Batteries have been used for long in human history. The battery is a device which converts chemical energy to electrical energy. Beginning with the invention of the lead acid battery in 1859, battery technology has developed to such an extent that batteries are now been used in many industries. Examples of industrial applications of batteries ranges from telecommunications, power supply, alarms, safety systems, medical equipment, etc. With renewable energy systems becoming increasingly mainstreamed into our electricity networks and improved demand for electrical vehicles, usage of batteries is only going to increase from here on.
A consequence of increasing usage of batteries is the need to ensure frequent testing of batteries, thereby ensuring proper maintenance and long-lasting batteries. An ideal way of prolonging the life of a battery is to maintain the charging discharging cycle. In this blog, we will discuss the factors affecting battery health, parameters to estimate the predictable life of the battery and the criteria for selecting an ideal battery discharge unit.
Factors affecting battery health
Let’s discuss the factors affecting battery health. Multiple factors affect performance of batteries, as enumerated below:
- Accidental shorting of terminals of the battery may lead to an electrical failure
- Overcharging a battery also affects battery health. In such instances, increase in voltage above the gassing voltage can generate excess hydrogen as one or more cells are damaged. As a result, the weak cell will complete its charging slowly on account of its low resistance. Another consequence is heating up of the battery
- Secondary/ rechargeable batteries have a self-discharge property. If rechargeable batteries are kept on idle mode for the very long time, the battery goes into a deep discharge state. Therefore, proper charging and discharging is essential.
- Oftentimes, the anticipated life of a battery is estimated by the battery manufacturer in an environment at or close to the reference temperature, i.e., 25°C or 77°F. Above this temperature, battery life is reduced. The corrosion increases exponentially as a function of temperature. It is estimated that an increase of 8.3°C (15°F) in ambient temperature can reduce lead-acid battery life by 50% or more
- Over discharge can also be a factor affecting performance of batteries. Hydration can occur when a lead acid battery is over discharged and not promptly recharged. The lead and lead compounds of the plates dissolve in the water of a discharged cell and form lead hydrate, which is deposited on the separators. Hydration can cause permanent damage of the cell.
- Excessive DC ripple current can also result in ageing of the battery. VRLA batteries are quite susceptible to ripple current as it can lead to cell heating, which accelerates the degradation of cells at risk from thermal runaway.
- Storing wet cells beyond the duration recommended by the manufacturer promotes sulfation. Excessive sulfation can lead to grid erosion which decreases the cell capacity and overall battery life
Parameters to estimate the predictable life of the battery
- Battery capacity is an important parameter which defines the state of health of the battery. During the discharge test, it is important to note whether the the defined capacity of the battery is fully discharging or not. If the charging – discharging cycle of the battery is not maintained then the actual capacity of the battery decreases over time
- During discharge, if the cell voltage is decreasing rapidly, user needs to decide whether to replace the faulty cell as a faulty cell often decreases the overall battery bank voltage
- Battery bank voltage defines the state of charge of the battery. During the discharge, if battery bank voltage rapidly reduces, it means that the state of charge of battery is low and other parameters like cell capacity needs to be checked
- The C rating of a battery defines the rated discharge time of the battery. The battery needs to be discharged as per the rated discharge time and if a battery is discharged before its rated discharge time, the actual battery capacity and battery bank voltage needs to be monitored.
By monitoring the parameters listed above, we can understand the predictable life curve of the battery. Based on these, it can be analysed whether further maintenance is required or the battery bank needs to be replaced.
Selecting the ideal battery discharge unit
As noted above, batteries need to be discharged as per the routine test and the ideal way to discharge a battery is to discharge it as per its C rating. Furthermore, parameters such as bank voltage, battery bank capacity, cell voltage and type of battery and C rating are to be monitored.
Battery health is estimated by comparing the actual battery capacity that has been discharged with the rated capacity. Additionally, state of charge is indicated by the drop voltage of the battery during discharge. Furthermore, other parameters to be monitored are:
- Battery string/bank end voltage: at 85%-90% of nominal voltage as per IEEE/IEC guidelines
- Cell end voltage: 85%-90% of the nominal voltage as per IEEE/IEC guidelines
- Rated discharge time – as per type and C rating of the battery
Sometimes, users tend to choose accelerated discharge in which the discharge current is greater than the rated discharge current and discharge time is less than the rated discharge time. However, we do not recommend this as the actual capacity of battery bank decreases over time and I2R loss will also increase. The chart below illustrates the same:
Thus, the best way to discharge the battery is to discharge as per C rating. In this way, battery performance is optimized and the life of the battery is also improved.
Conclusion
SCOPE’s battery loading units are ideal for controlled and monitored discharge of batteries. The kit is essential for optimizing the battery performance and maximizing the utilization of the battery by extending the life of the battery. To know more, please visit https://www.scopetnm.com/test-and-measurements/dc-test-equipment/battery-loading-unit or write to us at marketing@scopetnm.com
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