Abstract
In battery applications, particularly in automobiles, submarines and remote communications, the state of charge (SoC) is needed in order to manage batteries efficiently. The most widely used physical parameter for this is electrolyte density. However, there is greater dependency between electrolyte viscosity and SoC than that seen for density and SoC. This paper presents a Quartz Crystal Microbalance (QCM) sensor for electrolyte density-viscosity product measurements in lead acid batteries. The sensor is calibrated in H2SO4 solutions in the battery electrolyte range to obtain sensitivity, noise and resolution. Also, real-time tests of charge and discharge are conducted placing the quartz crystal inside the battery. At the same time, the present theoretical “resolution limit” to measure the square root of the density-viscosity product of a liquid medium or best resolution achievable with a QCM oscillator is determined. Findings show that the resolution limit only depends on the characteristics of the liquid to be studied and not on frequency. The QCM resolution limit for measurements worsens when the density-viscosity product of the liquid is increased, but it cannot be improved by elevating the work frequency.
Highlights
Lead acid batteries are among the most common types of batteries used in many applications such as electric vehicles, photovoltaic systems, remote stations, submarines, general support systems or Sensors 2012, 12 telecommunications systems
If a mass is adsorbed or placed onto the quartz crystal surface, the resonant frequency and the frequency of oscillation changes in proportion to the amount of mass. This property is widely used in research on mass adsorbed gasses, allowing quartz crystal oscillators to be used as high sensitivity microbalances intended to measure mass changes in the nanogram range by coating the crystal with a material which is selective towards the species of interest [4]
This paper describes the characterization and application of a 9 MHz Miller Quartz Crystal Microbalance (QCM) oscillator sensor for real-time monitoring of the state of the charge (SoC) during charge and discharge processes of a lead acid battery [6,7]
Summary
Lead acid batteries are among the most common types of batteries used in many applications such as electric vehicles, photovoltaic systems, remote stations, submarines, general support systems or Sensors 2012, 12 telecommunications systems. If the nominal frequency of the QCM sensor is increased, the sensitivity can be improved in order to measure the density-viscosity product changes in a tested liquid medium. It is possible to use a QCM sensor to detect changes in the acid concentration by means of the frequency shift due to the changes of the square of the density-viscosity product. This paper describes the characterization and application of a 9 MHz Miller QCM oscillator sensor for real-time monitoring of the SoC during charge and discharge processes of a lead acid battery [6,7]. A new expression for the resolution limit that can be achieved with QCM sensors to measure changes in the density-viscosity product of a liquid load is obtained in the theory section. It will be shown that the sensor is able to detect changes in the battery’s SoC of about 0.2% with a time interval of 2 s
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