Battery Power - September/October 2012 - (Page 6)

FEATURE The Use of Lithium-Ion Batteries in Uninterruptible Power Supplies Michael A. Stout, Vice President Engineering Falcon Electric, Inc. Being in the UPS industry, Falcon Electric, Inc. is frequently asked why the industry hasn’t adopted the use of Lithium-ion (Li-Ion) batteries inside more products. Li-Ion batteries have a much higher energy density allowing them to be smaller and weigh less than half of an equivalent Valve Regulated Sealed Lead-Acid (VRLA) battery currently used in UPS systems. LiIon batteries (Figure 1) provide much longer on-battery runtimes and can be recharged faster than their VRLA counterparts. Unfortunately, high energy density Li-Ion battery packs have a number of issues that preclude them from being used in the typical commercial off-the-shelf UPSs. At the present time, with few exceptions, their use is limited to custom UPS products specifically designed for highly specialized applications. generate enough heat to ignite the internal lithium. Once ignited, the remaining batteries in a shipping carton or on a pallet will ignite. The lithium fire would then burn at a high enough temperature to burn through an aircraft’s aluminum fuselage. Further, most standard fire extinguishers or aircraft fire systems are useless against a lithium fire due to its high burning temperature. Secondary batteries have a differing chemistry and are defined as being rechargeable. They are usually shipped from their manufacturer partially charged in an attempt to keep the energy density as low as possible during transportation. The DOT and UN regulations divide secondary batteries into two basic categories, which are defined by the level of energy density contained inside the individual cells or batteries. The batteries used inside cell phones, computers and power tools typically fall into the lower energy density category and have much fewer transportation limitations; hence why they are allowed to fly on commercial airliners with passengers. The batteries used in a typical UPS must be capable of supplying the high current demand of the UPS for a sustained period of time. The period of time may be from a few minutes to several hours, depending on the application. For many decades, the lead-acid battery (Figure 2) has met this demand. Its capability to supply the high current demands of the UPS is very good. However, its energy density to weight ratio leaves a lot to be desired. High power UPS systems capable of providing several hours of battery backup can have lead-acid battery banks weighing tons. The energy density of a lead-acid battery ranges from 30 to 50 Watt/Hours per Kg, while it is 110 to 160 Watt/Hours per Kg for Li-Ion chemistry batteries. This represents a weight reduction of two to three times that of an equivalent lead-acid battery. This makes Li-Ion batteries viable for use in elecFigure 2. Valve-regulated lead-acid tric vehicles as well (VRLA) battery as UPS products. Unfortunately, all shipments of UPS units containing high energy density Li-Ion batteries, battery banks or batteries packaged inside a UPS must be shipped as class 9 hazardous materials and cannot be shipped on commercial airliners. They must ship by ground cargo only. This becomes very impractical and drives the costs associated with the incorporation of lithium batteries up even further. There are substantial additional costs associated with the implementation of Li-Ion batteries in a UPS. First, there is the cost differential between lead-acid and Li-Ion batteries. Good quality Absorbed Glass Mat (AGM) VRLA batteries are very Figure 1. Lithium-polymer battery system containing a Battery Management System (BMS), a charger and a large number of lithium-polymer cells. With the large number of cell phones, computers and power tools now being sold with rechargeable Li-Ion batteries, it may seem a bit odd that their use inside a UPS would be a problem. The primary issues are cost, safety and federal regulations. Due to Li-Ion battery chemistries having differing levels of danger, the Department of Transportation (DOT) (in CFR 49, Sections 100 to 185) have divided the level of regulation based on primary and secondary battery types. Regulations are also based on levels of energy density. Other applicable regulations are United Nations UN3090 & UN3091. A primary battery is defined as one that is shipped fully charged and cannot be recharged. Due to their chemistry and high level of charge available when shipped, Li-Ion batteries are considered the most dangerous. The crash of a freight carrier’s aircraft was recently suspected to be caused by a large number of lithium primary batteries that were onboard. According to reports, the lithium primary batteries were not declared as hazardous materials. If lithium primary batteries become internally shorted, due to their high amount of stored energy and chemistry, they can 6 Battery Power • September/October 2012

Table of Contents for the Digital Edition of Battery Power - September/October 2012

PRBA Battery Proposals Adopted By UN Transport Sub-Committee
The Use of Lithium-Ion Batteries in Uninterruptible Power Supplies
Monitor Your Battery Cells for Superior Reliability
Juicing Up the Battery: Cutting Edge Research Delivers Battery Enhancements
PEM Fuel Cell Systems – Reliable Backup Power Source for Remote or Extended Run Power Outages
Why Your Next Renewable System Should be Built Around Energy Storage
ICs & Semiconductors
Charging, Testing & Monitoring
Power Supplies
Industry News
Calendar of Events

Battery Power - September/October 2012