ArticlePDF Available

Design and implementation of fast three stages SLA battery charger for PLC systems

Authors:

Abstract

New fast sealed lead acid (SLA) battery chargers must be able to charge the fully discharged batteries in a short time. In the same time, the charger must monitor the battery state of health in order to prevent over charge and to extend the battery life time. In this paper a Fast charger was presented to charge SLA batteries in short time and monitor the battery voltage to prevent over charge. The design was implemented practically. And 150 charger of similar type was produced for commercial use. They are now in service in different Mobile base station sites around Baghdad. It can charge a fully discharged 12V, 4.5Ah battery in less than 5 hours. To supply PLC control system on DC power to about 24 hour of continuous operation during main electricity faults. During one and half year of continuous operation three faults have been recorded in the 150 chargers. All of the three cases were because of bad components manufacturing.
Journal of Engineering Volume 17 June 2011 Number 3
448
DESIGN AND IMPLEMENTATION OF FAST THREE STAGES
SLA BATTERY CHARGER FOR PLC SYSTEMS
Anas W. Ata’a
1University of Baghdad Computer Engineering Department
Assistant teacher / email: anaswasill@gmail.com
ABSTRACT
New fast sealed lead acid (SLA) battery chargers must be able to charge the fully discharged
batteries in a short time. In the same time, the charger must monitor the battery state of health in
order to prevent over charge and to extend the battery life time.
In this paper a Fast charger was presented to charge SLA batteries in short time and monitor the
battery voltage to prevent over charge. The design was implemented practically. And 150 charger of
similar type was produced for commercial use. They are now in service in different Mobile base
station sites around Baghdad. It can charge a fully discharged 12V, 4.5Ah battery in less than 5
hours. To supply PLC control system on DC power to about 24 hour of continuous operation during
main electricity faults.
During one and half year of continuous operation three faults have been recorded in the 150
chargers. All of the three cases were because of bad components manufacturing.
ﺔﺼﻼﺨﻟﺍ
ﺕﺎﻴﺭﺎﻁﺒﻠﻟ ﻪﺜﻴﺩﺤﻟﺃ ﺕﺎﻨﺤﺎﺸﻟﺍﻪﻴﺼﺎﺼﺭﻟﺍ-ﻥﻤ ﺎﻤﺎﻤﺘ ﻪﻏﺭﺎﻔﻟﺍ ﻪﻴﺭﺎﻁﺒﻟﺍ ﻥﺤﺸ ﺓﺩﺎﻋﺍ ﻰﻠﻋ ﻩﺭﺩﺎﻗ ﻥﻭﻜﺘ ﻥﺍ ﺏﺠﻴ ﻪﻟﻭﺯﻌﻤﻟﺍ ﻪﻴﻀﻤﺎﺤﻟﺍ ﺭﻴﺼﻗ ﺕﻗﻭ لﻼﺨ ﻥﺤﺸﻟﺍ . ﺕﻻﺎﺤ ﻊﻨﻤﺘ ﻥﺍ لﺠﺍ ﻥﻤ ﻪﻴﺭﺎﻁﺒﻠﻟ ﺔﺤﺼﻟﺍ ﺔﻟﺎﺤﻟﺍ ﺕﺎﻨﺤﺎﺸﻟﺍ ﻩﺫﻫ ﺏﻗﺍﺭﺘ ﻥﺍ ﺏﺠﻴ ﺕﻗﻭﻟﺍ ﺱﻔﻨ ﻲﻓ
ﻪﻴﺭﺎﻁﺒﻟﺍ ﺭﻤﻋ ﻥﻤ ﺩﻴﺯﺘ ﻲﻜﻟ ﺽﺌﺎﻔﻟﺍ ﻥﺤﺸﻟﺍ.
