Page 22 - Energize March 2021

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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