• How uninterruptible power supplies (UPS) are designed and operate. Uninterruptible power supplies: an attempt to develop a comprehensive testing methodology

    Industrial solution: The UPS, together with the protected equipment, is mounted in a 19-inch rack

    Uninterruptible power supplies have evolved in parallel with computers and other high-tech devices to provide reliable power to this equipment, something that standard power networks cannot provide. :128 The most common designs are as a separate device, including a battery and a DC-AC converter. Flywheels and fuel cells can also be used as a backup source. Currently, UPS power is in the range of 100 W ... 1000 kW (or more), different output voltages are possible. :142

    Reasons for use

    Short-term disruptions to the normal operation of the electrical network are inevitable. Most short-term power outages are caused by short circuits. It is almost impossible to completely protect the electrical network from them, or, in any case, it would be very expensive. :With. 6 Short-term power interruptions occur much more often than long-term ones. Long power interruptions can be avoided using automatic transfer switch (ATS). In this case, short-term power interruptions will occur not only in the event of a short circuit on any of the lines supplying the ATS, but also on the lines supplying neighboring consumers. :With. 8

    Uninterrupted power supply differs from guaranteed power supply in that in the case of guaranteed power supply, a break is allowed during the commissioning of the backup source. In the case of uninterruptible power supply, “instant” activation of a backup source is required. This important requirement limits the range of backup sources suitable for use in uninterruptible power supplies. In practice, usually only one such source can be used - a rechargeable battery.

    The main function of a UPS is to ensure continuity of power supply through the use of an alternative energy source. In addition, the UPS improves the quality of the power supply, stabilizing its parameters within the established limits. UPS usually uses chemical current sources as energy storage. In addition to them, other storage devices can be used. :p. 1.1 The primary source can be power supplied from the mains or generator. :p. 3.1.3

    Industry

    Complex technological equipment of modern industrial production cannot function normally if the power supply is not uninterrupted. For many industrial plants, a power interruption of a few seconds or even tenths of a second leads to disruption of the continuous technological process and to a shutdown of production. :With. 5

    If the permissible power interruption time is less than 0.2 s, only the use of uninterruptible power supplies is possible; protection by circuit breakers with short circuits to reduce the power interruption time is in this case impossible or ineffective. If the permissible time is more than 0.2 s, it is possible to use power supply protection or use uninterruptible power supplies. With an acceptable time of 5...20 s, it is possible to abandon uninterruptible power supplies and use an automatic transfer switch. :With. 61

    For electric motors, voltage dips in a 0.4 kV network lasting 0.3...0.5 s can lead to the fact that the residual EMF vectors of electric motors may be out of phase with the network voltage vectors. As a result, when power is restored, the electromagnetic releases of the circuit breakers will operate and the electric motors will be completely turned off. At the same time, voltage dips lasting less than 0.3 s do not pose a danger, therefore, for electric motors, the fight against voltage dips is usually aimed at preventing contactors from disconnecting in the 0.4 kV main power circuit. One such measure is to power the contactor control circuits from an uninterruptible power supply. :With. 251

    The susceptibility of industrial controllers on logic chips to voltage sags is similar to the susceptibility of computers. :160

    Malfunction of contactors and relays can occur when the voltage is interrupted for 5...10 ms and 80...120 ms. The difference in operation of the same device arises due to the difference in the instantaneous magnitude of the AC voltage when the voltage dip begins. When the voltage passes through zero, the stability is more than 10 times greater. :165

    At home and in offices

    The most common application in everyday life and offices is to turn off the computer without losing data during a power outage. When voltage dips lasting 0.2 s, the computer read/write procedures stop; 0.25 s - blocking of the operating system; 0.4 s - reboot. :158

    Emergency

    Power supplies that are used in case of interruption of normal power supply are divided into backup and power supplies for safety systems.

    Regulation

    The International Electrotechnical Commission has adopted a group of standards:

    International classification of UPS

    The history of electronic AC UPSs begins with the invention of thyristors in 1957. In 1964...1967 UPSs with redundant power up to 500 kVA were created. To date, the main change in design has been the replacement of thyristors with IGBT transistors. :130

    Backup scheme

    Disadvantages: in the “on-line” mode it does not perform the function of filtering peaks, and provides only extremely primitive voltage stabilization (usually 2-3 stages of an autotransformer, switched by relay, the function is called “AVR”).

    In the “battery mode”, some, especially cheap, circuits output a frequency much higher than 50 Hz to the load, and an alternating current oscillogram that has little in common with a sine wave. This is due to the use of a large classic transformer in the circuit (instead of an inverter using semiconductor switches). Due to the fact that a transformer of this size has (due to the occurrence of hysteresis in the core) a limitation on the transmitted power, which increases linearly with frequency, this transformer (occupies 1/3 of the volume of the entire UPS) is enough to power the battery charging circuit at 50 Hz in "online" mode. But, in the “battery mode”, hundreds of watts of power must be passed through this transformer, which is only possible by increasing the frequency.

