Analysis of refractometric fiber optic state-of-charge (SOC) monitoring sensor for lead acid battery

In situ monitoring of the state of charge (SOC) of lead acid battery is important to understand the residual electrical energy. Usage of battery reduces the charge content of the active electrolyte which in turn changes its refractive index. This paper reports refractometric fiber optic sensor developed for on-line monitoring of SOC. The SOC is monitored during discharging phases of the battery using the developed fiber optic sensor probe along with terminal voltage, temperature and depth of discharge using a LABVIEW based data acquisition system. The paper gives the working principle, design and construction details, results and calibration of the fiber optic sensor (FOS) probe. The in situ monitoring capability of the developed FOS is demonstrated in comparison with the contemporary off-line methods of specific gravity and terminal voltage measurements.