User manual

 Charging Voltage
The charging voltage should be regulated according to the
type of service in which the battery will be used. Generally,
the following voltages are used at 25˚C (77˚F).
For standby (float) use . . . . . . . 2.25 to 2.30 volts per cell
For cyclic use . . . . . . . . . . . . . 2.35 to 2.45 volts per cell
In a constant voltage charging system, a large amount of
current will flow during the initial stage of charging, and
decrease as the charging progresses. When charging at 2.30
volts per cell, charging current at the final stage of charging
will drop to as little as 0.002CA.
Charging voltage should be regulated in relation to the
ambient temperature. When the temperature is higher, the
charging voltage should be lower. When the temperature is
lower, the charging voltage should be higher. For specific
recommendations, please refer to the section on Temperature
Compensation. Similarly, capacity (measured in ampere-
hours) attainable over time will vary in direct relation to the
ambient temperature. The capacity in a given period of time
will be larger at higher temperatures, and smaller at lower
temperatures.
 Initial Charge Current Limit
A discharged battery will accept a high charging current at the
initial stage of charging. High charging current can cause
abnormal internal heating which may damage the battery.
Therefore, it is recommended that the charging current be
normally limited to 0.25CA. However, in standby use, Genesis
®
NP batteries are designed so that even if the charging current
is higher than the recommended limit, they will not accept
more than 2CA, and the charging current will be reduced to a
relatively small value in a very brief period of time. Therefore,
in standby use, no current limit is required.
It is recommended that a current limiting function be provided
in the charger in order to prevent charger failure due to over-
heating of the transformer, or other damage resulting from
mishandling, i.e., short circuiting or reversing polarity.
 Refresh Charging
Since any battery loses capacity through self-discharge, it is
recommended that “refresh charging” be applied to any bat-
tery which has been stored for a long period of time, prior to
putting the battery into service. Excepting conditions in which
storage temperatures have been abnormally high, refresh
charging is recommended within the following
parameters:
Genesis NP batteries must not be allowed to self-discharge to
less than 2.08 volts per cell on open circuit. To recover deeply
discharged batteries, charge them for 24 hours using a
constant voltage charger set at 2.40 volts per cell at 25˚C
(77˚F) with a maximum current of 0.15C. A 16-hour recovery
charge is possible by setting the charge voltage at 2.45 volts
per cell and a maximum current of 0.25C.
In view of the above, consideration should be given to the fact
that if the charging method used is constant voltage in which
the charger employs current sensing for either state of charge
indication or for reducing voltage (a two step charger), during
the initial stage of charging an over-discharged battery the
charger may give a false “full charge” indication, or may
initiate charge at a float voltage.
 Temperature Compensation
As temperature rises, electrochemical activity in a battery
increases. Similarly, as temperature falls, electrochemical
activity decreases. Therefore, conversely, as temperature
rises, charging voltage should be reduced to prevent
overcharge, and increased as temperature falls to avoid
undercharge. In general, to assure optimum service life, use
of a temperature compensated charger is recommended.
The recommended compensation factor for Genesis NP
batteries is -3mV/
0
C/Cell (stand by) and -4mV/
0
C/Cell (cyclic
use). Figure 8 shows the relationship between temperatures
and charging voltages in both cyclic and
standby applications.
www.enersys.com
Publication No: US-NP-AM-003 • January 2011 11
Within 6 months
after manufacture
Within 12 months
after manufacture
4 to 6 hours at constant current of 0.1CA, or 15 to 20
hours at constant voltage of 2.40 volts per cell.
8 to 10 hours at constant current of 0.1CA, or 20 to 24
hours at constant voltage of 2.40 volts per cell.
Battery Age Refresh Charging Recommendations
54153_US_NP_AM_003.qxp:NP AppManual 1/21/11 1:45 PM Page 11