UPS, which stands for an uninterruptible power source or an uninterruptible power supply, is pivotal in modern systems. It acts as a precaution against power outages, voltage fluctuations, and power surges, usually due to faulty installations or natural disasters such as thunderstorms. It prevents any consequent damage, whether physical, such as equipment and infrastructure, or digital, like invaluable data stored on computers. Even home users without costly gear and electronics will benefit from UPS, because, as they say, an ounce of prevention is worth a pound of cure. With that in mind, let’s explore different types of UPS.
1. Online or double conversion UPS
Double conversion/online uninterruptible power supply got its name because it converts the incoming AC (alternate current), such as from an outlet to DC (direct current) and back to AC. In doing so, this type of UPS delivers stable, clean, continuous, high-quality AC to equipment and infrastructure. Because of its impeccable efficiency when it comes to eliminating voltage spikes, sags, or breakdown of the system, only this one among all types of UPS is suitable for mission-critical data or equipment.
In other words, online UPS is used in systems where even minute disturbances pose a risk. That’s because it can eradicate even subtle waveform distortion and nuanced harmonics. Case in point, looking at the output via an oscilloscope shows an ideal sine wave. This illustrates that it also regenerates the electrical sine wave, Whereas, other forms of UPS leave it alone and only treat the raw power supply. Unfortunately, the nearly perfect output performance means uninterrupted wear and tear on the components, reducing their durability and life cycle.
How does an online UPS work?
Online uninterruptible power source uses a rectifier and an inverter to convert AC to DC and power the battery and the corresponding load. As the primary power source is always connected to the DC to AC converter, no transfer switches are required. Additionally, if the AC output ever fails, the rectifier will drop within the circuit, allowing the power from the battery to power the UPS. Once input resumes, the rectifier takes the brunt of the load and starts filling up the battery.
Don’t fret if you aren’t familiar with this representative of UPS types or haven’t considered it for home use. It is dominant in systems where the power range exceeds 10 kVA, which yours likely doesn’t. Moreover, it’s the most expensive of the three. Thus, online/double-conversion UPS is typically only used for server rooms and data centers, where files of utmost importance are stored.
2. Offline or standby UPS
Standby or offline UPS, also known as battery backup, is an example you likely recognize. It’s the most basic of them all and a cost-effective choice for personal use or individual power outlets in small businesses. Common use cases include desktop and laptop computers, workstations, network equipment, consoles, and non-stop printing machines. In fact, any costly electronics prone to damage from a power outage or voltage fluctuations is an ideal candidate. However, this UPS technology is widely used only for a power draw of below 1500 VA or 1.5 kVA.
The functionality of standby UPS
Although you get what you pay for, that seems to be sufficient for most typical problems. Standby uninterruptible power supply is efficient against nearly 90% of all power outages. It can balance out spikes in power by bringing down the voltage to optimal levels. Unlike online UPS, it doesn’t react instantly. Instead, it has a 6 to 20-millisecond delay before it starts using power from the power backup. That’s because it has a transfer switch, which, when power gets cut, activates the inverter to convert DC to AC and connects the battery to the output.
Offline UPS is not suitable for all applications, though. First, you must consider its inability to ride out prolonged power outages. It can only supply a limited amount of power. In other words, it can only last long enough for users to safely save what they are working on, or turn off the machine/equipment. Unfortunately, it fails at voltage regulation, as surges and power sags can go straight to the main load. Also, it has no failsafe in cases of an excessive starting current, voltage overload, or invertor breakdown. If that happens, it may pass the entire load to the equipment, rendering its use meaningless.
3. Line-interactive UPS
Line-interactive UPS represents a middle ground between the online and offline UPS, both in price and functionality. It’s a low-cost solution for handling voltage fluctuations, both under and over, of around 20%. To provide conditioned power, a line-interactive uninterruptible power supply requires a multi-tap autotransformer with variable voltage or a buck-boost converter. Another great thing is that it neither uses battery power during normal operation nor under minimal variations in voltage. It is only when the fluctuations skyrocket that battery power kicks in. Finally, it’s power-efficient and silent during operation.
How does line-interactive UPS function?
We explained what makes it unique and in demand. As for the way it works, it’s similar to offline UP. It uses a transfer switch, so it has the same delay before it kicks in. This time it’s a tad shorter, usually 4 to 6 milliseconds. Likewise, it has an inverter that converts AC to DC and vice-versa to enable the battery to charge/supply power.
The only difference is that AC power from the outlet passes through a voltage regulator. For the reasons we mentioned, the inverter never stops working, unlike in offline UPS. This can reduce its lifespan substantially. Moreover, its normal operation tends to drain the battery more often than online UPS, requiring more frequent maintenance or replacement.
Where is it used?
Line-interactive UPS is one of the UPS types commonly employed anywhere power requirements don’t exceed 5000 VA or 5 kVA. Some examples include small businesses, small data centers, and corporate or web servers. That’s because it’s more affordable than an online UPS, yet shields against voltage inconsistencies better than offline UPS. It’s a happy medium between realistic protection needs and high operating costs.