A new battery plant configuration that eliminates thermal runaway in valve regulated lead-acid batteries

The traditional battery plant, originally intended for use with flooded lead acid batteries, is widely used in battery plants employing valve regulated lead acid, VRLA, batteries. However use of the traditional plant can lead to thermal runaway in VRLA batteries if the plant is deployed in an uncontrolled environment. Use of temperature compensated float voltage will tend to decrease the probability of thermal runaway, but can also shorten the life of the batteries if the float voltage is lowered too much. This paper introduces a battery plant configuration specifically designed for plants employing valve regulated lead acid batteries in uncontrolled environments. During float operation, the battery float current is limited. However the batteries are on line and isolated from the plant via a parallel combination of a diode and a contactor. Once the batteries are isolated from the rectifiers, a small charger that can be either a constant voltage or a constant current source, and requires less than 8 watts of power for up to four 48 volt strings of 12 volt, 100 ampere hour batteries, cycles through every battery in the plant and maintains each battery in its required float voltage range. This small amount of power is all that is required to maintain every battery in the plant at its required float voltage. Variations of the new plant configuration are discussed. These configurations of the new plant make this scheme easily adaptable to older technology rectifiers and plants as well as rectifiers and plants employing the latest technology.