Types of Uninterruptible Power Supplies

An uninterruptible power supply (UPS) is a source of clean electrical power that is stable, and readily available in the case of a power outage. It can generate 110VAC required to power equipment for a limited period until the grid power is restored. A typical uninterruptible power supply includes a battery that provides critical backup power. The rest of the conversion from the battery to AC power is done by an electronic voltage converter. In addition to providing backup power, a typical UPS also protects your equipment and peripheral devices from damage due to bad power quality, lightning strikes, etc. 

Not all UPS systems are the same, and protecting your equipment requires finding the right solution. Some parts of the process are straightforward, like determining how much battery life you'll need, while others are more complicated, like determining whether you need an online, offline, or line-interactive UPS. Let's break down the different UPS types and what you need to know about choosing one.

What Is an Uninterruptible Power Supply?

A regular gasoline or diesel generator backup system can be considered a UPS too, but the industry often associates the term “UPS” with an electronic voltage converter.  

Basically, a UPS provides reliable AC power to the load when power from the wall outlet stops or becomes unstable. There’s always a well-charged battery inside a UPS, which provides a DC voltage, typically 12 or 24V. An electronic voltage converter transforms the battery DC voltage to a 110V AC voltage, which is given out on a couple of sockets, similar to wall plugs. We plug our computer and peripherals into the outlet sockets.  

An “Offline” UPS comes ON only when the wall AC power fails. At other times it is charging its battery and just sits idle. When wall AC power fails, the UPS comes On or is manually turned ON. It runs till its battery drains out.  

An “Online” UPS system is always ON. And will remain on till its battery drains out. If AC wall power returns, it will not switch back. In other words, it is always on and always providing power to the devices plugged into it. In the Online UPS, the input AC wall power is received and re-converted or synthesized to new AC voltage. The synthesized AC voltage is stable and clean without any of the defects of wall power, hence the devices operate reliably without any failure.  

Some of the issues with wall AC power that may need a UPS as a remedy are: 

  • Surges and sags: Surges are brief spikes in electricity that can damage or destroy electronics, while sags are sudden and brief drops in voltage.
  • Blackouts and brownouts: Blackouts occur when the power goes out completely, typically from weather, damage to utility lines, or power grid failures. Brownouts refer to gradual voltage drops from normal to low which may damage electronics.
  • Frequency drift: Although rare, occasionally wall power may show a frequency drift from the usually 60 cycles (or Hertz). 
  • Transients: Man-made noise from heavy-moving systems like elevators, and heavy-duty electrical machines like welders can add noise to the “normally clean’ wall power, which can inflict damage on other devices plugged in.  

For critical infrastructure like medical facilities, data centers, and military operations where bad power quality and loss of power can cause losses due to downtime or damage, a UPS can be a great investment. 

Usually, you'll find a UPS with preset voltages at 110 volts (V) in North America or 220V in Europe or Asia. Their batteries are only meant for short-term use of about five to 30 minutes. While its backup time is limited, a UPS can provide enough time to initiate safe shutdown procedures, save important data or generally improve the reliability of installed systems.

types of uninterruptible power supplies

Types of Uninterruptible Power Supplies

You'll find three primary uninterruptible power supply types on the market.

Offline or Standby UPS Systems

An offline UPS also called a standby UPS, is the simplest and most affordable option. It typically stays "asleep" while the system uses wall power. When wall power fails, an automatic transfer switch starts to pull power from the UPS instead. When the AC power from the wall returns, the transfer switch reverts to wall power and the UPS goes back to sleep.

These systems can offer battery backups and light surge protection with high efficiency. While an offline UPS will switch on within seconds, it doesn't provide the instantaneous transfer that many electronics require. It may offer more limited protection, but it's a good choice for low-power devices such as computers or office equipment.

