Group 6 Final Presentation

Group Members:Brad Cox

Kevin BurkettTera Cline

Arthur Perkins

CS10 Battery Management System

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

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

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

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

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

System Overview

Microcontroller Board

Data Acquisition Board 1

MAX11068

Bypass Board 1

RS-232

I2C

+

-

Bypass Board 2

+

-

Bypass Board N

+

-

Data Acquisition Board 2

MAX11068

Bypass Board 1

+

-

Bypass Board 2

+

-

Bypass Board N

+

-

Data Acquisition Board N

MAX11068

Bypass Board 1

+

-

Bypass Board 2

+

-

Bypass Board N

+

-

3.96V

3.96V

3.96V

3.96V

3.96V

3.96V

3.96V

3.96V

3.96V

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.

Configuration

Configuration Window

Setting Parameters

Measuring

System Running

View Voltages or Temperatures Current

Configuration

Previous Commands

Different Color For Each Device

Measuring 8x3 Cells

Progress of Current

Measurement

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 Freescale Codewarrior

– Drag and drop I2C module

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

Controller Board• Main components

– Wytec Thunderbird12 Module

– Powered by +12V auxiliary battery

– Serial communication to laptop

– I2C communication to Data Acquisition Board

– Charger Control

Data Acquisition Board• Main components

– Maxim 11068– 5kV I2C Isolators– 18 pin Wire

Connection terminal

– LDO regulator– Jumper pins for

bypassing isolators Used on all boards

after first module

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

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

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

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

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

Questions?