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What to know before using li-ion battery technology in a UPS system

Lead-acid batteries were the norm for most UPS systems, but lithium-ion batteries are an attractive alternative. Here's what to know before bringing them into your data center.

Lithium-ion batteries have been a staple of the consumer electronics market for years, diversifying in chemistry and construction to provide reliable, high-density power storage for laptops, tablets, smartphones and other mobile devices.

But as lithium-ion (li-ion) battery technology evolves to tackle new high-capacity tasks, such as automotive power sources, designers and manufacturers recognize the potential role of li-ion batteries in the data center -- and especially for uninterruptable power supply (UPS) systems.

Let's take a closer look at li-ion battery technology, its role in UPS systems and considerations for implementation.

Q: What are the benefits of li-ion batteries in UPS systems?

As technologies like virtualization multiply effective computing densities, UPS systems must also evolve to better address the new data center environment. For example, modern UPS systems strive for smaller footprints and to make better use of available space. UPS systems also need to run cooler, and be smarter, so they can better track lifespans, predict battery faults and reduce maintenance requirements.

Lead-acid batteries are notoriously hard to monitor -- there's almost no meaningful way to check battery health and make intelligent predictions.

Li-ion battery technology generally provides several times more energy and power density than traditional lead-acid batteries. This means li-ion batteries and their corresponding UPS systems can be smaller and allow for more flexible placement within the data center. Smaller batteries also mean reduced weight, allowing organizations to place UPS systems in locations where traditional lead-acid UPS systems might not be practical.

Li-ion batteries are also more resilient to elevated temperatures than lead-acid batteries. Normally, increased operating temperatures allow the battery to produce more current, but decrease the time that the battery can provide that energy. This means traditional UPS systems are more sensitive to data center cooling requirements. By comparison, li-ion batteries are virtually unaffected by ambient temperatures -- within the range that typical data center equipment can safely operate.

Lead-acid batteries are notoriously hard to monitor -- there's almost no meaningful way to check battery health and make intelligent predictions. But li-ion battery technology is extremely predictable in terms of temperature and energy output, and includes a comprehensive battery monitoring system that can predict runtime and health. Li-ion batteries are sensitive to changes, so management is required to ensure proper charge rates and internal temperature control. In addition, li-ion batteries can last more than 10 years before replacement is required.

Q: Are there any disadvantages to li-ion battery technology in UPS systems?

There are a few considerations that potential li-ion UPS adopters should keep in mind.

First, li-ion battery chemistry is diverse. This is a big benefit -- li-ion batteries can be tailored for many different levels of energy demand -- but it's crucial to select li-ion battery technology that is best suited for the usage demands of UPS systems. For example, UPS batteries must be able to deliver a lot of energy quickly, but don't necessarily need a lot of runtime -- such as a li-ion battery that might be used in an electric car. Similarly, li-ion batteries for UPS applications don't need high cycle times because the UPS only runs on rare occasions.

One of the benefits of li-ion technology is its high energy capacity. But this is usually matched with high charging and thermal sensitivity. A li-ion battery system malfunction, such as a crash in-transit, can possibly lead to an explosion or fire. This has resulted in strict rules for li-ion battery transportation and storage.

Another limitation is that li-ion batteries are not typically hot-swappable in UPS systems. The physical differences between lead-acid and li-ion batteries mean that li-ion batteries are not necessarily a direct replacement for lead-acid batteries. Although it is theoretically possible for an existing lead-acid UPS system to accommodate li-ion replacement batteries as a direct or drop-in replacement, it would still require the existing UPS system to update its firmware to achieve the right charge algorithms and runtime predictions for the new li-ion cells.

Finally, cost can also be a factor in li-ion adoption. Li-ion battery technology costs more than similar lead-acid batteries, and the complexity of the battery management system also adds some cost to the compatible UPS.

Li-ion implementation challenges

The challenge with implementing new technologies in three-phase UPS products is that these really aren't off-the-shelf options. Battery availability and production time may cause issues, so reach out and contact the UPS manufacturer to determine whether a li-ion battery alternative is available.

Consider whether a conversion from lead-acid to li-ion is even possible for the specific UPS model, and  evaluate the related costs and possible downtime involved. Based on the vendor's details, data center teams might choose to wait until the current lead-acid UPS is due for replacement and implement li-ion as part of a full-scale data center technology refresh cycle.

Q: Are there any commercial li-ion UPS systems currently available for data centers?

In the private and light-industrial sectors, li-ion already plays a prominent role in personal battery backups, such as for personal computers and peripheral devices, and larger applications, such as home appliance power backups.

But power backups for data center tasks are also emerging. UPS manufacturers, such as Methode Electronics and Schneider Electric, have li-ion options for several UPS product lines. Li-ion availability should increase through the later part of 2016, and options for other three-phase UPS products should appear in 2017.

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