Embedded Systems and Design & Development - Feb 5, 2026 | Morning | VisionAstraa EV Academy

Overview of Electric Vehicle Battery Fundamentals

Introduction to Class and Review of Previous Sessions

• The session begins with a warm greeting, indicating the start of the class.

• A brief review is initiated, focusing on key learnings from previous sessions about vehicles and batteries, emphasizing their fundamental importance in electric vehicle (EV) design.

Types of Batteries Discussed

• Focus on secondary batteries: Lead acid (200-350 cycles), gel batteries (350-500 cycles), lithium-ion cells (200-800 cycles), and LFP (750-20,000 cycles).

• Discussion on why NMC is preferred over LFP in the market despite LFP's higher life cycle.

Battery Configuration Basics

Parallel and Series Connections

• Explanation of battery configurations: parallel connections maintain voltage while increasing capacity; series connections increase voltage while maintaining capacity.

Design Example

• A practical example involves designing a 12V battery pack using 18650 cells rated at 2,600 mAh and 3.7V.

Building Larger Battery Packs

Combining Cells in Parallel and Series

• Demonstration of creating larger packs by connecting multiple cells in parallel first to achieve desired capacity.

• Further explanation on combining these parallel packs into series to increase overall voltage.

Final Pack Configuration

• The final configuration discussed is a battery pack labeled as 16S14P, indicating 16 series connections with 14 parallel cells.

Key Parameters for Battery Management Systems (BMS)

Understanding SOC and Voltage Parameters

• Overview of important parameters such as cutoff voltage, nominal voltage, and full charge conditions critical for BMS selection.

Challenges with Cell Management

• Discussion on potential issues like overcharging or deep discharging individual cells within a pack; emphasizes the need for uniformity among cell conditions to prevent damage.

This structured summary captures the essence of the transcript while providing clear timestamps for reference.

Battery Pack Configuration and BMS Insights

Selecting Battery Packs Based on Voltage Ratings

• The discussion begins with the selection of battery packs based on voltage ratings, specifically focusing on a 60V battery pack requiring a 16S configuration for NMC (Nickel Manganese Cobalt).

• A question is posed regarding the S rating needed for a 72V battery pack, prompting participants to consider how it compares to the previously discussed 60V configuration.

• The answer reveals that a 72V battery pack should be configured as 20S, while for a 48V system, the appropriate configuration is identified as 13S.

Current Ratings and BMS Selection Criteria

• The conversation shifts to charging and discharging current parameters, highlighting maximum ratings of around 15A for charging and 30A for discharging.

• Participants are encouraged to think about how these current ratings influence the selection of Battery Management Systems (BMS), emphasizing that this choice may depend on various factors including age and overall battery pack specifications.

Understanding BMS Functionality

• An overview of how BMS protects the battery pack through circuit management is provided; it operates by creating closed or open circuits based on specific conditions.

• It’s noted that BMS connections are made in series with the battery pack, allowing it to monitor both total and individual cell voltages effectively.

Key Parameters in BMS Design

• Important parameters influencing BMS design include self-full charge voltage limits: for NMC it's set at 4.2V while LFP (Lithium Iron Phosphate) has a limit of 3.6V.

• Lower cutoff voltages are also critical; NMC should not drop below 3V per cell while LFP should not go below 2.8V.

Protection Mechanisms in BMS

• The total voltage of the entire battery pack must remain within specified limits; exceeding these can trigger protective measures from the BMS.

• If any cell's voltage exceeds its rated maximum or if inter-cell voltage differences exceed acceptable thresholds (0.009), the BMS will activate an open circuit to protect against damage.

Troubleshooting Unhealthy Battery Packs

• Overcurrent protection mechanisms are discussed; since the BMS monitors current flow through series connections, it can prevent potential damage from excessive currents or short circuits.

• Examples illustrate healthy versus unhealthy batteries based on calculated parameters such as minimum voltage levels and inter-cell differences; unhealthy batteries exhibit significant deviations from expected values.

Conclusion: Identifying Errors in Battery Packs

• A case study highlights an unhealthy battery due to low minimum voltage readings below acceptable thresholds for NMC configurations.

• Further examples reveal multiple errors leading to classification as unhealthy, setting up future discussions focused on troubleshooting methods for rectifying these issues.

Understanding Battery Management Systems and Cell Balancing

Introduction to Battery Management Systems (BMS)

• The discussion begins with an issue regarding a 14-series battery pack showing zero voltage, prompting the need for solutions to ensure the BMS operates effectively.

• The concept of cell balancing is introduced as a method to rectify issues within a battery pack, highlighting its importance in maintaining optimal performance.

