Many industries and businesses such as oil and gas, fuel and energy, hospitals, data centres, and airports require highly reliable backup power to prevent the damages from unpredictable power failures. In the absence of an effective backup power source, interruptions in critical operations can result in massive losses.
To avoid this, they are equipped with emergency backup power systems comprising an uninterruptable power supply (UPS) and a set of batteries. Maintaining the backup battery systems is important to efficiently keep essential processes functional in case of power outages.
Indicators of Battery Health
To understand how well your battery systems are working and how long until they require repair, maintenance or replacement, it is important to understand your battery health. The top indicators of battery health are:
- Internal Battery Resistance
- As the battery’s life is about to end, its internal resistance increases and battery capacity decreases. Until then, the battery resistance stays relatively constant.
- By keeping track of the battery’s internal resistance, you can identify when a battery needs to be replaced.
- Specialized battery testers can efficiently measure battery resistance while the battery is in service. By recording the voltage drops on the load current (conductance) or the AC impedances and comparing them over long periods of time, you can create a baseline and identify when your battery drifts away from it.
- Discharge Testing
- Discharge testing involves connecting a battery to a load and discharging it over a certain period. During this period, the current is regulated and a constant known current is drawn while the voltage is measured in fixed intervals of time.
- The results – the discharge current, the specified period for discharge testing, and the capacity of the battery in ampere-hours- can be determined and compared to the manufacturers’ specifications to identify the battery capacity.
- Healthy batteries should maintain a capacity above 90% of the manufacturer’s specifications. If the capacity goes below 80%, it is recommended that you replace the battery.
Recommended Battery Tests and Testing Schedules
The Institute of Electronics and Electrical Engineers (IEEE) sets the standard guidelines and practices for battery maintenance and testing. According to the IEEE, batteries should undergo a combination of periodic tests over its lifetime.
The various tests required and their respective schedules as recommended by the IEEE are:
- Acceptance test:
- An acceptance test is a capacity test performed on a new battery to determine if it meets all the necessary specifications or manufacturer’s ratings.
- This test is performed at the manufacturer’s factory or during initial installation
- Periodic discharge testing:
- Discharge testing determines the available capacity of a battery by discharging it under the influence of a load and comparing the recorded data with the manufacturers’ specifications.
- This test should be performed at an interval not greater than 25% of the expected service life, or two years, whichever is less.
- Annual discharge testing:
- This test is performed when any battery has reached 85% of the expected service life or dropped more than 10% from its baseline capacity.
Scheduling full-scale discharge testing can be complicated. So, regular maintenance of battery systems is paramount. By using the battery according to manufacturer guidelines and requirements and following the IEEE recommendations for battery maintenance and testing, you can maximize the life of your battery system.
Indicators of Battery Failure
Every battery system will degenerate with time and will eventually need replacement. Here are some indicators of failure while performing battery tests that you should keep in mind.
- Battery capacity of less than 80% of the manufacturers’ ratings
- A drop incapacity of more than 10% compared to the baseline or previous measurement
- An increase of 20% or more in impedance compared to the baseline or previous measurement
- Sustained high temperatures compared to the baseline and the manufacturers’ specifications
- Degradation in plate condition
Causes of Battery Failure
Some of the common causes of battery failure are:
- Loose terminals and inter-cell connections: Loose terminals and inter-cell connections cause a loss of energy due to their resistance. In some cases, battery terminals also become highly corroded, resulting in failure.
- Aging: With continuous usage, all batteries age and their performance decline with time. As the end of a battery’s life draws near, it is more prone to failure.
- Over-charging and over-discharging: If a battery is overly discharged and if operations are continued in such a state, battery plates can undergo buckling and ultimately fail. High charging rates and excessive charging can also cause failure from non-uniform distribution of current.
- Thermal runaway: If the battery’s rate of internal heat generation exceeds the rate at which heat is being expelled, it increases the overall temperature of the battery and dries out the cells. Eventually, the battery may melt or explode.
Standard Procedures to Conduct Battery Tests
While performing standard tests, it is important to make sure you are using the right battery test equipment and wearing proper personal protective equipment (PPE) to protect yourself from possible safety hazards.
- Float voltage
- Measure the individual cell voltage or string using a digital multimeter or battery analyzer on a monthly basis.
- Charger output
- Measure the charger output voltage at the charger output terminals using a digital multimeter or battery analyzer every month.
- Observe the output current shown on the charger current meter or use an appropriate DC current clamp meter once a month.
- DC float current
- Refer to manufacturers’ specifications for approximate values for expected float currents.
- Measure the expected float current on a monthly basis with an appropriate DC current clamp meter.
- Internal ohmic values
- Measure the individual battery ohmic values on a quarterly basis with the help of a battery analyzer.
- Establish reference values and record them in the battery database.
By taking timely measures to maintain your battery systems to maximize their lifetimes and by periodically testing your batteries, you can achieve maximum usage and reliability in the long run.