Embedded Systems and Design & Development - Feb 4, 2026 | Morning | VisionAstraa EV Academy

Battery Basics and Design Overview

Review of Battery Types

• The session begins with a recap of the previous day's learning about battery types, focusing on primary and secondary batteries.

• Primary cells are single-use; once depleted, they must be discarded.

• Secondary cells can be recharged multiple times, with cycle life varying by type: gel batteries (350-500 cycles), lithium-ion (1200-1800 cycles), and lead-acid (750-2000 cycles).

Key Characteristics of Batteries

• Discussion on different battery chemistries including LFP, NMC, sodium batteries, and lead-acid batteries.

• Emphasis on platform voltage's role in determining operational characteristics such as full charge voltage, nominal voltage, and cutoff voltage.

Circuit Design Fundamentals

• Explanation of parallel vs. series connections: in parallel configurations, voltage remains constant while current adds up; in series configurations, current remains constant while voltage adds up.

• A basic circuit design was demonstrated using an 18650 cell specification to illustrate dimensions and ratings.

Understanding Battery Specifications

• Participants learned to read specifications like full charge voltage for NMC (4.2V), LFP (3.6V), along with cutoff and nominal voltages.

• Full charge voltage is noted as FV = 4.2V for NMC; participants were asked to recall these values.

Practical Application of Concepts

• Calculation exercises involving series and parallel combinations helped solidify understanding of total pack configuration for a 60V battery pack.

• The configuration discussed was 16S15P (16 series and 15 parallel), totaling approximately 224 cells in the pack.

Problem-Solving Session

• A review problem was introduced regarding full charge voltages for various battery types at specified voltages (60V, 72V, 48V).

• Importance of mastering these fundamentals before advancing into embedded systems related to electric vehicles was emphasized.

This structured overview captures the essence of the session while providing clear timestamps for reference.

Battery Voltage Specifications and Safety Devices

Overview of Battery Types and Their Voltages

• The discussion begins with NMC (Nickel Manganese Cobalt) batteries, highlighting the need for clarity in voltage specifications.

• Key voltages for NMC are outlined: full charge voltage is 4.2V, cutoff voltage is 3.0V, and nominal voltage is approximately 3.7V.

• Lead acid batteries are introduced; they typically have a nominal voltage of 2V per cell, but packs are usually combined to create a standard 12V output.

• A lead acid battery pack consists of six 2V cells connected in series to achieve a total of 12 volts, which can be further detailed as having a full charge voltage of around 14.2 volts and a cutoff at about 10.2 volts.

• Sodium ion batteries are mentioned next; their nominal voltage is discussed along with the importance of understanding these parameters for design purposes.

Design Considerations for Protective Devices

• The speaker emphasizes the significance of knowing battery voltages when designing protective devices against overcharging or deep discharging conditions.

• A safety device designed for an NMC pack will measure individual cell voltages; if any exceed the maximum threshold (4.2V), it will activate protection mechanisms.

• It’s clarified that protective devices must be tailored to each battery type—what works for NMC cannot be applied directly to LFP or sodium ion batteries due to differing voltage thresholds.

• The necessity for distinct designs across different battery types reinforces the complexity involved in ensuring safety across various technologies.

Practical Application: Calculating Pack Configurations

• Transitioning into practical applications, the speaker discusses how to determine configurations based on desired output voltages (e.g., identifying components needed for a specific LFP pack).

• For example, achieving a target output of 60 volts requires calculating how many cells (19S configuration using nominal values like 3.2V per cell).

• The cutoff voltage calculation follows suit; understanding these calculations ensures proper design and functionality within specified limits.

This structured overview captures key insights from the transcript while providing timestamps that facilitate easy navigation back to specific discussions within the video content.

Battery Pack Design Fundamentals

Understanding Series Configuration in Battery Packs

• The calculation for the number of series (S) in a battery pack is derived from dividing the total pack voltage by the nominal voltage, resulting in approximately 18.75, which is rounded to 19.

• To determine the full charge voltage, multiply the number of series by either the cutoff or nominal voltage; for example, with a nominal load of 60.8 volts for lead-acid batteries, this results in specific calculations for full charge and cutoff voltages.

