Viewing posts from May, 2021

free EN 50272-2 Hydrogen Venting Calculator

Posted by :  Vanya Smythe in Battery Room Ventilation Requirements, Hydrogen calculations 4 years ago

Try our free EN 50272-2 hydrogen venting calculator:

Industrial Battery Capacity Variation During Life

Posted by :  Vanya Smythe in Battery aging, Battery life, IEEE485, Lead-Acid Batteries, Lithium Batteries, VRLA 4 years ago

# Lead-Acid Battery Capacity Variation Throughout Service Life ## IEEE-485-2010 Standard: Aging Margin Justification The IEEE-485-2010 standard recommends including a 1.25 aging margin in lead-acid battery sizing calculations due to predictable capacity degradation patterns. This understanding of end-of-life capacity "knee" characteristics proved instrumental during negotiations with a vendor regarding batteries that failed capacity discharge acceptance testing on an Australian LNG project. ## Capacity Degradation Patterns ### Vented Lead-Acid Batteries (Long-Duration Discharge) For long-duration discharges of vented lead-acid batteries, capacity remains relatively stable through most of the service life before declining rapidly in later stages. The characteristic "knee" of the life-versus-capacity curve typically occurs at approximately 80% of rated capacity. This behavior is well-documented for discharge rates of one hour or longer. ```svg Battery Service Life (%) 0 20 40 60 80 100 0 25 50 75 100 Capacity (%) Lead-Acid (Long Duration) 80% Capacity "Knee" Point ``` ### VRLA and High-Rate Discharge Applications For high-rate, short-duration discharges of vented lead-acid batteries and all VRLA battery discharges, multiple variables make it difficult to precisely identify when the "knee" occurs. Due to increased internal resistance affecting voltage drop more significantly during high-rate discharges, short-duration performance may decrease substantially below 80% of rating before reaching the rate-specific "knee" point. ## Warranty and Initial Capacity Considerations Most battery manufacturers warrant their products to 80% of published capacities. Initial capacity upon delivery typically ranges between 90-100%, with some batteries requiring several charge-discharge cycles or years of float operation to reach full rated capacity. IEEE Standards 450-2002 and 1188-2005 recommend battery replacement when actual capacity decreases to 80% of rated capacity. To ensure reliable performance throughout service life, the battery's rated capacity should be at least 125% (1.25 aging factor) of the expected end-of-life load requirements. ```svg Time Delivery End of Life 0 25 50 75 100 Capacity (%) 90-100% Initial Capacity 80% End-of-Life Capacity Required Load 1.25x Aging Factor ``` ## Exception Cases Rare exceptions exist where manufacturers of specific products (e.g., Planté cells) guarantee maintenance of 100% capacity throughout service life, potentially justifying a 1.00 aging factor. In such cases, batteries should be replaced whenever capacity drops below 100%. ## Application to Alternative Technologies While this aging margin approach was developed for lead-acid technologies, similar principles are applied to lithium iron phosphate (LiFePO₄) batteries. The industry standard remains oversizing by a factor of 1.25 (1/0.8), despite potentially different degradation characteristics. LiFePO₄ batteries lack sufficient field history in standby power applications to definitively characterize their aging curve shape. Additional research and operational data are needed to optimize sizing methodologies for these newer technologies. ## IEEE 485 Application to LiFePO₄ Battery Sizing LiFePO₄ batteries are currently sized using modified IEEE 485 methodologies, though the standard was originally developed for lead-acid batteries. Industry practice typically includes: 1. Using the same 1.25 aging factor despite potentially different degradation characteristics 2. Applying similar temperature correction factors (though modified for lithium chemistry) 3. Following the same load profile analysis approach 4. Using manufacturer-specific values for depth of discharge limits The IEEE 485 calculation framework provides a proven foundation that engineers adapt for lithium technologies. However, this represents a conservative approach since LiFePO₄ batteries typically exhibit more linear capacity degradation rather than the pronounced "knee" of lead-acid batteries. This linear degradation pattern results from different aging mechanisms - lead-acid batteries often fail due to grid corrosion and active material degradation that accelerates at end-of-life, while LiFePO₄ typically degrades through more consistent SEI layer growth and lithium inventory loss. ```svg Battery Service Life (%) 0 20 40 60 80 100 0 25 50 75 100 Capacity (%) Lead-Acid LiFePO₄ 80% Capacity "Knee" Point ``` Additionally, LiFePO₄ batteries generally demonstrate: - Better temperature performance - Support for deeper depth of discharge - Longer cycle life It's important to note that while the linear degradation pattern is the emerging consensus, long-term field data in standby applications remains limited. Different LiFePO₄ cell designs, manufacturing processes, and operating conditions can produce varied aging profiles. As the industry accumulates more operational data on LiFePO₄ performance in standby applications, sizing methodologies will likely be refined to better match their actual aging characteristics.