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Department of Electronic Engineering4th Year Electronic & ComputerFinal Year Project Presentation
Supervisor: Dr Maeve DuffyCo- Supervisor: Dr Peter Corcoran
Student: Noel Walsh Date : 13-08-08
Introduction
• The aim of the project was to design an intelligent back-up battery charger capable of charging various battery chemistries.
• The idea for the project was proposed by Ben Kinsella, Hardware Engineering Manager at Blue Tree Systems during my 3rd year PEP.
• The actual circuit itself was to be designed as a rechargeable secondary power source for Blue Trees R:COM device on a dry trailer configuration.
• The structure of the project was broken into the following sections
– Battery Chemistries properties and charge cycles
– DC-DC converters
– Hardware
– Software
– PWM
Battery Chemistries properties and charge cycles
• A Battery is composed of one or more electrochemical cells, which store chemical energy.
• Two types primary and secondary.• There are many battery chemistries available, characteristics vary• Charging algorithms vary for different secondary chemistries.• Selecting the battery for the project was based on:
– Rechargeable– Cost– Capacity– Physical Size– Customer requirements
Sealed Lead Acid
• Low cost battery available in a variety of sizes and designs.• Performs well over a range of temperatures.• Good service life
• Manufactured by panasonic Model number LC-X1220P/LC-
X1220AP • 6 cells connected in series 12v dc output • Capacity is equal to 20Ahours• Charging methods
– Fast charging ( CV/CC, rapid, 2 step CV)
– Slow charging ( CV , trickle, float)
Sealed Lead Acid Charge CycleDetermine a charge cycle
• Current Level
0.4C or smaller CV
0.15C or smaller trickle• Temperature
from 0°C to 40°C • Charge Time
Time CV I < 0.25C
Tch = Cdis / I + (6 to 10)
Trickle 24/48 hours • Capacity
From table
• Overcharging
Shorten battery life
SLA Charging AlgorithmCheck Battery Capacity
No
Yes
Check Battery Capacity
Is V less than 12v (cell<2)
Start charge cycleCharge V = 14.7v
(2.45 v/cell)Start charge timer
Test Cell voltage 2.12 = 100%
Terminate Charge cycle
Ic stable 3 hrs? Charge time?
No
Yes
Li-poly Battery
• Evolved from Lithium.• More robust, lighter and easier to shape.• Manufactured by WorleyParsons Model No. AES 555072.• 3 cell battery, nominal voltage 3.7• 4.2 voltage on terminals when fully charged.• Capacity is rated for 2Ahour.• Preferred charging method is constant current/ constant voltage,
which is composed of 3 stages– Trickle charge
– Fast Charge ( constant current CC)
– Constant voltage (CV)
Li-Poly Charge CycleDetermine a charge cycle
• Current Level1C for CC stage0.02C for end of charge
• Temperature for charging
from 0°C to 45°C • Charge Time
Trickle : < 1Hr Fast : < 1.5Hr CV : < 2Hr
• Capacity ( voltage across terminals)4.2v charged, 3v
discharged • Termination
Current level or timer.
Li-Poly Charge Algorithm
Start Charge CycleConstant Voltage
Start Per-conditionStage
Yes
YesYes
No
No
No
Check Battery Capacity
No
Yes
Check Battery Capacity
Is V less than 8.5v (cell<2.8)
Start charge cycleConstant current
I charge = 2 AMPSStart charge timer
Terminate Charge cycle
Is V = 9/9.6 cell 3/3.2
Is V = 12.6 cell 4.2
I charge = 0.02C Timer?
SEPIC DC to DC converter
• Single Ended Primary Inductance Converter.• Classified as a Switched-mode power supply.• Non-inverting output capable of generating output voltages above or
below the input voltage.• Operates in continuous mode.• The average current in inductor L2 is the same as the load current,
therefore offers low end current sense.