    This makes it impossible to power devices that use, for example, asynchronous motors (almost all household appliances, including heating systems).

    In fact, such a UPS can only power devices that are undemanding in terms of power quality, that is, for example, all devices with switching power supplies, where the supply voltage is immediately rectified and filtered. That is, computers and a significant part of modern consumer electronics. You can also power lighting and heating devices.

    Double conversion circuit

    Double conversion mode (English online, double-conversion, online) - is used to power loaded servers (for example, file servers), high-performance local area network workstations, as well as any other equipment that places increased demands on the quality of the network power supply. The principle of operation is double conversion of the current type. First, the input AC current is converted to DC, then back to AC using an inverse converter (inverter). If the input voltage fails, switching the load to power from the batteries is not required, since the batteries are constantly connected to the circuit (the so-called buffer mode of battery operation) and for these UPSs the “switching time” parameter does not make sense. For marketing purposes, the phrase “switching time is 0” can be used, which correctly reflects the main advantage of this type of UPS: the absence of a time interval between the loss of external voltage and the start of battery power. Double conversion UPSs have low efficiency (from 80 to 96.5%) in on-line mode, which is why they have increased heat generation and noise levels. However, modern medium- and high-power UPSs from leading manufacturers have a variety of intelligent modes that allow automatic adjustment of the operating mode to increase efficiency up to 99%. Unlike the two previous circuits, they are capable of adjusting not only voltage, but also frequency (VFI according to IEC classification).

    Advantages:

    • no switching time to battery power;
    • sinusoidal output voltage, that is, the ability to power any load, including heating systems (which have asynchronous motors).
    • the ability to adjust both voltage and frequency (moreover, such a device is also the best possible voltage stabilizer).

    Flaws:

    • Low efficiency (80-94%), increased noise and heat generation. Almost always the device contains a computer-type fan, and therefore is not silent (unlike a line-interactive UPS).
    • High cost. About two to three times higher than line-interactive.

    DC UPS

    UPS Specifications

    Design

    Electrical storage devices

    Chemical

    The implementation of the main function is achieved by operating the device from batteries installed in the UPS housing, under the control of an electrical circuit, therefore, any UPS, except control circuits, included charger, which ensures that the batteries are charged when there is mains voltage, thereby ensuring that the UPS is always ready to operate in stand-alone mode. To increase the battery life, you can equip the UPS with an additional (external) battery.

    Uninterruptible power supplies can use chemical current sources (CHS):

    Dynamic

    Capacitors

    When using a DC ATS using a relay circuit, you can use a large capacitor to avoid power interruptions during switching. :With. 229

    Bypass

    A bypass is one of the components of the UPS. Bypass mode (eng. Bypass, “bypass”) - powering the load with filtered mains voltage, bypassing the main UPS circuit. Switching to Bypass mode is performed automatically or manually (manual switching is provided in case of preventive maintenance of the UPS or replacement of its components without disconnecting the load). Can do so-called phasanul (“through zero”). It is used in online circuits, moreover, when turned off by the OFF online UPS button, it remains in bypass mode, the same thing happens when the power components of the circuit are destroyed, determined by the control circuits, as well as when the circuit is switched off in an emergency due to an output overload. In line-interactive UPS, the “on-line” operating mode is the bypass.

    AC voltage stabilizer

    Used in UPSs that operate on an interactive basis. Often the UPS is equipped only with a booster, which has only one or several steps of increase, but there are models that are equipped with a universal regulator that works both to increase (boost) and to decrease (buck) voltage. The use of stabilizers allows you to create a UPS circuit that can withstand long, deep “sags” and “sags” of the input mains voltage (one of the most common problems in domestic power grids) without switching to rechargeable batteries, which can significantly increase the “life” of the battery.

    Inverter

    Inverter- a device that converts the type of voltage from constant to alternating (similarly, alternating to direct). Main types of inverters:

    • inverters that generate rectangular voltage;
    • inverters with step-by-step approximation;
    • inverter with pulse width modulation (PWM).
    • converter with pulse-density modulation (PDM, English Pulse-density modulation)

    An indicator that characterizes the degree to which the voltage or current shape differs from the ideal sinusoidal shape - nonlinear distortion coefficient (English). Typical values:

    • 0% - the signal shape is completely sinusoidal;
    • about 3% - a shape close to sinusoidal;
    • about 5% - the signal shape is close to sinusoidal;
    • up to 21% - the signal has a trapezoidal or stepped shape (modified sine or meander);
    • 43% and above - a rectangular signal (meander).

    To reduce the influence on the voltage form in the supply network (if the input node of a UPS built according to a double conversion circuit is a thyristor rectifier, a nonlinear element that consumes a large pulse current, such a UPS causes the appearance of higher-order harmonics), a special one is installed in the UPS input circuit THD filter. When using transistor rectifiers, the nonlinear distortion factor (in English) Total Harmonic Distortion, THD) is about 3%, and no filters are used.