ﻪﻌﻴﺭﺴ ﻪﻨﺤﺎﺸ ﻡﻴﺩﻘﺘ ﻡﺘ ﺙﺤﺒﻟﺍ ﺍﺫﻫ ﻲﻓ ﺕﺎﻴﺭﺎﻁﺒﻠﻟﻪﻴﺼﺎﺼﺭﻟﺍ- ﻲﻓﻭ ﺭﻴﺼﻗ ﺕﻗﻭ ﻲﻓ ﻪﻴﺭﺎﻁﺒﻟﺍ ﻥﺤﺸ ﻥﻤ ﻥﻜﻤﺘﺘ ﻲﺘﻟﺍ ﻪﻴﻀﻤﺎﺤﻟﺍ ﻭﻟﺍ ﺱﻔﻨﺩﺌﺍﺯﻟﺍ ﻥﺤﺸﻟﺍ ﺕﻻﺎﺤ ﻊﻨﻤﻟ ﻪﻴﺭﺎﻁﺒﻟﺍ ﺔﻴﺘﻟﻭﻓ ﺏﻗﺍﺭﺘ ﺕﻗ .ﻲﻋﺎﻨﺼ ﻕﺎﻁﻨ ﻰﻠﻋﻭ ﺎﻴﻠﻤﻋ ﻩﺫﻴﻔﻨﺘ ﻡﺘ ﻡﻴﻤﺼﺘﻟﺍ ﺍﺫﻫ . ﻡﺘ ﺙﻴﺤ ﻊﻴﻨﺼﺘ150 ﻰﻠﻋ ﻪﻋﺯﻭﻤ ﻲﻫﻭ ﻉﻭﻨﻟﺍ ﺍﺫﻫ ﻥﻤ ﻪﻨﺤﺎﺸ 150 ﺔﻅﻓﺎﺤﻤ ﻥﻤ ﻪﻔﻠﺘﺨﻤ ﻕﻁﺎﻨﻤ ﻲﻓ ﻪﻴﻀﺭﺍ ﻱﻭﻠﺨ ﻑﺘﺎﻫ ﺔﻁﺤﻤ ﻊﻗﻭﻤ ﺩﺍﺩﻐﺒ . ﻪﻴﺭﺎﻁﺒ ﻥﺤﺸﺘ ﻥﺍ ﻪﻨﺤﺎﺸﻟﺍ ﻩﺫﻫ ﻥﺎﻜﻤﺎﺒ12V,4.5Ahﺭﺎﻓ ﺓﺭﻁﻴﺴ ﺔﻤﻭﻅﻨﻤ ﺯﻴﻬﺠﺘﻟ ﺎﺒﻴﺭﻘﺘ ﺕﺎﻋﺎﺴ ﺱﻤﺨ لﻼﺨ ﺎﻤﺎﻤﺘ ﺔﻏ ﻩﺩﻤﻟ ﺭﻤﺘﺴﻤﻟﺍ ﺭﺎﻴﺘﻟﺎﺒ ﻪﺠﻤﺭﺒﻤ24ﻲﺴﻴﺌﺭﻟﺍ ﺀﺎﺒﺭﻬﻜﻟﺍ ﺭﺩﺼﻤ ﻉﺎﻁﻘﻨﺍ لﻼﺨ لﺼﺍﻭﺘﻤﻟﺍ لﻴﻐﺸﺘﻟﺍ ﻥﻤ ﺔﻋﺎﺴ .
لﺼﺍ ﻥﻤ لﺎﻁﻋﺍ لﻼﺜ لﻴﺠﺴﺘ ﻡﺘ ﺕﺎﻨﺤﺎﺸﻟﺍ ﻩﺫﻬﻟﺭﻤﺘﺴﻤﻟﺍ لﻤﻌﻟﺍ ﻥﻤ ﻑﺼﻨﻭ ﻪﻨﺴ لﻼﺨ150ﻪﻤﺩﺨﻟﺍ ﻲﻓ ﻪﻠﺨﺍﺩ ﻪﻨﺤﺎﺸ . ﻩﺫﻫ ﻊﻴﻤﺠ ﻻﺎﺤﻟﺍﻪﻴﻨﻭﺭﺘﻜﻟﻻﺍ ﻊﻁﻘﻟﺍ ﻊﻴﻨﺼﺘ ﻲﻓ ﺄﻁﺨ ﺏﺒﺴﺒ ﺕﻨﺎﻜ ﺙﻼﺜﻟﺍ .
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
449
Keywords: SLA, VRLA, SoC, SoH, Battery Chargers, three mode charger, Fast charger,
DC PLC backup system.
1. INTRODUCTION
In the introduction a brief discussion about the
SLA batteries and charging algorithms will be
presented.
1.1.VRLA Batteries
Lead-acid batteries, invented in 1859
by French physicist Gaston Planté [1] .
VRLA stands for valve-regulated lead-acid and is
the designation for low-maintenance lead-acid
sealed rechargeable batteries. Because of their
construction, VRLA batteries do not require
regular addition of water to the cells.
These batteries are often called sealed lead-acid
batteries, but they always include a safety pressure
relief valve. As opposed to vented (also
called flooded) batteries, a VRLA cannot spill its
electrolyte if it is inverted.
The name "valve regulated" does not wholly
describe the technology; these are really
"recombinant" batteries, which means that
the oxygen evolved at the positive plates will
largely recombine with the hydrogen ready to
evolve on the negative plates, creating water thus
preventing water loss. The valve is strictly a safety
feature in case the rate of hydrogen evolution
becomes dangerously high.
Since VRLA batteries do not require (and make
impossible) regular checking of the electrolyte
level, they have been called Maintenance Free
(MF) batteries. However, this is somewhat of a
misnomer. VRLA cells do require maintenance. As
electrolyte is lost, VRLA cells may experience
"dry-out" and lose capacity. This can be detected
by taking regular internal resistance, conductance
or impedance measurements of cells.
1.2.Charging the lead-acid battery [2]
The charging algorithm for lead-acid batteries is to
use voltage rather than current limiting. The charge
time of a sealed lead-acid battery is 12-16 hours
(up to 36 hours for larger capacity batteries). With
higher charge currents and multi-stage charge
methods, the charge time can be reduced to 10
hours or less.
