electromechanical relays are usually installed to switch the circuit from the network to the battery. If this part is of high quality, then its resource is enough for the entire operation of the UPS. But most often, when a block breaks down, the problem lies precisely in this structural element.
Voltage stabilization is also present in many household devices, so if the deviations are insignificant, then there is no point in purchasing a more expensive linear-interactive model.
The presence of a transformer often forces the manufacturer to use forced cooling, which is why such UPSs are equipped with coolers. They emit noise comparable in intensity to the operation of a computer system unit.
The most complex and expensive double conversion devices also have the lowest efficiency. Electricity is lost into heat, which the device emits. Therefore, their use must be justified.
The most significant advantage of this type of uninterruptible power supply is the instant response to a power outage. But for most household appliances this is not so important. The same computers are usually equipped with a backup or interactive UPS.
The most important parameters
Now there are many offers on the market for the sale of household uninterruptible power supplies. In order to correctly determine their purpose and not make a mistake with the choice, you need to understand what parameters you should pay attention to first.
Main technical characteristics
The output power of the device determines the maximum permissible value that the unit can reliably provide to the consumer. It is measured in volt-amperes (VA). For the convenience of users, this value is often given and in watts.
To measure the load of devices, you can either use an ammeter or calculate it using the readings of a meter installed in the apartment.
When determining the real power of a computer, you should not be guided by the rating of the power supply, since it is always purchased with a reserve.
If you do not have an ammeter, then you need to do the following:
- Disconnect all circuits in the panel except the one that powers the computer.
- Turn off all devices in this circuit.
- Turn on the computer and run a typical program on it (for example, a video from YouTube).
- Wait until the meter changes the value of a tenth of a kilowatt.
- Time until the next change.
Average power consumption (P, watt) for this period (t, minutes) can be calculated using the formula:
P = 100 * (60 / t)
The next important characteristic is the battery life. This indicator depends on the load that the UPS is experiencing at that moment. At the maximum permissible power, the batteries of a household device operate for 1-3 minutes. And at half - much longer (up to 10 minutes).
This leads to two conclusions:
- during a power outage, it is necessary to reduce the load consumed by the devices as much as possible;
- It is advisable to purchase a UPS with a power that exceeds the calculated one by at least 30%.
The input voltage range shows the minimum and maximum permissible network voltage at which power will not be switched to the batteries. As a rule, all UPSs can withstand a range of 180-260 V.
Some manufacturers have very good (advertising) indicators, for example, the lower value is 110 V. Here you need to make sure that these numbers are taken specifically for the maximum load, and not for half.
Another important technical indicator is the noise level. UPSs made using line-interactive or online technology generate a lot of heat, so manufacturers install fans on them. If the coolers are cheap, then over time they will make a noise, which is undesirable for a living space.
Interface and setup
The appearance of blocks can be very diverse. They usually have a classic rectangular shape, with indicators or a display on the front side, and power connectors on the back. Their number is not so important, since an extension cord with a tee can be connected to the output.This will not contradict the UPS concept in any way.
The model may have an LCD display, which will display the situation with the supply of connected devices: availability of power, number of consumers, battery charge, etc.
To find out the power supply parameters, the condition of the UPS batteries and how it works, you can connect it to a computer. For many models this function has been implemented and software has been developed.
There are three main types of interface:
- USB. The most common connection between a computer and a UPS.
- RS-232 (COM port). Rarely present in household models.
- Ethernet 10/100. It is used for remote control of uninterruptible power supply.
The software for obtaining characteristics from the UPS and its management is developed not only for various versions of Windows. For example, the well-known manufacturer Powercom has an Android version of the software that allows you to remotely monitor the power status and, if necessary, adjust the operation of the uninterruptible power supply.
Uninterruptible power supplies are placed in close proximity to protected electricity consumers. They are usually placed on the floor or on shelves. Some models are equipped with fasteners that allow them to be mounted on walls.
Quality of output current
Uninterruptible power supplies must provide current of adequate quality.When operating on batteries, the inverter is responsible for this, and in the case of mains power, the problem areas should be smoothed out by filters and a stabilizer. Interference occurring in an electrical circuit has different origins and consequences for electronics. Therefore, this issue also needs to be carefully examined.
Network interference and protection
All modern UPSs are equipped with protection against problems associated with the devices being serviced. If the total load exceeds the maximum permissible or a short circuit occurs, the uninterruptible power supply will immediately turn off the power.
Interference in the network can be divided into frequency and pulse. The former are not so dangerous, especially for computer or TV power supplies that convert alternating current to direct current. The latter can cause problems with any electronics.
Therefore, most UPSs are equipped with surge and harmonic protection using varistors and high-frequency filters.
The problem of the appearance of high-voltage pulses is typical not only for power cables, but also for data transmission networks - computer or telephone. They can occur due to exposure to atmospheric electricity, breakdowns of nearby wiring, electrical interference and other reasons.
Many manufacturers produce models with the ability to protect a local network. For this, the UPS has two RJ-45 connector - one for entry and one for exit. The signal passes through a filter that suppresses voltage surges. For telephone lines, the system is the same, only the connectors are in RJ-11 format.
Low and high voltage
Voltage adjustment occurs using an automatic voltage regulator (AVR), the main element of which is an autotransformer. The principle of its operation is based on changing the number of turns of one of the windings, as a result of which the voltage changes towards increasing or decreasing its value.
The presence of AVR in the UPS allows you not to turn on the autonomous mode every time if the voltage deviates slightly from the standard values. This significantly increases the battery life.
According to GOST 29322-2014, a 10 percent voltage deviation from the reference value is allowed for a period of no more than 1 hour. All modern UPSs with regulators cope with such fluctuations.
