This is the tenth in a series of units that will educate the reader on the part played by a battery in an uninterruptible power supply (UPS) system. So you bought a battery with a nominal design life of “X” years. The realistic service life is actually significantly less than that, but you don’t know what it is. At around the “half-life” (i.e., half way through the design life) an individual cell-unit fails, then another. You replace the cell-units with new ones (maybe under depreciated warranty, or maybe at full price). Service technicians come in to replace the cells. Each visit costs money and disrupts the service while the work is being performed. You’re told that the new cells create an imbalance with the rest of the cells in the string. At some point you must decide that the entire battery string needs replacement. How do you know when that time has arrived? How do you know if your battery will be able to ride through the next power interruption? Several factors must be considered, including: How many cells (or multi-cell units) are in the string? What has been the maintenance history of the battery? Has the battery been exposed to abnormal conditions, such as extreme heat? Are there other strings in parallel with this one? Do you have a monitoring system capable of taking ohmic measurements on individual cell-units? Do you have reliable records capable of comparing the current measurements to the original base-line measurements? What is the impact of “down time” when a battery or battery string is removed from service for cell replacement? What is the labor cost of cell replacement? How did the battery perform during the last discharge (or planned discharge test)? A lead-acid cell or battery is considered to have reached “end of life” [...]
This is the ninth in a series of units that will educate the reader on the part played by a battery in an uninterruptible power supply (UPS) system. Measuring the health of a valve-regulated lead-acid (VRLA) battery means more than just taking a voltage reading. A cell or battery can have the desired voltage when it has been sitting on float charge, but it might not have enough stored energy to support the critical load for more than a few minutes or even seconds. IEEE 1881[i] defines two terms that are of great interest to battery owners and operators: state of charge (SOC) is “the stored or remaining capacity in a battery expressed as a percentage of its fully charge capacity.” SOC is akin to “energy,” that is, “What is the voltage output of this battery at this moment?” A battery can be fully charged, but because of age or other factors it might not be able to hold up the load for the desired time. state of health (SOH) is “a measurement representing the present state of a battery’s available capacity or remaining service relative to rated capacity or specifications.” SOH is akin to “power,” that is, “How long can my battery support my load?” It adds the element of time and is useful in predicting the “life expectancy” of the battery. While these two terms sound a lot alike, there is a difference. The term “state of charge” is often misunderstood and misused when the speaker is really referring to “state of health”. SOC tells you the capacity of a battery at the time it is measured (e.g., 95% of its rated capacity). SOH is more predictive, telling us the expected service life (usually expressed in units of time or number of cycles) remaining in the battery before [...]
This is the eighth in a series of units that will educate you on the part played by a battery in an uninterruptible power supply (UPS) system. IEEE Standard 1187 establishes the recommended practices for the design and installation of valve-regulated lead-acid (VRLA) batteries. The purpose of this paper is to highlight the most significant considerations identified in that standard, including: Safety considerations Design consideration Receiving and installation procedures IEEE 1188, which was discussed in Unit 8, describes the procedures for acceptance (commissioning) tests, including Pretest requirements Test procedures Corrective actions In general, work on batteries should only be performed by knowledgeable personnel who have proper training/certification, proper tools, and personal protective equipment (PPE). IEEE Standard 1657 establishes minimum curriculum for battery technician certification. Prior to any task involving contact with a battery, a job hazard analysis should be conducted to identify any potential hazards that might be encountered. Safety considerations HAZARD NOTIFICATION - Proactive notification of an impending failure is far better than reactive alarms after a failure has occurred. Continuous (real-time) monitoring is an indispensable tool that, when properly used, can detect and predict failures before they turn into fires, melt-down, arc flash, or other catastrophic failures. Battery monitoring should always be installed by certified technicians, preferably prior to commissioning. SHOCK HAZARD - Because most UPS system batteries are rated for greater than 50 Vdc, electrically-rated and/or insulated gloves should be worn. Energized parts, such as terminal posts and intercell connections, should be insulated or shielded; shields should be removable when a section of the battery is being serviced. GROUND FAULT DETECTION - GFD is recommended (or may be required by code) for most battery systems, depending upon the grounding method used. Refer to local codes or IEEE 1187 for guidelines. The UPS design will usually dictate the [...]