It takes about 5 times as long to recharge a lead-
acid battery to the same level as it does to
discharge. A multi-stage charger first applies a
constant current charge, raising the cell voltage to
a preset voltage (Stage 1 in Figure 1). Stage 1 takes
about 5 hours and the battery is charged to 70%.
During the topping charge in Stage 2 that follows,
the charge current is gradually reduced as the cell
is being saturated. The topping charge takes
another 5 hours and is essential for the well being
of the battery. If omitted, the battery would
eventually lose the ability to accept a full charge.
Full charge is attained after the voltage has reached
the threshold and the current has dropped to 3% of
the rated current or has levelled off. The final
Stage 3 is the float charge, which compensates for
the self-discharge.
Correct settings of the voltage limits are critical
and range from 2.30V to 2.45V. Setting the voltage
limit is a compromise. On one end, the battery
wants to be fully charged to get maximum capacity
and avoid sulfation on the negative plate. A
continually over-saturated condition at the other
end, however, would cause grid corrosion on the
positive plate. It also promotes gassing, which
results in venting and loss of electrolyte.
The voltage limit shifts with temperature. A higher
temperature requires slightly lower voltages and
vice versa. Chargers that are exposed to large
temperature fluctuations should be equipped with
temperature sensors to adjust the charge voltage
for optimum charge.
The battery cannot remain at the peak voltage for
too long; the maximum allowable time is 48 hours.
When reaching full charge, the voltage must be
lowered to maintain the battery at between 2.25
and 2.27V/cell. Manufacturers of large lead-acid
batteries recommend a float charge of 2.25V at
25°C.
Car batteries and valve-regulated-lead-acid
batteries (VRLA) are typically charged to between
2.26 and 2.36V/cell. At 2.37V, most lead-acid
batteries start to gas, causing loss of electrolyte and
possible temperature increases.
Large VRLA batteries are often charged with a
float-charge current to 2.25V/cell. A full charge
may take several days. It is interesting to observe
that the current in float charge mode gradually
increases as the battery ages in standby mode. The
reasons may be electrical cell leakages and a
reduction in chemical efficiency.
Aging affects each cell differently. Since the cells
are connected in series, controlling the individual
Journal of Engineering Volume 17 June 2011 Number 3
450
cell voltages during charge is virtually impossible.
Even if the correct overall voltage is applied, a
weak cell will generate its own voltage level and
intensify the condition further.
Lead-acid batteries must always be stored in a
charged state. A topping charge should be applied
every six months to avoid the voltage from
dropping below 2.10V/cell on an SLA. Prolonged
storage below the critical voltage causes sulfation,
a condition that is difficult to reverse.
1.3.State-of-charge (SoC) reading based on
terminal voltage
The state-of-charge of a lead-acid battery can, to a
certain extent, be estimated by measuring the open
terminal voltage [4] . Prior to measuring, the
battery must have rested for 4-8 hours after charge
or discharge and resided at a steady room
temperature [4] . A cold battery would show
slightly higher voltages and a hot battery would be
lower. Due to surface charge, a brief charge will
raise the terminal voltage and provide inflated
state-of-charge reading. For example, a 30 minute
charge could wrongly indicate 100% SoC if no rest
is applied.
With sufficient rest and stable temperature, voltage
measurements provide an amazingly accurate State
of Charge (SoC) estimation for lead acid batteries.
It is important that the battery is free of
polarization. If connected in a system, such as in a
car, there are steady auxiliary loads, not to mention
frequent starting and driving.
Table 1 BCI standard for SoC estimation of a
12V flooded lead acid car battery [2]
Open circuit
voltage
State-of-
Charge in %
12.65V 100%
12.45V 75%
12.24V 50%
12.06V 25%
11.89V or
less Discharged
Proposed charger and backup system
A simplified block diagram of the system is shown
in Fig. 2. This block diagram represents the
functional blocks of the system. The first block is
the SMPS, which is a standard SMPS. The output
of the SMPS is DC voltage about 19V. This DC
voltage is transferred to the second block which is
charging control and output conditioning circuit.
This block is the main block of the system and the
design of this block is the state of art, which
contains the charging algorithms and output
control circuits and contains all the protections.
2. DESIGN AND IMPLEMENTATION
In this section, the design and implementation of
each block of Fig. 2 will be demonstrated.
2.1.SMPS
The first block is the SMPS. To implement this
block a standard SMPS that is available
commercially was used. Fig.4 shows the circuit
diagram and Fig.3 shows the PCB picture of
similar SMPS. The output of this power supply is
set to 19V DC through the voltage divider R4 and
R5. This value is limited by the MOSFET used.
For the IRF3205, the max threshold voltage is
4V [13] . Since the max battery voltage during
charging is 14.75, the total power supply voltage
must be14.75+4=18.75V. 19V was used for safe
circuit operation. The TL431 is an Adjustable
Precision Shunt Regulator. It is responsible for
keeping the output voltage fixed by controlling the
feedback loop. The max current that can be drawn
from similar supply is 1A.
The operation of the SMPS can be summarized as
follows:
The 220V AC is converted to about 311V DC
through the diode bridge D1 and high voltage
chemical capacitor C3.
