Why different Battery Pack has different Insolation Resistance Value ?

 

Illustration of IR Measurment 

The Fundamental variation in insulation resistance (IR) readings of Lithium Batteries are due to below reasons namely,

1. Battery Pack Design and Construction
2. Voltage Level
3. Environmental Conditions
4. Contamination or Aging
5. Measurement Path and Method
6. Capacity/Size of the Pack

Different OEM's battery Pack Types have different IR readings through their software like Tesla Model S is having 25MΩ or 25000KΩ, The Indian Manufacturing giant TATA and its Vehicle's battery possibly have 5MΩ or higher.

The above measurments are dipendent on the applied Voltage levels to measure IR readings, Higher Voltage levels to measure leads to lower IR Values.

As per international standards like below;

1. SAE J1766 (Society of Automotive Engineers),
2. ISO 6469-3 (Electrically Propelled Road Vehicles – Safety Specifications),
3. IEC 61851-23 (Electric Vehicle Conductive Charging System),
4. UN ECE R100 (Uniform Provisions for Battery Electric Vehicles)

All the above standards specify minimum IR of 100 Ω/V for DC systems and 500 Ω/V for AC systems, measured between HV components and the chassis, also at the time of crash or vibration, thermal shock, environmental tests like water ingress IR must remain above these thresholds.

For an 800V system (e.g., BYD Seal EV Vehicle):

• DC Side IR Measurment: 100 Ω/V × 800V = 80 kΩ.
• AC Side IR Measurment: 500 Ω/V × 800V = 400 kΩ.

And for EV Chargers , it must maintain IR >1 MΩ under normal conditions to prevent leakage to the grid or chassis, It has to ensures safe interaction between the vehicle and charging infrastructure. Diagnostic monitoring Devices monitor IR has to detect faults during charging.

EV manufacturers like Tesla and BYD calibrate their Battery Management Systems (BMS) and diagnostic tools to monitor IR in realtime, typically displaying values in megaohms (MΩ).

Healthy systems show IR values significantly above the minimum requirements, often >1500 to 4000 kΩ (1.5 to 5 MΩ), as seen through diagnostic tools like CANALYZER & PEAK CAN with monitoring softwares.

There are 3 measuring methods in IR measurment, Which are;

1. BMS Internal IR Measurement: 

BMS applies a known voltage through a high-value resistor to the chassis from either the positive or negative terminal and measures the resulting current

2. Insulation Resistance Tester (Megger or Megohmmeter) :

By Connecting the megohmmeter Positive terminal to ground or Negative terminal to ground and applying a DC test voltages 500V or 1000V DC will show us the resistance value either in KΩ or MΩ depending upon the fault condition. Higher resistance mean no leakage of power and IR is OK.

The Physical method with known applied voltage to get the IR Value is same for all the batteries and there wont be any changes in IR Value shown for healthy systems of any OEM batteries and battery types.

3. Midpoint Method

This method identifies whether the leakage of power is stronger toward the positive or negative side of the HV line.

Please refer below link to know more.....

How Insulation Resistance in EV Vehicles measured and Why?.

It uses Voltage divider circuit to find the midpoint Voltage and once any variation in the branches of HV line then it informs the VCU to disconnect the main battery pack through opening of HV Contactors.

Conclusion: 

Insulation resistance is not a fixed value it is a function of physical build quality, environmental conditions, pack size, and testing method. It should typically be >1 MΩ or 10000KΩ  for safety.

I hope the above explanation about IR measurment and types cleared why different pack have different IR Values only through diagnoistic and monitoring softwares.

Why there is a measurable HV voltage between the Battery Terminals to Chassis?

 

HV voltage between the Battery Terminals to Chassis

The voltage between the HV battery positive terminal and chassis ground measures approximately half of the total HV battery voltage and this behavior is expected due to the high resistance grounding method often used in isolated high voltage systems, such as in electric vehicles (EVs) and industrial battery systems.

