Embedded Systems and Design & Development - Feb 9, 2026 | Morning | VisionAstraa EV Academy

Battery Charger Selection and Overview

Introduction to the Session

• The session begins with an apology for the delay and a question regarding the audibility of the voice.

• A question is posed about selecting chargers for various NMC battery pack voltages: 48V, 51.2V, 60V, 72V, and 96V.

Parameters for Charger Selection

• Participants are encouraged to think about what parameters are necessary when selecting chargers for batteries.

• The importance of understanding how to select Battery Management Systems (BMS) based on battery series is emphasized.

Recap of Previous Sessions

• A brief overview of previous sessions will be provided before delving deeper into charger selection.

• Key topics from past discussions include types of batteries and their characteristics.

Types of Batteries

• Two main types of batteries discussed: primary (single-use) and secondary (rechargeable).

• Different battery types reviewed include lead-acid (350 cycles), gel batteries (500 cycles), lithium-ion cells, and lithium iron phosphate (LFP).

Battery Configuration Concepts

• Explanation of series vs. parallel configurations:

• In parallel: voltage remains constant while capacity increases.

• In series: voltage increases while capacity remains constant.

Technical Data Understanding

• Importance of technical data from manufacturers is highlighted; dimensions like "18650" indicate width and height specifications.

• Discussion on full charge voltage, cutoff voltage, nominal voltage, and their roles in design calculations.

Design Considerations for Battery Packs

• Emphasis on designing parallel packs first before adding them in series to meet requirements.

• Noted that imbalances can occur if there’s a missing cell in configurations like "16S14P".

BMS Insights

• Overview of BMS functions including selection criteria based on series count and C rating for current ratings.

Fault Diagnosis in Battery Packs

• Identification of eight potential faults that could prevent a battery pack from functioning properly despite all other parameters being correct.

Battery Management System (BMS) Troubleshooting

Understanding BMS Faults

• The discussion begins with troubleshooting the Battery Management System (BMS), emphasizing that if all eight parameters are functioning correctly, a lack of output indicates a fault in the BMS itself.

• Multiple live examples of BMS data sharing illustrate various faults, including total voltage and individual cell voltages, highlighting the importance of monitoring these metrics.

Cell Voltage Differences

• A critical point raised is the maximum acceptable voltage difference between cells, which should not exceed 0.009 volts.

• If significant differences are observed, the battery pack is deemed unhealthy and requires rectification.

Balancing Techniques in Battery Packs

Types of Balancing

• Two primary types of balancing are discussed: active balancing and passive balancing. The choice between them often depends on specific application needs.

• Active balancing is frequently preferred due to its advantages over passive methods.

Motor Functionality Overview

Motor Types and Mechanisms

• Different motor types are explored, specifically mid motors and hub drive motors, along with their applications.

• The working principle involving push and pull actions between magnets within motors is explained.

Hall Sensor Integration

• The role of hall sensors is highlighted; they send signals based on magnet polarity to microcontrollers for processing motor control signals.

Controller Design Insights

Microcontroller Role

• An overview of how microcontrollers interact with MOSFET gates to manage power distribution within the system is provided.

Throttle Functionality

• Throttles control acceleration by sending resistance-based signals to the controller regarding power transmission from battery to motor.

Throttle Resistance Dynamics

Initial Conditions at Startup

• At vehicle startup, throttle resistance is at its maximum, resulting in minimal current flow to the motor—this leads to zero speed initially.

Battery Pack Configuration

Series and Parallel Combinations

• The configuration of series and parallel combinations within battery packs is discussed alongside safety measures provided by BMS systems.

Practical Application Example

• A practical example illustrates a 60V 36Ah battery pack design connected to a controller for operational insights.

Controller Wiring Details

Wiring Components Explained

• Detailed descriptions of wiring connections for hall sensors and other components necessary for sensing purposes are provided.

Understanding Electric Vehicle Components

Speed Control and Features

• The discussion begins with the speed control modes of an electric vehicle (EV), including high, low, reverse parking mode, and hill hold mode. These features are essential for effective motor control.

• The session will cover how to enable and disable these various features in detail. Understanding these controls is crucial for operating the EV efficiently.

Basic Components of an EV

• Key components identified include the BLC motor, throttle, and additional important parts necessary for building a basic EV. These components form the foundation of an operational electric vehicle.

