Batteries for Small VehiclesPhilosophy, Design and Development
Prabhjot Kaur, PhD
CEO, Centre for Battery Engineering and Electrical Vehicles (C-BEEV)
IIT Maras
Batteries dominate the cost of an EV
• Larger the battery, more the cost• Bigger batteries impact energy efficiency
• Smaller battery will create range anxiety
• We are generally thrilled with longer RangeBut, who can afford?
• Batteries can be swapped when they run out
September 1, 2018 2
Dilemma
Category Percentage
Buses and Trucks 3%
Economy Cars 12%
Premium Cars 2%
2 Wheelers 79%
3 Wheelers 4%
We clearly need affordable vehicles
Batteries have to be small, LAST LONGER
Small Batteries: Swap in addition to Charge
• Answer : Separate vehicle business & energy business
• Energy Operator to procure bulk batteries and lease charged batteries
• For business viability, design• Lowest cost battery
• Long Life with temperature Compensation / control
• Charge at 0.5 C and at 25deg C, discharge at ambient (Indian temperatures)
• Safety against Theft
September 1, 2018 3
ReliabilityInvestment
“Fear of Dead Investment”
DemandRight balance of stock
Ownership of batteries
Swapping Concerns
Designing Batteries
September 1, 2018 4
Right Cells
BMS
Thermal Mgmt
Mech.Design
Accurate SOC / SOH
Protection
Charge, Discharge
Control
✓ Chemistry✓ Lifecycles✓ charge/dis rates✓ power, range✓ operating conditions
✓ Stability: vibration, shock / impacts, drops
✓ Determination / Managementalgorithms, Cell balancing,Optimization
✓ Over Current✓ Over/Under Voltage✓ Over/Under Temperature✓ Short-Circuit✓ Reverse battery/charger
Connection✓ Pre-Charge
✓ Cooling requirement of pack
✓ Optimal charging✓ limiting the discharge✓ Life cycle control and tradeoffs
To Handle Indian Temperatures (45 – 55 degrees)
September 1, 2018 5
Battery Thermal Management Various Methods Modes
Active
Air LiquidRefriger
antHybrid
Passive
PCMMicro
Channel
Technically and Commercially ViableApt for Swappable Batteries
Unaffordable and too complex for a small battery
What did we Do?
• Mix of Internal and External Cooling• Phase Change material (PCM) internally for limited hours duration
• Cool before operation (start at 25 deg C)
• Discharge at ambient temperature – make sure that internal battery is retained at 35deg C mostly during four-five hours operation (PCM + battery starts at 25)
• Refrigerant based Cooling while Charging• Thermal Plates for heat exchange while charging batteries at 0.5C
• Ensure that charging is done at below 25 deg C
September 1, 2018 6
So Batteries Have
September 1, 2018 7
Featured Packed BMSWell Engineered
Battery Pack
Certifications compliance
Safety and Protection:
AIS-048 and UN-38.3 IEC62133
Heading towards Functional Safety
compliance
ISO 26262
Safety against theft
Locked Smart Batteries (LS Batteries)
• Can not be charged except through authorised Chargers
• Can not feed power except to authorised vehicle• Encrypted Key exchange between Charger / vehicle
and LS-batt
• Relay turns on only after authentication (each LS-batt has unique ID)
8September 1, 2018
Relay
MonitorBatteries while charging
while In-useto maximise life,
performance and value
September 1, 2018 9
Accurate battery health calculation and easier sorting
of batteries
Battery sends multiple data points during
operation
Regular monitoring of
each parameter
LS VBCC Protocol Suite(Locked Smart- Vehicle Battery Charger Cloud)
September 1, 2018 10
Demo
UI
UIDB
Swapping & Charging Station
EV Driver
EV
Some Early Trials and Learnings
September 1, 2018 11
5 OEMsLohia, Goenka, Kinetic,
Electrotherm, Mahindra
3 Battery ManufacturersAmaraja, Exide, Exicom
EO: Essel
Bulk Charger: Exicom
Software and Management PlatformsEsmito
Vehicles on DrivePilot of LS Battery swapping at IITM Campus
Test vehicle with school kids, residents and staff in IITM campus
September 1, 2018 12
Battery pack energy, voltage and current during driving
Discharging current
Gradually decreasing voltage during drive
Gradually decreasing energy during drive
13September 1, 2018
Individual Cell Voltage and Temperature while charging
Gradual increase
of voltage while
charging
Gradual increase of
temperature while
charging
14September 1, 2018
Cell voltage and temperature monitoring during driving
Gradual decrease
of cell voltages
while driving
Gradual increase of
cell temperatures while driving
15September 1, 2018
Performance Comparison
September 1, 2018 16
S.No Make and Model Wh/Km
Distance
travelled
(Kms)
1 Make 1, Model A 44 36
3 Make 1, Model C 38 27
4 Make 2, Model A 42 43
5 Make 2, Model B 37 51
6 Make 3 39 46
7 Make 4 58 31
8 Make 5 41 46
Sample Dated: 14th June, 2018
S.NoVehicle Make Total Rides Avg. Wh/Km
1 Make 1/C 164 40.36
2 Make 2 331 44.15
3 Make 3 324 44.28
4 Make 4 419 46.29
5 Make 5 82 52.18
All 1320 45.45
Cumulative of 4 Months
Driving – All Cell temperatures for all sessions (34 Million data points)
17
Incorrect range – To be analyzed. 11,815 points above 100 deg.C
September 1, 2018
Charging – All Cell temperatures for all sessions (~ 6 Million data points)
18
Normal operating range –25 to 50 deg.C
Wrong values - to be analyzedSeptember 1, 2018
How is this data helpful?
September 1, 2018 19
• All use cases: Driving (Discharge and driving pattern) and charging impact batteries
• Battery Performance evaluation and optimization• Redesigning • Cycles assurance• Redo Mechanical Design, Redo Thermal: all required corrections • Better cut offs and control
• Aiding in Driving Patterns• Reduced / Increased discharge rates (current drawn)• Warnings and alarms • Go back to drawing board (learnings from problematic batteries)
• Business cases