Group 6 Final Presentation

1. Group 6 Final Presentation CS10 Battery Management System Group Members: Brad Cox Kevin Burkett Tera Cline Arthur Perkins

2. Outline • Introduction • Software • Hardware • Budget • Challenges • Conclusion

3. Project Overview • Designed and created a scalable, accurate battery management system to monitor NiMH batteries • Measures voltage and temperature in real time • After nominal voltage is obtained, current is bypassed • Automates Charging: • Switches to Current Mode before bypassing current • If max temperature is exceeded, charger is shutdown • Created a Windows Application that allows user to interface with system • User sets configuration parameters • Shows cell voltages and module temperatures • Saves measured values for future analysis

4. Commercial System • Most systems are designed for Lithium batteries • Greater risk of failure if overcharged • Cost varies from $500 - $2500 depending on the size of the battery pack • Many are designed to work with the CAN bus of the vehicle • Integrated to the vehicle subsystems • Some measure voltage, current, and temperature

5. Project Design Goals • Provide a simple low maintenance, scalable solution for monitoring the charging of batteries in an electric vehicle • Accurately measure the temperature and voltage of the battery cells and displays this information to the user • Insure the batteries are charging properly by closely monitoring the voltage and temperature • Prevent battery failures caused by overcharging and overheating by bypassing current around fully charged cells • Shut down the charger if the max operating temperature of the batteries is exceeded

6. NiMH Batteries • Have large capacity compared to other batteries • Have high energy density • Average cell voltage: 1.2 – 1.5V • Overcharging can permanently damage capacity • Suffers from battery memory effect • Works best with slow trickle charge

7. System Overview

8. Windows Application • Coded using Visual C# • Sends and receives data from microcontroller • Allows user to configure system with different monitoring parameters • Displays the measured voltage and temperature values as column charts • Recovers system if communication failures occur between microcontroller and MAX11068 • Notifies user of what cells are bypassing and when all of the cells are fully charged.

9. Configuration Configuration Window Setting Parameters

10. Different Color For Each Device View Voltages or Temperatures Measuring Current Configuration Previous Commands Measuring 8x3 Cells Progress of Current Measurement System Running

11. Microcontroller • Design Change: • Decided to use Freescale HCS12 Microcontroller over PIC microcontroller • Model: MC9S12DG257CFUE • Justification: • Ability to drag and drop components (i.e. components preconfigured) • Previous experience using FreescaleCodewarrior • Drag and drop I2C module

12. Software Challenges • Application Challenges: • No one in the group had any previous experience using C# or creating a GUI • Struggled creating function to receive from the serial port asynchronously • Microcontroller Challenges: • Provided I2C interface would not work with MAX11068 data acquisition chip • Difficult to code I2C driver • Hard to find the correct clock frequency so that the microcontroller would not lock-up

13. Controller Board • Main components • Wytec Thunderbird12 Module • Powered by +12V auxiliary battery • Serial communication to laptop • I2C communication to Data Acquisition Board • Charger Control

14. Data Acquisition Board • Main components • Maxim11068 • 5kV I2C Isolators • 18 pin Wire Connection terminal • LDO regulator • Jumper pins for bypassing isolators • Used on all boards after first module

15. Bypass Board • Bypasses 1 Amp of current • 3.96 Ohm, 5 Watt Resistor • External MOSFET triggered by MAX11068 • LED notification • Easily mounts on provided NiMH batteries using nylon screws

16. Hardware Challenges • PCB Design • Learning Design Program • Creating Parts • Running traces • Making board schematic exactly like circuit • Ground planes create more issues than they solve • Soldering and De-soldering • Little to no soldering experience • Some parts only came in surface mount packages • Ordering enough parts to compensate for mistakes • Burning Chips • Melting Sockets

17. Budget • Controller Board • Cost = $160 • Main Component: • Wytec Thunderbird12 Dip Module - $60 • Data Acquisition Board • Cost = $150 • Main Component: • Maxim 11068 – $30 soldered • Bypass Boards • Cost = ~$100 for 12 Boards • ~$8.50 per board • Project Boxes - $30

18. Possible Improvements/Additions • Design bypass boards to fit multiple types of batteries • Add current measurement to system • Add additional system protection • Water Proofing • EMI Shielding • Make system mass producible • Transition from using Thunderbird12 module to only using microcontroller • Use all surface mount parts • Add USB capability • Serial is outdated • Add additional MUX to allow for more temperature measurements

19. Reflections • Learned and performed many new tasks in all aspects of the project • Creating a graphical application • Using I2C protocol • PCB design • Debugging PCBs • Things we would have done differently if possible: • Had a more balanced team in terms of skill sets • Looked for an alternative to I2C or chosen a microcontroller that had more examples of interfacing with I2C

20. Questions?