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General Information
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September 25, 2009
• Vol.31 Issue 24
Page(s) 38 in print issue
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Battery Strategy
Maintenance & Monitoring Are Critical For Seamless DC Power Transfer
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| Key Points
• Regardless of how much they’re actually used, batteries degrade over time, driving home the need for regular monitoring and maintenance to prevent downtime.
• Installation of new batteries should follow a precise pattern to ensure they’re ready for use when connected to equipment and also to indicate their initial baseline capacity.
• Maintenance of batteries in larger, three-phase equipment should be conducted only by personnel specifically trained to handle advanced DC products. | For data center managers, an energy crisis has nothing to do with rising prices at the gas pump. Instead, crisis mode hits when data center power fails, and the battery backup systems designed to carry the load can’t save the day. Whereas these systems generally can provide peace of mind, poor battery maintenance and monitoring habits can render them useless in times of need.
 Never Assume Reliability
Batteries are a must-have component in any critical power system, but they’re not a foolproof component, particularly if they’re not properly maintained. According to Jeff Donato, service product manager with Emerson Network Power’s Liebert Services (www.liebert.com), batteries not only represent a significant part of the cost of power systems, but they’re also the least reliable component.
Batteries can wear down over time regardless of whether they’re actually used, Donato says. Short power disruptions can accelerate that wear, even if the disruptions aren’t noticed in the facility because the batteries are working as expected. Further, one bad cell in a battery string could jeopardize a data center by compromising the entire backup system.
Even when UPSes manage to properly respond to power failures, they might simply be switching the data center’s power to a near-depleted set of batteries. Rich Feldhaus, product manager at Tripp Lite (www.tripplite.com), notes that battery systems that remain in use all the way until the end of their usable service life—or beyond that point—can reduce UPS efficiency and increase BTU (British thermal unit) output because the battery charger must run almost continuously with more current than usual to attempt to recharge batteries that are past their prime.
Be Proactive
For some data centers, battery maintenance consists of little more than sporadic inspections to verify batteries are working as they should. But proper maintenance begins prior to startup, Donato explains, adding that batteries need to be fully charged, properly installed (physically, electrically, and environmentally), and their condition verified to minimize the likelihood of costly retests and equipment damage.
Donato recommends proper inspection and acceptance testing of the batteries before startup, which will deliver a baseline for testing conducted throughout the service life of the batteries. Trend analysis depends heavily on the process of collecting, analyzing, and understanding battery information, and without it, data centers cannot guarantee that the batteries will perform as needed. Undetected abnormalities can leave facilities managers scrambling to replace or repair damaged items while the threat of serious downtime looms over their heads.
Mike Stout, vice president of engineering for Falcon Electric (www.falconups.com), says that when new batteries are installed, they should be allowed to charge for 24 hours. Further, he recommends verifying that all of the equipment to be backed up is connected and turned on. Next, turn off the utility power running to the UPS and use a stopwatch to measure the amount of time that elapses until the low battery warning is active and then immediately connect the utility power to the UPS.
Using the data from this test, create a label that includes the date and time of test, along with the runtime in minutes and seconds, and attach it to the top of the UPS. Repeat this runtime test every three months and update the date, time, and runtime on the label. When the battery runtime drops to 80% of the first recorded runtime, replace the battery (or batteries), Stout says.
Batteries and wiring in many larger three-phase UPSes allow for individual testing and inspection, but Feldhaus warns that due to the risk of severe injury or death, staff members tasked to perform battery maintenance for these products must be trained and certified as electronics technicians and fully versed in the use of eye, hand, and body protection required for data center environments and the use of nonconductive rubber matting, insulated tools, and other safety equipment.
“Customers typically will schedule a full internal review and testing of each battery pack at least annually, and sometimes as often as four times a year to ensure proper operation,” Feldhaus says. “These battery checks will typically consist of a visual inspection of all connections for corrosion, checking the torque of each bolt-on battery connection, and an individual professional load test for each individual battery in the string. Some individual internal batteries may need to be temporarily removed for fluid checks and replacement as the service life nears the end.”
Proactive monitoring also can help data center personnel gauge the condition of batteries. Donato suggests using a predictive battery monitoring system, which acts similarly to an ultrasound in that it delivers a “look inside” the battery and assesses its state of health. Such systems can supply knowledge about all critical battery parameters, including cell voltage, overall string voltage, current, and temperature.
Watch The Temperature
Battery life not only is affected by workload, but also by the ambient operating temperature. Falcon’s Stout notes that maximum battery life (three to five years) can be attained when batteries are kept in a 25 degrees Celsius (77 degrees Fahrenheit) environment. By comparison, if batteries are used in a 55 C (131 F) environment, their life will be shortened to one year or less, and if they’re used in sustained temperatures below -10 C (14 F), batteries can lose their ability to properly accept a charge.
Data centers can opt to employ a third-party battery service, which generally offers a mix of battery maintenance, monitoring, replacement, and disposal. Such services can be advantageous for the maintenance and replacement of hot-swappable batteries, which require the disconnection and reconnection of wiring to the battery terminals. Stout warns that if new batteries are connected improperly or the wiring terminals are allowed to short, the UPS will shut down and turn off power to the connected equipment. 
by Christian Perry
What Can Happen To Batteries?
According to Eaton’s Power Quality Division (800/386-1911; www.eaton.com/upsservices), batteries have a slow degradation of capacity until they reach 80% of their initial rating. At that point, degradation advances in a hurry. Here’s a look at what can go wrong with batteries.
| Condition | Cause | | Plate separation | Repeated cycling (charging and discharging), damage during handling and shipping, and overcharging | | Grid corrosion | Normal aging, operating in an acidic environment, and high temperatures | | Internal short circuit | Heat (plates expand, causing shorts), separator failure, handling and shipping, and grid corrosion | | External short circuit | Human error (shorting terminals) and leaks | | Sulfation of plates | Sitting discharged for an extended period, not on charge, or being undercharged | | Excessive gassing | Often due to high temperatures or overcharging | | Drying out | Excessive gassing, high temperatures, or overcharging |
SOURCE: EATON UPS BATTERY HANDBOOK, 2009 |
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