SEPIC Switching
SEPIC Waveforms
SEPIC Operating ConditionsValue Unit Note
US Truck Battery 12 Volts DC Range 9-14
EU Truck Battery 24 Volts DC Range 20-28
Vin minimum 9 Volts DC
Vin maximum 36 Volts DC
Vout range 14.5-14.9 Volts DC For lead Acid
Vout range 12.3-12.6 Volts DC For Lithium
I out 2 Amps
Switching Frequency 330 KHz
SEPIC circuit DiagramD 3
D 1 N 4 1 4 8
TD = 0
TF = 1 0 nP W = 1 . 9 uP E R = 3 . 0 3 u
V 1 = 0
TR = 1 0 n
V 2 = 1 0
U 2
S I 4 4 5 0 D Y
D
G
S
4
1
2
V 12 4 V d c
R 1
7 . 3 5
2
1
L 1
1 3 . 1 u H
C 1
1 u
C 2
1 u
C 3
2 2 u F
L 2
1 3 . 1 u H
SEPIC Simulation
Duty cycle Relationship with output current
Vin DC volts Duty cycle(usec) Duty Cycle % Vout DC volts
SLA 24 1.2 40 14.7
SLA 12 1.83 60 14.7
Li-Poly 24 1.17 39 12.6
Li-Poly 12 1.72 57 12.6
Duty cycle Relationship with output voltage
MSP403x2xx Micro
• Ultra low power 16 RISC mixed signal processor.• Designed for battery powered measurement applications• The mixed-signal and digital technologies implemented in the MSP430 allow
for simultaneous interfacing to analogue signals, sensors and digital components while maintaining low power
• Hardware development tools
• Software development tools • Micro-controllers perpherials used in project.
– Digitally controlled oscillator DCO
– 10 bit analog-to-digital converter.
– 2 configurable Op-amps
– 4 Digital I/O ports
MSP430x2xx Architecture
MSP430 Firmware
• First task is to configure the microcontroller and initialise some data variables.
• Configures ports, DCO, Timer_A, ADC, Op-amps• Initialise ADC data array, timedelay, PWM period, PWM duty cycle• ADC is interrupt enabled and the ADC ISR executes when this
process is invoked.• ADC value is read in and if required the value in CCR1 is changed
to adjust the PWM duty cycle.• Timer_A is set in up mode and counts to CCR0. • CCR1 is configured to OUTMOD_7, reset/set.
Firmware FlowchartIdle
YesNo
Check Battery
Capacity
ExecuteCharge algorithm
Truck supply R:COM
Battery supply
R:COM
BatteryCharged
truckconnect
TruckConnected
Yes
No
Check Battery
Capacity
BatteryCharged
No
Yes
ConfigureMicrocontroller
Yes
ADCInterrupt
No
Proposed System
• Microcontroller is powered through a buck converter by the back-up battery
• Input voltage from the trucks battery is measured with a voltage divider ( R3 = 13k and R4 = 1k ohms)
• SEPIC output voltage has to compensate fro the sense resistor on the battery and the voltage ripple. ( R1= 7k and R2 = 1k ohms)
• Battery current measured through resistor R sense 2 = 1.25 ohms • SEPIC output current is source with the sense resistor R sense 1
and it equals 1 ohm. Rated for peak current in the inductor L2.• Switching power sources in implemented with two N0channel
MOSFETS connect to pins TB0 and TB1 of Timer_B.
Circuit Block Diagram
Back-up Battery System
SEPIC
Micro
Switches
R:COMTruck
Battery
+ --
Back-upBattery
+ --
Charge controlSignals
PWM Signal
Switch Select
R:COM Power lines
Charge Voltage
Input Voltage
Output Voltage
Output Voltage
Problems Encountered
• Software development tools for the microcontroller• Driving the power MOSFET from the microcontroller.• Simulating with Pspice.• Configuring microcontroller for an interrupt service routine.• Charging algorithms and component ratings.
Conclusion
• Most of the design is finished to enable the system to be built• Charging algorithms difficult to finalise• Lacked a power electronics background.• I am satisfied with the overall outcome of the project as it introduced
me to various new subjects.• The work completed was mostly successful. Wished I had more
time with the microcontroller.• Remain work to do.
– Firmware– Micro interfaces– Test SEPIC