Datasheet

16
Valve Regulated Lead-Acid Batteries
17
Valve Regulated Lead-Acid Batteries
3 | Characteristics
1. Charging
Charge characteristics (constant voltage-constant current
charging) of VRLA batteries are exemplified below.
Example of constant-voltage charge
characteristics by current
In order to fully utilize the characteristics of VRLA batteries,
constant-voltage charging is recommended. For details of
charging see pages 19 – 23.
2. Discharging
a) Discharge current and discharge cut-off voltage
Recommended cut-off voltages for 6V and 12V batteries
consistent with discharge rates are given in the figure below.
With smaller discharge currents, the active materials in the
battery work effectively, therefore discharge cut-off voltages
are set to the higher side for controlling overdischarge. For
larger discharge currents, on the contrary, cut-off voltages
are set to the lower side. (Note) Discharge cut-off voltages
given are recommended values.
Discharge current vs. Cut-off voltage
b) Discharge temperature
(1) Control the ambient temperature during discharge within
the range from -15°C to 50°C for the reason described below.
(2) Batteries operate on electrochemical reaction which con-
verts chemical energy to electric energy. The electrochemi-
cal reaction is reduced as the temperature lowers, thus,
available discharge capacity is greatly reduced at tempera-
tures as low as -15°C. For the high temperature side, on the
other hand, the discharge temperature should not exceed
50°C in order to prevent deformation of resin materials which
house the battery or deterioration of service life.
c) Effect of temperature on discharge characteristics
Available discharge capacity of the battery varies with ambient
temperature and discharge current as shown in the figure below.
Discharge capacity by temperature
and by discharge current
d) Discharge current
Discharge capability of batteries is expressed by the 20 hour
rate (rated capacity). Select the battery for specific equipment
so that the discharge current during use of the equipment falls
within the range between 1/20 of the 20 hour rate value and 3
times that (1/20 CA to 3 CA): discharging beyond this range
may result in a marked decrease of discharge capacity or
reduction in the number of times of repeatable discharge.
When discharging the battery beyond said range, please
consult Panasonic in advance.
e) Depth of discharge
Depth of discharge is the state of discharge expressed by the
ratio of amount of capacity discharged to the rated capacity.
(Test condition)
Discharge : 0.05 CA constant-
current discharge
Cut-off voltage; 1.75 V/cell
Charge : 2.45 V/cell
2.30 V/cell
Temperature : 20˚C
0 3 6 9 12 15 18
2.5
2.0
0.4
0.3
0.2
0.1
0
Current Voltage
Charge time (hours)
(CA)
(V/cell)
~
~
~
~
120
100
80
60
40
20
0
-20 -10 0 10 20 30 40 50
Capacity (%)
Temperature <˚C>
0.05CA
0.1CA
0.25CA
1CA
Discharge current (CA)
Discharge cut-off voltage (12V battery) Discharge cut-off voltage (6V battery)
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
10.8
10.4
10.0
9.6
9.2
8.8
8.4
8.0
0.05 0.1 0.2 0.3 0.5 1 2 3
3 | Characteristics
3. Storage
a) Storage condition
Observe the following condition when the battery needs to
be stored.
(1) Ambient temperature: -15°C to 40°C
(preferably below 30°C)
(2) Relative humidity: 25 to 85%
(3) Storage place free from vibration, dust, direct sunlight,
and moisture.
b) Self discharge and refresh charge
During storage, batteries gradually lose their capacity due to
self discharge, therefore the capacity after storage is lower
than the initial capacity. For the recovery of capacity, repeat
charge/discharge several times for the battery in cycle use;
for the battery in trickle use, continue charging the battery
as loaded in the equipment for 48 to 72 hours.
c) Refresh charge (Auxiliary charge)
When it is unavoidable to store the battery for 3 months or
longer, periodically recharge the battery at the intervals
recommended in the table below depending on ambient tem-
perature. Avoid storing the battery for more than 12 months.
d) Residual capacity after storage
The result of testing the residual capacity of the battery which,
after fully charged, has been left standing in the open- circuit
state for a specific period at a specific ambient temperature
is shown in the figure below. The self discharge rate is very
much dependent on the ambient temperature of storage. The
higher the ambient temperature, the less the residual capacity
after storage for a specific period. Self discharge rate almost
doubles by each 10°C rise of storage temperature (Figure 1).
e) Open circuit voltage vs. residual capacity
Residual capacity of the battery can be roughly estimated by
measuring the open circuit voltage as shown in the figure (2).
Fig. 1 Residual capacity test result
Fig. 2 Open circuit voltage vs. Residual capacity 20°C
4. Internal Resistance
The internal resistance is an important parameter of batteries.
Internal resistance varies with the state of charge of the battery
and temperature as shown on the chart below.
Storage temperature
Interval of auxiliary charge
(refresh charge)
Below 20°C 12 months
20°C to 30°C 9 months
20°C to 40°C 6 months
40°C 30°C 20°C
100
80
60
40
20
0
0 3 6 9 12 15 18
Storage Time(months)
Residual Capacity(%)
(Temperature: 20˚C)
7.00
6.75
6.50
6.25
6.00
5.75
5.50
5.25
5.00
14.0
13.5
13.0
12.5
12.0
11.5
11.0
10.5
10.0
0 20 40 60 80 100
Residual capacity (%)
Open circuit voltage (6V battery) Open circuit voltage (12V battery)
Internal resistance (%)