Lead Acid Battery Specifications

• For lead-acid batteries, each unit is typically considered as 12 volts; thus, to achieve a total of 60 volts, six series connections are required. This leads to further calculations regarding full charge and cutoff voltages.

• The full charge voltage for five series configurations is calculated as 5 times 14.2 volts, yielding approximately 71 volts; while the cutoff voltage is determined as five times 10.2 volts resulting in around 51 volts.

Sodium Ion Battery Calculations

• Transitioning to sodium-ion batteries, the nominal voltage used is approximately 3.1 volts; hence for a target of 60 volts, about 20 series connections are needed based on similar calculations as before.

• The full charge and cutoff voltages are calculated using these series: with a full charge at around 76 volts (3.8V x 20) and a cutoff at about 50 volts (2.5V x 20). Nominal voltage totals around 62 volts (3.1V x 20).

Generalizing Voltage Parameters Across Different Battery Types

• The discussion emphasizes that similar calculation parameters can be applied across various battery types such as NMC and LFP when designing packs with different voltages like those rated at either 60 or even up to higher values like 72 or more volts.

• Understanding basic values such as full charge voltage, cutoff voltage, and nominal voltage is crucial for designing both high-voltage (HV) and low-voltage (LV) packs effectively based on user requirements or specifications outlined during design processes.

Practical Application: Designing Higher Voltage Packs

• When calculating how many series connections are necessary for a higher target like a total of approximately 96 volts using an NMC configuration involves dividing by its nominal value (~3.7), leading to an approximate requirement of 26 series connections after rounding up from 25.9 due to standard practices in design considerations where values above certain thresholds are rounded up accordingly.

• Full charge and cutoff voltages can then be quickly computed: Full Charge = 26 times4.2 gives 109 volts; Cutoff = 26 times3 yields 78 volts; Nominal remains consistent at 26 times3.7, equating to roughly 66.2 volts.

Importance of Accurate Cell Configuration

• A critical note was made regarding previous design mistakes where one cell was missing from an entire battery pack configuration involving multiple parallel packs within several series combinations—highlighting the importance of thorough checks during assembly.

Understanding Battery Parameters and Management

Key Concepts in Battery Charging and Discharging

• The first battery pack discharges quickly due to one cell being lesser, affecting overall performance. Understanding how to find the power (P) is crucial, as it remains consistent across different battery types like NMC, LFP, lead acid, or sodium ion.

• To calculate P, knowing the voltage of the battery pack is essential. For instance, a 60V battery pack with a certain age (Ah) will be analyzed for its parameters.

• The age mentioned on the cell is critical; for example, an NMC cell typically has fixed voltage values (e.g., 3.7V). However, Ah can vary by manufacturer.

• The capacity of an NMC cell can range from a minimum of 0.5 Ah to a maximum of 5 Ah. This variability must be considered when calculating P.

• To find P: divide the total Ah (30 Ah in this case) by the specified cell capacity (2.6 Ah), resulting in approximately 11.5 P—rounded to 12 P for practical design considerations.

Calculating Required Capacity

• When aiming for a specific capacity (e.g., 50 Ah), determining how many parallel connections (P) are needed becomes necessary; if each cell has a capacity of 5 Ah, then dividing gives around 10 P required.

• Using an example where one cell's capacity is set at 5 Ah simplifies calculations: with a configuration of 16S and needing to achieve specific voltage and current ratings.

• A configuration of 16S and 8P results in a calculated output of 60 volts and approximately 40 Ah based on individual cell capacities multiplied by their respective configurations.

Advanced Configuration Examples

• Exploring another configuration with parameters like "19S6P" for LFP batteries shows how nominal voltage calculations work; multiplying cells yields around 60.8 volts while considering parallel connections provides total amp-hour ratings.

• Emphasis on using nominal voltages during rating selection ensures accurate charger specifications and safety device selections based on full charge versus cutoff voltages.

Importance of Battery Management Systems (BMS)

• Discussion transitions towards BMS—Battery Management System—which plays a vital role in managing battery packs effectively to prevent issues such as overcharging or deep discharge scenarios that could damage cells.

• The upcoming focus will delve into what management functions BMS performs within battery systems and how it contributes to overall safety and efficiency in operation.