The TOP224 is a Three-terminal Off-line PWM
MOSFET switch. It chops the 311VDC at
frequency of about 100 kHz. The chopping
frequency is set by the internal oscillator of the
TOP224. This high voltage signal will be
reduced to low voltage through the ferrite step-
down transformer TP.
The high speed rectifier Diode D4 will rectify
the output of the transformer into DC voltage.
This DC voltage will pass through low pass
power filter to reduce switching noise.
The TL431 regulator is responsible of keeping
the output voltage constant. The TL431compare
the voltage at the middle terminal with the
internal Precision Reference Voltage of 2.495V.
This voltage is the R4 and R5 divider voltage. If
the voltage is less than the reference voltage,
the TL431 will conduct and the optocoupler
will pass current to the C terminal of TOP224.
This current will increase the duty cycle of the
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
451
PWM signal generated and more power will be
transferred to the output. If the divider voltage
is larger than the reference voltage, the TL431
will not conduct and the optocoupler will not
pass current to the C terminal of TOP224. This
will decrease the duty cycle of the PWM signal
generated and less power will be transferred to
the output. For farther details on the operation
please refer to the datasheet of TOP224 [9] and
TL431 [10] ICs. The output voltage of this
power supply is set to19V DC through choosing
appropriate values of the divider R4 and R5.
2.2.Charge Control
The charge control circuit consists of the following
parts:
Constant current charge circuit.
Constant voltage charge circuit.
Float charge circuit.
Under voltage alarm circuit. This circuit will
turn ON red LED when battery voltage is
reduced under 10V. This indication means the
battery is damage and must be replaced. Also
there is an output control signal that will be
activated with the red LED. This signal could
be used to generate Battery LOW ALARM
and to indicate that battery is completely
discharged. The circuit will never disconnect
the battery even if the battery is fully
discharged.
These circuits are interconnected such that at each
power ON of the supply voltage the charge
controller will do the following sequence:
1. Start the constant current charging mode first.
This represents the fast charge mode. During
this mode the circuit will supply a constant
current of about 0.7A to the battery and will
continue supplying this current until the battery
voltage reaches 14.5V.
2. When the battery voltage reaches 14.5V, the
second charging stage is started. This stage is
the constant voltage stage. In this stage, the
circuit will behaves like a constant voltage
source of 14.5V. This stage represents the slow
charge mode. During this stage, the voltage will
stay constant at 14.5V and the charging current
will decrease gradually as the battery charge.
When the charging current reduced to a
specified value, the float charge stage is started.
3. The float charge stage is the final charging
stage. In this stage the charger will provide a
very small charging current. This small current
will account for self discharge in the battery
cells after the battery get fully charged. The
float charging is neither constant voltage nor
constant current it is simple charging through
resister. The battery voltage and the exact
charging current will depend on the battery
state and battery rest.
Fig. 5 shows the complete circuit diagram of the
three charging modes and the low battery
indication circuits. The Battery charging current
will be designated by IBAT and the Battery
Charging voltage will be designated VBAT in the
next sections.
2.3.Constant Current Charging Circuit:
The circuit below (Fig.6b) is the constant current
charging circuit. The OPAMP U1:A is the core of
this circuit. It always compares the SENS2 voltage
with the 0.7V reference voltage. The voltage
SENS2 is the voltage across the 1 ohm resister R1
connected in series with the Battery to monitor the
charging current (see Fig.6a).
SENS2 = IBAT X 1 (1)
When the charging current drop below 0.7A,
SENS2 voltage will be less than 0.7V and the
comparator output will be low this will turn off D5
which in turn, turns ON the power MOSFET to
supply more power to the Battery.
When the charging current rise above 0.7A,
SENS2 voltage will be greater than 0.7V and the
comparator output will be high. This will turn ON
Q5 and D5 which in turn, turns OFF the power
MOSFET to reduce the Battery charging current.
This negative feedback operation will maintain the
Battery Charging current IBAT@CC constant at
0.7A. If it is required to increase this current for
larger batteries, the value of R1 must be reduced.
The power dissipated inside R1 is:
PR1 = (IBAT)2 X R1 (2)
PR1 = 0.49 X 1 = 0.49 W,
Choosing 1W resister gives 50% safety margin.
The resister R4 is used to limit the base current
for Q2 to about 225µA:
IB2 = (3.65-1.4)/10k = 225µA (3)
Since the minimum value of β in the transistor
datasheet is 100 for collector currents less than
100mA [6] . This IB2 will results in collector current
of about 22.5mA, but since R8 is 4.7k then max IC2
will not exceed 19/4700=4mA. Then Q2 will be
heavily in saturation and the MOSFET gate
voltage is zero. Also the resister R22 is used to limit
Journal of Engineering Volume 17 June 2011 Number 3
452
IB5 to 70µA which will give about 7mA at the
collector to turn the LED1 ON.
