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Reliable power is more essential than ever, with the widespread adoption of IIoT and big data in industrial applications. Choosing the proper UPS critical solution for a business can minimize the risks and expenses associated with a power outage.
Critical control systems require uninterruptible power supplies (UPS) to prevent brief power interruptions that may cause an industrial PC or other industrial controllers to fail. This may affect all the processes of the company so knowing how to choose an industrial UPS is crucial. That’s why we have prepared this post explaining major points to consider when implementing a USP.
The Industrial Internet of Things (IIoT) is based on a quick and precise data transmission. Control systems cannot afford to lose power for a second, as it might crash an industrial PC or controller. This problem is prevented by uninterruptible power supplies (UPSs). Understanding the fundamentals of selecting a UPS can help you choose the proper one for your needs.
Though UPS systems have different designs and form factors, in this post we will focus on DIN rail-mounted UPSs, which are utilized in a wide range of applications across numerous sectors and industries.

What are the UPS requirements?

Type of loads

First of all, you need to define the type of loads that the UPS will be feeding. It can be AC or DC type.
Many legacy systems run on AC power, so the replacement of old systems will almost certainly need AC power. However, the development of the industrial PC market over the previous twenty years has resulted in a move to DC power supply.
The next step is to consider the UPS application power and runtime needs. The UPS’s size must be determined. This is when you should set reasonable goals. It’s simple to state that a system must operate for 48 hours. However, implementing this requirement might not be that easy.
If a long-term power outage occurs, the goal of UPS engineering is to maintain a secure and organized shutdown of the control platform to minimize data loss, system failures, and malfunctions. The system must be designed with a battery that will last long enough for the PC to shut off or the primary electricity supply to return in a reasonable amount of time. Oversized battery systems may take a long time to charge back up.

Type of battery

Next comes batteries. While there are many different battery types available, most UPS manufacturers stick to a few industry-standardized kinds. Some manufacturers provide just one form of technology, such as valve-regulated lead acid (VRLA). Others will provide a range of options, such as VRLA and wide-temperature VRLA. Lithium iron phosphate is also available. Batteries might differ significantly in performance and service life, as explained later.
The operator of a UPS has no means of knowing the battery’s condition with most UPSs, though some will have a failure indication, which might be too late if the system is remote. Ideally, a UPS should include several stages of health into the battery system so that operators may take preventative measures before the battery reaches its end of life.

Type of communication

Finally, consider how UPS delivers these data points. The majority of UPS systems use LEDs, but a few alternatives give dry contact outputs with a preset threshold point. These standards can be met with modern UPS critical systems that include a full data stream into the control platform. EtherNet/IP, Profinet, and Modbus TCP/IP are examples of industrial protocols that can be used for communication, as well as EtherCAT.

AC UPS: pros and cons

An AC uninterruptible power supply maintenance is most appropriate in control systems that rely on alternating currents. An AC UPS comes in a variety of forms.
The regular, offline, or standby architecture is quite simple. These systems are cheap, making them the most popular types of AC UPSs. An offline UPS is designed to transfer mains power from the input to the output without any manipulation, other than a battery charging circuit in parallel with the mains circuit. If the mains goes down, the UPS will switch from the mains circuit to the battery circuit.
The time it takes for the UPS to switch from mains power to battery power cannot be more than 10 milliseconds. The 10 ms transfer is typically unnoticeable to downstream equipment, but it’s a crucial consideration in systems that are vulnerable to voltage fluctuations.