Understanding Closed and Open Circuits in Battery Management Systems

Basic Circuit Concepts

• The discussion begins with the identification of two types of circuits: closed circuit (A) and open circuit (B). A closed circuit allows current to flow, while an open circuit does not.

• In a closed circuit, power flows from the positive terminal of a battery pack through a switch to the load, allowing continuous operation.

• An open circuit has a disconnection due to a switch, preventing power from reaching the load. Consequently, the load will not function as there is no complete path for current flow.

• The fundamental difference between these circuits is highlighted: in a closed circuit, devices like lamps will operate; in an open circuit, they will not due to lack of connectivity.

Battery Management System (BMS) Overview

• The BMS board integrates multiple battery cells connected in series (e.g., B1, B2, B3, B4), treating them as one unit for functionality.

• The positive terminal connects directly to the load while the negative terminal routes through the BMS before connecting back to the load.

• A MOSFET acts as a switch within this system. It controls whether the connection between components is made or broken based on signals received.

Functionality of MOSFET in Circuits

• The role of MOSFET is emphasized: it can act as either an open or closed switch depending on its operational state. This determines if current can flow through the circuit.

• If considered as an open circuit initially, without connectivity between components, power cannot reach the load; thus it remains inactive.

Operational Conditions of BMS

• The BMS operates by determining when to act as an open or closed circuit based on conditions such as faults within the battery pack.

• When functioning correctly (closed), power flows from positive through loads back to negative via MOSFET; if faulty (open), discharge does not occur due to interrupted paths.

Voltage Measurement Capabilities of BMS

• With four cells connected in series labeled 4S, each cell's voltage can be measured by establishing connections at both terminals—positive and negative—of each cell.

• To measure voltage accurately across any two points requires connections at both ends; hence each cell's voltage reading becomes feasible with proper wiring from BMS.

• As each cell’s positive and negative terminals are connected appropriately within this setup, it enables comprehensive monitoring capabilities for all four cells involved.

Understanding BMS and Battery Pack Selection

Overview of BMS Functionality

• The Battery Management System (BMS) can now read individual cell voltages, allowing for precise monitoring of battery pack performance.

• Users can determine the specifications of their battery packs directly from the BMS, which displays ratings such as "7S" indicating a series configuration.

• For a 10S battery configuration, the BMS can measure up to 10 series connections; however, any additional cells beyond this will be considered as zero.

Selecting the Appropriate BMS

• A 60V battery pack requires a 16S BMS, while a 72V pack necessitates a 20S BMS. Understanding these requirements is crucial for proper selection.

• For designing an LFP (Lithium Iron Phosphate) battery pack at 60V, one should select a 19S configuration based on voltage needs.

Circuit Connections and Protection Mechanisms

• The positive terminal connects directly to the load while the negative terminal goes through the BMS for switching purposes in both open and closed circuit scenarios.

• The BMS measures both total pack voltage and individual cell voltages, enhancing its ability to monitor overall system health.

Importance of MOSFET in BMS Design

• Understanding how to design and trigger MOSFET switches is essential since they play a critical role in power management within the vehicle ecosystem.

• The combination of power electronics and embedded systems is vital for effective operation of the BMS.

Key Operational Criteria for Effective Performance

• There are approximately seven to eight fundamental criteria that dictate how well a BMS operates under various conditions.

• Important parameters include full charge voltage, cutoff voltage, nominal voltage, and other working conditions that ensure optimal performance.

Charging Process Monitoring by BMS

• During charging, if any cell exceeds its maximum safe voltage (e.g., above 4.2V), the BMS will switch from closed circuit to open circuit to protect that cell from damage.

• This protective mechanism ensures that when one cell reaches critical levels during charging, it disconnects from power supply automatically.

Battery Management System (BMS) Protection Mechanisms

Individual Cell Voltage Monitoring

• The BMS protects the battery pack by monitoring individual cell voltage, specifically when it reaches 4.2 volts, which triggers an open circuit to prevent overcharging.

• The first protective condition is activated at 4.2 volts for each cell; this ensures that the battery pack remains safe during charging.

