Get best of the week

5 myths about UPS, their refutation and the real situation



Uninterruptible power supplies for more than a decade - an important, but inconspicuous attribute of corporate offices and home offices. Many of us recall them in the rare moments of a power outage or when you need to buy new UPSs or replace batteries in them. This is where the desire to save comes up. And where there is a desire to save - there are all sorts of myths and "stories of experienced". Today, 5 of these myths will be less.

Myth 1. The UPS will protect against all power problems.


This myth is most common among small businesses and home users. In contrast to the corporate sector, where the purchase of UPSs (aka UPS) are treated as mandatory expenses in the IT budgets of companies, “physicists” and small businesses purchase them on a residual basis. The reason for the purchase is usually born by itself - when a sudden power outage leads to the loss of significant results. But if you already bought it, many users consider the power protection of their computers to be 100% complete. Is it so?

Truth:The UPS protects the load from interruption of the main power supply, but for a relatively short time. Depending on the battery capacity and the load, the UPS is able to support the operation of the protected equipment for a dozen or two minutes. If the voltage in the mains disappears for a longer time, autonomous power supply devices will be required - generators or even solar panels, for example.

Most UPS models of the line-interactive type and double voltage conversion type incorporate an input mains filter and a voltage regulator, also protecting the load from high-frequency interference and voltage deviations in the network within certain limits. If the voltage parameters deviate to higher values, the UPS switches to battery power.

It is also worth pointing out that a UPS is not required to power equipment that already has an autonomous mode of operation from its own battery, for example, laptops. However, even such equipment is recommended to be connected through a surge protector.

We can talk about about a dozen options for disruption of normal power supply, which modern UPSs cope with. Complex cases, such as frequency instability in the power grid and significant distortion of the sinusoidal voltage shape, can only be corrected by the most advanced type of UPS, called a double conversion UPS (aka Online UPS). In such UPSs, the alternating input voltage is first converted to direct, and then again to alternating, already with an ideal sinusoid shape.


List of possible violations in the power supply system. Source (hereinafter, unless otherwise indicated): Eaton

But there are violations that the UPS will not cope with. A long-term power outage has already been called, but there is another danger - powerful high-voltage power surges that occur, for example, when lightning strikes a power line, and these are power and voltage surges with characteristics of more than 20 kV.

To protect the load, including household appliances, from damage, the UPS is used together with a surge protection device (surge protector, or surge arrester). In an urban environment, the user may not pay attention to this moment, since the SPD is installed from the network side, but if you live in an individual country house you need to take care of organizing the lightning protection system and installing the SPD yourself.

Myth number 2. If you “train” the UPS battery by periodically discharging it, this will extend its service life


This myth traces its history to the methods of prolonging the life of ancient generations of car batteries (batteries). The idea is this: since lead batteries are in the UPS and car batteries are also lead, why not try to apply the same method to extend their service life? In Soviet times, in the magazine “Behind the Wheel” there was a heading “Tips of Experienced”, in which motorists shared similar experiences of extending the battery life (even then this experience was very controversial).

Truth: UPS manufacturers do not recommend such procedures, because they are ineffective. Moreover, deep discharge is thought to shorten the life of lead batteries in the UPS.

It is important that you follow the simplest UPS battery guidelines:

  • fully charge before first use;
  • observe the temperature regime (if possible, install the UPS in a cool place, at a distance from radiators, do not cover);
  • use advanced UPS settings to control battery charge (if any).

And how much does the battery serve in the UPS? On average, manufacturers orientate users towards a 5-year lead battery life, although in practice about half of them require replacement after 3-4 years due to non-compliance with operating conditions or other reasons. A promising new type of battery, lithium-ion batteries, can count on a service life of 8-10 years.

Typical lead battery design for UPS. In most cases, they use lead-acid batteries (VRLA, Valve-regulated lead acid) with an internal pressure regulating air valve, also known as sealed or maintenance-free batteries. The electrolyte, which is an aqueous solution of sulfuric acid, is bound inside them by additives in a gel-like substance. The batteries are made in polypropylene plastic, and the valve design prevents electrolyte leakage when the battery is tilted

Since water cannot be added to lead-acid batteries for UPSs, recycling the water inside the battery is critical to its life, and any factor that increases the rate of evaporation or loss of water, such as increased ambient temperature or heat from the charging current, shortens battery life . Here is a more detailed list:

  • — , ;
  • : 25 °, , ( Eaton, 9 ° 25 ° 50%);
  • 25° , ;
  • , , ; , +5 +10°, , . . , , , .

To prevent the UPS from operating excessively short after a power failure, it is necessary to periodically evaluate the remaining battery capacity. All UPS, except the cheapest household models, such information is displayed on the UPS built-in display or can be obtained using special software.

Are there any other options for extending the life of the battery, other than “keep in a cool place”? Yes, there are two such methods - with limited effect and cardinal.

Let's start with a limited option. Lead batteries have been used in UPSs for more than 30 years, and during this time repeated attempts have been made to find ways to extend the life of the battery by changing the charge mode. In general, we managed to do this, and for about 10 years already, many enterprise-class UPS models use a special battery charging technique.