Output Purity
The type of output signal depends on the model of the inverter that is installed in the uninterruptible power supply. Ideally, the AC voltage waveform should be a sine wave. But after conversion through an inverter, it takes on a stepped form.
For equipment that contains asynchronous electric motors (refrigerator, air conditioner), transformer power supplies (high-quality audio equipment), APFC power supplies (servers and powerful computing computers) you need a pure or well-approximated sine wave.
Not a single inverter, and therefore any UPS, produces a pure sine wave, no matter what equipment manufacturers write in advertising brochures. The approximation of the output signal to a sinusoid is assessed through the total harmonic distortion (THD).
The signal output from the unit can be considered sinusoidal at THD<5%. For some models, such as IMV NetPro 2000, this figure is only 2%.
Rules for using UPS
When purchasing an uninterruptible power supply to organize backup power, you need to understand which devices it can be used with. Sometimes it is impossible to get by with just a UPS and then you need to take additional measures to provide your home with electricity.
Connecting household appliances
Computers, modems, routers, video and audio equipment are typical home or office devices to which uninterruptible power supplies are connected. If this technique contains ordinary switching power supplies, then it will be enough to purchase relatively cheap models that do not produce a pure sine wave.
There is also no need to purchase expensive products for lighting. The main thing here is to correctly calculate the maximum power and battery life.
With frequent outages, the problem of unplanned defrosting of refrigerators and food spoilage is relevant. When protecting such equipment with asynchronous motors, UPSs of a more complex design will be needed, since a “pure” sinusoidal signal will be required.
In addition, it is necessary to take into account the presence of starting currents that arise when starting the engine.Simplified for refrigeration equipment, their value can be determined by multiplying the power value by 5.
If, for example, the kitchen has a refrigerator with a total power of 300 W (at startup - 1500 W) and a freezer at 200 W (at startup - 1000 W), then you need a power supply with a pure sine wave and a maximum power of at least 1700 W. This value was obtained for the case when the freezer is working, and at this time the refrigerator is turned on. The simultaneous start of both motors is unlikely, and such a UPS will withstand a one-second surge of 2.7 kW.
An online type unit with a maximum power of 2000 W can operate for about half an hour with a total consumption of 500 W. Since the cooling mode takes about 5 minutes, the uninterruptible power supply is guaranteed to be enough for 6 starts of both devices.
Uninterruptible power supply systems are also actively used for work gas heating boilers. Considering the cost of the connected equipment, you should not skimp on the quality of the UPS in this case.
Backup and additional power supply
For many household appliances it is impossible to select an inexpensive UPS, since significant maximum power will be required with a long period of autonomous operation. Washing machines, electric ovens, and distributed air conditioning systems consume a lot of electricity.
You can, of course, do without these devices during a power outage. This is advisable if such interruptions occur rarely and for a short time.But if a decision is made to provide powerful consumers with autonomous power, then it is better to use a gasoline or diesel generator. To quickly start them in the absence of voltage, an automatic transfer system (ATS) is used.
If you have an additional power source, a UPS is still worth using, at least for computers. It is impossible to achieve instant start of the generator and restoration of power supply.
Low voltage stabilization
The problem of low voltage is relevant for facilities connected to old or low-power electrical networks. If this situation occurs constantly, then it is better to use the input stabilizer.
When the voltage is reduced, the current flowing through the intra-house network increases. For example, let the total power of consumers connected to the UPS be 1.5 kW, and the supplied voltage be 190 V.
Then by Ohm's law:
- I1 = 1500 / 190 = 7.9 A – current in the circuit up to the UPS without a stabilizer;
- I2 = 1500 / 220 = 6.8 A – current strength in the circuit up to the UPS with a stabilizer.
Thus, an intra-house network without a stabilizer will experience increased load, which may not have been taken into account when choosing the wiring cross-section.
Therefore, with a constant low voltage, it is better to install a stabilizer. In this case, the load on the UPS autotransformer will be less, which will extend its service life. In addition, taking into account voltage equalization, you can purchase cheaper uninterruptible power supplies.
Uninterruptible power supply to DC consumers
For some devices, it is necessary to provide uninterrupted power supply with DC 12, 24 or 48 V. A UPS of this type is also available for sale. Their markings contain the abbreviation “DC”. Units with a voltage supply of 60, 110 or 220 V also exist, but they are used in industry or energy.
The difference between DC uninterruptible power supplies in the internal structure from classical models is the absence of an inverter. The batteries are connected directly to the output through a contactor with a current-limiting measuring shunt to prevent unacceptably deep discharge of the batteries.
Sometimes there may be a stabilizing converter at the output if the devices powered by the UPS are sensitive to small voltage fluctuations.
These backup power supplies are used to protect the following DC-powered household equipment:
- CCTV systems and security;
- all kinds of sensors (leakage, smoke, fire, movement, etc.);
- lighting systems;
- telecommunication devices;
- communication systems;
- control system components "smart House".
Many DC UPSs have the option of connecting external batteries. In this case, the autonomous functioning of the devices they serve can be very long.
Conclusions and useful video on the topic
Briefly about the main characteristics of household UPS:
The variety of UPS types and their characteristics is a consequence of the different conditions of their use: the power and type of connected devices, parameters and typical problems of a particular electrical network.An uninterruptible power supply is usually not the most expensive element in the system, but the stability of its operation depends on it. Therefore, you need to determine the operating conditions and carefully select a model.
Still have questions about the topic of the article? Or can you supplement this material with interesting information about UPS? Please write your comments, ask questions, and share your experience in the block below.
