GaN chips for monitoring density and temperature of lead-acid batteries

Abstract

Lead-acid batteries are indispensable in various applications, and it is crucial to monitor their status. However, the existing sensing units for lead-acid batteries are limited by their bulky size, slow response time, and lack of temperature sensing and compensation capabilities. In the current work, a compact GaN-based sensing device was proposed to simultaneously measure the electrolyte density and temperature. The device comprises a light-emitting diode (LED) and a photodetector (PD) integrated on a GaN-on-sapphire chip in a monolithic configuration. The forward voltage of the LED reflects the electrolyte temperature, while the photocurrent of the PD varies with electrolyte density due to optical reflection changes at the exposed sapphire interface. The measured signals were processed using a decoupling matrix to achieve temperature compensation. The device exhibits a sensitivity of −29.1 μA/(g/cm³) for density in the range of 1.09 g/cm³ to 1.29 g/cm³, and -1.07 mV/°C for temperature in the range of 25 to 45 °C. The performance of the device was also validated through comparisons with commercial meters and real-time monitoring during the charging and discharging of the batteries. The device has notable advantages in size, cost, and fast response/recovery time (134.3/201.4 ms), rendering it a promising tool for monitoring lead-acid batteries.