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.

What is VECU received BMS derate flag? Where and What to check.

 

VECU received BMS Derate Flag

The Battery Management System (BMS) is responsible for monitoring and controlling the battery pack to ensure safe and efficient operation in any ev vehicle.

 When it detects conditions that may affect battery health or vehicle performance, it can send a derate flag to the Vehicle Electronic Control Unit (VECU) over the Controller Area Network (CAN) bus.

This derate flag instructs the vehicle to reduce power output, limiting acceleration, regenerative braking, or other power-intensive functions. The derate condition is temporary and will be lifted once the issue that triggered it is resolved.

 Possible reasons for the BMS derate flag to be triggered:

High battery temperature: The BMS may derate the power output to prevent the battery from overheating.

Low battery voltage: The BMS may derate the power output to prevent the battery from being over-discharged.

High current: The BMS may derate the power output to prevent the battery from being damaged by excessive current draw.

Cell imbalance: The BMS may derate the power output to prevent further imbalance between the battery cells.

Other BMS faults: The BMS may derate the power output due to other faults detected by the BMS, such as a sensor failure or a communication error.

 

What will the VCEU do after receiving derate flag CAN messages from BMS?

Reduce the power output of the vehicle: This may involve limiting the motor power, disabling certain features, or even reducing the vehicle's speed.

Display a warning message in the Cluster: This will inform the driver of the issue and the reduced performance of the vehicle.

Store a diagnostic trouble code (DTC): This will help technicians diagnose the issue.

BMS Derate Flag is a critical signal that protects the battery from damage. By diagnosing the exact cause (temperature, voltage, current, or internal faults) we can troubleshoot the problem within the EV Vehicle.

 

 

AC vs DC Which is more dangerous?

 

AC Vs DC

AC vs DC Danger:

• Both are dangerous: Both AC and DC can be lethal. The severity depends on voltage, current, duration of contact, and the path the current takes through the body. It's a misconception that DC is inherently "safer."

• Specific dangers of AC: AC's changing polarity can cause sustained muscle contractions, making it difficult to let go of the source. This prolonged exposure increases the risk. As you mentioned, the peak voltage of AC is higher than its RMS value (e.g., 120V RMS has a peak of around 170V), which can be significant.

• Specific dangers of DC: While less likely to cause fibrillation, DC can still cause severe burns due to its constant current flow. It can also cause a single, powerful muscle contraction that can throw someone away from the source (which can be both a blessing and a curse).

Current Levels and Effects:

• 0-5mA: Generally, a tingling sensation.
• Around 10mA: "Let-go current" - the point where muscle contractions make it difficult to release the source.
• Above 25mA: Risk of serious injury and death increases significantly. This is where ventricular fibrillation becomes a serious risk with AC.

Note:  The Let Go Current :  AC is around 10mA to 20mA 

                                                 DC be around 60mA to 75mA, 

Exceeding this threshold can cause severe muscle contractions and make it difficult to let go.

The severity of the shock depends on factors like voltage, current, Resistance and duration of contact.

Key Takeaway:

While the body's impedance plays a role, the primary reason AC is often considered more dangerous is its frequency, which can disrupt the heart's rhythm. 

DC or AC till some lower voltages can be touched by both the hands but if you cross certain voltage levels specifically above 40V then both DC & AC are dangerous.

Means AC Voltage of 50V could be equal to 120V DC, Above which both AC and DC are leathel.

 However, both AC and DC are potentially lethal, and safety precautions should always be taken with any electrical source.