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.

BMS Daisy Chain Fault in an EV Lithium Battery

BMS DaisyChain Fault in EV Battery Fault Code

A BMS (Battery Management System) Daisy Chain Fault occurs when the communication link between multiple modules inside a lithium-ion EV battery pack is disrupted.

This fault can cause battery performance issues, failure to monitor individual cells, or even a complete shutdown of the vehicle’s power system.

What is a Daisy Chain?

A daisy chain is a wiring scheme in which multiple devices are connected in a sequence, or a chain.The daisy chain configuration is a common way to connect multiple BMS modules in a series communication network. 

Each module receives data from the previous one and passes it to the next, forming a continuous chain of data transmission. This method reduces the number of communication wires but makes the system vulnerable to faults.

Each BMS module collects voltage, current, and temperature data from its assigned battery cells.

The data is transmitted from one module to the next in the daisy chain using a communication protocol for example., SPI(Serial Peripheral Interface), UART(Universal Asynchronous Receiver-Transmitter), or CAN(Controller Area Network).

The final module in the chain sends all the collected information to the main BMS controller.The BMS controller makes real-time decisions about charging, discharging, thermal management etc.

Possible Causes of Daisy Chain Fault:

• Loose or No Connection – A damaged wiring harness or loose connector between BMS modules can break communication.

• Faulty BMS – A defective or malfunctioning BMS due defective microcontrollers,sensors can disrupt the communication chain.

• Firmware or Software Issue – Incorrect firmware updates or corrupted software can lead to communication errors.

• Damaged Busbars or Harnesses – If the signal routing on the battery pack is broken, communication can fail.

Effects of a Daisy Chain Fault:

• Battery Critical Warning Light on Dashboard.
• BMS Fails to Communicate with the Vehicle Control Unit (VCU)
• Cells Not Being Monitored Properly
• Battery Shutdown or Reduced Performance Mode or Limphome mode Alert

Troubleshooting Steps:

1. Check Wiring and Connectors for physical damage, Fix or replace loose or corroded connections.
2. Firmware reflash or reset the BMS system, Even after reflashing or resetting the BMS doesnt work, then replace with new BMS.
3. Check for any open busbars,If the battery pack has damaged busbars, repair or replace them.

Reasons for Sudden SOC jump in your EV Vehicle

 

SOC Jump in EV Vehicle Cluster

• Battery Management System (BMS) Recalibration:

The BMS is the "brain" of your EV's battery. It constantly monitors various parameters like voltage, current, temperature, and the state of individual cells within the battery pack. One of its crucial functions is to estimate and display the State of Charge (SOC). Over time, minor inaccuracies can creep into the SOC calculation. To maintain accuracy, the BMS periodically performs a recalibration.

How?: During recalibration, the BMS might make adjustments to its internal algorithms based on the latest readings. This can sometimes result in a sudden jump in the displayed SOC, especially near the extremes of the charge range (close to 0% or 100%). Think of it like the BMS "double-checking" its calculations and making a correction.

Is it normal? Yes, occasional recalibration is a normal and healthy part of battery management. It ensures the SOC reading remains as accurate as possible.

• Software Update:

EV manufacturers regularly release software updates to improve various aspects of the vehicle, including the battery management system.

How?: A software update might change the way the BMS calculates or displays the SOC. It could also introduce new algorithms for estimating SOC or refine existing ones. These changes can sometimes lead to a noticeable jump in the SOC display.

Is it normal? Generally, yes. Software updates are designed to improve performance and accuracy. A change in SOC display after an update isn't usually a cause for concern, as long as the overall battery performance remains normal.

• Charging Behavior:

If you consistently charge your EV to a certain level (e.g., 80%) and then suddenly decide to charge it to 100%, the BMS needs to adjust to this change.

How?: The BMS learns your charging habits. If you always stop at 80%, it might have optimized its SOC estimation for that range. When you charge to 100% for the first time in a while, the BMS might need to recalibrate its understanding of the full battery capacity, leading to a jump in the SOC display.

Is it normal? Yes, this is a normal response to a change in charging habits. It's the BMS adapting to the new charging pattern.

• Temperature Changes:

Battery performance is affected by temperature. Extreme heat or cold can impact the battery's chemical reactions and its ability to hold a charge.

How?: The BMS takes temperature into account when calculating SOC. If the temperature changes significantly (e.g., you park your car in the sun on a hot day), the BMS might adjust the SOC reading to reflect the temperature's impact on the battery. This adjustment can sometimes appear as a sudden jump.

Is it normal? Fluctuations in SOC due to temperature are possible, but they are usually gradual. A very sudden jump due to temperature alone is less likely.

• Battery Balancing:

An EV battery pack consists of many individual cells. For optimal performance and longevity, these cells need to be balanced, meaning they should have roughly the same charge level. The BMS performs this balancing act.

How?: During the balancing process, the BMS might redistribute charge among the cells. This can sometimes cause small fluctuations in the overall SOC, which might be perceived as a jump.

Is it normal? Yes, battery balancing is a necessary process. Minor SOC fluctuations during balancing are usually not a problem.

Summary: 

A sudden jump in SOC isn't always a reason to panic. It can often be attributed to normal BMS operations like recalibration, software updates, changes in charging habits, or temperature variations. 

However, it's always a good idea to monitor the situation. If the jumps are frequent, large, or accompanied by other issues like reduced range, charging problems, or error messages, then it's best to consult with your EV's service centre. They can diagnose the issue and ensure your battery is healthy.