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VRLA BATTERIES-FAILURE MODES. Sulphation: Negative Plates Corrosion: (a) Negative top- lead corrosion (b) Positive Grid Corrosion Dry-Out/Water-Loss Thermal Runaway/Heat Generation. BATTERY FAILURE PREDICTION THE IMPEDANCE METHOD.
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VRLA BATTERIES-FAILURE MODES Sulphation: Negative Plates Corrosion: (a) Negative top- lead corrosion (b) Positive Grid Corrosion Dry-Out/Water-Loss Thermal Runaway/Heat Generation
BATTERY FAILURE PREDICTIONTHE IMPEDANCE METHOD • Definition: Any device through which an electrical current will flow exhibits an impedance to that flow • Significant research in cell impedance has demonstrated a proportional relationship with cell age and discharge history • Cells of similar size, age and manufacture consistently exhibit similar AC Impedance readings until cell conditions deteriorate. • A cell in poor condition because of sulphating plates or deficient internal connections displays a higher than normal impedance.
BATTERY FAILURE PREDICTIONTHE IMPEDANCE METHOD • By testing the capacity & impedance of new cells, baseline data can be established • Baseline data will vary, according to cell size and manufacturer, but individual cell condition can be determined by comparing the impedance value against its baseline. • This technique can also be used to highlight problem cells in a battery bank. Good cells exhibit a similar impedance value. • 30% deviation indicates problem cells.
