High Rate Momentary Load Test
The high rate momentary load test is a functional
test of the individual battery within the series
string. It does not replace a capacity test but it
does indicate if the battery is functional at least
up to the ampere capability of the test load.
A typical load used for batteries in the 30 to 600
ampere range is 100 amperes. The voltage of
the unit 10 seconds after application of the test
load should be at least 1.7 v/c average (10.2,
5.1, 3.4,and 1.7 VDC) for 12, 6, 4 and 2 volt
batteries respectively) or the battery should be
suspected of being open, shorted, discharged or
of very high resistance and low capacity.
Never
perform the high rate momentary load
test on a battery suspected of having a shorted
or open cell. Full face protection should always
be worn during this test, since a spark internal
to a cell could ignite the residual gasses within
the cell.
More information concerning this test and
the minimum voltages to be expected by part
number is contained in the Technical Bulletin
"Integrity Testing" #41-7664.
Impedance Testing
The normal wear out mode of the VRLA
battery includes corrosion of the plate grids,
deterioration of the plate active material and
some drying of the electrolyte. Abnormal failure
modes would include deterioration of the
conductive path and excessive drying of the
electrolyte. These processes will all increase the
resistance of the affected cells and periodic
measurement of the impedance, resistance or
conductance of the cells and trending of this data
can indicate string uniform gradual degradation
and loss of capacity with time. This is shown in
Figure 4.
Rapid changes in individual units may indicate
shorted, open and drying cells and cells with
deteriorating conductive paths.
individual units in the string proportional to their
relative resistance. Therefore in the absence of
an impedance, resistance or conductance test
set, the AC ripple voltage across the individual
units can be measured with a DVM and compared
to each other and the norm as an indication of
their relative resistance and condition.
If the resistance of the batteries has increased by
30% over that when it was new, the battery
should be further tested to determine the cause
and if necessary the battery or system should be
capacity tested to assure reliability.
More information on this topic is contained in the
Technical Bulletin "Impedance and Conductance
Testing" #41-7271.
Interunit Connecting Resistance
High resistance in the interunit connections and
loose connecting hardware can cause excessive
voltage drop during discharge resulting in reduced
operating time and in the extreme case even
cause melting of the battery terminals and
potentially a fire.
The contacting surfaces of all connections should
be brushed clean, removing all lead oxide and
contamination, protected with a special
antioxidation grease, and tighten.
70
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Figure 4 - VRLA Battery Impedance and
Conductance Vs. Capacity and Age
When an AC ripple voltage appears across a
string of batteries it will be subdivided across the
41-7546/0213/CD 10 www.cdtechno.com
