Introduction
After installation, batteries are an energy source ready to be used
whenever necessary. It is very important that batteries are:
¡ñ Float charged in order to be maintained in a fully charged condition
during the standby period.
¡ñ Completely recharged after a discharge. Recharged as soon as possible
to ensure maximum protection against subsequent power outages. Early
recharge also ensures the maximum battery life.
Recharge can be done in many ways, depending on the needs of recharge
time or life of the batteries. In general, charging is performed
as follows:
¡ñ at recharge voltages equal to the float voltage and low currents
(long recharge time);
¡ñ at recharge voltage not higher than 2.4 V/cell and high currents
(faster recharge).
The IU recharge method, also known as modified constant potential,
has been used for many years and in a variety of applications, as
it combines the need of having the battery quickly recharged while
ensuring maximum battery life. With this method, recharge starts
at a constant current rate. The voltage increases up to a pre-set
value. The pre-set voltage is maintained and the current then decreases
to a minimum defined value. Finally, the recharge is completed at
a final constant voltage value equal to or less than that defined
for float charge with the current decreasing to the value used in
float.
Recommended procedure for charging and floating
of FIT batteries
It is important to recharge valve regulated recombination batteries
using methods which do not cause excessive gassing. Such methods
would cause excessive water consumption and a loss of battery life
in addition to the venting of gases. The only charging methods which
should be used are those which operate automatically with a preset
constant voltage value supplying a charging current whose maximum
value cannot be exceeded; i.e., constant voltage charging with current
limit and automatic crossover.
Float charge
The voltage recommended for float charge, which will ensure the
maximum life of the FIT batteries is 2.27 V at 20¡ãC. These batteries
can operate over a temperature range of ¨C20 to +60¡ãC, as performance
and life are greatly reduced outside of this temperature range.
The recommended float voltages to maximise the battery life over
the range of temperatures between -20 and +60¡ãC are shown in the
figure 5.
The normal float current observed in fully charged FIT batteries
at 2.27 VPC and a temperature of 20¡ãC is approximately 0.3 mA/Ah.
Because of the nature of recombination phenomena, the float current
observed in the case of the FIT batteries is normally higher than
that of vented batteries and is not an indication of the state of
charge of batteries
Recharge following discharge
The recommended recharge method of FIT batteries to maximise the
battery life is to use a constant voltage equal to the float charge
voltage (2.27 VPC at 20¡ãC) with a maximum charge current of 0.25
C10 amperes. Using this procedure, the recharge times at different
values of maximum current, for a fully discharged cell (100%) are
shown on the following figure 6.
If it is necessary to reduce the recharge time, the IU recharge
method previously explained can be used with a maximum voltage of
2.4 V/cell at 20¡ãC with a maximum current of 0.25 C10. However this
recharge should be limited to no more than once per month to ensure
the maximum service life of the battery.
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