    Transformer

    Galvanic isolation between the input and output (as a rule, in a UPS this is not done at all for fundamental reasons of passing a “through zero” to the load, that is, the absence of any switching of the neutral wire from the UPS input to its output) is carried out by the UPS installed in the input circuit (between the electrical network and rectifier) input isolation transformer. Accordingly, in the output circuit of the UPS between the converter and the load there is a output isolation transformer, which provides galvanic isolation between the input from the UPS circuit and the output to the connected load.

    Interface

    For advanced monitoring of the state of the UPS itself (for example, battery charge level, output electric current parameters), various interfaces are used: for connecting to a computer - a serial (COM) port or USB, while the UPS manufacturer supplies proprietary software that allows, after analyzing the situation , determine the operating time and give the operator the opportunity to safely turn off the computer, ending all programs. To monitor the status of uninterruptible power supplies and other equipment via a local area network, the SNMP protocol and specialized software are used.

    In order to increase the reliability of the entire system as a whole, redundancy is used - a scheme that consists of two or more UPSs.

    Manufacturers

    Distribution of UPS sales by manufacturer (2017, IT Research).

    UPS stands for "uninterruptible power supply". Abbreviation in English - UPS (Uninterruptible Power Supply) , therefore the names UPS, YUPS, and oopsnik are also common.

    The main function of an uninterruptible power supply is to ensure the supply of electricity to the equipment connected to it during outages in the main network. But, depending on the type of equipment, the parameters of such autonomous power supply may be required to be radically different. Accordingly, the UPS market offers different types of devices, which differ in a lot of parameters:

    • principle of operation: offline, linear-interactive, online;
    • type of automatic voltage regulation;
    • quality of filtering network interference;
    • capacity (number of ampere-hours, or in other words - how long the battery life will last);
    • time to switch to batteries during a power outage;
    • possibility of connecting additional external batteries;
    • various additional functions (filtering sockets, sockets for telephone and network cables, LCD display, synchronization with a PC), etc.

    How to choose a UPS with such a variety of models ? How to understand how they differ? In this article we will look at the main types of uninterruptible power supplies, their differences, and what additional functions manufacturers equip UPS with. In the next one - how to choose a UPS depending on the features of your equipment, how to calculate its required power, etc.

    Three main types of UPS

    Off-line (Back-UPS, backup, Standby) uninterruptible power supply

    Example of a backup UPS: model .

    The operating principle of this type of uninterruptible power supply is very simple:

    As long as there is electricity in the network within the set values, the UPS supplies the connected devices with voltage directly from the network, while simultaneously recharging the battery. The power passing through the UPS is not regulated; pulses and noise are filtered at the simplest level, using passive filters. The signal shape corresponds to the network signal, i.e., a sinusoid.

    As soon as the mains power is lost, the UPS switches to battery power. The inverter that converts direct current from the battery into alternating current output is one of the simplest installed in this type of UPS, so the waveform does not correspond to the correct sine wave. The maximum that manufacturers do is to bring it somewhat closer to a sinusoid, making it stepwise.

    The UPS also switches to off-line autonomous power supply if the voltage level in the network falls below or rises above the threshold values, they can be different depending on the brand of uninterruptible power supply.

    The switching time to batteries in various models ranges from 5 to 20 ms. This is relatively long, and for some equipment models such a long delay may adversely affect operation . The long-term operation of the relay is due to the fact that the device needs the phases of the mains and battery voltages to coincide when the autonomous power supply is turned on, and since they are not synchronized, this takes some time.


    Scheme of operation of a backup uninterruptible power supply.

    Pros of Standby UPS:

        • inexpensive price,
        • high efficiency,
        • silent operation.

    Flaws:

        • long switchover to battery operation (from 5 to 20 ms);
        • the output signal shape is not a sinusoid;
        • filtering interference, noise and impulsesquite rough on the line;
        • there is no voltage and frequency adjustment when operating from the network.

    Line-interactive UPS

    Example of a line-interactive UPS: model

    Buyers choose this type of uninterruptible power supply most often, as it optimally combines functionality and price.

    The principle diagram of the operation of line-interactive UPS includes AVR - a module for automatically adjusting the incoming network voltage. That is, unlike a backup UPS, it not only passes power through itself, but also stabilizes it, although not smoothly, but in steps.

    When operating from the mains at a normal voltage level, the line-interactive uninterruptible power supply passes the incoming signal through passive interference and noise filters, while the battery is charged.

    When the voltage in the network increases or decreases, the line-interactive UPS makes its stepwise adjustment. When the voltage reaches a certain threshold, the AVR lowers or lowers it by a fixed amount (or percentage). Several such threshold-steps can be specified in the AVR operating scheme; also, for working with a lower and higher level, a different number of adjustment steps can be assigned (for example, 2 for an increase, and 1 for a decrease).

