APPLICATION OF THE QUARTZ-CRYSTAL MICROBALANCE TO MEASUREMENT OF THE CONCENTRATION OF ELECTROLYTE IN LEAD-ACID-BATTERIES

The density of the electrolyte in a lead/acid battery may change by 10 to 20% during the discharge/charge cycle and the value within this ra nge can be used as an indication of the fraction of available energy s tored in the battery. We describe the application of a quartz crystal microbalance to the determination of the density of sulfuric acid solu tions over a range of temperatures and during the discharge of a typic al lead/acid battery. The sensor response varies linearly with tempera ture, and in a quadratic manner with the density of the solution. Good agreement with the theoretically predicted behaviour of thickness she ar mode oscillators immersed in liquids was observed. The sensor perfo rmed well in the laboratory experiments under artificial conditions. B y contrast, initial studies using the sensor in a lead/acid battery op erating under real conditions revealed that stray capacitances can inf luence the stability of the oscillator.