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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
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
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
Current Progress
• Topology finalized – 4 parallel packs of 30 cells
each
• Monitoring IC and sensors ordered and
waiting on arrival
• Began programming onboard microcontroller
Battery Pack Topology – Dual Power Bus
Solar Cells
Charge Bus
Discharge Bus
Pack 0
Pack 1
Pack 2
Pack 3
Motor
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
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
LTC6802 BMS IC
• Can monitor up to 12
batteries in series
• Stackable architecture
allows for >1000 V
systems
• Measures voltages,
temperatures, balances
individual cells
• Outputs measurement
data via serial
From Higher
Voltage
LTC6802
To Lower
Voltage 6802
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 PIC’s
onboard analog-to-digital
converter
• Data will be output over a
RS485 main data line
Battery Module PCB Design
LTC6802
Current
Sensor/Voltage
Sensor (top
module only)
RS485 bus,
Serial input from
previous module
PIC microcontroller
(bottom module
only)
10 battery cells
Project Completion Flow Chart
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