This is the seventh in a series of units that will educate you on the part played by a battery in an uninterruptible power supply (UPS) system. Early on in a UPS design a decision must be made on whether batteries should be installed on racks or in cabinets. Both have pros and cons. The following are typical design considerations. Battery technology Vented lead-acid (VLA) (frequently referred to as “flooded” or “wet cell”) batteries, which are sometimes used on very large UPS systems, are ALWAYS rack-mounted. Valve-regulated lead-acid (VRLA) batteries can be mounted on racks or in cabinets. The remainder of this paper will address considerations for VRLA placement. Size Generally speaking, the larger the battery (both physically and ampere-hour rated), the more likely a rack configuration will be considered. There are no hard and fast rules, but typically once a battery unit (single-cell or multi-cell) gets above 100 AH, it favors rack-mount. Below that, cabinet mounting should be considered. Number “Number” refers both to the number of cells in a string, and the number of strings. UPS systems frequently operate at high dc voltages (e.g., 250 to 800 Volts). An analysis must be made on whether to have a minimum number of battery strings using physically large units, or to have multiple strings of physically smaller units. Such decision is outside the scope of this paper, but it would include analysis of reliability (e.g., where and how many could the single-point failures be?) and maintainability (e.g., when is a unit too large for a person to handle, thereby requiring special handling equipment?). Every cell-to-cell connection is a potential single point of failure. Redundancy can increase or decrease reliability, depending upon the number of failure points. Anything over about 23 kilograms (50 pounds) is probably too heavy to lift safely. [...]
This is the sixth in a series of units that will educate the reader on the part played by a battery in an uninterruptible power system (UPS). Following are definitions of terms that are used throughout this collection of technical papers.
This blog, discussing battery Environmental and safety considerations, is the fifth in a series of units that will educate the reader on the part played by a battery in an uninterruptible power system (UPS). Environmental considerations fall into two categories: - the effects upon the battery by the environment in which it sits (small “e”); and - the effects of the battery upon the Environment in which it was produced, used, and disposed (big “E”) Impact of the environment on batteries Earlier units have discussed the impact of such things as temperature and grid reliability upon the life of a battery system. We will simply state here that it is wise to follow the manufacturer’s recommendations. A lead-acid battery, and in particular a VRLA battery, needs: well ventilated and temperature-controlled air flow. Cells that are packed tightly against each other will not be able to dissipate heat. The result is that cells in the middle of a row will run hotter – and therefore die sooner – than cells at the end of a row. Likewise, cells on the bottom shelf or tier will be cooler – and therefore live longer – than cells at the top of a cabinet or rack. Hot cells are more likely to vent gas, which then must be ventilated to prevent accumulation to hazardous levels. clean air. Dirt and humidity can have a corrosive effect on the battery, and can even be conductive, creating short circuits. Batteries should be inspected and cleaned periodically. chemical free maintenance. No chemical should ever be used to clean a battery unless it has been approved and/or recommended by the manufacturer. Some chemicals can deteriorate the cell container, causing leaks. sunshine-free location. UPS batteries should never be installed outdoors where they can be exposed to the damaging effects of [...]
Despite a century of experience, collective knowledge, and wide-spread preference for lead-acid batteries, they are not without some short-comings. An earlier unit mentioned a couple of issues. In this unit we go into more depth about how, when and why a lead-acid battery might be made to fail prematurely. Most conditions are preventable with proper monitoring and maintenance. This list is not all inclusive, but some of the main considerations are...
This is the third in a series of units that will educate the reader on the part played by a battery in an uninterruptible power supply (UPS) system. In a previous unit we discussed various stationary lead-acid battery chemistries for UPS applications. In this unit we look at the role of battery charger subsystem. Charging regimes can generally be categorized into two types: intermittent and float