FIAMM Industrial Batteries
December 2012
FIAMM AGM Valve Regulated Recombination Batteries: FLX Series- Engineering Manual
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7
Float operation for standby use
For standby applications the recommended float voltage window is between 2.25 to 2.30 volts per cell
depending on the model and on site temperature, as showed in table 4 (charger’s float voltage
tolerance is within
±
0.005 volt per cell).
Table 4 – FLOAT VOLTAGE VS SITE TEMPERATURE
Site Temperature
(
°°°°
F)
Float voltage per cell
FLX
60
2.29
64
2.285
68
2.28
72
2.275
75
2.27
77
2.27
79
2.265
82
2.26
86
2.255
90
2.25
93
2.245
97
2.24
100
2.235
104
2.23
Residual current
Whenever battery chargers are working properly (and in accordance with manufacturer instructions) it is
normal to have a residual float current in fully charged batteries. Residual float currents will slowly
increase during a batteries life and according to cycle frequency. Although the charger is set on a fixed
average voltage, it is normal to record a spread in voltage between each block inside a string. Voltage
variation within
±
250mV/battery is considered as a normal value particularly in the first 12 months from
initial installation.
Recharge following discharge for standby use and boost charge
At the first installation, or soon after a discharge, the recommended recharge method is to use a
constant voltage equal to the float charge voltage with a maximum charge current of 25% of nominal
capacity.
To reduce the recharge time, the IU recharge method can be used with a higher voltage of 2.35-2.40
V/cell at 77° F for 24 hours and a current limit of 0.25 C
10
. This process, also called boost charging,
should be applied only when batteries are not in a fully charged condition and need to be recovered in a
short period of time.
The battery should be placed back on float as soon as possible, ideally as soon as the charge current
has dropped below 20 mA/Ah (or lower if the application has frequent power failures).
Boost charge should be used only when necessary. Frequent equalize charging can result in more
water consumption, which will lead to reduced capacity and shortened battery life.
Float voltage and recharge procedures for frequent discharge applications
Whenever FIAMM
FLX
batteries are used in applications with frequent power failures (such as several
discharges a month) float voltage should be set at a higher range compared with a standby applications
range (i.e. from 2.27 to 2.30 volt per cell at 68-77° F). The recommended float voltage values necessary
to maximize the battery life at different temperatures are shown in table 4. The most important target in
this type of environment is to have the batteries recovering promptly after a discharge
