User manual

10 www.enersys.com
Publication No: US-NP-AM-003 • January 2011
Proper charging is one of the most important factors to
consider when using maintenance free sealed lead-acid
batteries. Battery performance and service life will be directly
affected by the efficiency of the charger selected. The two
charging methods are:
 Constant Current Charging
 Two Step Constant-Voltage Charging

Constant Current Charging
This charging method is not often utilized for sealed lead- acid
batteries, but is an effective method for charging a multiple
number of batteries at one time, and/or as an equalizing
charge to correct variances in capacity between batteries in a
group. Caution should be exercised when charging by
constant current. If the charge is continued at the same rate
for an extended period of time after the battery has reached a
fully charged state, severe overcharge may occur, resulting in
damage to the battery.
 Two Step Constant Voltage Charging
Two step constant voltage charging is the recommended
method for charging a sealed lead-acid battery in a short
period of time, and maintaining the battery in a fully charged
standby or float condition,thereafter. Figure 7 illustrates the
characteristics of a two step constant voltage charger.
The characteristics shown in Figure 7 are those of a constant
voltage, constant current charger. In the initial charging
stage, the battery is charged by constant current. The
charging voltage rises, as the charge continues, until it
reaches 2.45 volts per cell, at which point the charging mode
automatically changes to constant voltage charging. During
the constant current charging stage (A-B) the charging current
which has decreased to point B is sensed, and the charging
voltage is switched to the float level of 2.3 volts per cell from
the recovery level of 2.45 volts per cell. The switch to
constant voltage trickle charging occurs after the battery has
recovered approximately 80% of the rated capacity over a
given period of time. This charging method is one of the most
efficient. The recharge time is minimized during the initial
charging stage while the battery is protected from overcharge
by the system switching over to float charge at the switching
point B.
Charging
Figure 7. Charging Characteristics of a Two Step Constant-Voltage
Charger
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