VRLA BATTERIES-FAILURE MODES
Sulphation:
Negative Plates
Corrosion: (a) Negative toplead corrosion (b) Positive
Grid Corrosion
Dry-Out/Water-Loss
Thermal Runaway/Heat
Generation
BATTERY FAILURE PREDICTION
THE IMPEDANCE METHOD
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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 PREDICTION
THE IMPEDANCE METHOD
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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.
Impedance as a function of cell life