    If the mains voltage drops or rises to values ​​that lie outside the available input range of the uninterruptible power supply, the device switches to battery operation, just as in the case of a complete power outage. These minimums and maximums may vary depending on the load on the UPS. For example, if the UPS is 70% loaded and the voltmeter shows 160V in the network, the uninterruptible power supply switches to the batteries. And at 30% load and a voltage of 150V, it still makes adjustments using an AVR transformer.

    Some linear-interactive models are no different in the shape of the output signal from backup-type uninterruptible power supplies: they have a stepped sine wave. Some manufacturers, especially with the growing demand for UPS for boilers, equip their uninterruptible power supply systems with inverters that produce the correct sine wave.

    The switchover time to battery operation in a pure sine wave line-interactive UPS is faster than that of its standby counterparts. The reason is that in UPSs of this type, the voltage waveforms coincide (both from the network and from the battery, this is a sinusoid), which speeds up phase synchronization and, accordingly, the start of autonomous power supply.

    Pros of line-interactive UPS:

        • reasonable price,
        • silent operation,
        • automatic regulation of incoming voltage,
        • in some models - pure sine wave at the output,
        • switching time is less than in backup ones (on average 4-8 ms, in some models 2-4 ms).

    Flaws:

        • no frequency adjustment,
        • insufficiently complete filtering of interference, noise and network impulses,
        • voltage regulation is not smooth, but stepwise,
        • The efficiency is lower than in an off-line uninterruptible power supply.

    Double conversion UPS (on-line)

    Double conversion UPS example: model .

    This is the most expensive, but also the best type of UPS. It is optimally suited for expensive, capricious equipment, for which not only constant voltage is important, but also frequency, as well as effective noise filtering, a signal in the form of a pure sine wave, and the absence of delays when switching to battery operation.

    In fact, such an uninterruptible power supply operates constantly, stabilizing, filtering the incoming signal, equalizing the frequency and shape of the output signal.

    In mains mode, the incoming AC voltage is stabilized and converted to DC by the rectifier and distributed between the battery (for recharging if necessary) and the inverter. The inverter converts direct current into alternating current, producing an output signal in the form of a pure sine wave, the correct frequency, the correct voltage. Interference and noise are completely absent - they simply do not remain after double conversion.

    This constant “inclusion” of the uninterruptible power supply into the network provides one of its significant advantages: Instant switching to battery operation. Actually, it’s hard to even call it “switching”, since power passes through the rectifier, battery (during charging) and inverter constantly. When the voltage in the network drops below threshold values ​​or there is a complete power outage, the inverter simply begins to take part of the energy from the battery, and not from the rectifier. It happens instantly.

    Double conversion UPSs usually have another operating mode: bypass. This is a backup line that goes directly from the input to the output of the UPS, bypassing the rectifier, battery and inverter. It allows in critical moments for the UPS: overload (for example, with starting currents), failure of the inverter and others - to supply electricity directly to the connected devices, avoiding failure of the device elements.

    Constant operation of the UPS has a certain disadvantage: increased heat generation, which requires effective cooling. Therefore, UPS online are most often equipped with fans, which makes their operation in residential areas not as comfortable as other types of silent uninterruptible power supplies.

    Pros of online UPS:

        • constant voltage stabilization,
        • constant frequency stabilization,
        • pure sine wave at the output,
        • effective filtering of noise, impulses and interference,
        • Instant switching to batteries.

    Flaws:

        • high price,
        • increased noise level,
        • the lowest efficiency among all types of UPS.

    When choosing an uninterruptible power supply, you need to take into account that there are exceptions. Some line-interactive UPSs may cost more than online models from another manufacturer, the switching time to battery operation in a backup UPS may be no more, or even less, than in some line-interactive UPS, etc. Therefore, In any case, it is necessary to read the characteristics of a specific model.

    Additional UPS functionality

    In addition to determining the type of uninterruptible power supply you need, when choosing a UPS you should also pay attention to what functionality is included in it. UPS can have various additional functions and design features:

    Synchronization with PC. This feature is not present in the cheapest models, but it is very convenient. Using special software, the UPS transmits data in real mode to the computer about the state of the power line and battery charge level. In addition to the purely informational component, there are also features such as, for example, autonomous shutdown of the computer while saving data in all applications during a power outage.

    Cold start. An uninterruptible power supply equipped with this function can be turned on when there is no power in the network. For example, the lights went out, you saved the documents, turned off the computer and UPS, but after some time there was an urgent need to copy the document to a flash drive. A UPS with cold start support can be turned on, even if there is still no power, and get the job done.

