When it comes to ailments that affect batteries in uninterruptible power systems (UPSs), few have the capacity to spark disaster like thermal runaway. Occurring most often in valve-regulated lead acid (VRLA) batteries, this potentially hazardous condition is created when the rate of internal heat being generated exceeds the rate at which it can be expelled. Ultimately, the increasing temperature dries out battery cells until the container softens, breaks and melts, triggering a range of possible catastrophes — from load failure and costly unplanned downtime to electrical fires, exploding batteries and the release of toxic chemicals.
Although thermal runaway clearly has the capacity to evolve into a true disaster, the good news is, it is unlikely to occur if just a few simple rules are followed. Above all else, heed the old adage “an ounce of prevention is worth a pound of cure.” To that end, be sure to:
1. Keep cool — Because heat is one of the primary factors that leads to thermal runaway, it is critical to maintain the temperature of the battery environment at 77°F or below. The second factor related to thermal runaway is the charge current. As the battery heats up, the internal resistance to the charging current is lowered, which allows more current and in turn, creates more heat. Once thermal runaway begins, it cannot stop itself; the only cure is to remove and replace the batteries.
2. Trust the experts — Performing regularly scheduled preventative maintenance on the UPS and batteries in instrumental in avoiding thermal runaway. During a PM visit, technicians can spot problematic batteries or cells before they fail, as well as adjust the charging voltage and current to ensure batteries are not overcharged. In addition, while VRLA batteries are often deemed “maintenance-free,” they still require regular cleaning, checking and testing by trained professionals.
3. Replace the batteries — Some VRLA batteries may be pro-rated up to 10 years, but in reality, their average life expectancy generally falls between 5 to 7 years. All UPS batteries have a rated capacity that is based on specified conditions, and any variation from these guidelines can alter the battery’s performance, shorten its expected life and lead to conditions such as thermal runaway. To be safe, experts recommend replacing batteries when they reach 5 years.
4. Monitor your environment — Although battery monitoring systems have historically been more prevalent in higher cost, wet-cell installations, the fact is, thermal runaway is more common in VRLA battery strings. With an array of offerings available for lead-acid battery applications, a monitoring system will record the voltage and temperature of every jar, saving data so it can be reviewed to establish trends. A monitoring system can also identify if a particular jar has abnormal conditions, enabling it to be isolated and replaced long before thermal runaway has the chance to rear its ugly head. Laboratory tests by battery vendors have shown that it takes hours or days for thermal runaway to be self-sustaining.
5. Be aware — While routine service calls, regular battery replacement and a monitoring system go a long way toward avoiding thermal runaway, don’t forget the value of simply keeping your eyes open and ears on the ground. Visually inspect batteries for signs of corrosion or other defects, and keep your ears pealed for any unusual rattling or other sounds coming from the UPS.
By adhering to these simple guidelines, you can significantly reduce the likelihood of thermal runaway running away with your critical load!