1. Department of Electronic Engineering 4th Year Electronic & Computer Final Year Project Presentation Supervisor: Dr Maeve Duffy Co- Supervisor: Dr Peter Corcoran Student: Noel Walsh Date : 13-08-08

2. 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 3 rd 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

3. 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

4. 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)

5. Sealed Lead Acid Charge Cycle Determine 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

6. SLA Charging Algorithm Check Battery Capacity No Yes Check Battery Capacity Is V less than 12v (cell<2) Start charge cycle Charge 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

7. 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)

8. Li-Poly Charge Cycle Determine a charge cycle Current Level 1C for CC stage 0.02C 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.

9. Li-Poly Charge Algorithm Start Charge Cycle Constant Voltage Start Per-condition Stage Yes No Check Battery Capacity No Yes Check Battery Capacity Is V less than 8.5v (cell<2.8) Start charge cycle Constant current I charge = 2 AMPS Start 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?

10. 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.

11. SEPIC Switching

12. SEPIC Waveforms

13. SEPIC Operating Conditions ValueUnitNote US Truck Battery12Volts DCRange 9-14 EU Truck Battery24Volts DCRange 20-28 Vin minimum9Volts DC Vin maximum36Volts DC Vout range14.5-14.9Volts DCFor lead Acid Vout range12.3-12.6Volts DCFor Lithium I out2Amps Switching Frequency330KHz

14. SEPIC circuit Diagram

15. SEPIC Simulation Duty cycle Relationship with output current Vin DC voltsDuty cycle(usec)Duty Cycle %Vout DC volts SLA241.24014.7 SLA121.836014.7 Li-Poly241.173912.6 Li-Poly121.725712.6 Duty cycle Relationship with output voltage

16. 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

17. MSP430x2xx Architecture

18. 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.

19. Firmware Flowchart Idle YesNo Check Battery Capacity Execute Charge algorithm Truck supply R:COM Battery supply R:COM Battery Charged truck connect Truck Connected Yes No Check Battery Capacity Battery Charged No Yes Configure Microcontroller Yes ADC Interrupt No

20. 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.

21. Circuit Block Diagram Back-up Battery System SEPIC Micro Switches R:COM Truck Battery +-- Back-up Battery +-- Charge control Signals PWM Signal Switch Select R:COM Power lines Charge Voltage Input Voltage Output Voltage

22. 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.

23. 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