Specifying an uninterruptible power supply (UPS) battery system solution involves a trade-off between cost, performance and safety. Some users place too much emphasis on cost and too little on safety. Discounting safety increases the risk to both business assets and to those individuals who work in the vicinity of the equipment. Improperly configured battery systems can develop problems such as thermal runaway, excess hydrogen gas emission, fire, and chemical and/or acid leakage from inside of the batteries.
The Electricity Storage Association (ESA) estimates that sales of industrial batteries, as might be used in UPS applications, amount to $5 billion each year. Many end users who purchase batteries assume that a UPS battery system consists of a simple group of batteries connected together. Specifying and configuring battery systems, however, can be tricky and configuration mistakes can result in higher operational costs and safety risks.
Although new battery technologies are emerging (such as lithium-ion and nickel-metal-hydride), the vast majority of battery systems being shipped today in support of UPS applications consist of various types of lead-acid batteries. For cost calculation comparison of battery types, download the APC by Schneider Electric Lithium Ion vs. VRLA Battery Calculator.
When specifying and configuring UPS battery systems, three general approaches are common in the marketplace today-standardized battery systems, custom solutions that are vendor engineered, and battery solutions that are customized by end users.
Standardized battery systems
Standardized battery systems which are configured based on proven and field tested designs are optimal from a risk minimization and system reliability standpoint. Standardized systems are pre-engineered and often modular and they eliminate the risks of onetime engineering. These pre-engineered solutions are analyzed, designed, tested, qualified, and proven out over an installed base of many systems. When configuring these systems, designers need only to select a specified/required back-up time.
Customized battery systems
If a customized UPS battery system is required, a vendor-engineered battery solution is recommended. Most vendors have applied their best practices to many different end user environments. They have already taken into account parameters such as UPS performance, charge and discharge characteristics, battery service life, types of potential faults, customer maintenance plan or schedule, and environment. They also have learned how to manage problematic situations and are aware of issues to avoid.
End User customized battery systems
If end users choose to customize a UPS battery system themselves, then they should follow a best practices checklist in order to ensure a safe and reliable system. That checklist should include the steps listed below:
- From a design perspective properly select and size the batteries, calculate the discharging current, select the conductor size (conductors refer to the areas of batteries and the UPS where connections are made), calculate the short circuit current, and select the appropriate protection devices (like circuit breakers, fuses or switches).
- Then analyze and validate the safety of the whole battery system assembly and the entire UPS system, under normal and abnormal operation, as well as at full charge and end-of-discharge.
- Perform strict quality control of critical devices including UPS, batteries, and protective devices. Ensure that enough spare parts are kept in inventory
- Consider a battery monitoring system. Over time, battery system performance decreases and monitoring systems are capable of checking on the health status of the various battery blocks. The best solutions monitor the health status of each individual battery unit, ensure normal operation during charging and discharging modes, and open the circuit and/or alarm under specified abnormal conditions.
- Set up a periodic maintenance plan and ensure the implementation of the defined plan.
To learn more about methodologies for specifying and configuring UPS battery systems, download the APC by Schneider Electric white paper #207 “Design and Specification for Safe and Reliable Battery Systems for Large UPS”.