Thermal runaway is the rapid uncontrolled increase in temperature when the rate of internal heat generation exceeds the rate at which the heat can be expelled. The cells in a battery pack are generally close to one another, and if thermal runaway is not detected, damage to the battery as well as equipment nearby can occur, as well as system failure and service disruption. Thermal runaway in one cell can start a chain reaction that spreads to surrounding cells increasing damage.
Thermal runaway occurs most frequently in valve regulated lead acid batteries, but it can also happen in VLA batteries. Thermal runaway is not a “sudden occurrence” as it may seem. There are a few warning signs which include an increase in cell temperature and an increase in charge current. The factors involved in creation of thermal runaway include:
- Plate discharge & sulfation
- Increases in float current
- Internal resistance changes of battery cells
- Dry out of the cells
Over-temperature in a standby battery is a potentially serious condition. Operating the battery in higher temperatures than specified can seriously shorten its life. Every 10°C above 25°C reduces the service life of the battery by 50%. To compensate and minimize the risk, the battery charger must be temperature controlled, and the charging voltage and current must be properly limited.
Thermal runaway can also be caused by either a fault condition within the battery such as a ground fault or localized heating, such as sunlight, on a portion of the battery, of which can lead to higher current draw. Eagle Eye also offers a ground fault monitor system that can also help in preventing damages due to ground faults and thermal runaway.
It is the “positive feedback” progression of exponentially increasing temperature that leads to thermal runaway. First, hydrogen gas is released which creates an explosion risk, followed by hydrogen sulfide gas which is poisonous and highly corrosive to electrical equipment. Then, if this is continued unnoticed, the batteries can catch fire.
Eagle Eye’s Battery Temperature / Thermal Runaway Monitor is compliant with IFC 608.3 and NFPA 1 Article 52. IFC 608.3 is intended to prevent a catastrophic explosion damaging the surrounding environment, batteries with smaller total amounts of acid should also be protected as they are just as vulnerable to thermal runaway as larger installations.
Our Battery Temperature / Thermal Runaway Monitor will safely and accurately monitor your batteries to prevent thermal runaway. Contact us or request a quote for the BTM Series Battery Temperature Sensor and Thermal Runaway Monitor.