    Previously, connectors for connecting devices in a UPS looked basically like this:

    This IEC 320 standard connector is perfect for connecting various computer equipment. However, equipment with a regular power cord, such as a WiFi router, cannot be connected to it. For these purposes, you can use a surge protector with a similar connector, which is connected to the UPS, and then connect various equipment to it. But this is not always convenient.

    Therefore, now many models have simply begun to be supplemented with Schuko-type sockets (in our country they are often called Euro sockets) so that the equipment can be turned on directly:

    Sockets for filtering interference. A UPS may be equipped with an outlet or several for sensitive equipment that does not provide power support during a power outage but protects the connected equipment from utility power interference.

    Sockets for telephone line, twisted pair. High-voltage pulses can be transmitted not only directly via an electric power cable, but also in the event of various accidents and breakdowns - both via a telephone cable and twisted pair cable. To protect telephone, network and computer equipment, some manufacturers provide special connectors (input/output) where you can connect a telephone or Internet line.

    To be continued in the next article.


    website

    Hi all! When selecting an uninterruptible power supply, you need to be prepared, know and understand several important points that you should pay attention to. All this and more will be discussed in this material.

    An uninterruptible power supply is a device with built-in battery(s) to provide backup power to various devices during a power outage.

    In practice, UPSs are used in enterprises, various institutions, and less often in everyday life. An uninterruptible power supply runs not only personal computers, but also network and communication equipment. For example, thanks to a UPS, you can safely shut down your personal computer after first saving all documents.

    In order to choose the right uninterruptible power supply, decide on several parameters:

    1) Where and for what will the UPS be used ( here we select the device type)?
    2) The total power of connected devices, the required number and type of sockets.
    3) How long should the UPS operate without power?

    Perhaps these are the most basic parameters when choosing. Let's look at each in more detail.

    Spare

    Due to its low cost, this type of UPS is available to the mass consumer. As soon as the electricity disappears or “exceeds” the established norms, the UPS switches the load power to offline mode, i.e. from the battery. As soon as the power supply returns to normal, the device goes into normal mode and charges the dead batteries. The design and circuitry of the devices is simple, and the transition time to battery power varies from 4 to 15 ms. Such UPSs are suitable for those who cannot afford other types of UPS.

    Linear - interactive

    The line-interactive type of UPS has a more complex circuit design. There is a step voltage regulator (AVR) here. It maintains a stable output voltage even with significant deviations in the input voltage, when the backup UPS will constantly switch to offline mode during power surges. That is why such UPSs last much longer. The switching time to the battery is 4-7 ms in this case.

    Line-interactive UPSs are a common type today; the scope of application in this case is slightly wider than that of backup ones. You can connect several computers, network and telecommunications equipment to such a UPS, and use it not only at home, but also in factories and enterprises.

    Double conversion UPS

    The principle of operation is much more complicated: the alternating voltage of the network is converted into direct voltage thanks to the rectifier, then the inverter converts the voltage back into alternating voltage. Therefore, this type is called “double conversion” or “on-line”. Thanks to this approach, any changes in the external network are not dangerous and do not in any way affect the functioning of the equipment powered by the UPS.

    Double conversion UPSs are more suitable for installation in server or industrial premises, where power quality is one of the important parameters during the operation of all equipment (servers, gateways, network and communication equipment, audio-video equipment).

    In this case, the UPS has all the batteries always connected to the installed inverter, so if there is a loss of power in the electrical network, all consumers automatically begin to be powered by the batteries.

    Double conversion UPSs have high power, which is why many UPSs of this type have a high noise level and increased heat generation, and are also very expensive.

    UPS power

    The main parameter when choosing a UPS is its output power, which manufacturers indicate in volt-amperes VA. How to understand how much power is needed?

    1. Find out the power of your equipment that you are going to connect to the UPS. You can see the power consumption in the passport/instructions or on the body of any electrical appliance.
    2. Let's sum it up.
    3. Because The total power of the UPS is indicated in volt-amperes (VA, VA), and the power of the devices is indicated in watts (W, W), we also need to convert our total power into VA. To do this, divide the resulting total power by the power factor, which is 0.6.
    4. We add 20% on top for a reserve so that the UPS does not constantly work at the limit.

    For greater clarity, I will give examples of calculations:

    Example No. 1. Typical budget PC

    Summing up the power of each device, we get that the total power is 340 W.

    Next, we convert the power from watts to volt-amperes. We use the formula Pva = Pw/0.6 . In our case, it turns out that 340 / 0.6 * 1.2 = 680 VA. Where did parameter 1.2 come from, you ask? Everything is very simple, the power of the UPS should always be at least 20% greater than the total power. Taking into account all the parameters, it turns out that for this example an uninterruptible power supply with a capacity of at least 680 VA is required; for this, a backup UPS that can operate for no more than 10 minutes under load is quite suitable. This time is quite enough to successfully complete the job and turn off the PC.