Types of Cell Balancing

• Two primary types of cell balancing are identified: active balancing and passive balancing.

• Active balancing involves redistributing charge from higher voltage cells to lower voltage cells, while passive balancing operates differently.

Active Balancing Explained

• An example illustrates that in a 16-series configuration, certain cells have varying voltages (e.g., some at 3.1 volts), necessitating action from the BMS.

• The BMS will discharge higher voltage cells (like series number 10) and transfer that energy to lower voltage cells, aiming for uniformity across the pack.

• This process ensures that power is transferred from higher charged cells to those with lower charges, effectively equalizing their voltages.

Mechanism of Active Balancing

• The BMS's microcontroller can read individual cell data due to its design, allowing it to manage charging and discharging processes efficiently.

• For instance, if one cell has 3.2 volts and another has 3 volts, the microcontroller will automatically discharge the higher-voltage cell until balance is achieved.

Transitioning to Passive Balancing

• After explaining active balancing thoroughly, the focus shifts towards passive balancing systems which operate under different principles compared to active systems.

• A new example is set up for discussing how passive balancing functions within a battery pack context.

This structured overview captures key insights into battery management systems and their critical role in ensuring effective operation through various methods of cell balancing.

Understanding Passive and Active Balancing in Battery Management Systems

Overview of Passive Balancing

• The passive balancer adds resistors across battery series to equalize voltage levels, specifically reducing higher voltages (e.g., 3.2V) to match the lowest (e.g., 2.6V).

• When a resistor is added to a cell, it acts as a load, discharging that cell and consuming energy from the battery pack.

• In an example with four cells, if one cell is at 3V while others are at 3.2V, the passive balancer will discharge the higher voltage cells until they equalize to 3V.

• This process ensures all cells reach the same voltage level through controlled discharge, demonstrating how passive balancing works effectively.

Transitioning to Active Balancing

• The discussion transitions towards understanding active versus passive balancing methods in battery management systems (BMS).

• Emphasis on selecting BMS based on current ratings and other specifications is introduced as a critical next step in battery design.

Practical Application: Designing a Battery Pack

• Participants are tasked with designing a battery pack for practical application; specifics include creating diagrams showing cell configurations and parameters.

• A smaller battery pack design of around 48 volts and 25 Ah is suggested for hands-on learning about BMS selection criteria.

Importance of Balancing Techniques

• Without proper balancing, risks such as overcharging or deep discharging can occur within individual cells during charging cycles.

• Two primary methods for maintaining balance are highlighted: active balancing (which redistributes charge among cells without wasting energy) and passive balancing (which dissipates excess energy as heat).

Market Demand for BMS Solutions

• There’s significant market demand for effective BMS solutions focusing on both active and passive balancing techniques.

• Passive balancing's reliance on resistors introduces risks due to heat generation; thus, careful consideration must be given to thermal management within battery packs.

BMS Selection and Battery Pack Design

Understanding Active vs. Passive Balancing

• The discussion begins with the emphasis on using active balancing for battery management systems (BMS), indicating that passive balancing is largely avoided.

• Clarification is sought from participants regarding their understanding of active and passive balancing before moving forward to BMS selection.

Importance of Full Charge Voltage

• It is highlighted that a BMS cannot effectively protect a battery pack without knowing the full charge voltage and other critical parameters.

Designing Higher Voltage Battery Packs

• Participants are encouraged to design a higher voltage battery pack, specifically targeting an architecture of 300 volts, while considering cell specifications.

• The specific requirements for the battery pack are outlined: 300 volts, 100 cells per series, and each cell rated at 50 Ah.

Calculating Series and Parallel Configurations

• Participants share their calculated configurations: 94S2P for LFP batteries and 81S2P for NMC batteries, which will influence BMS selection.

• To determine the number of series connections (S), the nominal load (3.2V per cell) is used to calculate S as approximately 94.

Finalizing Cell Configuration

• The total number of cells required is calculated by multiplying series (S) by parallel (P), resulting in a total of 188 cells for LFP configurations.

• A discussion on limitations arises when working with different Ah ratings; it’s noted that certain configurations may not be feasible based on available cell sizes.

Adjusting Designs Based on Capacity Requirements

• For NMC batteries, similar calculations yield around 81 series connections; adjustments are made based on previous discussions about rounding values appropriately.

• The importance of ensuring achievable parallel configurations is reiterated; examples illustrate how certain capacities can limit design options.

Market Considerations in Cell Selection

• Emphasis is placed on market availability when selecting cell capacities; various combinations are discussed to meet specific energy requirements.

