Datasheet

20
Valve Regulated Lead-Acid Batteries
21
Valve Regulated Lead-Acid Batteries
4 | Charging Methods
charge current has reduced to the preset value, the device
is switched over to the second SW(2) of low set-up voltage
(setup for trickle charge voltage). This method has the ad-
vantage that the battery in trickle use can be charged in a
comparatively short time for the next discharge.
Charging characteristics of the two-step constant
voltage control charger
Block diagram of the two-step constant voltage
control charger
(2) Stand-by/Back-up use (Trickle use)
The application load is supplied with power from AC sourc-
es in normal state. Stand-by/back-up use is to maintain the
battery system at all times so that it can supply power to the
load in case the AC input is disrupted (such as a power fail-
ure). There are two methods of charging for this use.
(a) Trickle charge (Compensating charge)
Trickle charge
In this charge system, the battery is disconnected from the
load and kept charged with a small current only for compen-
sating self discharge while AC power is alive. In case of power
failure, the battery is automatically connected to the load and
battery power is supplied. This system is applied mainly as a
spare power source for emergency equipment. In this use, if
rapid recovery of the battery after discharge is required, it is
necessary to consider the recovery charge with a compara-
tively large current followed by trickle charge, or alternative
measures. While the type and capacity of the battery is de-
termined by the back-up time and the load (current consump-
tion) during power failure, some reserve power should be
taken into account considering such factors as ambient tem-
perature, capability of the charger and depth of discharge.
Trickle charge system model
(b) Float charge
Float system is the system in which the battery and the load
are connected in parallel to the rectifier, which should supply
a constant power.
Float charge system model
In the above-illustrated model, output current of the rectifier
is expressed as: l
o
L
c
+ l
L
where l
c
is charge current and l
L
is
load current. Consideration should be given to secure ade-
quate charging because, in fact, load current is not constant
but irregular in most cases.
In the float system, capacity of the constant-voltage power
source should be more than sufficient against the load. Usually,
the rectifier capacity is set at the sum of the normal load current
plus the current needed in order to charge the battery.
(Precautions on charging)
1. As the battery continues to be charged over a long period, a small
difference in charging voltage may result in a significant difference
in the battery life. Therefore, charge voltage should be controlled
within a narrow range and with little variation for a long period.
2. As charge characteristics of the battery are dependent
on temperature, compensation for temperature variation is
required when the battery is used over a broad temperature
range, and the system should be designed so that the bat-
tery and the charger are kept at the same temperature.
Charge current
Battery voltage
Charging time
Battery voltage / Charge current
AC
input
Charging power supply
Current
detection
circuit
Voltage
switch
SW(2)
SCR
Voltage
switch
SW(1)
Battery
Load
Power
detection
relay
Rectifier
Battery
AC
A
C
Rectifier
Load
I 0 I L
I C
4 | Charging Methods
(Precautions on charging)
1. (a) in constant voltage charging (cycle use): Initial current
should be 0.4 CA or smaller (C: rated capacity)
(b) in constant voltage charging (trickle use): Initial current
should be 0.15 CA or smaller (C: rated capacity)
2. Relation between standard voltage value in constant
voltage charging and temperature is given in the Table.
Relation between standard voltage value in constant
voltage charging and temperature
a) Temperature compensation of charge voltage
Charge voltage should be compensated to the ambient tem-
perature near the battery, as shown by the figure below. Main
reasons for the temperature compensation of charge voltage
are to prevent the thermal runaway of the battery when it is
used in high temperature conditions and to secure sufficient
charging of the battery when it is used in low temperature con-
ditions. Prolongation of service life of the battery by the above-
described temperature compensation is expected as follows
– At 30°C: prolonged by approx. 5%
– At 35°C: prolonged by approx. 10%
– At 40°C: prolonged by approx. 15%
In low temperature zones below 20°C, no substantial prolon-
gation of the battery life can be expected by the temperature
compensation of charge voltage.
Compensated voltage value
b) Charging time
Time required to complete charging depends on factors such
as depth of discharge of the battery, characteristics of the
charger and ambient temperature. For cycle charge, charging
time can be estimated as follows:
(1) when charge current is 0.25 CA or greater:
 4CH#DIS)HTOH
(2) when charge current is below 0.25 CA:
 4CH#DIS)HTOHWHERE
Tch : Charging time required (hours),
Cdis : Amount of discharge before this charging (Ah)
I : Initial charge current (A)
Time required for trickle charge ranges from 24 to 48 hours.
Application/
Charging Method
Normal charging in 6 or more hours;
Constant voltage control
Two-step constant voltage
control
Constant Current
Control
Cycle Use Control voltage: 7.25 to 7.45V / 6V battery
14.5 to 14.9V / 12V battery
Initial current: 0.4 CA or smaller
Trickle Use Control voltage: 6.8 to 6.9 / 6V battery
13.6 to 13.8V /12V battery
Initial charging with current of
approx. 0.15 CA, followed by
switching voltage to trickle charge
Float Use Control voltage: 6.8 to 6.9 / 6V battery; 13.6 to 13.8V / 12V
battery. Float charging compensates for load fluctuations.
Refresh charge
(Auxiliary charge)*
When charging two or more batteries at a time, select
only those which have been left under the same condition.
Charging with current
of approx. 0.1 CA
Application
example
General uses, Cellular phones (bag phones), UPS,
Lanterns, Electric tools
Medical equipment,
Personal radios
Charging Methods and Applications of VRLA-Batteries
Note * Refresh (auxiliary) charge amount should be 120 to 130% of self-discharge amount. For details, please contact us.
0°C 20°C 40°C
Cycle use
6V 7.7 7.4 7.1
12V 15.4 14.7 14.2
Trickle use
6V 7.1 6.8 6.7
12V 14.1 13.7 13.4
-20 -10 0 10 20 30 40 50
Temperature (˚C)
Charge voltage / cell
2.7
2.6
2.5
2.4
2.3
2.2
Minimum
voltage
Minimum
voltage
Maximum
voltage
Maximum
voltage
Cycle
u
se
Trickle use