• While it is possible to design a basic EV with just these four components, mechanical factors such as the chassis are also critical for functionality. A harness is highlighted as a vital connection element within the vehicle's system.

Wiring Harness and Connectors

• The wiring harness consists of various wires that connect different parts of the vehicle integrally; understanding this component is essential for proper assembly and function.

• Different types of connectors (male/female) are required to establish connections between components like the battery pack and other systems in the vehicle. This knowledge is fundamental when working on electrical systems in EVs.

Importance of Charging Systems

• A significant component discussed is the charger, which plays a crucial role in recharging the battery pack after use; without it, vehicles can only operate temporarily on battery power alone. Understanding charging mechanisms is vital for long-term operation.

• The charger converts AC from home sockets into DC suitable for storage in batteries; this conversion process involves rectification to ensure safe energy transfer into the battery pack.

Charger Functionality Overview

• The charger includes safety systems designed to protect against short circuits during operation; fuses are employed to prevent damage by interrupting current flow if it exceeds safe levels. This safety feature ensures reliability during charging processes.

• After rectification, output may not be pure DC but rather pulsating DC; filters are used within chargers to refine this output into stable DC suitable for battery storage, ensuring efficient energy management within electric vehicles.

Understanding the Basics of AC to DC Conversion

Overview of AC to DC Conversion Process

• The device ensures that both the AC and DC sides are safeguarded during operation, highlighting the importance of safety in electrical devices.

• The charger converts 230V AC input into a desired lower voltage DC output, emphasizing the need for specific voltage categories based on application requirements.

Charger Selection Criteria

• Different applications require different DC outputs (e.g., 60V, 72V, or 48V), necessitating careful selection of chargers tailored to these specifications.

• After filtering the output from AC to DC conversion, there is an additional step where filtered DC is converted back to AC. This process addresses line disturbances in the original AC input.

Voltage Regulation Techniques

• To achieve a consistent and pure DC output, it’s necessary to convert filtered DC back to AC before stepping down or regulating voltage as per requirements.

• The discussion includes how voltage regulation can be achieved using controllers like the 7805, which manage power levels effectively.

Charging Methods Explained

• The charger operates by rectifying AC power into DC and then potentially converting it back into AC for further processing based on user needs.

• Two primary charging methods are introduced: Constant Current Variable Voltage (CCVV) and Constant Current Constant Voltage (CCCV), each serving distinct purposes in battery management.

Key Concepts in Charging Techniques

• CCVV involves maintaining a constant current while allowing voltage to vary; this method is crucial for certain charging scenarios.

• CCCV focuses on maintaining constant voltage while allowing current to vary; understanding these concepts is essential for effective charger design.

Summary of Important Points

• It’s important for participants to note down key terms related to charging methods as they will be fundamental topics throughout their internship learning experience.

• A problem regarding charger selection was posed earlier in relation to various voltages (60V, 72V, etc.), indicating practical applications of theoretical knowledge discussed.

Charger Selection for Battery Packs

Understanding Basic Charger Parameters

• The discussion begins with the selection of a basic charger for an NMC battery pack, emphasizing the importance of noting down key parameters for easier calculations in charger design.

• A specific example is introduced: a 60-volt battery pack with a capacity of 40 Ah. This sets the stage for further discussions on charger specifications.

C Ratings and Their Importance

• It is noted that all EV battery packs typically have a C rating of 3C, while the maximum charging current should not exceed 0.2C. This establishes guidelines for safe charging practices.

• The speaker transitions to how to select a charger, highlighting that understanding BMS (Battery Management System) selection is crucial before moving on to charger selection.

Charger Voltage and Current Specifications

• For the selected 60V NMC pack, it is confirmed that it consists of 16 series cells (16S), leading to a full charge voltage calculation of 67.2V (4.2V per cell).

• The need for both voltage and current ratings in charger design is emphasized; thus, determining maximum amps based on C ratings becomes essential.

Calculating Charging Current

• The method to calculate charging current involves multiplying amp-hour capacity by the C rating; specifically, using 0.2C results in determining maximum charging current.

• Clarification is provided regarding different types of C ratings: discharging and charging C ratings are differentiated, which aids in understanding their respective implications on performance.

Finalizing Charger Ratings

• For the discussed battery pack (60V, 40Ah), it concludes that the maximum charge current should be set at 8A with a voltage output requirement of 67.2V.

• Maximum discharge capability is also mentioned as being up to 120A based on BMS requirements for this configuration.

