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Issue 7, Dec 09/Jan 10


Action is needed to reduce the risk of Data

Centre failure during outages By David Fremlin, Powershield Europe

“I was talking to a data centre manager about how his UPS system had failed during a power outage. What you probably want to know is, could this happen to me? And as a data centre manager, am I responsible for this sort of thing? If so, what do I do to prevent it?”


Despite every effort to ensure the security of a data centre’s electrical supply, power outages from the grid still happen. When they do there is a brief period of time when the operation of the whole data centre is supported by a bank of lead acid batteries.

It might be assumed that for this reason the batteries are meticulously maintained; but this is rarely so. Failure of the battery will only become apparent during loss of utility power when a transfer of the UPS system to bypass is not an option; resulting in complete data centre shutdown.


There is little doubt that with any UPS topology which uses lead acid standby batteries, the battery is frequently the cause when the system fails to perform correctly during a power outage. It is commonly reported that over 80% of UPS failures are due to battery faults. The reason for this is that the maintenance regime employed is insufficient to ensure reliable operation.

The battery must be maintained at all times in a reliable operating condition and a suitable maintenance regime should be put in place to achieve this. Unfortunately the importance of the battery is often ignored. For instance, a rotary UPS may need the bearings greased every 6 months; so maintenance is performed at six monthly intervals. While the UPS service engineers are on site they also check the battery. Therefore the battery is tested simply based on the needs of the UPS; the best regime for the battery, the power source of the UPS, is not even considered. Frankly this is like buying a new car and only having it serviced when the tyres need replacing. The engine, the power source of the car, would not last long under those conditions.


Commonly employed battery maintenance regimes do not monitor the cells constantly, consigning battery maintenance to being fault reporting rather than preventative. The best that can be achieved by this kind of maintenance is the detection of already failed or failing cells. The reliability of the UPS system is compromised and will continue to be so until remedial action is taken. UPS manufacturers may employ rudimentary “battery test” features that try to assess battery condition by connection to the end terminals of the battery. These systems are unable to detect the early indications of individual cell failure; hence the problem with battery reliability still exists.


Battery cells rarely fail instantaneously but tend to deteriorate over time. However, the rate of deterioration varies greatly and can be over the course of days, weeks or months and can start at any time. With this understanding it becomes clear that each battery cell needs continuous monitoring similar to that employed by the electronic circuitry of the UPS.

By installing a battery monitoring system a preventative maintenance regime is created which continually monitors each cell in the battery system. A 24/7 monitoring system will detect any significant shift in parameters immediately; something which is unachievable by 6 or 12 monthly battery checks.

Other advantages achieved include a substantial ROI to be gained by the introduction of battery monitoring due to the reduction in time required for maintenance. Health and Safety is also improved as engineers only need to complete a visual inspection, taking all required data from the monitor; including when doing a discharge test on the UPS. The ability to analyse and understand battery condition facilitates the prediction of the future life and assists budgeting for replacement.

The most significant plus point is that the risk of data centre shut down caused by failing batteries is virtually eliminated.


Phone: David Joshua 01672 522959 35
