Exide Technologies Section 92.61 - Manual (Page 23)

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12.6 Effects of Float Voltage
Float voltage has a direct effect on the service life
of your battery and can be the cause of thermal instability.
A float voltage above the recommended values reduces ser-
vice life. The chart below shows the effects of float voltage
(temperature corrected) on battery life.
Temperature corrected 77°F (25°C) Percent
Float voltage per cell Reduction
Minimum Maximum in Battery Life
2.23 2.27 0%
2.28 2.32 50%
2.33 2.37 75%
Voltage records must be maintained by the user in accor-
dance with the maintanence schedule published in this manual.
To obtain the optimum service life from the battery, it is impor-
tant to make sure the battery’s float voltage is within the rec-
ommended range.
12.7 Float Current and Thermal Management
Increased float current can portend a condition known as
thermal runaway, where the battery produces more heat than
it can dissipate. VRLA batteries are more prone to thermal
runaway because the recombination reaction that occurs at
the negative plate, and reduces water loss, also produces
heat. High room temperature, improper applications,
improper voltage settings, and incorrect installation practices
can increase the chances of thermal runaway.
As with good record-keeping practices, monitoring float
current can prevent a minor excursion from becoming a
major issue.
12.8 AC Ripple
AC ripple is noise or leftover AC waveform riding on the DC
charge current to the battery that the rectifier did not remove.
It is usually more pronounced in UPS than telecom systems.
Proper maintenance of the UPS capacitors will reduce the
amount of ripple going into the battery.
Establishment of absolute limits for AC ripple has always
been problematic because the degree of damage it causes
depends on the wave shape, peak-to-peak magnitude and
frequency. Accurate characterization of AC ripple requires an
oscilloscope and even then, only represents a picture of the
ripple at that moment in time.
Whatever its exact characteristics, AC ripple is always
harmful to batteries. Depending on its particular properties,
ripple can result in overcharge, undercharge and micro-
cycling that can prematurely age the battery. The most
common and damaging result of AC ripple is battery heating
which can lead to thermal runaway. AC ripple will decrease
battery life and should be reduced as much as possible.
12.9 Ohmic Measurements
Impedance, resistance and conductance testing is collectively
known in the industry as ohmic measurements. Each
measurement is derived using a manufacturer-specific and
proprietary algorithm and / or frequency. This means that one
type of measurement cannot be converted or related easily to
another.
“Reference” ohmic values are of dubious value because so
many factors can affect the way the readings are made and
displayed by the devices. Connector configuration and AC
ripple as well as differences between readings of temperature
and probe placement will prevent the ohmic devices from
generating consistent and meaningful data. The meters work
better with monoblocs and small capacity VRLA products
and less well with large (>800-Ah) VRLA and flooded battery
designs. Users should be particularly skeptical of data
taken on series-parallel VRLA battery configurations as the
feedback signal to the device may follow unforeseen paths
that can overwhelm it.
It is best for users to establish their own baseline values
for their battery as specifically configured. Do not rely on
reference values.
If users wish to enhance normal maintenance and record-
keeping with ohmic measurements, GNB recommends the
trending of this data over time. Use a first set of readings
taken 6 months after initial charge and installation as the
baseline data. Subsequent measurements should be taken
using the same device over the life of the battery. Because
cell positioning within the string (connector configuration to a
particular cell) can affect the reading, always compare each
cell at baseline to itself in the new data. Standalone ohmic
data is not sufficient to justify warranty cell replacement.
Responsible ohmic device manufacturers acknowledge that
there is no direct relationship between percent ohmic change
from baseline and battery capacity. A change from baseline
of 25% or less is in the normal noise or variability range.
Changes between 25% and 50% may call for additional
scrutiny of the system. An IEEE compliant discharge test is
usually warranted on systems exhibiting more than a 50%
change from baseline. Consult an GNB representative for
specific questions about ohmic data.
SECTION 13
13.0 Equalizing Charge
Under normal operating conditions an equalizing charge is
not required. An equalizing charge is a special charge given
a battery when non-uniformity in voltage has developed
between cells. It is given to restore all cells to a fully charged
condition. Use a charging voltage higher than the normal float
voltage and for a specified number of hours, as determined by
the voltage used.
Non-uniformity of cells may result from low float voltage due
to improper adjustment of the charger or a panel voltmeter
which reads an incorrect (higher) output voltage. Also, varia-
tions in cell temperatures greater than 5°F (2.78°C) in the
series string at a given time, due to environmental conditions
or module arrangement, can cause low cells.
13.1 Equalizing Frequency
An equalizing charge should be given when the following con-
ditions exist:
A. The float voltage of any cell (as per Section 14.0) is less
than 2.18 VPC.
B. A recharge of the battery is required in a minimum time
period following an emergency discharge.