It may not have quite the same acclaim as Valentine’s Day, but today marks a holiday that data center operators across the country can appreciate – National Battery Day. These useful power sources are crucial to a facility’s power reliability, especially when it comes to the uninterruptible power system (UPS) where they’re also one of the most vulnerable parts.
In fact, battery failure is a leading cause of load loss, and knowing how to maintain and manage your UPS batteries will extend their life and save you time and potential trouble in the future. When it comes to UPS deployments in larger systems, there are five primary factors to consider in maximizing battery life.
Shelf life, storage and acceptance testing
In order to improve service life expectations and reliability, it’s important to ensure that the batteries are properly stored prior to being installed and placed into service. Storage facilities should be climate controlled with proper ventilation capabilities so batteries can be kept cool and dry. Failure to comply with proper storage will lead to shortened runtimes and reduced capacity.
All battery manufacturers have shelf life and storage parameters. A rule of thumb, in terms of time, is no more than six months of storage in a properly designed storage facility.
To validate runtime and capacity expectations, an acceptance test should be performed. The acceptance test will be able to determine if there are any flaws within the manufacturing process, improper storage or perhaps even hidden damage as a result of shipping and handling. This test might be the most important and best valued test that any operator can have performed to ensure reliability of the battery systems when they’re needed most.
Ambient temperature
The rated capacity of a lead acid battery is based on an ambient temperature of 77°F (25°C). It’s important to realize that any variation from this operating temperature can alter the battery’s performance and shorten its expected life. To help determine battery life in relation to temperature, remember for every 15°F average annual temperature above 77°F, the life of the battery is reduced by 50 percent. Ambient temperatures below 77°F may reduce the battery backup time, similar to a car battery on a cold morning.
Battery chemistry
UPS batteries are electrochemical devices whose ability to store and deliver power slowly decreases over time. Even if you follow all the guidelines for proper storage, usage and maintenance, batteries still require replacement after a certain period of time.
Positive grid corrosion has been the most common end-of-life factor for UPS batteries, which is a result of the normal aging process due to UPS battery chemistry and involves the gradual breakdown of the inner segments of the positive grid within the battery.
Cycling
During a utility power failure, a UPS operates on battery power. Once utility power is restored, or a switch to generator power is complete, the battery is recharged for future use. This is called a discharge cycle. At installation, the battery is at 100 percent of rated capacity. Each discharge and subsequent recharge reduces its relative capacity by a small percentage. The length and quantity of discharge cycles determine the reduction in battery capacity.
A good analogy is a loaf of bread. It can be sliced into many thin slices, or a few thicker slices. You still have the same amount of bread either way. Similarly, a UPS battery’s capacity can be used up over a large number of short cycles or fewer cycles of longer duration.
Lean-acid chemistry, like others used in rechargeable batteries, can only undergo a maximum number of discharge/recharge cycles before the chemistry is depleted. Once the chemistry is depleted, the cells fail and the battery must be replaced.
Maintenance
Battery service and maintenance are critical to UPS reliability. A gradual decrease in battery life can be monitored and evaluated through voltage checks, load testing or monitoring. Periodic preventive maintenance extends battery string life by preventing loose connections, removing corrosion and identifying bad batteries before they can affect the rest of the string.
Even though sealed batteries are sometimes referred to as maintenance-free, they still require scheduled maintenance and service. Maintenance-free simply refers to the fact that they don’t require added water.
Without regular maintenance, your UPS battery may experience heat-generating resistance at the terminals, improper loading, reduced protection and premature failure. With proper maintenance, the end of battery life can be accurately estimated and replacements scheduled without unexpected downtime or loss of backup power.
Batteries are a critical part of the UPS, and determining battery life can be a tricky business. It’s often promoted based on design life, defined as how long the battery can be expected to perform under ideal conditions.
Article written by Ed Spears, The DataCenter Journal
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