IB5 = (1.4-0.7)/10k=70µA (4)
The other function of R4 is to protect the OPAMP
output stage when the output is high. D5 and Q2
will clipdown the opamp output voltage to about
1.4V. This will provide low resistance path to the
OPAMP output stage. R4 will prevent this short
circuit.
The Capacitor C2 compensates the feedback
control loop by adding integration function to the
error amplifier output (U1:A).
2.4.Constant Voltage Charging Circuit
Fig.7 is the constant voltage charging circuit. The
OPAMP U1:C is the core of this circuit.
It always compares the precisely adjusted
reference voltage of RV1 with the battery voltage.
The OPAMP U1:B is subtraction circuit. It subtracts
the voltage drop across the 1 resister (SENS2)
from the Battery positive terminal voltage
(SENS1) to get accurate Battery voltage (see
Fig.6a). The output of U1:B is fraction of battery
voltage.
VBAT = SENS1 – SENS2 (5)
VO U1:B = SENS1 X R3/(R2+R3) X (1+R6/R7)–
SENS2 X R6/R7 (6)
VO U1:B = (SENS1 – SENS2) X R6/R7
Then:
VO U1:B = VBAT X R6/R7 (7)
When the voltage VO U1:B drop below the voltage at
the moving terminal of RV1, the comparator output
will be low this will turn off D4 which in turn,
turns ON the power MOSFET to supply more
current to the Battery. When the Battery voltage
rise above the voltage at the moving terminal of
RV1, the comparator output will be high. This will
turn ON Q6 and D4 which in turn, turns OFF the
power MOSFET to reduce the Battery charging
current. This process will continue till the battery
get fully charged and the charging current reduced
greatly. At this point, the float charging will start.
The two fixed resisters R9 and R10 are added to
RV1 to limit the max and min voltage at the
moving terminal (terminal 3) of RV1. The values
are selected such that the voltage at terminal 2 of
RV1 is:
Vterminal 2 = 5 X R10/(R10+R9+RV1)
= 5 X (10/35) = 1.4285V (8)
Similarly, the voltage at terminal 1 of RV1 is:
Vterminal 1 = 5 X (R10+RV1) / (R10+R9+RV1) = 5
X (20/35) = 2.8571V (9)
From Eq. (7), these voltages correspond to battery
voltages of
1.4285V X R7/R6 = 9.7397V and (10)
2.8571V X R7/R6 = 19.4802V (11)
It is required to set the value of constant Voltage to
14.75V. This value will be in the middle range of
the trimming pot. The trimming pot must be
adjusted such that the charging voltage in this stage
is near VBAT@CV = 14.75V.
The resister R13 is used to limit the base current for
Q3 to about 478.723µA, for +5V supply of the
LM324, the comparator high level will be
3.65V [8] :
IB3 = (3.65-1.4)/4.7k = 478.723µA (12)
Since the minimum value of β in the transistor
datasheet is 100 for collector currents less than
100mA [6] . This IB3 will results in collector
current of about 47.872mA, but since R8 is 4.7k
then max IC3 will not exceed 19/4700 = 4mA. Then
Q3 will be heavily in saturation and the MOSFET
gate voltage is zero. Also the resister R24 is used to
limit IB6 to 70µA which will give about 7mA at the
collector to turn the LED3 ON.
IB6 = (1.4-0.7)/10k=70µA (13)
The other function of R13 is to protect the OPAMP
output stage when the output is high. D4 and Q3
will clipdown the opamp output voltage to about
1.4V. This will provide low resistance path to the
OPAMP output stage. R13 will prevent this short
circuit.
The function of Capacitor C3 is similar to C2 in the
last section, it compensates the feedback control
loop.
2.5.Float Charging Circuit
The next figure (Fig.8) is the float charging circuit.
The OPAMP U1:D is the core of this circuit. It
always compares the battery charging current with
reference value. When the charging current
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
453
reduced below 167mA (see eq.14 below), the
comparator output will be high to turn ON LED2
and Q3 which will turn off the Power MOSFET.
This reference value is determined by R15 and
R16, in this case with the resister values shown in
the Fig., the voltage at pin12 will be:
V12 = 0.7 X R16/(R16+R15) = 0.7 X (4.7/19.7) =
0.167V (14)
The resister R11 (in Fig.5) is used to limit the base
current for Q3 to about 478.723µA:
IB3 = (3.65-1.4)/4.7k = 478.723µA (15)
Since the minimum value of β in the transistor
datasheet is 100 for collector currents less than
100mA [6] . This IB3 will results in collector
current of about 47.872mA, but since R8 is 4.7k
then max IC3 will not exceed 19/4700 = 4mA.
Then Q3 will be heavily in saturation and the
MOSFET gate voltage is zero.