Typically a voltage divider circuit is used  in the insulation resistance measurement to scale down the high voltage present in an electric vehicle's HV system, allowing safe measurement and assessment of insulation resistance.

HV battery system in EV vehicles are generally floating ( not directly grounded ) . so, both the positive and negative HV lines are connected to chassis ground via high-value resistors (e.g, 500kΩ to 10MΩ).These resistors are sometimes called symmetrical voltage dividers or bleeder resistors.

How it Works: 

The high voltage (HV) is applied to the first resistor, and the second resistor is connected to chassis ground.

A measurement point or Test point is placed at the junction between the two resistors, where a lower voltage proportional to the HV battery voltage is obtained.

This scaled down voltage is used by the insulation monitoring device to assess the insulation resistance without exposing the measurement circuitry to full HV.

To read more on Insulation measurment click below...

How Insulation Resistance in EV Vehicles measured and Why?.

Lets say, for 400V Battery EV Vehicle.

HV+ to chassis: ~ +400 V

HV− to chassis: ~ −400 V

HV+ to HV−: 800 V

This is normal and expected behavior in a floating HV battery connected to an EV Vehicle.

Conclusion : 

Measuring approximately half of the HV battery voltage between either HV+ or HV− and chassis is normal behavior in electric vehicles (EVs) that use a floating high-voltage system.

Intentional and compliant with international standards such as:

ISO 6469-3:2018 - Electric shock protection

ISO 21498-1/2 - HV power supply systems

UNECE R100 - Legal compliance for EV safety in many countries

These standards explicitly allow such floating systems with high-resistance paths to chassis and require insulation monitoring (IMD) to detect loss of isolation. The presence of a measurable voltage to chassis confirms the system is working correctly as long as it's symmetric and monitored.

The above design ensures Electrical safety,Improved fault detection and Compliance with global EV regulations.

How Insulation Resistance in EV Vehicles measured and Why?.

Measuring Insulation Resistance in EV Vehicles

                                    

EV high-voltage systems are designed to be extremely safe, and insulation integrity is a cornerstone of this safety. Regulations such as ISO 6469-3 and IEC 61557-8 set stringent requirements for isolation resistance in EVs. The use of IMDs and such resistor networks is a direct implementation of these safety standards to

1. Prevent electric shock: By ensuring that a single fault does not create a dangerous path for current through a person touching the vehicle.

What are the resistance acting upon a car.

Resistance acting upon a Car

Air Resistance (Aerodynamic Drag)

• This is the force exerted by the air opposing the car's motion as it moves forward.
• It depends on factors like the car's speed (drag increases with the square of velocity), its shape (aerodynamic design reduces drag), frontal area, and air density.
• For example, a sleek sports car experiences less air resistance than a boxy truck due to its streamlined shape.
• Mathematically, drag force can be expressed as:
  $F_d = \frac{1}{2} \rho v^2 C_d A$, where:
• $\rho$ = air density,
• $v$ = velocity,
• $C_d$ = drag coefficient,
• $A$ = frontal area.

Rolling Resistance

• This is the force resisting the motion of the car's tires as they roll over a surface.
• It arises mainly from the deformation of the tires and friction between the tires and the road.
• Factors affecting rolling resistance include tire material, pressure, road surface, and vehicle weight.
• It’s typically much smaller than air resistance at high speeds but significant at lower speeds.
• The rolling resistance force can be approximated as:
  $F_r = C_r m g$, where:
• $C_r$ = rolling resistance coefficient,
• $m$ = mass of the car,
• $g$ = gravitational acceleration (9.8 m/s²).

Gravitational Resistance (Gradient Resistance)

• This occurs when a car is moving up an incline, as gravity pulls it downward.
• The force depends on the slope angle and the car’s weight.
• On a flat surface, this component is zero, but on a hill, it can significantly resist forward motion.
• It’s calculated as:
• $F_g = m g \sin(\theta)$, where:
• $\theta$ = angle of the incline.