Summary of Key Specifications

• A recap highlights key specifications such as voltage ratings and capacity variations across different battery packs, reinforcing the need for careful consideration during design.

Understanding Battery Management Systems and C Ratings

Overview of Battery Pack Configuration

• The discussion begins with the importance of calculating nominal voltage when selecting battery configurations, specifically in the LFP (Lithium Iron Phosphate) category.

• The speaker introduces a battery pack setup, highlighting its two terminals: positive and negative. A 60V, 30Ah battery pack is considered for further calculations.

• A question is posed regarding the number of cells in a 60Ah pack with each cell rated at 5Ah, prompting audience engagement for quick calculations.

Calculation of Cells in Battery Pack

• The calculation reveals that there are 96 cells in total within the battery pack, derived from dividing the total capacity by individual cell capacity.

• The configuration includes connections to a load where the positive terminal connects to the load while the negative terminal connects back to the battery pack.

Current Rating and C Rating Concept

• The focus shifts to determining the current rating for a BMS configured for a 16S (series connection of 16 cells), emphasizing understanding maximum current output capabilities.

• Introduction of "C rating," which defines how much current can be drawn from an individual cell without damaging it. This concept is crucial for understanding performance limits.

Practical Application: Motor Load Example

• An example involving connecting a motor load to illustrate practical applications of C ratings is presented.

• A specific scenario describes using a motor that requires 5A at 4V, leading into discussions about runtime based on different loads connected to the battery.

Runtime Calculations Based on Load

• If running at full charge (100%), with a consumption rate of 5A, it’s calculated that the motor can run for approximately one hour before depleting its energy source.

• Adjustments are made to demonstrate how varying loads affect runtime; if increased to 10A, runtime decreases significantly to around half an hour.

Impact of Increased Loads on Runtime

• Further examples illustrate how lower loads (e.g., 2.5A or higher loads like 20A and beyond up to 100A) impact operational timeframes drastically.

• It’s emphasized that while higher currents can be supplied momentarily (like at 100A), doing so risks damaging internal chemistry due to overheating or other factors related to wire gauge limitations needed for such currents.

Understanding C Ratings in Battery Cells

What is C Rating?

• The thickness of the wire or cell affects its ability to deliver higher currents; this is where the C rating comes into play.

• The C rating indicates the maximum current that can be drawn from a cell. For example, a 5 Ah cell's maximum output depends on its C rating.

Calculation of C Rating

• The formula for calculating maximum current is based on amp-hour (Ah) and the C rating: Maximum Current = Ah × C.

• A 1C rated 5 Ah cell can provide a maximum of 5 amps; exceeding this may damage the cell as per manufacturer specifications.

Discharge Capacity and Ratings

• If a battery has a 2C rating, it can output up to 10 amps; understanding these ratings is crucial for battery pack design.

• Most cells used in electric vehicles (EVs) are rated at 3C, allowing them to discharge at three times their capacity.

Current Selection for Battery Packs

• In high-demand applications like drones, cells may have ratings up to 10C or more, enabling higher discharge rates.

• For instance, with a 3C rated battery pack, one could draw up to 90 amps safely.

BMS and Charging Considerations

• Battery Management System (BMS) selection relies on both voltage and current ratings derived from the C rating.

• Charging rates differ from discharging rates; typically, charging might be limited to around 0.1C or 0.2C depending on manufacturer specifications.

Summary of Parameters for Battery Pack Design

• For a given battery pack with a total capacity of 30 Ah at a discharging rate of 3C, one can expect about 90 amps during discharge.

• Conversely, if charging at a rate of approximately 0.2C yields about 6 amps for charging purposes.

This structured overview provides insights into how C ratings influence both discharging and charging capabilities in battery cells while emphasizing critical parameters necessary for effective battery management system design.

Battery Pack Charging and BMS Selection

Understanding Battery Charging Limits

• The speaker discusses the limitations of charging a battery pack, noting that while a charger can provide 100 amps, it is not feasible to charge the battery at this rate. The maximum safe charging current is identified as 6 amps.

Parameters for Charger and BMS Selection

• Emphasis is placed on selecting appropriate chargers and Battery Management Systems (BMS). Key parameters include the number of series (S) and parallel (P) cells in the battery pack.

Voltage Considerations

• To determine S and P configurations, essential voltage metrics are discussed: full charge voltage, cutoff voltage, and nominal voltage. These parameters guide the selection process for both chargers and BMS.

C Rating Importance

• The concept of C rating is explained in relation to the entire battery pack configuration. Understanding C rating helps in assessing how much current can be safely drawn or charged without damaging the cells.

