Lifetime Estimation for Plastic Optical Fibers in Harsh Acid Environments

The work described in this paper explores the suitability of using plastic optical fibers (POFs) as sensors for the development of fast battery chargers. Lead–acid batteries, widely used in the automotive industry, contain an electrolyte formed by a high concentration of sulfuric acid (35%
$ \hbox{H}_{2}\hbox{SO}_{4}$
), an acid environment that can maintain an elevated temperature during the charge and discharge processes. This presents a challenge for the selection of sensors that can withstand such harsh conditions over extended periods of time, in order to monitor the charge cycle and state of health of the battery. POFs can be used as density sensors immersed in the electrolyte at different places within the battery—density varies with location. The accuracy of the density readout must be maintained throughout the useful life of the battery, up to 15 years. In this paper, we present results of over 9000 h of lifetime tests of POFs used as sensing elements for electrolyte density, as well as a procedure to estimate their lifetime for the target application.