Note: 

At low speeds (e.g., city driving), rolling resistance dominates.

At high speeds (e.g., highway driving), air resistance becomes the primary opposing force.

Car manufacturers reduce these forces through aerodynamic designs, low-rolling-resistance tires, and lightweight materials to improve fuel efficiency and performance.

Difference between CP Vs PP in EV Vehicles

CP vs PP in electric Vehicles

Control Pilot (CP)

The CP manages the actual charging process by establishing communication between the EV and the EVSE. It ensures that charging starts and stops safely, and it controls the amount of current delivered to the vehicle.

How it works:

Voltage Levels: The EVSE generates a square wave signal on the CP line. Different voltage levels of this signal represent different charging states:

• State A (Disconnected): +12V - No connection
• State B (Connected, EV Ready): +9V - Cable connected, EV ready to charge
• State C (Charging): +6V - Charging in progress
• State D (Charging with Ventilation): +3V - Charging with ventilation required (* NA in India*)
• State E (Fault): 0V or other abnormal voltage - Fault detected

Pulse Width Modulation (PWM): When in State C (Charging), the CP signal uses PWM to communicate the maximum available charging current from the EVSE to the EV. The duty cycle of the PWM signal (the proportion of time the signal is high) corresponds to the available current.

 

Key Functions:

• Connection confirmation
• EVSE current capacity advertisement
• Charging start and stop control
• Fault detection
• Ventilation request (if needed)

Proximity Pilot (PP)

The PP is primarily about connection detection and safety interlocks. It ensures that the charging cable is physically connected to the vehicle before charging can begin and prevents hazardous situations like driving off while still plugged in.

How it works:

Resistance: The EV applies a specific resistance across the PP pin and the Protective Earth (PE) pin. This resistance value is determined by a resistor in the charging cable.

Current Rating: The resistance value corresponds to the maximum current the cable can safely handle. This helps prevent overloading the cable.

Detection: The EVSE (charging station) detects this resistance. If the resistance is within the expected range, it confirms a valid connection.

Connector Locking (Type 1): In Type 1 connectors (common in North America), the PP also controls a mechanical locking mechanism that secures the connector to the vehicle during charging. This prevents accidental unplugging.

Connector Locking (Type 2): In Type 2 connectors (common in Europe and increasingly in India), the locking mechanism is separate, but the PP still provides the connection confirmation.

Key Functions:

• Cable connection detection
• Cable current rating identification
• Preventing drive-away during charging (connector locking)

Relationship between CP and PP

The PP and CP work together in a sequence:

Connection: The charging cable is plugged into the EV. The PP detects the connection and the cable's current rating.

Readiness: If the PP signal is valid, the EV signals its readiness to charge via the CP (State B).

Current Information: The EVSE uses the CP signal (PWM in State C) to inform the available charging current.

Charging: The EV's OBC (On-Board Charger) starts drawing current based on the advertised value.

Monitoring: Both CP and PP are continuously monitored during charging. If the PP signal is interrupted (e.g., the cable is unplugged), charging stops immediately. If the CP detects a fault, charging is also interrupted.

                                  

CP vs PP

Pyrofuse or Pyroswitch and how does it works?

 

Pyrofuse or Pyroswitch 

The "pyro" part refers to the small explosive charge within the device.

When triggered, this charge detonates, breaking a connection within the fuse and interrupting the electrical circuit.

This process happens very rapidly, within milliseconds after the collision and triggered by the VECU of an electric vehicle.

Pyro switch or Pyro fuse is an electrical fuse that uses a small explosive charge to quickly and permanently cut off the flow of current in a circuit.

This is typically used in high-voltage battery systems, such as those found in electric vehicles, to prevent fires or other hazards in the event of a crash or short circuit.

