Thermal Management

Thermal management is critical for EV performance, safety, and longevity. Batteries, motors, and power electronics all generate heat that must be managed. Too hot or too cold — both are problems.

Why Thermal Management Matters

Battery

• Accelerated degradation
• Reduced cycle life
• Thermal runaway risk

• Reduced capacity
• Limited charging rate
• Increased internal resistance

Motor & Inverter

• Motor windings: 150-180°C max
• Power electronics: 125-150°C max
• Magnets: Demagnetize above ~150°C (NdFeB)

• Power derating (reduced performance)
• Permanent damage
• Shortened lifespan

Cabin

• Summer: 20-25°C interior when ambient 40°C+
• Winter: 20-25°C interior when ambient 0°C or below
• India: Primarily cooling challenge

Thermal Architecture

Integrated Thermal System

Modern EVs use integrated thermal management:

• Battery thermal circuit
• Powertrain thermal circuit
• Cabin HVAC circuit
• Refrigerant circuit (heat pump)

• Shared coolant in some regions
• Heat exchangers between circuits
• Intelligent routing based on needs

Coolant Loops

• Temperature: 20-35°C
• Lower temp for battery longevity
• Water-glycol (50/50 mix)

• Temperature: 50-70°C
• Higher temp acceptable for motor/inverter
• Can share heat with cabin in winter

Battery Cooling Methods

1. Air Cooling

• Fans blow air over cell surfaces
• Air ducts between modules

• Simple, low cost
• Lightweight

• Limited cooling capacity
• Uneven cooling
• Dust/moisture ingress

2. Liquid Cooling

• Coolant channels in cold plate
• Cold plate contacts cell bottoms
• Pump circulates coolant to radiator/chiller

• High cooling capacity
• Uniform temperature distribution
• Can also heat battery

• Complex, expensive
• Leak risk
• Added weight

3. Immersion Cooling

• Cells immersed in dielectric fluid
• Direct contact for heat transfer
• Emerging technology

• Excellent thermal uniformity
• Best cooling capacity
• Potential fire suppression

• Heavy (fluid weight)
• Complex servicing
• Limited real-world deployment

Heat Generation

Battery Heat Sources

$$Q_{ohmic} = I^2 \times R_{int}$$

• Dominates at high current (acceleration, fast charging)
• Internal resistance increases at low temperature
• R_int typically 0.5-2 mΩ per cell

$$Q_{entropic} = I \times T \times \frac{dV_{oc}}{dT}$$

• Reversible heat from electrochemical reactions
• Can be positive or negative
• Smaller than ohmic heating

Heat During Fast Charging

• Battery voltage: 400V
• Charging current: 125A
• Pack internal resistance: 100 mΩ
• Heat: 125² × 0.1 = 1.56 kW

Plus losses in charger, cables, and contactors.

Motor Heat Sources

• Stator winding resistance
• 2-5% of motor power at full load

• Hysteresis and eddy currents
• Increase with frequency (speed)

• Bearing friction
• Windage

Cooling System Design

Heat Balance Equation

$$\frac{dT_{battery}}{dt} = \frac{Q_{gen} - Q_{cool}}{m_{battery} \times C_p}$$

Where:

• Q_gen = heat generation rate (W)
• Q_cool = cooling rate (W)
• m_battery = battery mass (kg)
• C_p = specific heat capacity (J/kg·K)

Cooling Rate

$$Q_{cool} = h \times A \times (T_{battery} - T_{coolant})$$

Where:

• h = heat transfer coefficient (W/m²·K)
• A = heat transfer area (m²)
• T_battery, T_coolant = temperatures

Sizing Example

• Heat generation: 3 kW (during fast charging)
• Battery target: 35°C
• Coolant supply: 25°C
• Temperature difference: 10°C

$$Q_{cool} = 3 \text{ kW}$$

$$h \times A = \frac{3000}{10} = 300 \text{ W/K}$$

This determines cold plate size and coolant flow rate.

Cabin Thermal Management

Cooling (Air Conditioning)

• Compressor compresses refrigerant (R134a or R1234yf)
• Condenser rejects heat to ambient
• Expansion valve drops pressure
• Evaporator absorbs heat from cabin

Heating

• Resistive heating
• Simple, reliable
• 2-5 kW power consumption
• Inefficient: COP ≈ 1.0

• Reversed A/C cycle
• Extracts heat from outside air
• Efficient: COP ≈ 2.0-3.0
• Struggles below -10°C

• Capture heat from motor/inverter
• Route to cabin via heat exchanger
• Most efficient when available

Heat Pump Advantage

Thermal Runaway Prevention

What is Thermal Runaway?

Self-accelerating heat generation leading to cell destruction:

• Initial heat (short circuit, overcharge, damage)
• SEI breakdown (~120°C)
• Electrolyte decomposition (~150°C)
• Separator melting (~180°C)
• Thermal runaway (>200°C)
• Venting, fire, explosion

Prevention Strategies

• Separator coatings (ceramic)
• Current interrupt devices
• Vent mechanisms

• Thermal barriers between cells
• Fire-resistant materials
• Cooling to absorb initial heat

• BMS monitoring (temperature, voltage)
• Cooling capacity to remove heat
• Enclosure venting

• Contactors to isolate pack
• Warning systems
• Crash-safe design

Preconditioning

Battery Preconditioning

• Heat cold battery to 25-30°C before arrival
• Reduces internal resistance
• Enables faster charging

• Heat battery before departure
• Uses grid power, not battery
• Improves initial performance

Cabin Preconditioning

• Cool/heat cabin while plugged in
• Uses grid power
• Saves battery range
• Comfortable from start

Indian Context

Challenges

• Ambient 40-45°C common
• Significant cooling load
• Battery must stay below ~40°C

• Air filters clog quickly
• Corrosion risk for components
• Sealed systems preferred

Solutions

• Larger radiators
• More powerful A/C compressors
• IP67 battery enclosures
• Reflective surfaces

• Nexon EV: Liquid-cooled battery, IP67 rated
• Ather 450X: Air-cooled, thermal management optimized for Indian summers

Key Takeaways

• Battery optimal temperature: 20-35°C
• Liquid cooling is standard for passenger EVs
• Heat pump heating is 2-3× more efficient than resistive
• Heat generation = I²R (increases with current squared)
• Thermal runaway prevention requires multiple safety layers
• Preconditioning improves charging speed and comfort

Course Complete!

Congratulations on completing EV Fundamentals! You now understand:

• Battery chemistry and pack design
• BMS functions and cell balancing
• Motor types and control
• Power electronics and powertrain
• Charging systems and range factors
• Thermal management

Take the quiz to test your knowledge and earn your completion certificate.