What Are the Types of Uninterruptible Power Supplies?

Uninterruptible Power Supplies/Sources (UPS) are backup electrical energy sources designed to kick in when main power fails. Scenarios can include voltage interruptions, spikes, surges—pretty much any instance where the UPS detects a significant enough reduction. Sizes and output can vary from small units meant to power a single computer to large units used to power buildings.

What Are Uninterruptible Power Supplies Used For?

Most UPS should turn on almost instantly when a power disruption is detected, providing uninterrupted electrical power to the connected systems. The amount of time a UPS can operate depends on the model, lasting anywhere from a few minutes to several hours, to always-on. Then users have time to safely shut down their hardware or connect to another power source. In the case of an always-on UPS, they continually protect critical equipment.

UPS most commonly protect data communication systems or data centers and are available for small office or personal use. You can also use them to keep other critical electronic devices powered during outages and surges, like cordless phones and security systems.

Offline/Standby

Offline/Standby UPS are the simplest type of UPS and function as battery backups. These models are designed to detect changes in voltage above and below specific points, switch to internal batteries, then convert that energy to AC power. The process can take up to 25 milliseconds, depending on the unit. AC power is then used to keep connected devices running. Offline/Standby UPS provide the smallest window of power backup, typically offering five to up to 20 minutes.

Examples of Standby UPS use include consumer electronics, security systems, and point-of-sale systems for retail stores.

Line Interactive

Line Interactive UPS detect voltage fluctuations and act as a backup power source during blackouts and surges, just like Standby models. What sets a Line Interactive UPS apart is that they use an internal autotransformer to detect and adjust for small changes in voltage without switching to internal batteries. This function allows Line Interactive UPS to protect connected devices from small voltage changes and brownouts without affecting its ability to act as a separate power source. Line Interactive UPS typically provide a slightly larger power backup window—up to half an hour—but can last for several hours with capacity expansion.

Examples of Line Interactive UPS include the same kinds of devices used with Standby UPS and networking equipment, mid-range servers, and home theaters.

Online/Double-Conversion

Online/Double-Conversion UPS are the most advanced types of UPS and provide a constant stream of power. They convert AC power to battery power and then back to AC, eliminating power transfer time since the units never need to switch power modes. The constant stream of energy keeps internal batteries charged, which will activate when there's power loss. The internal batteries will automatically recharge once external power restores and the UPS starts cycling from AC to the battery to AC power again. Online/Double-Conversion UPS are used for critical electronic equipment.

Usage examples include data centers, IT equipment, telecom systems, and high-end server banks.