Offline AC UPS subtypes

Within the offline portion of AC UPS solutions, there are two subtypes, which generate the AC output in different ways. They are modified sine-wave output devices and pure sine-wave output devices.
The former (modified sine-wave output devices) take the voltage from the battery bank and, in their most basic form, attempt to simulate a sinusoidal wave. Despite its low price, this UPS has several drawbacks.
The large voltage changes might cause harm to the input circuits of downstream equipment. The constant cycling of the batteries also leads to a large number of switching transients from the UPS’s output. This can cause small power supplies in industrial PCs and PLCs (programmable logic controllers) to deteriorate prematurely over time.
A sine-wave UPS produces the same sinusoidal waveform as the mains power feed. The pure sine-wave UPS is the best choice for such delicate control equipment as programmable logic controllers, distributed control systems, and IPCs (industrial PCs).
In addition, a more complex design is required to achieve this level of output, so it is also more expensive. However, in most cases, the investment will repay itself many times over, since any control devices powered by the UPS will survive longer and result in a lower overall cost of ownership over time.

Online AC UPS

To be truly mission-critical, an application will require an even more sophisticated UPS, commonly known as double conversion or online UPS critical solutions. The UPS of this architecture is never kept in standby mode. The battery circuit is in continual communication with the rest of the system. There is no interruption or voltage sag on the output if the mains power supply is stopped, ensuring smooth battery operation.
The online mechanism also incorporates a degree of filtration and regulation. It changes the incoming AC power feed into DC and then back to AC through an inverter while operating normally. Voltage fluctuations and minor power disturbances on the input side are prevented at this degree of isolation. However, with greater functionality comes greater expense and larger housing.

DC UPS systems vs AC UPS systems

The disadvantage of an AC UPS is that everything downstream depends on the single UPS. That’s why a complex AC UPS is required to provide power to all the downstream devices in a control cabinet system. If the AC UPS crushes, all of its downstream devices will be affected. That’s where a distributed DC UPS can help you save space and money.
The majority of today’s control cabinets use direct current (DC) voltage. The difference between the AC and DC systems is that everything at the point of entry is backed up and supported by an AC UPS, while in the case of DC, the backup occurs after the AC/DC power supply.
You may divide the loads into buffered and unbuffered ones with this UPS orientation. During a mains voltage outage, the unbuffered loads are the devices that do not cause a system failure if they lose power. The power supply, which is an AC/DC unit, can directly furnish the necessary power to the loads.
The buffered loads would be powered by the DC UPS, which would also supply electricity to devices that are required for critical tasks. This lowers the load on the DC UPS considerably. The reduction in amperage translates to a smaller UPS and lower battery requirements.
Not only do DC UPS solutions require less power, but they are also easier to implement than AC UPS systems. DC devices do not require AC-to-DC converters or DC-to-AC inverters.
The UPS maintains the voltages at nominal safety extra-low voltage (SELV) levels of 24 Vdc, which is more energy-efficient for both the power supply and battery bank.
Incorrect usage of extra DC/DC converters for other DC voltages consumes additional current and becomes parasitic on the system. The only DC conversion that takes place in a higher-functioning UPS system is within the battery charging circuit.

The advantages of a DC UPS critical system

A DC UPS system can prioritize the load, giving higher priority to the power source connected to the UPS. When a UPS is in mains mode and charging its battery bank, it watches the load current. The UPS cuts the charge current automatically if the combined load current and charge current would put an excessive strain on the main ac/dc power supply, preventing an overload.
Because they feature simpler circuitry, DC UPS units are frequently physically smaller than their AC counterparts. The reduced size might be advantageous in a control cabinet with restricted DIN rail space.
Some modular DC UPS critical systems include built-in diagnostics, and though many UPSs have a “battery OK” or “system fault” indicator, advanced UPS systems can provide real-time insight into system health and function.
Thus, the UPS engineering and maintenance staff can look at real-time data on the battery’s health, voltage level, current load, and more. They can inspect the battery and see if there is any damage or charge condition, then replace it before it fails. They have real-time information and can replace the battery before it goes bad.

Need help?

If you are still in doubt about what type of UPS system suits your business, our team of qualified UPS management experts can help you find the best UPS critical solution in your particular case.
Bowtie Engineering also offers UPS management training programs to educate you on the way a UPS system functions and how it is monitored.