    Example No. 2. Gaming PC

    Adding up the power again, we get a total power of 850 watts. Following the example above, we make calculations: 850 / 0.6 * 1.2 = 1700 VA. For this example, an uninterruptible power supply with a capacity of at least 1700 VA is required; a line-interactive UPS is ideal. Such UPSs perfectly support autonomous operation for 15-30 minutes at full load.

    Types of connectors and interfaces

    When choosing a UPS, you need to think in advance about how many devices will be connected to the UPS, and what types of connectors are needed?

    Not only a PC is connected to the UPS, but also often other peripheral equipment. The most important thing is that the number of connectors matches the number of connected equipment; it is better to always choose with a reserve of 1-2 connectors.

    UPSs usually have two types of connectors:

    CEE 7 Schuko (plug for Euro socket);
    - IEC 320 C13 (computer plug);

    It is important that all connectors match the type of connectors of the equipment being connected. For example, if the equipment has connectors of the CEE 7 Schuko type, and the UPS only has a couple of connectors of the IEC 320 C13 type, then you simply will not be able to connect the desired device to it. You will have to buy an additional adapter for such a connector, and this is a waste of money. To avoid getting into trouble, carefully look at the types of connectors of the UPS you purchase.

    Depending on the UPS model, the number of connectors varies from 1 to 10, however, the number that provides uninterruptible power supply is different everywhere; their increase leads to an increase in the cost of the device. It is better to select models that have several direct power output connectors ( SURGE ONLY), since through UPS connectors ( low power) not all electrical appliances can be powered. Thus, the UPS will also be a kind of “tee-extension cord” for connecting equipment “directly”.

    Service connectors USB-B or RS-232 are designed for configuring the UPS; using special software, you can control the operating modes of the UPS, monitor or configure automatic shutdown of the UPS for certain operating tactics.

    Recently, UPSs for the home that have USB-A connectors are relevant; they can be used to charge various devices (smartphones, tablets, MP3 players and other devices).

    Battery life

    The battery life of the UPS directly depends on the capacity of the batteries used. To avoid acquiring excess “lead,” think in advance about how much time you need to complete tasks during a power outage. Manufacturers in their technical characteristics of devices provide examples of the duration of UPS operation from rechargeable batteries. However, this time, as a rule, is indicated at the maximum load involved; in practice, this rarely happens, and this time is significantly higher. For example, if a UPS with a power of 700 VA has an output power of 405 W, then the operating time of the UPS under a load of 405 W will be 4 minutes, but if a system unit and a monitor with a total power of 320 W are run through such a UPS, then naturally the actual operating time from the battery will be there will be a little more. In 10 minutes of such work, you can safely save all documents, projects and turn off your PC.

    In order for the UPS to maintain constant and uninterrupted operation of the connected equipment, you need to choose a UPS with the ability to connect additional batteries. This can be either separate housings or direct connection of batteries using special wires. In this case, purchase the required number of additional batteries.

    Some facilities that have expensive uninterruptible power supplies with additional battery modules cannot be disconnected, even for maintenance. Therefore, it is so important that such UPSs have the ability to hot-swappable batteries without shutting down the equipment.

    Display, cooling and noise level

    Is the uninterruptible power supply equipped with control buttons? Then you should pay attention to the presence of a display, because it makes it easier to use the device. The LCD displays all useful information: input-output voltage, battery percentage, battery life, power and frequency.

    Redundant power supplies have a low noise level, as does their heat dissipation, which cannot be said about double conversion UPSs and some line-interactive models. Such devices are equipped with additional fans that promote cooling. That is why they have a high noise level and heat generation.

    Before you buy a new UPS, you should familiarize yourself with some of the “internal” aspects of its operation. To ensure that your uninterruptible power supply serves you as long as possible and that your investment is as effective as possible, try to follow the tips below.

    What batteries are used in the UPS

    All UPS products manufactured by APC (and other well-known major UPS manufacturers) use lead acid batteries, much like the most common car batteries. The difference is that, if we are to make such a comparison, the batteries used by APC are made using the same technology as the most expensive car batteries available today: the electrolyte contained inside is in a gel-like state and does not spill if the case is damaged; The battery is sealed, as a result of which it does not require maintenance, does not emit harmful and explosive gases (hydrogen) during operation, it can be “turned over” in any way without fear of spilling the electrolyte.

    How long do UPS batteries last?

    Although different UPS systems appear to use the same battery technology, the lifespan of UPS batteries from different manufacturers varies widely. This is quite important for users, since replacing batteries is expensive (up to 30% of the original cost of the UPS). Battery failure reduces system efficiency, causing downtime and unnecessary headaches. Temperature has a significant impact on battery reliability. The fact is that the natural processes that cause battery aging largely depend on temperature. Detailed test data provided by battery manufacturers shows that battery life decreases by 10% for every 10°C increase in temperature. This means that the UPS must be designed to minimize battery heating. All UPSs with an online topology and hybrid online sources heat up more than standby or line-interactive ones (which is why the former require a fan). This is the most important reason why UPSs of standby and line-interactive types require battery replacement less often than UPSs with an online topology.