The circuit of Q4, C5, R18 and R20 is to turn off
the comparator (make the output low) when there
is no AC power. When the AC power is OFF, the
base of Q4 is connected to ground through R19
and R18. Q4 will be ON and IB4 is -215µA:
IB4 = (-5+0.7)/(10k+10k) = -215µA (16)
Since the minimum value of β in the transistor
datasheet is 100 for collector currents less than
100mA [7] . This IB4 will results in collector current
of about -21.5mA, but since R17 is 2.2k, then max
IC4 will not exceed 5/2200 = -2.2727mA. Then Q4
will be heavily in saturation and the voltage at
pin13 is +5V. When the AC power is ON, the
transistor Q4 will be OFF because the base of Q4
will be connected to equivalent voltage of about
+9.5V through equivalent base resister of about
3.333k. This operation will not happen fast
because of the charging time of C5. The initial
value of C5 voltage is:
VC5initial = (5-0.7) X R18/(R18+R19) = 2.15V (17)
The final value of C5 is:
VC5final =19V/2 = 9.5V (18)
The transistor will turn OFF when the capacitor
value reaches 4.3V. The charging time constant is:
τ = C5 X 5k (19)
Using the capacitor charging equation to find the
estimated time for the transistor Q4 to turn OFF.
τ
-t
C5initialC5finalC5finalC5 e )V(V V = V (20)
Solving for C5 yield:
0.3465
0.3465)
VV
VV
ln( =t
5
5
C5C5final
C5initialC5final
5
=
=
kt
C
CkCReq
(21)
For 100ms delay, C5 must be 57µF. Select 47 µF
as the nearest standard value. This delay is
important at start-up, because the charging current
initially rises from zero to its constant value
gradually. This delay will disable the comparison
circuit till the charging current exceeds the 167mA.
This will insure that the constant charging will start
first. The capacitor discharge when the power is
off will be through the resister R18, R19 and the
base of transistor Q4. This discharge time has no
effect on the circuit operation.
2.6.Low Battery indication Circuit
Fig.9 shows the Low Battery indication and alarm
circuit. The OPAMP U3:A is the core of this circuit.
It always compares the battery voltage with the
reference voltage. The circuit is Schmitt Trigger
circuit to prevent LED and alarm fluctuation.
When the battery voltage drops under 10 volt the
LED will be ON and it will stay ON until the
voltage become larger than 11V. Consider the
output of the OPAMP is low then the voltage at
pin3 is:
V3 = 5 X R30/(R26+R30+R31) =5 X (4.7/15.7) =
1.4968V = VTL (22)
This voltage corresponds to battery voltage of:
1.4968V X R7/R6 = 10.2054V (23)
The output of the comparator will stay low unless
the battery voltage reduced below the 11.7V. If the
battery voltage reduced below this value, the
comparator output will be high (about 5V-
1.35V=3.65V [11] ) and the current in D9 is about
ID9 = (3.65-0.7)/(100k) = 29.5µA (24)
Referring to the diode Datasheet [12] , VD9 will be
about 440mV. Then the reference voltage will be:
V3 = 5 X (R30||R29)/(R26+ R30||R29+R31) +
Journal of Engineering Volume 17 June 2011 Number 3
454
(3.65V-VD9) X (R30||(R26+R31))/(
(R30||(R26+R31))+R29) (25)
= 5 X (4.489/15.7) + 3.21 X
3.29299/(3.29299+100) = 1.449V + 0.10233V =
1.55133V= VTH
This voltage corresponds to battery voltage of:
1.55133V X R7/R6 = 10.5772V (26)
At the same time the red LED of the bicolour LED
will be ON to indicate Low Battery ALARM. The
comparator output will stay high till the Battery
voltage exceeds the VTH value. Practically the
measured values are VTH=1.573V and VTL=1.518V
and the transitions are at VBAT = 11V and 10.6V
respectively.
This difference between the measured and the
calculated voltages is due to the subtract circuit of
U1:B non exact gain.
2.7.Output Power MOSFET Circuit
The Power MOSFET Q1 is the main power
transistor in the circuit. It was fixed on heat sink to
disspate extra heat generated inside it.
Q3 and Q2 are the driving transisters. Both of them
must be OFF inorder to make the MOSFET ON. If
any one of them is ON, the gate of the MOSFET
will be about zero and the MOSFET will be turn
OFF see Fig.10.
R12 will provide the float charging current to the
Battery. Changing this value will change the float
charge current. For steady battery voltage of 12.8V
and supply voltage of 19V, the current will be:
IBAT@float = (19-12.8)/(220)
= 28.1818mA (27)
This small current will count for the self discharge
inside the battery cells and will prevent the battery
from being over charged.
D1 is the diode that supply the DC voltage from the
Battery to the system when the power is turned
OFF. Therfore the output voltage will be 0.7V less
than the battery volatage incase of AC power
failer.
2.8.The Voltage regulator circuit
In order to make the circuit operation and reference
voltages independent of battery voltage, 7805
voltage regulator was used to supply the OPAMP
circuit. As shown in Fig.11.
2.9.The PCB
After passing all the primary tests, the circuit have
been send to PCB factory to produce the mass
production. The circuit was printed on 10cmx13cm
double layer PCB to fit inside the plastic enclosure.
See the figure below.
2.10. The enclosure
A standard industrial plastic enclosure was selected
for the case. See the figure below. It has standard
din rail fixing accessories and high current barrier
terminal block.