Pyro switch function:

• Initiator: This is the small explosive charge. When an electrical signal is sent, it ignites.
• Gas Generation: The explosion creates a rapid expansion of gas.
• Piston: The force of the expanding gas pushes the piston. This piston is the key to how the switch works.

How this translates to a pyro switch:

1. Enclosure: All of this would be contained within a robust, insulated enclosure (likely plastic or ceramic). This enclosure would be the visible "pyro switch" itself.
2. Terminals: The enclosure would have electrical terminals connected to the circuit that needs to be interrupted.
3. Piston Action: The piston's movement is used to break the electrical connection. There are a couple of ways this could happen:
• Direct Break: The piston could directly separate two electrical contacts, physically opening the circuit.
• Cutting Element: The piston could drive a small cutting element (like a blade) that severs a conductive link within the switch.

Structure of the Pyro switch:

Internal Structure of Autoliv Pyro Saftey switchs

                                                                                      

Imagine a small, rectangular or cylindrical box.

• Casing: The outer casing is made of a dark-coloured, robust plastic or ceramic.
• Terminals: Two or more metal terminals protrude from the casing.
• Internal Mechanism (Invisible): Inside, the initiator, gas generation chamber, and piston are arranged as shown in your image.
• External Indication (Possible): There might be a slight bulge or a line on the casing indicating where the piston moves internally. After activation, this area might be visibly deformed or cracked.

Can we use 250KW charger to charge a 20KW EV battery Vehicle ?

Yes, We can generally use a 250kW charger for a 20kW EV battery, but with some important thing need to remember :

Key Considerations

• Battery Management System (BMS): The car's BMS is crucial. It communicates with the charger to regulate the charging process. It will ensure that the battery receives the appropriate voltage and current, preventing damage from overcharging or excessive heat.

• Charging Rate Limit: Every EV battery has a maximum charging rate it can safely handle. Even if you plug into a 250kW charger, the BMS will limit the charging rate to the battery's maximum capacity. With a 20kW battery, the maximum charge rate will likely be significantly lower than 250kW.

• Charging Pattern: EV batteries don't charge at a constant rate. They typically charge faster initially and then gradually slow down as they approach full capacity. This is known as the charging curve. The BMS manages this process to optimize charging speed and battery health. 

What to Expect: 

• Faster Initial Charging: You might experience a faster initial charging rate compared to using a lower-powered charger, but this will quickly taper off as the battery gets closer to full.

• No Damage to the Battery: If your EV and its BMS are functioning correctly, using a higher-powered charger will not damage the battery. The BMS will act as a protector.

• Not Necessarily the Fastest Charge: While you can use a 250kW charger, it doesn't mean your 20kW battery will charge incredibly fast. The limiting factor is the battery's capacity and its maximum charging rate.

Example:

Take the case of the TATA Nexon Vehicle, The battery pack is 320V & 90AH Capacity, Energy is 28.8KWh.

The maximum energy the Nexon battery accepts for charging depends upon the BMS inside the battery pack and the nominal charging ampere of a 90AH battery is 45Amps, 

The 55KW charger can charge the 28.8KW Pack of Nexon Car with a maximum of 16.4KW , 

How. Since the Lithium cell's maximum voltage is 3.65v and we multiply 3.65*100 Cells is 365v. then multiply 365v*45A (Nominal Charging Current ) which is 16.4KW.

Note:

There are different types of chargers available,

1. Slow Chargers.

2. Fast Chargers.

3. Ultra Fast Chargers or rapid chargers.

To learn more about the types of chargers, click the below post...

The charging speed and time depend on the power supplied by each type of charger and also depend on the capacity of the battery.

In Summary

Using a 250kW charger with a 20kW EV battery is generally safe, thanks to the BMS. However, don't expect a dramatically faster charging time compared to a lower-powered charger. The battery's limitations will determine the actual charging speed.