Practical Application: Selecting Chargers for Different Packs

• A new scenario involving a different battery pack (60V, 26Ah) prompts participants to calculate appropriate charger specifications including full charge voltage and current ratings.

• Participants are guided through calculating full charge voltage as approximately 67.2V again while determining that the corresponding current rating would be around 5.2A based on its capacity and C rating.

Battery Pack Voltage and Current Calculations

Maximum Full Charge Voltage of 48V Battery Pack

• The maximum full charge voltage for a 48V battery pack is calculated as follows: 13 cells in series multiplied by 4.2 volts per cell results in approximately 54.6 volts.

Current Rating for the Battery Pack

• The current rating remains consistent with previous packs, calculated at 8 amps based on a capacity of 40 amp-hours (40Ah). This is derived from multiplying the capacity by a factor of 0.2.

Discharge Current for Different Capacities

• For a battery pack rated at 26Ah, the maximum discharge current is determined to be 5.2 amps, while for a higher capacity of 40Ah, it reaches up to 120 amps. This indicates significant differences in performance based on capacity.

Calculating Parameters for Higher Voltage Packs

Full Charge Voltage of a 72V Battery Pack

• A quick calculation shows that the full charge voltage for a 72V battery pack with 20 cells in series is around 84 volts (20 x 4.2). This consistency across different configurations highlights the importance of understanding series connections in battery design.

Current Ratings Consistency

• The current rating remains constant at approximately 120 amps across various configurations, emphasizing that this parameter does not fluctuate significantly with changes in voltage or capacity within similar designs.

Exploring Additional Configurations

Parameters for Different Capacities

• For another configuration using a 51.2V system with 40Ah, calculations yield a maximum full charge voltage of 58.8 volts and maintain an output capability of 120 amps during discharge operations, showcasing versatility across different setups.

Commonly Used Combinations

• The discussion emphasizes commonly used combinations such as:

• 48V/40Ah

• 60V/26Ah

• 51.2V/40Ah and/or 26Ah

These combinations are prevalent within the electric vehicle industry due to their reliability and efficiency characteristics.

Charger Selection Based on BMS Criteria

Understanding BMS Functionality

• The selection process for Battery Management Systems (BMS) involves understanding its operational criteria—78 major parameters dictate how it functions based on input data provided during setup.

Charger Design Considerations

• When designing chargers, it's crucial to consider both maximum full charge voltages and output capabilities tailored specifically to each type of battery chemistry (e.g., NMC vs LFP). For instance, NMC batteries have specific requirements that differ from those needed by LFP batteries.

LFP vs NMC Charging Compatibility

Series Configuration Calculation for LFP Batteries

• For an LFP battery pack rated at 60 volts, dividing by its nominal voltage (3.2 volts) reveals that it requires approximately 19 series connections to achieve optimal performance.

Charger Compatibility Insights

• It’s confirmed that while an LFP charger can technically be used to charge an NMC battery pack, there are critical considerations regarding charging efficiency and safety due to differing full charge voltages between these two types of batteries.

Understanding Battery Charging and BMS

Charger Functionality for NMC Battery Packs

• A charger boosts the voltage of a battery pack (e.g., from 58V to 68.4V), but NMC batteries require a maximum charge of 67.2V.

• The Battery Management System (BMS) protects the battery by disconnecting the charger when it reaches the maximum voltage, ensuring safety during charging.

Importance of BMS in Charging

• If the charger exceeds 67.2V, the BMS will open the circuit to protect the battery pack; thus, both charger and BMS must operate within specified parameters.

• Using an NMC charger on an LFP battery is possible since it operates below full charge requirements (68.4V), but it won't fully charge the LFP pack.

Limitations of Charger Compatibility

• An NMC charger can only charge an LFP battery up to approximately 95%-98%, leaving about 1 volt uncharged, which affects range.

• Not fully charging leads to reduced range due to insufficient energy storage in the battery pack.

Understanding State of Charge (SOC)

• The session discusses how to match battery voltage with charger voltage and BMS across different chemistries like NMC and LFP.

• A practical example illustrates calculating SOC based on operating voltages between minimum (48V) and maximum (67.2V).

Calculating SOC at Different Voltages

• For a 60V NMC battery pack, understanding its percentage involves determining how much voltage corresponds to specific SOC levels.

• The operating voltage range is identified as critical for calculating SOC; for instance, if at 60 volts, this equates roughly to around 55% SOC.