    Should you pay attention to the design of the charger when choosing a UPS?

    The charger is an important component of the UPS. The conditions under which batteries are recharged have a significant impact on their longevity. The UPS battery life is maximized if it is continuously charged from a constant or floating voltage charger. In fact, the service life of a rechargeable battery significantly exceeds the period of simple storage. This happens because some natural aging processes are halted by constant recharging. Therefore, it is necessary to charge the battery even if the UPS is turned off. In many cases, the UPS is turned off regularly (if the protected load is turned off, then there is no need to keep the UPS on, since it may trip and cause unwanted wear and tear on the battery). Many commercially available UPSs do not provide the important feature of continuous charging.

    Does voltage affect reliability?

    Batteries are made up of individual cells of approximately 2V each. To create a higher voltage battery, individual cells are connected in series. A 12-volt battery has six cells, a 24-volt battery has 12 cells, etc. When the battery is on trickle charge, as in UPS systems, the individual cells are recharged simultaneously. Due to the inevitable dispersion of parameters, some elements take a larger share of the charging voltage than others. This causes premature aging of such elements. The reliability of a group of series-connected elements is determined by the reliability of the least reliable element. Therefore, when one of the cells fails, the battery as a whole fails. It has been proven that the rate of aging processes is directly related to the number of elements in the battery; therefore, the rate of aging increases with increasing battery voltage. The best types of UPS use fewer higher-power elements instead of more lower-power elements, thereby achieving increased reliability. Some manufacturers use high-voltage batteries, which, for a given power level, can reduce the number of wiring connections and semiconductors, thereby reducing the cost of the UPS. The battery voltage of most typical UPSs with a power of about 1 kVA is 24...96 V. At this power level, the batteries of APC UPSs, in particular the Smart-UPS family, do not exceed 24 V. Low voltage batteries in UPSs manufactured by APC, have a longer service life compared to competing devices. The average service life of APC batteries is 3-5 years (depending on temperature conditions and frequency of discharge/charge cycles), while some manufacturers indicate a service life of only 1 year. Over the 10-year lifespan of a UPS, some system users spend twice as much on batteries as they do on the unit itself! Although developing a UPS using high-voltage batteries is easier and less costly for the manufacturer, there is a hidden cost to the user in the form of a shorter UPS life.

    Why "pulsating" current reduces battery life

    Ideally, to increase usage time, the UPS battery should be kept on a “float” or constant charge. In this situation, a fully charged battery draws a small amount of current from the charger, called float or self-charging current. Despite battery manufacturers' recommendations, some UPS systems additionally expose batteries to ripple current. Ripple currents occur because the inverter that produces AC current for the load consumes DC current at its input. The rectifier, located at the input of the UPS, always produces a pulsating current. The coefficient remains non-zero even when using the most modern rectification and ripple suppression circuits. Therefore, a battery connected in parallel with the output of the rectifier has to supply some current at those moments in time when the current at the rectifier output decreases, and vice versa - to be recharged when the current at the rectifier output drops. This causes mini-discharge/charge cycles at a frequency typically equal to twice the operating frequency of the UPS (50 or 60 Hz). These cycles wear out the battery, heat it up and cause it to age prematurely.

    In a UPS with a battery in reserve, such as a classic backup, a ferroresonant backup, or a line-interactive UPS, the battery is not exposed to ripple currents. The online UPS battery varies to varying degrees (depending on the design features), but is nevertheless always exposed to them. To determine whether ripple currents are occurring, it is necessary to analyze the UPS topology. In an online UPS, the battery is placed between the charger and the inverter, and there will always be pulsating currents. This is the classic, “historically” earliest type of “online double conversion” UPS. If in an on-line UPS the battery is separated from the inverter input by a blocking diode, converter or switch of one type or another, then there should be no pulsating current. Naturally, in these designs the battery is not always connected to the circuit, and therefore UPS with a similar topology are usually classified as hybrid.

    What you can't rely on in a UPS

    The battery is the least reliable element of most well-designed UPS systems. However, the UPS architecture can affect the longevity of this critical component. If you keep the battery under continuous charging even when the UPS is turned off (as is done in all UPS manufactured by APC), its service life increases. When selecting a UPS, topologies with high battery voltage should be avoided. Beware of UPSs that expose the battery to ripple currents or overheating. Most UPS systems use the same batteries. However, design differences between different UPS systems result in significant differences in battery life and, consequently, in operating costs.

    Before turning on your new UPS for the first time, be sure to charge the batteries.

