Lucent Technologies Enhanced VR Series Batteries
7 - 2 Operation
Issue 5 December 1998
produced by flooded lead-acid batteries under similar charging
currents, and are designed to achieve greater than 95%
recombination efficiency at normal float charge and
temperature. However, charging at voltages greater than the
nominal float voltage, charging at elevated temperatures,
shorted cell(s), and a number of other possible conditions may
result in significantly greater charging current and hydrogen
gassing. It is important to note that the hydrogen gassing rate at
0% recombination, the worst case condition, is the same for both
flooded and valve-regulated technologies at equivalent charging
currents and temperatures.
From electrochemical theory, if all the charging current is used
to generate gas, each cell will generate 0.016 cubic feet of
hydrogen per hour, per ampere of charging current at 77°F
(25°C) and one atmosphere pressure. For example, a 48V string
of lead-acid batteries requiring 1 ampere of float current at 77°F
can produce as much as 0.4 cubic feet of hydrogen per hour
(0.016ft3/hr x 1 ampere x 24 cells), or as little as 0.004 cubic feet
per hour at 99% recombination efficiency, a factor of 100
difference.
The quantity of fresh air required to maintain an explosion-safe
environment in the battery area (enclosure) will vary greatly
depending on many factors including, but not limited to, the age
and condition of the battery, the number of cells in the battery
area, the battery temperature, and the current flowing through
the batteries. Therefore, the design of a ventilation system for
batteries in a specific application requires careful consideration
of factors other than the gassing rate of new batteries in typical
operation. Typical gassing rates may be useful as a “best case”
condition, but cannot adequately address “worst case” or any
other operating condition that may occur during the service life
of the battery.
Service Life
Since battery temperature exceeding 77°F (25°C) will decrease
expected life by approximately 50% for each 15°F (8.33°C)
increase in average temperature, it is important to consider the
temperature of the battery environment when designing
equipment or determining battery life expectancy.
Charging
In order to reduce the effects of sustained high temperature
operation, the battery float voltage should be reduced at higher
battery temperatures. This adjustment is performed in systems