An example is Eaton’s ABM (Advanced Battery Management) charging technology , which significantly (up to 50%) extends the life of lead batteries by using a sophisticated charge mode: since a typical UPS operates most of the time in idle mode, the ABM technology charges batteries only when necessary. Most of the time, the battery operates in the "rest" mode and recharges within certain time intervals.


UPS battery charging schedule using AVM technology

The traditional method of charging (constant recharging with a low current), in comparison with the AVM, dries the electrolyte faster and accelerates the process of plate corrosion. In addition, when using the AVM, more careful monitoring of the battery replacement period is provided, which is important for corporate clients. In Eaton UPSs, AVM technology is used in Series 5 and higher models.

And finally, a cardinal way to extend battery life is to switch to lithium-ion batteries. This is a promising new type of battery; in Eaton UPSs, these batteries are available starting with certain 5-series models. Lithium-ion batteries last up to 10 years, they have a weak self-discharge, they have less weight and a larger capacity in comparison with lead-acid batteries of a similar size, and also an order of magnitude more charge-discharge cycles. For example, Eaton believes that for a rack-mountable UPS model 5P 1U 1500 VA UPS for 8 years of operation, the use of one lithium-ion battery instead of 2-3 lead ones will lead to savings of about 600 US dollars.

Myth number 3. The batteries sold for replacement are worse than those originally installed in the UPS at the factory and are noticeably smaller.


By this myth, as well as by the following two, we will go over in an accelerated order, because they are easily refuted by literally one or two paragraphs of text.

True: Branded batteries sold as spare parts are identical to those installed in the UPS at the factory. The different service life is explained by the fact that users can buy batteries that have already lied in the warehouse, as well as the fact that they - that is, the same users - often do not configure UPS modes after installing a new battery (which is done at the factory), although this procedure it is simple and described in the user manual for many UPSs (excluding the cheapest models - there is no such function).


The battery pack from the spare parts is identical to the factory one.

For example, for the Eaton 9-Series UPS, the settings should be:

  • ABM cycling Battery charge mode;
  • : Temperature compensated charging = enabled;
  • (Automatic battery support test = Enabled), 25 .

4.


:Car batteries emit hydrogen and a whole bunch of other harmful substances when charging, including sulfuric acid vapors, so they can not be used inside residential premises and in offices. Not for nothing that at service stations, for the purpose of charging the batteries, a separate box with powerful ventilation is allocated. In addition, there is a different structure of plates for different operating modes: for automotive batteries, they are designed for high inrush currents (in fact, automobile batteries are designed for starting), and UPS batteries are designed for long-term discharge with moderate currents. The battery in a car is only 99.9% of the time, because a generator is used to power consumers. Riding “on battery” with a failed generator is a rare emergency mode for such a battery. Consequently, the car battery in conjunction with the UPS will last significantly less than its normal life (5-7 years).

Also for fans of economy and / or "green" energy: the service life of a car battery will be especially reduced if you try to use it in conjunction with a solar battery and a UPS in cold start mode for autonomous power supply of a country house (that is, when the solar panel charges in the afternoon battery, and in the dark, the UPS switches to cold start mode and feeds home consumers). The batteries for solar energy systems, like standard batteries for UPSs, are made according to the gel scheme and are designed for a long and deep discharge, but for an automobile battery this will be an extreme mode leading to plate destruction.

Conclusion - you won’t be able to save on the use of a car battery, it’s better to monitor different stocks of battery suppliers and try to buy cheaper regular batteries for UPSs (or solar energy systems, respectively).

Myth 5. It is possible to improve the reliability of protection by connecting two or more UPSs in series with each other.


This is perhaps the most ridiculous myth about UPS.

Truth: Reliability Theory directly says that system reliability increases only with parallel redundancy. In professional IT equipment, such as servers and switches, two power supplies are provided for data centers. Therefore, they can be powered from two separate power lines. However, most computer equipment has a single power supply, and there, for parallel redundancy, additional switching devices between power supplies will be required.


Power Reliability Depends on Redundancy

To increase the reliability of power supply, it is recommended to create parallel systems when two or more UPSs simultaneously operate on the same load. In case of failure of one of them, the faulty source is disconnected from the system, and the load is evenly distributed between the remaining ones.

Such power switching devices are called ABP (Automatic Transfer Switch) and are available for various types of loads. There are single-phase and three-phase ATS, with installation in a 19 ”rack, in an electrical panel and portable. An example of rack-mount ABP is the Eaton STS Static Switch. The switching time between inputs for it is about 6 ms, which does not affect the operation of computer equipment.

An example of a system where switching between more than two power sources with reliability up to “five nines” (99.999%) is required is Eaton's patented Hot Sync technology . It allows you to organize a parallel UPS system with redundancy according to the N + 1 scheme (for example, two modular UPSs to protect the load and one for redundancy). The difference between Hot Sync and other intelligent redundancy systems is the absence of a single point of failure, which is usually the control unit of several UPSs.

Read more about Eaton uninterruptible power systems for the corporate sector, medium and small business (SMB) and home users can be found on the company's website .

More articles:


All Articles