INTERPRETING TEST RESULTS
AVTM246004 BITE 2/2P Rev 4 July 2011
63
BASE
WARN
FAIL
20.25
25%
40%
After each cell/strap measurement, the
receiver
displays the
percent variation and the cell status. Also, the
receiver
will
remember the last values entered since they were saved when they
were entered.
Short-Term Interpretation
Impedance readings for individual cells can be used in the
short term to compare each cell with the average impedance
reading for the entire battery. Cells with the deviations listed
below require further investigation:
•
Flooded lead-acid cells of more than 15% deviation
from the string average
•
Valve-regulated, lead-acid cell of more than 35%
deviation from the string average
•
Nickel-cadmium cells of more than 50% deviation from
the string average and may be exhibiting “memory.”
The deviations are shown in the bar graph accompanying the
printout of a closed test.
Additional investigation of cells exhibiting the above
deviations is recommended (cell temperature and specific
gravity, if appropriate) and perhaps a load cycle test. Megger
recommends that you perform a complete analysis before
replacing cells due solely to high or increasing impedance
values.
Long-Term Interpretation
Impedance readings for the entire battery can be used in the
long term to determine the need for replacement. Battery cell
impedance values should be recorded and compared to
previous readings to determine the position of the cell on the
curve of impedance versus cell life. Generally speaking, cells
with the following variations require immediate attention:
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