What Is a UPS?

Commonly known as a battery backup, an uninterruptible power supply (UPS) is a rechargeable battery used to backup main power feeds and provide seamless power when there is a main line utility outage.

This seamlessness distinguishes the UPS from standby generators. Generators come online within seconds of a power outage but create a break in the power current as their fuel engines turn on. The UPS can be positioned between backup generators and critical equipment to ensure continuous power until those longer-lasting power sources can engage.

A UPS unit is more than just batteries as it also offers power conditioning for added protection against problems such as surges and voltage spikes. They use active filters to remove harmonic distortions for a clean, consistent AC waveform. 

The average consumer may be familiar with small UPS devices for the home and office space, which are designed to provide sufficient power for a controlled shutdown needed to protect against equipment damage or data loss. These small units may even provide line conditioning and surge protection but are not intended to supply power for long durations — sometimes only minutes at a time.

However, enterprise or data center UPS units found in  healthcare, transportation control and monitoring, or financial services facilities provide top-class power protection for heavy loads.

UPS Use Cases

Applications of the UPS device range based on the unit’s design and quality. They fit a variety of cases from everyday to extreme. Some normal operating conditions demand high-quality power for sensitive electrical loads in industrial applications or even rugged situations. Some typical circumstances include:

• General everyday power backups for offices and home systems, which are simple and market-friendly
• Industrial and process-sensitive applications that require a UPS to provide high-capacity, three-phase, seamless power
• Medical centers and emergency facilities that need UPS units to provide clean and reliable power for critical life-saving equipment
• Data centers and vital telecommunications facilities that need backup for high-load and highly sensitive electronics
• Military-grade and rugged applications that require protection from humidity, altitude, shocks and vibrations, and sand and dust

Learn More: Future Proofed Critical Power Systems

The Three Main Types of UPS Devices

UPS devices fulfill many use cases, but their topology or type comes in three basic configurations.

Single-conversion UPS devices are the simplest UPS topology. AC power input is directly sent through the UPS to the output loads. At the same time, AC power is also channeled through an inverter to recharge its batteries. If the main power supply drops out of pre-defined limits, then the main power flow is switched to batteries until the main power returns to normal.

There are two popular single-conversion UPS designs. Standby UPS units act as described above, feeding utility power until a problem is detected and then switching over to batteries. Line-interactive UPS units act like a standby UPS, but with the addition of a power regulator that conditions input voltage to normal levels before passing through to sensitive equipment. In line-interactive units, if power should drop out of pre-defined regulated limits, batteries take over.

Double-conversion UPS devices create an added layer of protection for output devices. AC power is fed into the UPS, immediately converted to DC power, and then reconverted back into AC power — a double-conversion. This double conversion isolates loads from the raw utility power entirely, outputting only clean and reliable electricity for critical equipment. If the main power should fail or drop below the UPS limit, batteries take over.

Multi-mode UPS devices offer features that define single- and double-conversion UPS devices. Under normal operations, multi-mode UPS units act as line-interactive systems, regulating AC power input within safe tolerances and supplying directly to loads. This method is the most efficient. If power should drop out of this tolerance, the UPS switches to a double-conversion power method, converting AC power twice.

Learn More: Industrial AC and DC Power Systems

UPS Battery Life

The useful service life of UPS batteries is an important consideration and varies based on many factors starting with the battery chemistry. Valve-regulated lead-acid batteries (VRLA), for example, typically last 3-10 years while lithium-ion may last 8-15. Although they are designed with a specific life expectancy, actual battery service life differs from designed battery life because of four factors:

• Ambient temperature plays a significant factor in shortened battery life. Battery capacity ratings are measured at a particular ambient temperature or range. A typical range is 55-77 degrees Farenheit (15-25 C). Some studies indicate that operating a UPS in hotter ambient temperatures reduces battery life, and sometimes a 15 F increase can reduce battery service life by 50%.
• Battery chemistry is such that its ability to store and deliver power diminishes over time, despite following all the usage guidelines.
• Discharge cycling occurs when the UPS switches from main power to battery power. Every time this cycling happens, the relative battery capacity reduces by a fraction of a percent of the total capacity. For example, the lead-acid chemistry has a maximum number of discharge/recharge cycles before the chemistry is depleted.
• Maintenance plays another significant but actionable factor in battery life. Although often marketed as maintenance-free, UPS devices do require periodic maintenance to ensure maximum service life. Maintenance-free refers to the fact that the batteries do not require fluid.

Buying the Right UPS: Key Considerations