Page 22 - Energize March 2021
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NEWS


        Maintaining backup battery systems for maximum usage


        and reliability


        Standby battery backup systems play a critical role in keeping essential operations functional in the event of a utility outage.



            acilities like data centers, hospitals, airports, utilities, oil and   known current is drawn while voltage is measured periodically. Details
            gas facilities, and railways can’t operate without 100% backup   of the discharge current, the specified time period for discharge
       Fpower reliability. Even standard commercial and manufacturing   testing, and the capacity of the battery in ampere hours can be
        facilities have backup power systems for their emergency systems,   calculated and compared to the manufacturers’ specification.
        alarms and controls, emergency lighting, steam and for control systems.  For example, a 12 V 100 Ah battery may require a discharge current
           Most backup power systems use an uninterruptable power supply   of 12 A for an eight-hour period. A 12V battery would be discharged
        (UPS) and a string of batteries. The UPS backs up the digital control   when the terminal voltage is 10,5 V.
        system (DCS) to keep control of plant operations until systems can be   Batteries cannot support critical loads during and immediately
        safely shut down or until the auxiliary generator kicks in. Although   after a discharge test. Transfer critical loads to a different battery bank
        most batteries used in modern day UPS systems are “maintenance   until well after the test is complete and then reconnect a temporary,
        free”, they are still susceptible to deterioration from corrosion, internal   comparably sized load to the batteries under test. In addition, before
        shorts, sulphation, dry-out, and seal failure. This article outlines best   conducting the test, prepare a cooling system to compensate for a rise
        practices for keeping these “battery banks” at optimum performance,   in ambient temperature. When large batteries discharge, they release a
        so that if an outage does occur, the backup is ready.  significant amount of energy expended as heat.

        Top two indicators of battery health                   Healthy batteries should maintain a capacity above 90% of the
        Internal battery resistance                            manufacturer’s rating; most manufacturers recommend replacing the
        Internal resistance is a life-span test, not a capacity test. Battery   battery if it falls below 80%. When conducting battery tests, look for
        resistance stays relatively flat up until the end of life draws near.   these indicators of failure:
        At that point, internal resistance increases and battery capacity   •   Drop in capacity of more than 10% compared to the baseline or
        decreases. Measuring and tracking this value helps identify when a   previous measurement
        battery needs replacing.                               •   20% or more increase in impedance compared to baseline or
           Only use a specialised battery tester designed to measure battery   previous
        resistance while the battery is in service. Read the voltage drop on the   •   Sustained high temperatures, compared to baseline and
        load current (conductance) or the AC impedance. Both results will be in   manufacturer’s specs
        ohmic values.                                          •   Degradation in plate condition
           A single ohmic measurement is of little value without context. Best
        practice requires measuring ohmic values over months and years, each   How to conduct standard battery tests
        time comparing them to previous values on record to create a base line.  1.  Float voltage
                                                                  -   Isolate the battery or batteries from the charging system and
        Discharge testing                                            the load.
        Discharge testing is the ultimate way to discover the true available      -   Measure the individual cell voltage or string using a digital
        capacity of a battery but can be complicated to perform. In discharge   multimeter or battery analyzer such as on a monthly basis.
        testing, a battery is connected to a load and discharged over a specified   2.  Charger output
        period. During this test period, current is regulated, and a constant      -   Measure the charger output voltage at the charger output
                                                                     terminals using a digital multimeter or battery analyzer such
                                                                     as the Fluke 500 Series Battery Analyzer on a monthly basis.
                                                                  -   Observe the output current shown on the charger current meter
                                                                     or use an appropriate DC current clamp meter. Measure monthly.
                                                               3.  DC float current
                                                                  -   Refer to manufacturer’s specifications for approximate values
                                                                     for expected float currents.
                                                                  -   Use an appropriate dc current clamp meter to measure
                                                                     expected float current on a monthly basis.
                                                               4.  Internal ohmic values
                                                                  -   Use a battery analyzer such as the Fluke 500 Series to measure
                                                                     the individual battery ohmic values on a quarterly basis.
                                                                  -   Establish reference values and maintain in the battery
                                                                     database.                                  n

                                                               Video: https://www.youtube.com/watch?v=S8HyJTHnMEc
                                                               Contact Comtest, Tel 010 595-1821, sales@comtest.co.za



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