Line Interactive UPS Systems

Line interactive UPS systems can smooth out minor glitches and distortions in wall AC power by Instantly synthesizing the portion of the missing or distorted AC cycle and “adding” it to the mains feed wire. It uses an electronic converter and a multi-tap variable-voltage autotransformer. Since this system works off the wall AC power, it doesn’t need a battery. So, this system can provide the partial function of a UPS, hence cannot be called a real UPS. It is more appropriate to call this a power conditioner.  

A line-interactive UPS is a good choice for moderate protection against fluctuations and battery backups for complete outages. These units eliminate switching times. Still, they can be heavier and larger than online and offline UPS systems. 

Online or Double Conversion UPS Systems

The most common type of UPS is the online system, also called a double conversion system. An online UPS system always keeps the DC-AC inverter on to provide clean AC power to the user. Since the inverter is always on, there's no transfer time involved. When wall power fails the user can continue working and may hear beeps to alert that they’re running on backup battery power. Other than that, their computer or printer will not see any difference. 

These systems are typically the most reliable, protecting against all major interruptions, which makes them the first choice in UPS systems. 

Again not all online or double-conversion UPS systems are the same. Some of them are very compact while others are bulky. The difference lies in the fact that there are modified sine-wave and true sine-wave, the latter being the bulkier and more expensive. Some devices like hand-held tools and laptops may not care about the above difference, For a high-end system, it is advisable to not compromise on the quality of backup power, hence pure sine-wave should be preferred. 

How to Choose the Right UPS System

Selecting your UPS system isn't always straightforward. There are many factors to consider, including:

  • Standards and regulations: Many industries have specific standards your UPS will need to meet to ensure power delivery in critical applications, such as medical equipment and military operations. Regulations or standards may require you to use a power supply with certain technologies like immediate switching or pure sine waves to ensure critical equipment stays functional.
  • UPS type: Consider which problems are the most pressing to your situation. If your incoming power frequently surges or sags in small amounts, consider a line interactive UPS. If it creates harmonic distortion, line noise, or frequency variations, you may need a double conversion UPS. An offline system may be perfectly suitable for simple power outages and brownouts.
  • Battery life: Are you more worried about having enough time to shut down a few critical electronics to save data, or do you need to wait for your emergency generator to come online? Determine how much time you'll need and select a short or long-backup-time UPS with a large enough battery. Loads with higher wattages will drain your battery faster.
  • Sine wave demands: A UPS creates either simulated sine waves or pure sine waves. Simulated sine waves can have gaps between cycles that cause problems for your system, while pure sine waves are more reliable for sensitive electronics, such as appliances with AC motors and some kinds of medical equipment. Without pure sine waves, you might experience shutdowns or stress on your devices.
    The quality of AC power available may sometimes become relevant. What may appear to be a normal 110V AC source may not actually be a pure sine wave source and some systems may have a problem with it. They may glitch, flag errors, or simply fail to perform well. Medical diagnostics, instrumentation, and precision moving parts run by precision motors and such can be sensitive to the quality of AC waveform. A pure sine wave is considered perfect and some synthesized sine waves may be imperfect but may end up working well. The system engineer determines what’s suitable for their system. 
  • Replacement costs: Calculate the value of everything that depends on wall power to operate. Create a business case for how your UPS can mitigate risk and what important resources it might protect, including the equipment itself, data loss, and downtime costs. Consider how each type of power interruption, such as harmonic distortion or slow switching times, will impact the specific electronics you use.

find the ideal UPS system with Astrodyne TDI

Find the Ideal UPS System With Astrodyne TDI

A well-selected UPS can control nearly any power interruption to help you avoid damage, prioritize safety, and reduce costs. The best solution depends on your unique application, but it always starts with high-quality components. Here at Astrodyne TDI, we offer an array of UPS systems to fit moderate and high-demand applications. From compliant, medical-grade power supplies to protective industrial units, we can help you find or build the right system for your needs.

With ISO-certified facilities and over half a century of expertise, we're a global leader and the trusted source for some of the most demanding industries. Reach out today to request a quote and learn more about Astrodyne TDI's vast capabilities.