Battery Management System for a Solar Powered Race Car

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Battery Management System for a Solar Powered
Race Car
Joshua Durham Nathan Murdaugh David Trawick
Georgia Institute of Technology School of
Electrical and Computer Engineering
Georgia Tech Solar Jackets
March 14th, 2011
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Project Overview

• A Battery Management System (BMS) monitors
  voltage, temperature, and current and balances
  the batteries, as well as cuts the batteries off
  when limits are reached
• BMS ensures batteries stay within safe charge and
  temperature limits for maximum efficiency
• Meets requirements for World Solar Challenge 2011
• Estimated cost of system - 500

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Design Objectives

• Continuously monitor voltage of individual cells,
  current in and out of a pack, and temperatures
• Balance individual cells
• Output measurement data over RS485
• Implement cutoff voltage, current, and
  temperature limits to protect batteries

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Current Progress

• Topology finalized 4 parallel packs of 30 cells
  each
• Monitoring IC and sensors ordered and waiting on
  arrival
• Began programming onboard microcontroller

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Battery Pack Topology Dual Power Bus
Solar Cells
Charge Bus
Discharge Bus
Motor
Pack 1
Pack 0
Pack 2
Pack 3
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Individual Pack Fail-safes

• Each battery pack contains up to 3.4 MJ of energy
• Every pack will contain a mechanical safety
  switch for transport/assembly
• A fuse will provide absolute current limiting
• During normal operation, the pack will be
  switched using a FET controlled by its
  microcontroller

Fuse
Mechanical Switch
FET
Pack X
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Measuring Pack Voltage and Current

• Bidirectional current sensor measures charge and
  discharge currents
• Voltage sensor across the FET at the top of the
  pack compares the pack voltage to the bus

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LTC6802 BMS IC

• Can monitor up to 12 batteries in series
• Stackable architecture allows for gt1000 V systems
• Measures voltages, temperatures, balances
  individual cells
• Outputs measurement data via serial

From Higher Voltage LTC6802
To Lower Voltage 6802
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Data Collection and Output

• A PIC18LF4321 will be used to collect and output
  all data
• Data from the LTC6802 will be collected via a
  serial peripheral interface
• Voltage and current sensors will go though the
  PICs onboard analog-to-digital converter
• Data will be output over a RS485 main data line

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Battery Module PCB Design
LTC6802
RS485 bus,Serial input from previous module
Current Sensor/Voltage Sensor (top module only)
PIC microcontroller (bottom module only)
10 battery cells
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Project Completion Flow Chart
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Schedule, Future Work, and Final Delivery

• Now until April 1 Complete prototype
• April 1-20 Complete full size packs
• No later than May 5 Finish demonstration and
  final report/presentation
• Will deliver two full-size packs that can
  interact properly