Discharge Condition and Cutoff Voltage

• During discharge, if any individual NMC cell voltage drops to 3 volts or below, the BMS will again create an open circuit to protect the battery from further discharge.

• This mechanism ensures that no cell goes below its critical cutoff voltage of 3 volts, maintaining overall battery health.

Full Charge and Pack Voltage Monitoring

• The BMS can measure the entire battery pack's voltage and will cut off charging once it reaches a full charge voltage of 67.2 volts for a 16S configuration.

• Even if the charger continues to supply power after reaching full charge, the BMS automatically disconnects to prevent overcharging.

Lower Cutoff Voltage for Battery Packs

• For a 16S pack, the lower cutoff voltage is set at 48 volts; if this threshold is reached during discharge, the BMS will also trigger an open circuit to protect against over-discharge.

• This protection mechanism ensures that even if some cells have higher voltages above their minimum thresholds, the entire pack remains safeguarded from excessive discharge.

Balancing Cell Voltages

• A crucial aspect of BMS functionality involves ensuring that differences between cell voltages remain less than 0.009 volts; this prevents imbalances in performance across cells.

• An example illustrates how minor discrepancies in cell voltages (e.g., one cell at 4.1V while others are at 4V), can lead to significant issues if not monitored properly.

• Understanding these differences helps maintain optimal performance and longevity of each individual cell within a multi-cell configuration.

Battery Management System (BMS) Voltage and Protection Mechanisms

Understanding Voltage Differences in Battery Cells

• The maximum voltage difference between cells is critical; a healthy range is around 0.009 volts, while the observed difference was approximately 1.1 volts, indicating an unhealthy state.

• The BMS will act as an open circuit when the voltage difference exceeds this threshold, preventing both charging and discharging of the battery pack.

• For safe operation, individual cell voltages should ideally be at or near 4 volts, with a maximum acceptable variation of about 0.03 to ensure safety and efficiency.

BMS Protection Mechanisms

• The BMS provides protection by disconnecting the battery from loads or chargers when unsafe conditions are detected, effectively becoming an open circuit. This mechanism ensures that no current flows under hazardous conditions.

• A temperature sensor (T1) integrated into the BMS monitors operating temperatures to prevent overheating or excessive cooling, which can damage battery cells; for NMC batteries, this range is typically between 0 to 60 degrees Celsius.

Overcurrent Protection Strategies

• Overcurrent protection is achieved through devices like fuses or MCBs (Miniature Circuit Breakers), which interrupt current flow when it exceeds rated levels; however, the BMS also plays a role in monitoring current flow directly through its circuitry.

• The BMS measures current flowing through it by being connected in series with the load; this allows it to monitor real-time consumption accurately and respond accordingly if thresholds are exceeded.

Microcontroller Programming for Safety

• The microcontroller within the BMS has programmed criteria for safety:

• It opens circuits if any cell voltage reaches 4.2 volts.

• It also opens circuits if any cell drops below 3 volts.

• Additionally, it monitors overall battery pack voltage and temperature extremes to maintain operational integrity and safety standards.

Current Ratings and Applications

• Current ratings specified for discharging (30 amps) and charging (15 amps) indicate limits for safe operation within smaller applications; these ratings help ensure that users do not exceed safe operational parameters during use of the battery system.

Battery Management System (BMS) Overview

Current Rating Selection for Battery Packs

• The design of the battery pack for two-wheelers includes a current rating limited to 40 or 50 amps. The selection process for the BMS voltage and current ratings will be discussed in detail.

• The choice of microcontroller used in the BMS is application-dependent, with options for programmable or pre-programmed controllers. A live demo of the actual BMS readings will be provided.

Protection Mechanisms in BMS

• Key protection features include cell full charge voltage monitoring and current over-protection. The BMS can measure current due to its series connection, ensuring that if the rated current is exceeded, it opens the circuit to protect the battery pack.

• Discussion on short circuit protection: It questions whether this feature is necessary and explains how Ohm's Law indicates that zero voltage leads to infinite current flow, which can cause overheating and potential fire hazards.

Understanding Voltage Measurement

• When voltage drops to zero due to a short circuit, there are no two points available for measurement, leading to infinite current flow through the circuit. This scenario poses risks of damage to the battery.

