| 3.2 Charging
3.2.1 Charging Methods
Correct charging is one of the most important factor to
consider when using valve regulated lead acid batteries.
Battery performance and service life will be directly affected
by the charging methods.
There are four major methods of charging.
Constant voltage charging.
Constant current charging.
Two stage constant voltage charging.
Taper current charging.
3.2.1.1 Constant Voltage
Charging
This is the recommended method of charging for VRLA batteries.
It is necessary to closely control the actual voltage to
ensure that it is with the limits advised.
Standby service: 2.23-2.30 vpc at 25oC/77oF
Cycle service: 2.40-2.50 vpc at 25oC/77oF
It is suggested that the initial current be set within
0.3CAmps. Frigure 5 and 6 indicate the time taken to fully
recharge the battery. It is also seen that the charging
current is decreased to approx 0.5-4mA/Ah under charging
voltage 2.30 vpc, and 3-10mA/Ah under charging voltage 2.40vpc
when the battery is fully charged at 25oC/77oF.
Note: it is necessary to ensure that the voltage is correctly
set. The charging voltage set too high will increase the
corrosion of the positive plates causing loss of capacity
and ultimately shortening the life of the battery.
3.2.1.2 Constant
Current Charging
This method of charging is generally not recommended for
VRLA batteries. It is necessary to understand that if the
batteries are not removed from the charger as soon as possible
after reaching a state of full charge. Considerable damage
will occur to the batteries due to over charging. The required
recharged capacity is 1.07 to 1.15 times discharged capacity.
3.2.1.3 Two Stages Constant
Voltage Charging
This method should not be used where the battery and load
are corrected in parallel, however, if this method is to
be used, it is suggested that the FirstPower technical department
is contacted.
3.2.1.4 Taper Current Charging
This method is not recommended for VRLA batteries, however,
if this method is to be used it is suggested that the First
Power technical department is contacted.
3.2.2 Effect of Temperature
on Charging Voltage
As temperature rises, electrochemical activity in the
battery increases. Similarly, as temperature falls, electrochemical
activity decreases. Therefore, as temperature rises, charging
voltage should be reduced to prevent overcharge, as temperature
falls, charging voltage should be increate to avoid undercharge.
In general, to assure optimum service life, use of a temperature
compensated charger is recommended. The recommend compensation
factor for FirstPower VRLA batteries is ¡À3mV/oC
Cell (standby use) and¡À4mV/oC cell(cyclic
use). The standard centre point for temperature compensation
is 20oC/68oF. Figure7 shows the relationship
between temperatures and charging voltages in both cyclic
and standby applications.
3.2.3 Charging
Time
The time required to complete each charge depends on the
discharge condition of battery, caracteristics of charge
used, or the temperature during charge. For cyclic use,
using constant voltage charging, this time can be estimated
by the following expression at 25oC/77oF.
(1)Discharge current: Larger than 0.25CA
Tch =Cdis/i + 3 ~5
(2)Discharge current: Less than 0.25CA
Tch = Cdis/I+ 6 ~10
Tch: time required for charge (hours)
Cdis: ampere-hour discharged before charge started(Ah)
I : initial charging current(A).
Complete charge time for float service will be slightly
more than 24 hours.
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