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Application Note CC-002-A
87
33 Application Note CC-002-A
Internal Resistance Measurement Procedures
INTRODUCTION
Intercell resistance problems account for a great many battery system
failures. In UPS or other high current applications, the failures can lead
to explosions and fires that are not only costly but also represent safety
hazards.
Most battery manufacturers, unfortunately, do not supply baseline
resistance values, so presently users must establish their own values. The
recommended procedures for establishing base lines are:
New systems
. . . read all the resistance values after installation and
calculate the average value.
Older systems
. . . disassemble 10 sets of intercell connections; burnish,
neutralize and clean them; reapply corrosion inhibiting compound,
reconnect, retorque, and then calculate the average of the new readings.
Intercell resistance measurements should be taken once a year of
all cells
(IEEE-450-1995 and forthcoming IEEE VRLA maintenance
recommendations). Any connection that is 20% or greater than the
baseline or installation value requires corrective action. The importance
of these measurements is illustrated by the new VRLA standard that
recommends
quarterly sampling 25% of the intercell connection re-
sistances. If an upward trend is detected, all connection resistances
should be measured to aid in determining the cause and corrective
actions.
HOW TO TAKE READINGS
When taking intercell connection resistance readings, it is important that:
a) the test leads are connected properly. Measurements should include the
post to intercell connector resistance. Always check your connections
and connect
only to posts, not nuts, bolts or straps. (See figs. 1-5. This is
the main area where connection problems occur;) and,