Analysis and interpretation of AC-measurements on batteries used to assess state-of-health and capacity-condition

Two AC-measuring methods, conductance and impedance testing, have been proposed as possible methods of assessing state-of-health and capacity-condition of VRLA (valve regulated lead acid) batteries. The difference between the two methods is, that the impedance method measures the numeric value of the induced AC-signal, while the conductance method includes the effect of the phase-angle in the induced AC-signal. This paper presents data gathered in cooperation with Danish Power Stations, as well as analyses and interpretations of the material. The gathered data are recorded from VRLA-batteries as well as flooded batteries. It describes a very simple method of measuring and calculating the internal battery impedance-parameters the internal resistance and the phase-angle, based on the equivalent circuit of the battery, using an injected AC-signal passing through the battery. The measurements can take place with the battery on- or off-line. It includes identification and description of variables and sources of failure in the battery, which primarily affect the internal impedance-parameters, and significantly affect the linearity and the accuracy of the measurement results. It includes studying the variance in measurements and development of the exact correlation-factor between measured values versus state-of-health and capacity-condition. The variation in float-voltage is exposed, as well as the ratio of influence this variation has on the measured values and the developed correlation factor.