Transitioning from Partial Charge to Full Charge

• When transitioning from a partial charge (50% or 57.6 volts), connecting a suitable charger is essential for reaching full capacity.

• The appropriate charger should gradually increase from current voltage (57.6 volts) up to its maximum output of 67.2 volts without exceeding safety limits.

Charging Concepts: Variable Voltage and Constant Current

Understanding Variable Voltage

• The charging process begins at 57.6 volts, gradually increasing to 67.2 volts, indicating a variable voltage scenario during battery charging.

• As the charge increases over time (e.g., from 1 p.m. to 2 p.m.), the voltage changes, demonstrating that voltage is not constant but varies with the state of charge.

Constant Current Explained

• In this context, "CC" stands for Constant Current; while voltage varies during charging, the current remains steady at a specified level (e.g., 4 amps).

• The charger maintains a constant current output throughout the charging process, ensuring that it delivers consistent power to the battery pack.

Types of Charging: CC-CV Methodology

• The first type discussed is variable voltage with constant current (CC), where voltage fluctuates while maintaining a steady current output.

• The second type is constant voltage with variable current (CV), where the charger provides a fixed maximum voltage (e.g., 67.2 volts), but allows current to decrease as needed.

Practical Applications in Fast Charging

• Understanding these concepts lays the groundwork for exploring fast charging techniques and various types of chargers used in practical applications.

• Emphasis on building foundational knowledge before delving into advanced topics like pulse charging and different socket types for fast charging.

Microcontroller Role in Charging Process

• Microcontrollers play a crucial role by sensing battery pack voltages and adjusting charging parameters accordingly; they ensure safe and efficient operation during varying charge states.

• The microcontroller's ability to monitor incoming voltages helps determine when to initiate or adjust charging processes based on real-time data.

Recap of Key Concepts

• A brief overview reiterates that variable voltage combined with constant current is essential for effective battery management during initial charge phases.

• Further clarification on achieving full charge involves understanding how additional required voltage impacts overall battery performance and efficiency.

Charging Mechanism and Battery Management Systems

Understanding Voltage and Current in Charging

• The battery management system (BMS) opens the circuit when the battery pack voltage reaches 67.2 volts, preventing further current flow.

• If the charger attempts to push voltage at 67.2 volts, the BMS disconnects, but the battery may still read 66 volts due to floating charge conditions.

• The BMS detects a fully charged state from floating charge, prompting adjustments in charging behavior to avoid overcharging.

Charger Behavior Under Different Conditions

• The charger maintains a constant current up to 67.2 volts; if it exceeds this threshold, it becomes an open circuit.

• As charging progresses towards full capacity, current decreases from 4 amps to around 2 amps for effective floating charge management.

Analogy of Water Filling

• An analogy is drawn comparing battery charging to pouring water into jugs; as one jug fills up (battery nearing full), the flow rate slows down significantly.

• This slow filling represents how charging current diminishes as the battery approaches its maximum capacity.

Concepts of Charging Types

• The discussion covers variable voltage and constant current (CCCV), emphasizing that different stages of charging require different strategies for optimal performance.

• Slow charging occurs during final stages as current decreases, ensuring safe completion of the charge cycle without risking damage.

Overview of Charger Functionality

• Key concepts include understanding CCCV principles and how chargers adapt their output based on battery requirements.

• Chargers perform rectification and filtering processes before delivering DC output tailored to specific battery types like NMC or LFP.

Practical Applications and Future Learning

• Emphasis on C rating importance for selecting appropriate chargers and understanding their operational limits based on various factors.

• Upcoming sessions will focus on practical demonstrations involving different socket types used in chargers, enhancing hands-on learning experiences.

Understanding Socket Types and Connectors in Practical Applications

Introduction to Socket Types

• The session introduces a new type of socket, emphasizing its distinct characteristics compared to traditional sockets. The speaker expresses enthusiasm for the upcoming evening session focused on this topic.

Learning Objectives

• The discussion outlines the learning goals leading up to the evening session, which includes understanding connectors and their practical applications.

• Key topics include major operational mechanisms (OM) and big operational mechanisms (OMS), indicating a comprehensive exploration of these concepts.

• Participants are encouraged to engage with the material actively; they can seek clarification on any topics they find challenging.

• The speaker reassures attendees that various examples will be provided to enhance understanding, fostering an interactive learning environment.