    The batteries of the new UPS naturally lost most of their “factory” charge during transportation and storage in the warehouse. Therefore, if you immediately put the UPS under load, the batteries will not be able to provide adequate power support. Moreover, a self-test routine that automatically runs each time the UPS (except Back-UPS) is turned on, among other diagnostic operations, checks whether the battery is able to handle the load. And since an uncharged battery cannot cope with the load, the system may report that the battery is faulty and requires replacement. All you need to do in such a situation is to let the batteries charge. Leave the UPS connected to the network for 24 hours. This is the first charging of the batteries, so it takes longer than the usual standard charging, regulated in the technical description. The UPS itself may be turned off. If you brought the UPS in from the cold, allow it to warm up at room temperature for a few hours.

    Connect only those loads to the UPS that truly require uninterruptible power.

    The use of a UPS is justified only where a loss of power can lead to data loss - in personal computers, servers, hubs, routers, external modems, streamers, disk drives, etc. Printers, scanners, and especially lighting lamps do not require a UPS. What happens if the printer loses power while printing? A sheet of paper gets damaged - its value is not comparable to the cost of a UPS. In addition, a printer connected to an uninterruptible power supply device, when switching to battery power, consumes their energy, taking it away from the computer that really needs it. In order to protect equipment from discharges and interference that does not carry information that can be lost as a result of a power failure, it is sufficient to use a network filter (for example, APC Surge Arrest) or, in case of significant fluctuations in the network voltage, a network stabilizer.

    If your source frequently switches to battery mode, check that it is configured correctly. It may happen that the response threshold or sensitivity is set too demanding.

    Test the UPS. By periodically running a self-test, you will always be sure that your UPS is fully operational.

    Do not unplug the UPS. Turn off the UPS using the button on the front panel, but do not unplug the UPS unless you are leaving it for an extended period of time. Even when turned off, the APC UPS charges the batteries.

    ComputerPress 12"1999

    An uninterruptible power supply is an important element when building complex systems where a guarantee of safety against unexpected power outages is needed

    An uninterruptible power supply is an important element when building complex systems that require a guarantee of safety from unexpected power outages and other problems in the electrical network. Let's talk about what criteria need to be taken into account when choosing a UPS.

    Now the market is filled with many devices that differ in both price tag and quality. It is incredibly difficult to understand all this diversity. If the budget is limited, then you need to approach the choice as responsibly as possible. So first you should ask yourself a few questions:

    How much critical equipment are you going to protect?

    What is the optimal battery life of equipment in the event of a power failure?

    In order to answer the questions posed, it is worth understanding what classes of UPS currently exist, and deciding on the main criteria that need to be taken into account when choosing a UPS.

    UPS classes

    The classes of UPS available on the market differ from each other in their behavior in different operating modes and schematics. Highlight:

    Backup or off-line UPS (BackUp),
    - Line-interactive UPSs (Line-interactive),
    - UPS with double conversion (on-line, double-conversion).

    Off-Line UPSs are considered the simplest and most unpretentious. In normal operation from the network, electricity is supplied to the input of such an uninterruptible power supply, and then in transit is supplied to the main load. If network problems occur (voltage surges and losses), the UPS automatically switches to battery operation.

    The disadvantages of this operating scheme are the long switching of power to batteries (from 4 to 10 milliseconds). In addition, when the UPS operates from a battery, the equipment is supplied not with the sine usual for the network, but with an approximated sine.

    The next class of uninterruptible power supplies, Line-interactive, does not differ fundamentally from the Off-line circuit. In the event of an accident, the power is also switched to the battery, and the same time is spent on this (from 4 to 10 milliseconds). The output also produces an approximated sine.

    However, in a UPS of this class there is a transformer at the input, thanks to which it is possible to compensate for those same voltage drops. It is worth emphasizing that Off-line and Line-interactive class UPSs are not intended for connecting critical equipment.

    When connecting critical equipment, it is recommended to use a double conversion UPS or On-line UPS. The operation of such uninterruptible power supplies is designed in such a way that the incoming voltage is corrected thanks to the rectifier. After this, the inverter converts the DC voltage into AC voltage. With this scheme, the batteries are connected to the output of the rectifier and the input of the inverter, which provides an instantaneous transition (0 milliseconds) to battery operation.

    In addition, efficiency determines how much heat the UPS emits into the environment. This indicator is important when designing a server room. For example, if a small power UPS is installed, it will not generate much heat. On the contrary, with a high power of the “uninterruptible power supply” of several tens of kilowatts, the heat generation will be large. To avoid equipment overheating, you will have to somehow remove heat from the room, which means additional expenses for powerful air conditioners. The bottom line is this: the higher the efficiency of the UPS, the less heat will be generated.

    As an example, we present several options for the effective and ineffective use of a UPS:

    In the first case, equipment with a power of 50 Watt was connected to an 800 Watt UPS. The UPS uses about 70 watts for self-sufficiency. We calculate the efficiency using the formula and get 42%.

    In the second case, with a load of 600 W, the efficiency of the UPS will be significantly higher - 89%. This option is more preferable and effective.

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