The IEEE, Kansas City Section

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Institute of Electrical and Electronics Engineers

JAN. 1995

A publication provided by Power Engineering, Inc., to share information regarding methods and procedures available for maintenance and testing of electrical generation, storage and distribution systems.

A lead acid battery is the heart of your UPS or telecommunications system. It is the power source for your standby generators and may provide backup power for your switchgear. The battery will provide continued operation of your computer, voice and data communications systems, or operate critical electrical distribution equipment when needed IF IT WORKS ! The key to ensuring the reliable operation of your battery plant is a comprehensive predictive maintenance and testing program. The following are guidelines that can help establish or reinforce your maintenance program.

Periodic inspection should be performed of the battery installation. On-site personnel should include Daily walk-thrus of the battery, generator and switchgear rooms as well as more thorough Weekly and Monthly inspections. Off-site locations should also be inspected on a regular basis. Inspections should also be performed of 'sealed battery' installations. The term 'maintenance free' has long been forgotten as an unrealistic and misleading description of a sealed battery. The fact that the battery may be in an enclosure should not prevent you from performing periodic inspections. Establish a pilot cell program. The pilot cells provide a quick overview on the electrical and physical conditions of the battery and should be reviewed during Monthly inspections.

In addition to the inspection, electrical measurements should be recorded periodically of the battery installation. Readings should be performed on a Quarterly and Annual basis. The Quarterly readings should include individual cell and bank voltages, electrolyte and ambient temperatures. The Annual readings should also include the Intercell resistance's of all connections. A relatively new procedure that may be included is the recording of Internal cell resistance or impedance. Through experience, Power Engineerings' field personnel have been able to identify suspect cells using internal cell measurements that voltage and specific gravity readings alone could not. In the case of a sealed or valve regulated battery, this information can be critical in the identification of weak units. Annual readings on your flooded cells and Quarterly readings on sealed batteries will provide useful information on the condition of your battery plant.

The true measure of the condition of your battery is how it performs under load. Industry standards recommend the replacement of a battery when it reaches 80% of its rated capacity. Load testing is the only accepted way to determine where the battery is on the capacity vs. time curve for the particular cell or unit. Our experience has shown that the best method of performing a battery load test is to monitor each individual cell or unit during the discharge. Weak or bad cells can be easily identified and scheduled for replacement. In addition, load testing the battery can verify the integrity of the DC conduction path. Thermographic scanning should be performed during the discharge. In the case of a UPS battery, consideration should be given to incorporating the load test into a functional test procedure of the system.

All data should be maintained for review and to track the performance of the battery over time. Establishing benchmark data will greatly enhance your success in the maintenance of a reliable system. Consideration should be given to installing diagnostic equipment to record discharges and help evaluate the battery under load. This may be a simple "hit" monitor that records overall voltage, current and the duration of the discharge or a system that can track the performance of each cell.