BMS Design Considerations

• When designing a 72V battery pack, considerations for BMS selection include:

• Number of series connections (S)

• Charging current (CC)

• Discharging current (DC), which refers to how much power can be drawn from the battery.

Key Components of Battery Management Systems

Full Charge Voltage Requirements

• The importance of knowing the maximum full charge voltage is highlighted as crucial for effectively charging a battery pack. This ensures that batteries are charged within safe limits.

Overview of Battery Types Covered

• A summary of various types of batteries discussed includes lithium-ion, LFP (Lithium Iron Phosphate), sodium-ion, and lead-acid batteries. Each type has unique characteristics relevant to their application in electric vehicles.

Transitioning to Motor Concepts

Introduction to Electric Motors

• Following completion of discussions on battery packs, attention shifts towards electric motors—key components in electric vehicles. The session will cover motor operation principles and embedded system connections.

Types of Motors Explored

• Future sessions will delve into different types of motors such as induction motors and synchronous motors. Similar foundational concepts used for understanding batteries will apply here as well.

Understanding Battery Basics and Specifications

Introduction to Battery Components

• The discussion begins with an overview of essential battery components, including motors, batteries, controllers, and throttle pedals. A solid understanding of these basics is crucial for further learning.

Reading Battery Data Sheets

• The speaker introduces the concept of a battery data sheet and emphasizes its importance in understanding battery specifications. They prepare to share a data sheet for practical reference.

C Rating and Cell Specifications

• The C rating is highlighted as a critical specification not typically found on the cell itself (e.g., 18650 cells). The speaker indicates that this information can be located within the data sheet.

• For offline students, hands-on experience with high voltage packs will include examining the internal components of a battery bank to understand specifications like C ratings.

Nominal Voltage and Charging Parameters

• The nominal voltage of an LG cell is discussed, revealing it to be approximately 3.63 volts. Different cells have varying nominal voltages based on manufacturer specifications.

• Standard charge constants are introduced; for instance, charging at 0.3C is mentioned as part of the charging process for individual cells.

Discharge Characteristics

• Maximum discharge rates are explored, indicating that discharging at different rates (e.g., 1.5C into a 5Ah cell) yields specific current outputs (up to 2.5 amps).

• Verification of discharge data is encouraged; students should confirm whether specified discharge currents align with calculated values based on C ratings.

Comparison Between Different Cell Types

• A comparison between LG and Panasonic cells highlights differences in dimensions and capacities—LG cells being larger (21700 vs. 18650), with varying mAh ratings.

• Key characteristics such as weight, capacity, length, and other parameters are noted as essential details included in each cell's data sheet for comprehensive understanding.

This structured summary provides insights into battery basics while linking directly to timestamps for deeper exploration of each topic discussed in the transcript.

Battery Management System (BMS) Overview

Key Concepts and Parameters of BMS

• The session concludes with a discussion on the discharging capabilities of various battery cells, including Panasonic, LG, and DMAG. Participants are encouraged to research data sheets for detailed specifications.

• A summary of the session highlights the selection criteria for BMS based on C rating and maximum current requirements, emphasizing the importance of understanding these parameters.

• Discussion includes why specific voltage ratings (e.g., 24 volts) are mentioned, along with details about maximum discharging (30 amps) and charging currents.

• The fundamentals of how BMS operates were covered, including C ratings and potential errors that can occur in battery packs.

• Two types of balancing methods were introduced: active balancing and passive balancing. Understanding these methods is crucial for ensuring all operational criteria are met.

Troubleshooting Battery Packs

• The session addressed common issues that may arise in battery packs. Identifying eight possible errors is essential for effective troubleshooting.

• Emphasis was placed on the necessity of being able to design a battery pack before one can effectively diagnose its issues.

• Participants are encouraged to develop diagnostic skills by learning to identify faults within a battery pack through practical sessions.

Practical Applications and Future Sessions

• Students attending offline classes will have hands-on opportunities to troubleshoot real battery packs under guidance.

• An overview of upcoming sessions indicates a shift towards motor types such as mid-drive and hub motors, which will be discussed in future meetings.

• Offline setups will be available for students in Belgavy, allowing them to engage in practical assembly and disassembly exercises related to batteries.

Summary of Learning Outcomes

• Today's notes should reflect an understanding of balancing concepts—both active and passive—and their implications for selecting a BMS based on critical ratings like C rating, P rating, etc.

• The interconnectedness between P rating, C rating, BMS selection, and charger compatibility was emphasized as vital knowledge moving forward into further discussions about motors.