3. Test and results
In the following sections a typical data taken from
one of the chargers, it was charging a 12V 4.5Ah
Battery. The Battery was about 75% discharged
when connected to the charger. The max charging
current for the battery is 1.3A in the battery
Datasheets [3] . All charging current in the
following figures was normalized to this max
value. All voltage readings also normalized to the
max allowable voltage of 15V.
3.1.Constant Current stage
Fig. 14 shows the change in battery voltage during
the constant current charging stage. As seen in the
figure, the voltage change is non-linear.
In Fig. 15, the charging current is approximately
constant. However there is small change in the
value of the charging current as the battery voltage
increase. This small change represents the
accuracy of the constant current source circuit that
was implemented. The change is 0.69A -0.64A =
0.05A. This is about 4%.
3.2.Constant Voltage stage
Fig. 16 shows the charging current variations
during the constant voltage stage. It is clear that the
charging current in this stage is reduced in
exponential form.
Fig. 17 shows the charging voltage in this stage. It
is clear that the voltage is approximately constant.
However there is also a small change in the battery
voltage. This change is clearer in the first 1000
points of the curve. This small change represents
the limit of the constant voltage source circuit
used. It is 14.42V-14.53V = 0.11V. This is about
1%.
3.3.Float charge stage
Fig. 18 and 19 shows the charging current and
voltage variations during the float charge stage
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
455
respectively. At the start point of this stage, the
charging current reduced sharply to about few milli
amperes. The battery voltage will drops gradually
until reaches the battery steady state voltage. The
charge current will increase for decreasing battery
voltage.
4. CONCLUSION
Fast three stages SLA battery charger was
designed, implemented and tested. This charger
was able to charge 12V, 4.5A/h SLA Battery in
about 2 hours and 23minutes. The three stages
charger can charge the SLA batteries in short time
while protecting the battery from over charge and
self discharge. In the Constant Current Source the
deviation was about 4% while the deviation for the
constant voltage source is about 1% as seen in the
results section. The control circuit is completely
analogue electronic circuit. No digital parts were
used. This will reduce time to fault and the system
will be less sensitive to noise.
The main disadvantage of this design is that we
need power supply of about 19V to supply the
required power. It is about 4V above the maximum
Charging voltage (15V). This is because of the
MOSFT gate threshold voltage.
Better designs could use a supply voltage that is
slightly above 15V to perform the same tasks
without reducing the charging performance. The
ambient temperature could be used to make the
transition voltages between the stages more
precise, also the Battery temperature could be used
to monitor the Battery health and preventing over
charge.
5. ACKNOWLEDGEMENT
This work was under the supervision and funding
of Integrated Engineering Services Company. It
was done under the project of installing 128 mobile
Base transceiver station (BTS) around Baghdad.
6. REFERENCES
[1] “Lead-acid battery”, Wikipedia, the free
encyclopedia,
http://en.wikipedia.org/wiki/Lead-
acid_battery, last modified on 5 March 2010.
[2] Buchmann, “Charging the lead-acid battery”
(BU13), batteryuniversity.com,
http://www.batteryuniversity.com/partone-
13.htm, April 2003.
[3] “GP 1245 12V 4.5Ah Battery Datasheet”,
CSB BATTERY TECHNOLOGIES INC.
(U.S.A), http://www.csb-battery.com, 2005.
[4] Chiasson, J. Vairamohan, B, “Estimating the
State of Charge of a Battery”, Control
Systems Technology, IEEE Transactions,
Volume: 13 Issue: 3, pp. 465 – 470, May
2005.
[5] Jiang Yong, Xie Ye, "TOPSwitch-based
flyback converter optimal design of feedback
circuit", Zhejiang University, Hangzhou
310027,
http://www.cp315.com/mdc/news/view.asp?id
=3033, 9Oct.2005.
[6] "BC337, BC337-16, BC337-25, BC337-40,
BC338-25 Amplifier Transistors NPN
Silicon", Datasheet, Semiconductor
Components Industries, LLC,
http://www.onsemi.com/pub_link/Collateral/B
C337-D.PDF, Rev. 2, October 2001.
[7] "BC327, BC32716, BC32725, BC32740
Amplifier Transistors PNP Silicon",
Datasheet, Semiconductor Components
Industries, LLC,
http://www.onsemi.com/pub_link/Collateral/B
C327-D.PDF, Rev. 5, March, 2007.
[8] "LM124/LM224/LM324/LM2902 Low Power
Quad Operational Amplifiers", Datasheet,
http://www.national.com/ds/LM/LM124.pdf,
August 2000.
[9] "TOPSwitch-II Family Three-terminal Off-
line PWM Switch", Datasheet, Power
Integrations, Inc.,
http://www.powerint.com/sites/default/files/pr
oduct-docs/top221-227.pdf , 2001.
[10] "TL431/TL431A Programmable Shunt
Regulator", Fairchild Semiconductor
Corporation,
http://www.fairchildsemi.com/ds/TL/TL431A
.pdf, Rev. 1.0.3, 2003.
