1. EV Battery Gauge Design:
Project in progress
Project no. 4203-1535

2. 2222
Project Team Members and Roles
Name: Pat McGoldrick
Role: Industry Mentor (Creative Power Technologies)
Contact Details: pat@creativepower.com.au
Name: Grahame Holmes
Role: University Supervisor (RMIT University)
Contact Details: grahame.holmes@rmit.edu.au
Names: Curtis Moses, Declan Lammers, Ilia Andreev,
John Francia, Long Nguyen, Olivia McCombe
Roles: Student Researchers and Designers
Contact Details: s3409016@student.rmit.edu.au

3. 3333
Nominal full
charge 6.630 kWh
Energy drawn
over 22 km 6.596 kWh
SoC after 22 km <1 %
Project Background
From Lap Simulator of RMIT Car
in Formula Student Event:

4. 4444
Project Background
Image sources: plugincars.com, RMIT Electric Racing
 Fuel gauge for an EV  battery State of Charge (SoC)
 SoC  % of maximum charge remaining
 BENEFITS:
• Driver control of battery
• Foundation for automated
battery management
 CHALLENGES:
• Direct measurement inaccurate
• Many estimation techniques

5. 5555
Project Background
Image sources: plugincars.com, RMIT Electric Racing
Objectives:
Battery gauge
- Li-ion chemistry
- Amateur EVs
SoC
Estimation
Program
Display +
Validation
Programs
Product

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Discharge +
Measurement
Circuit
SoC
Estimation
Program
Display +
Validation
Programs
Our Estimation System
Battery
Image sources: Arduino, pngwebicons.com

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Project Plan
Research Phase:
Project Benefit, Scope,
+ Estimation Techniques
1 March – May 30
Circuit Team Arduino Team Display + Validation Team
Discharge/measure
ment circuit built
19
July
SoC estimation
program (simulation
data)
Display code
Open-circuit-voltage
measurements
2
August
Circuit-Arduino
connection code
2
August
Arduino-computer
connection
Circuit-Arduino
operation
31
August
Validation code
Arduino-computer
operation
15
September
GANTT Chart Extract

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SoC Estimation Program
1. Before charging/discharging:
estimate initial SoC
2. During charging/discharging:
± charge entering/exiting

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Constant Current
Pulses discharge
battery
1. Estimate Initial SoC
Open Circuit Voltage (OCV) – SoC Table
Measurement
Circuit
Test Phase
OCV SoC
3.75 100%
3.70 99%
3.65 98%
SWITCH
VOLTAGE
SENSE
OCV = Battery Terminal Voltage

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1. Estimate Initial SoC
Open Circuit Voltage (OCV) – SoC Table
Initial SoC
Measurement
Circuit
Estimation Phase
Battery Terminal
Voltage
OCV SoC
3.75 100%
3.70 99%
3.65 98%
VOLTAGE
SENSE

11. 11111111
Coulomb Counting
2. ± Charge Entering/Exiting
Convert
Current to
Charge
(Coulombs)
± From Initial
SoC
Measurement
Circuit
CURRENT
SENSOR
Current
over Time

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Coulomb Counting
2. ± Charge Entering/Exiting
Convert Current  Charge (Q) (in coulombs)

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Coulomb Counting
2. ± Charge Entering/Exiting
SoC Calculation

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Components Focus

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Battery
Lithium-Ion Chemistry
One Cell
3.7V, 100mAh

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Discharge + Measurement Circuit

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Discharge + Measurement Circuit
1
1
2
2
3
3
4
4
D D
C C
B B
A A
Title
Number RevisionSize
A4
Date: 1/10/2015 Sheet of
File: H:TestBed.SchDoc Drawn By:
2
3
6
47
1
8
5
Op Amp
VAUX
+5V
5v
+5vDC
10K
R-Trimpot
GND
GNDGND
1
RLOAD
5W
GND
S2
MOSFET N-type
3
2
1
.
6
5
4
. +5v
GND
V-I/O
CurrentSensor
.
2
3
6
47
1
8
5
Op Amp
5v
+5vDC
GNDGND
GND
5v
+5vDC
GND
Cap
GND
D4
Diode 1N4004
D3
Diode 1N4004
RSense(I)
CSense(I)
GND GND
VBatt
Battery
5
4
3
2
1
0
ARDWINO (ANALOG IN)
2
3
6
47
1
8
5
Op Amp
GND
5v
+5vDC
GND
Cap
GND
D2
Diode 1N4004
D1
Diode 1N4004
RSense(V)
CSense(V)
GND GND
Cap
GND
15K
RAUX
Switching
MOSFET-N
GNDGND
Unused I/O
Ardwino
Switching
GND

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Discharge + Measurement Circuit

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SoC Program
Arduino

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Display Program
MATLAB

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MATLAB
Battery Simulation Model
Validation Program
Validation Program
Estimate Initial SoC
Simulation:
Pre-defined Variable
Read Current
Simulation: Data Array
Identify SoC for
Current Range
Switch Statements
Current Range-SoC
Look-Up Table
Outputs:
Voltage

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Results + Conclusions
 Achievements
 Current Product Limitations

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Acknowledgements
 AutoCRC
 Professor Grahame Holmes
 Pat at Creative Power Technologies
 RMIT Electric Racing Team
 RMIT Staff