• Voltage is defined as the potential difference between two points; without both points present during a short circuit, measuring becomes impossible.

BMS Protection Strategies

• The BMS protects against overcharging and deep discharging by disconnecting from loads or chargers when necessary. Open-circuit protection is crucial for maintaining battery integrity.

• Important criteria for effective BMS operation include monitoring cell full charge voltage, lower cutoff voltages, temperature limits, overcurrent conditions, and short circuit protections.

Types of Battery Management Systems

• Two types of BMS are identified: standard BMS (which acts solely as a protective device without data display capabilities), and smart BMS (which provides data via Bluetooth communication).

• Smart BMS offers insights into individual series pack voltages and temperatures while also managing overall battery safety functions.

Smart BMS Connection Overview

Understanding Smart BMS Functionality

• The smart Battery Management System (BMS) displays total voltage available in the battery pack, crucial for monitoring performance.

• It indicates maximum voltage per cell, essential for assessing individual cell health within a 14-series NMC battery pack.

• Cell voltage readings are highly accurate, with variations noted among cells; the highest reading is from cell number 12 at 3.344 volts.

• The BMS identifies which series has the lowest voltage, highlighting potential issues in battery performance and balance.

Data Verification Process

• To verify data accuracy, average voltage calculations are performed; an average of 3.3 volts is established across cells.

• Multiplying average voltage by the number of series confirms total voltage readings provided by the BMS are correct.

• The difference voltage between cells should not exceed 0.009 volts; current measurements show it is at 0.008 volts, indicating healthy operation.

Circuit Conditions and Voltage Calculations

• The system operates under closed circuit conditions due to healthy readings; this ensures optimal functioning of the BMS.

• Difference voltage is calculated as maximum minus minimum cell voltages to ensure all cells operate within safe limits.

Maximum and Minimum Voltage Standards

• For a 14S NMC pack, full charge maximum should be around 58.8 volts; each cell must not exceed a maximum of 4.2 volts for safety.

• Healthy condition verification shows no cells exceed this threshold, confirming operational integrity of the battery system.

Monitoring Minimum Voltage Levels

• Minimum operating voltage for NFC should remain above 3 volts; current readings indicate all cells are above this threshold at approximately 3.3 volts.

• Consistent monitoring ensures that both maximum and minimum voltages remain within specified limits to maintain battery health and efficiency.

Battery Health Criteria and Design Considerations

Understanding Battery Health Conditions

• The difference voltage should not exceed 0.009 for a battery to be considered healthy, indicating a closed circuit under optimal conditions.

• The minimum voltage for a battery pack (potiness) is calculated to be around 42 volts; falling below this threshold will trigger an open circuit in the Battery Management System (BMS).

• A total voltage of 46 volts indicates that all health criteria are satisfied, confirming the battery's status as healthy.

Key Health Criteria for Batteries

• Important criteria include:

• Cell full charge voltage must not exceed 4.2 volts.

• Cell lower cutoff voltage should remain above 3 volts.

• Pack full charge voltage must stay below 58.8 volts in a 14S configuration.

• Lower cutoff voltage of the battery pack must be above 42 volts.

• Additional checks include ensuring no short circuits and verifying operating conditions without connected loads.

Conclusion on Battery Status

• All seven to eight health criteria have been met, confirming that the battery pack is functioning properly and can be deemed healthy based on these evaluations.

Upcoming Practical Session

• An evening session will focus on practical design applications where participants will create a battery pack using theoretical knowledge gained earlier.

• The session aims to integrate BMS considerations into real-world designs, moving from theory to practice with hands-on activities.

Summary of Learning Outcomes

• Today's lessons covered series-parallel combinations, nominal voltages, full charge voltages, and cutoff voltages across various battery types including LFP and NMC.

• Emphasis was placed on understanding BMS selection based on charger requirements and managing imbalance conditions effectively in future classes.

Insights into BMS Functionality

• The BMS plays a crucial role in protecting batteries from over-discharge by monitoring key parameters such as pack voltage and implementing safety measures when necessary.

Verification Process

• Verification involved checking total, minimum, maximum, average voltages along with temperature readings to ensure compliance with established health criteria for a 14S pack configuration.