[11] "LM158/LM258/LM358/LM2904 Low Power
Dual Operational Amplifiers", Datasheet,
http://www.national.com/ds/LM/LM158.pdf,
October 2005.
[12] "1N/FDLL 914/A/B / 916/A/B / 4148 / 4448
Small Signal Diode", Fairchild Semiconductor
Corporation
http://www.fairchildsemi.com/ds/1N/1N4148.
pdf, Rev. B2, January 2007.
[13] "IRF3205 HEXFET® Power MOSFET",
International Rectifier, PD-91279E,
http://www.irf.com/product-
info/datasheets/data/irf3205.pdf, 25 Jan 2001.
Journal of Engineering Volume 17 June 2011 Number 3
456
Figure 1: Charge stages of a lead-acid battery. The battery charges at a constant current to a set
voltage threshold (Stage 1). As the battery saturates, the current drops (Stage 2). The float charge
compensates for the self-discharge (Stage 3).
SMPS
AC to DC converter Charging control
and switching
12V
4.5 to 7 Ah
Battery
AC 90-250 V
50-60 Hz
Input
12V DC output to
PLC system
Figure. 2 simplified block diagram of the system
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
457
Figure. 3 SMPS board component side and solder side
Figure. 4 Standard SMPS circuit diagram [5]
Ferritetransformer
Polecompensationcircuit
Journal of Engineering Volume 17 June 2011 Number 3
458
Figure. 5 Charge control circuit Diagram
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
459
(a) (b)
Figure. 6 (a) SENS1 and SENS2, (b) Constant Current Charging Circuit
Figure. 7 Constant Voltage Charging Circuit
Journal of Engineering Volume 17 June 2011 Number 3
460
Figure. 8 Float Charging Circuit
Figure. 9 Low Battery indication Circuit
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
461
Figure. 10 Output Power MOSFET Circuit
Figure. 11 Voltage Regulator Circuit
Journal of Engineering Volume 17 June 2011 Number 3
462
Figure. 12 PCB inside the enclosure
Figure. 13 the enclosure
Figure.14 Battery voltage change during constant current stage
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
463
Figure.15 Battery Current change during constant current stage.
Figure.16 Battery Current change during constant voltage stage
Journal of Engineering Volume 17 June 2011 Number 3
464
Figure.17 Battery Voltage change during constant voltage stage
Figure.18 Battery Current change during float charge
Anas W. Ata’a Design And Implementation Of Fast Three
Stages SLA Battery Charger For PLC Systems
465
Figure.19 Battery Voltage change during float charge
ResearchGate has not been able to resolve any citations for this publication.
Article
A lead-acid storage battery is described comprising in combination: a casing member having perimeter walls and a bottom wall defining a cavity and a plurality of partition walls dividing the cavity into cell compartments; a battery cell received in each compartment comprising a stack of horizontally disposed negative active plates each containing a plurality of tigs spaced along a first edge aligned in vertical registration with tigs on other negative active plates in the stack to form a set of columns, positive active plates each having a plurality of tigs spaced along an edge opposed to the first edge and aligned with the tigs in the other positive plates in the stack to form a second set of columns, the positive active plates alternating with the negative active plates and the negative plates having a capacity greater than the capacity of the positive plates, and porous, liquid electrolyte-containing separator sheets disposed between each of the plates; vertical, positive bus bars interconnecting each column of positive tigs; a plurality of vertical, negative bus bars interconnecting each column of negative tigs; connector means joining a positive bus bar to the negative bus bar on the opposite side of a partition wall; a negative strap interconnecting the negative bus bars at one end cell; a positive strap interconnecting the positive bus bars at the other end cell; a positive terminal connected to the positive strap; a negative terminal connected to the negative strap; and a top sealingly received on the casing.
Article
This brief considers the state of charge (SOC) estimation problem for electrochemical batteries. Using an electric circuit model of the battery given in the literature, it is shown how the open-circuit voltage (which is directly related to the SOC) can be estimated based on the terminal voltage and current measurements provided there is sufficient variation in the battery current.
TOPSwitch-based flyback converter optimal design of feedback circuit
  • Jiang Yong
  • Xie Ye
Jiang Yong, Xie Ye, "TOPSwitch-based flyback converter optimal design of feedback circuit", Zhejiang University, Hangzhou 310027, http://www.cp315.com/mdc/news/view.asp?id =3033, 9 Oct. 2005.
TOPSwitch-II Family Three-terminal Offline PWM Switch
"TOPSwitch-II Family Three-terminal Offline PWM Switch", Datasheet, Power Integrations, Inc., http://www.powerint.com/sites/default/files/pr oduct-docs/top221-227.pdf, 2001.
  • Small Signal Diode
Small Signal Diode", Fairchild Semiconductor Corporation http://www.fairchildsemi.com/ds/1N/1N4148. pdf, Rev. B2, January 2007.
GP 1245 12V 4.5Ah Battery Datasheet
"GP 1245 12V 4.5Ah Battery Datasheet", CSB BATTERY TECHNOLOGIES INC. (U.S.A), http://www.csb-battery.com, 2005.