Relationships Between Energy,Power & torque in EV Vehicles

 

High Torque, Low Power example

• Energy: The ability to do work.
• Torque: The twisting force that can cause rotation.  
• Power: How quickly work is done or energy is used.

Relationships Between Them

• Torque and Power: In rotating systems (like engines and motors), torque and power are directly related. Power is proportional to torque multiplied by rotational speed. This means that you can have high torque at low speeds or high power at high speeds.  

• Energy and Power: Power is the rate of energy use or transfer. If you use a lot of energy quickly, you have high power. If you use the same amount of energy slowly, you have low power.  

• Torque and Energy: Torque can be thought of as the "effort" that can transfer energy in a rotational system. The more torque you apply, the more energy you can potentially transfer (given enough rotation).

Major types of Electric Vehicles in the world

                    

Several types of electric vehicles (EVs) are available in the market, each with unique characteristics and ways of using electricity as a power source. Here's a breakdown of the main types:  

1. Battery Electric Vehicles (BEVs)  or Pure EVs

• How they work: These are "pure" electric vehicles that run solely on electricity stored in a battery pack. They have no internal combustion engine (ICE).  
• Key features:
• Plug-in charging: BEVs are plugged into an external power source (charging station or wall outlet).  
• Zero tailpipe emissions: They produce no emissions from the vehicle itself.  
• Examples: TATA Nexon, TATA Tiago, Mahindra XEV 9e and BE 6e, Tesla Model S etc...

2. Hybrid Electric Vehicles (HEVs)

• How they work: HEVs combine an electric motor with a traditional internal combustion engine (usually gasoline). The electric motor assists the engine, improving fuel efficiency.  
• Key features:
• Regenerative braking: HEVs capture energy during braking and use it to recharge the battery.  
• Cannot be plugged in: The engine and regenerative braking charge the battery, not an external source.
• Examples: Maruti Grand Vitara, Toyota Innova Hycross, Honda City e: HEV

3. Plug-in Hybrid Electric Vehicles (PHEVs)

• How they work: PHEVs are similar to HEVs, but they have a larger battery pack and can be plugged in to charge. They can also drive for a certain distance on electric power alone.  
• Key features:
• Dual power sources: Can run on electricity, gasoline, or a combination of both.
• Longer electric range than HEVs: Allows for some emission-free driving.  
• Examples: Chevrolet Volt, Toyota Prius Prime, Mercedes AMG GT 63 SE and BMW XM.

4. Fuel Cell Electric Vehicles (FCEVs)  

• How they work: FCEVs use a fuel cell to generate electricity from hydrogen. They combine hydrogen with oxygen from the air to produce electricity, with water as the only byproduct.  
• Key features:
• Refuelled with hydrogen: Similar to refuelling a gasoline car, but with hydrogen instead.
• Zero tailpipe emissions: Only emit water vapour.
• Examples: Toyota Mirai, Hyundai Nexo

	BEV	HEV	PHEV	FCEV
Power Source	Battery only	Engine + Electric Motor	Engine + Electric Motor + Plug-in Charging	Hydrogen Fuel Cell
Charging	Plug-in	Self-charging	Plug-in + Self-charging	Hydrogen refueling
Range	Long	Short	Medium	Long
Tailpipe Emissions	Zero	Reduced	Reduced/Zero (in EV mode)	Zero

What are IP Ratings?Types of IP ratings

                                           

What are IP Ratings?

IP rating or Ingress Protection Rating are the indicator which defines the protection of electrical or Mechanical enclosures Components from the external Intruders like Water,Dust,Oil splash etc...

or simply IP Ratings shows how any enclosure is protected against Water and Solids.

The IP rating has a two digit number after a letter IP X X (X)--->optional

IP - Ingress Protection

X - Solids ( Dust,sand etc..)

X - Liquids ( Moisture,Oils,Water etc..)

X - Pressure (Optional)

Note: The Higher the number after IP ,the better the Protection.

IP Ratings

Architecture of Electric Vehicles

                          

 EV Architecture is complex and are comprises of Battery,Motor,PDU,MCU,Sensors,Harness,Controls and Aux Systems.

There are 2 types of major architecture in EV Vehicles.

1. 400V EV Architecture which are already available and got matured already.

2. 800V EV Architecture. which are taking control in Luxury space and automotive OEM's now switching focus on this architecture, why? will cover below.

There are advantages and disadvantage in both architecture, will see in details below.

1. 400V EV System Architecture

The 400V architecture is the standard EV architecture which uses Voltage range from 300V to 500V and it is also cheaper to implement, the main reason is that most OEMs have already established suppliers of components and the supply chain is very strong unlike 800V Systems.

The Production cost of 400V Systems are cheaper to manufacture than 800V systems and finally the end users can reap benifit from this cost reduction in the over all purchase price of the EV vehicle.

Thats the reason the 400V Architecture ev vehicles tends to sell more and placed in the mid and cheaper catogory.

TATA  Nexon Max

Lithium ion battery Voltage - 332.8V

Capacity - 120AH

Power - 39.9KW

The TATA Nexon EV Car uses 400V architecture.

2. 800V EV System Architecture

The 800V architecture are usually found in the Luxuary segments of EV vehicles where the arrangements of the components and systems are neater and less clumsey.

There are lot more advantages in 800V system than the 400V systems, simply put the voltages of a system increases then the current needed decreases to get the same amount of power.

Eg: 

Case 1: 400V,200A = 80000W or 80KW

Case 2: 800V,100A = 80000W or 80KW

Take Case 1, Since it uses 400V architecture the max current it can withdraw is around 1C that is 200A to achieve 80KW of power to the load(Motor).

Click to know about C -Rate?

Take Case 2, The 800V architecture uses only 100A to draw maximum power output of 80KW.

Advantages of 400V Architecture:

1. Widespread Infrastructure availability of charging stations upto 150KW Fast chargers and increasing.

2. Lower costs of Subsystems & Components.

3. Overall vehicle purchase cost is low.

4. Matured industry from production to supply chain availablity.

5. Reliable and proven technology.

Disadvantages of 400V Architecture:

1. Limited power output levels due to lower system voltages cap at 400V.

2. Doesnt support Ultra Fast Charging, Limited fast charging capability capped to its system voltage.

3. Increased resistive losses at higher power output.

Advantages of 800V Architecture:

1. Supports Ultra Fast Charging upto 350KW due to its high voltage and lower current requirements.

2. Resistive power losses are low compared to 400V systems since the current needed is less and losses will be low.

3. The sizes of HVcomponents and the cables will be lighter since it uses high voltage and lower current than 400V systems.

4. Higher efficiency and Performance.

5. Overall reduction in Weight of the vehicle.

6. Future proof since the coming years OEM's increasing their focus on 800V architecture.

Disadvantages of 800V Architecture:

1. Few Ultra Fast Charging stations, Infrastucture is not widespread compared to 400V architecture ev vehicles.

2. Higher costs of Components.

3. The overall vehicle costs are higher.

What is Powertrain in EV Vehicles?

Figure : EV drivetrain architecture (reference : MDPI energies).

The Powertrain in EV Vehicles are responsible for delivering and managing electrical power to move a Vehicle.

The EV Power train consists of  below components and systems,

1. Batter Packs (Lithium Ion Battery);
2. Inverters or MCU(Motor Control Unit);
3. E-drive (PMSM Motor);
4. VCU(Vehicle Control Unit;
5. i-PDU(Integrated Power Distribution Unit or All in one combo PDU);
6. Mechanical Transmission (drive shafts, differential gears & EV axles );
7. Thermal management systems ( Liquid Coolant Unit,Refrigerent Unit,Cabin air HVAC Unit).
   

References:

• Fault Diagnosis Methods and Fault Tolerant Control Strategies for the Electric Vehicle Powertrains