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.

What is a BMS & What are the Components in Lithium-ion battery BMS?

AI generated Image of BMS

A Battery Management System (BMS) is an electronic system that manages a rechargeable battery (cell or battery pack), by monitoring its state, controlling its environment, and protecting it from operating outside its safe operating area.

1. Battery Monitoring Unit (BMU)

The BMU is the "sensory" part of the BMS. It's typically distributed throughout the battery pack, with individual monitoring circuits for groups of cells or even individual cells in high-precision systems.

These circuits are connected to a central communication bus that relays data to the Battery Control Unit (BCU).

 

Components:

Voltage Sensors: High-precision analog-to-digital converters (ADCs) that measure the voltage of each cell or cell group. Accuracy is crucial here, as even small voltage differences can indicate significant state-of-charge variations.

Current Sensors: Devices that measure the current flowing into and out of the battery pack. Common types include:

Shunt Resistors: Measure voltage drop across a small resistor in the current path. Simple and cost-effective but can generate heat.

Hall Effect Sensors: Measure the magnetic field generated by the current. More accurate and efficient than shunt resistors.

Current Transformers: Measure the current by inducing a current in a secondary winding. Used for high-current applications.

Temperature Sensors: Thermistors or thermocouples placed at strategic locations within the battery pack to monitor temperature.

 

Working:

1. Voltage sensors continuously measure the voltage of each cell or cell group.
2. The current sensor measures the total current flowing in and out of the battery pack.
3. Temperature sensors monitor the temperature at various points in the pack.
4. The BMU converts these analog measurements into digital signals using ADCs.
5. This digital data is then transmitted to the BCU via a communication bus (e.g., CAN, SPI).

2. Battery Control Unit (BCU)

The BCU is the "brain" of the BMS. It's a central processing unit that receives data from the BMU, makes decisions, and controls the battery's operation.

 

Components:

Microcontroller (MCU): A powerful processor that executes the BMS software, performs calculations, and controls the other components.

Memory: Stores the BMS software, battery parameters, and historical data.

Communication Interfaces: Allow the BCU to communicate with the BMU, other vehicle systems (e.g., VCU), and external devices (e.g., chargers).

Gate Drivers: Control the switching of power electronic devices (e.g., MOSFETs) in the charging and discharging circuits.

 

Working:

1. The BCU receives data from the BMU (voltage, current, temperature).
2. The MCU processes this data to:
3. Calculate State of Charge (SOC) and State of Health (SOH).
4. Determine if any protection thresholds have been exceeded.
5. Implement cell balancing algorithms.
6. Control the charging and discharging process.
7. The BCU sends control signals to:
8. Cell balancing circuits: To equalize cell voltages.
9. Charging/discharging circuits: To regulate current and voltage.
10. Cooling/heating systems: To maintain optimal temperature.
11. External systems: To communicate battery status and receive commands.

3. Cell Balancing Circuit

Cell balancing circuits are integrated into the BMU or as separate modules. They are connected to each cell or cell group.

 

Components:

Passive Balancing:

• Resistors: Used to dissipate excess energy from higher-voltage cells.

• Switches (e.g., MOSFETs): Control the connection of the resistors to the cells.

Active Balancing:

• DC-DC Converters (e.g., buck-boost converters): Transfer energy between cells.

• Capacitors or Inductors: Used as energy storage elements in the transfer process.

• Switches (e.g., MOSFETs): Control the flow of energy between cells.

Working:

Passive Balancing: When a cell's voltage exceeds a certain threshold, the corresponding switch is closed, connecting the resistor. The resistor dissipates the excess energy as heat, lowering the cell's voltage.

Active Balancing: Energy is transferred from higher-voltage cells to lower-voltage cells using the DC-DC converter and energy storage elements. This is a more efficient method as it doesn't waste energy as heat.

4. Protection Circuit

The protection circuit is typically implemented within the BCU and uses dedicated hardware and software to ensure fast and reliable response to fault conditions.

Components:

Comparators: Compare measured values (voltage, current, temperature) to predefined thresholds.

Logic Gates: Combine the outputs of the comparators to generate protection signals.

Switches (e.g., MOSFETs, relays): Disconnect the battery from the load or charger in case of a fault.

Working:

1. Comparators continuously monitor voltage, current, and temperature.
2. If any of these parameters exceed their safe limits, the comparators trigger a protection signal.
3. Logic gates combine these signals to generate a final protection command.
4. This command activates the switches, disconnecting the battery to prevent damage.

5. Communication Interface

The communication interface is implemented within the BCU and provides connectivity to external systems.

 

Components:

Communication Controllers: Implement communication protocols such as CAN, LIN, SPI, or UART.

Transceivers: Convert digital signals into signals suitable for transmission over the communication bus.

 

Working:

1. The BCU formats data into messages according to the communication protocol.
2. The transceiver converts these messages into electrical signals.
3. These signals are transmitted over the communication bus to other systems.
4. The receiving system decodes the messages and extracts the data.

Benefits of using a BMS

Using a BMS has many benefits, including:

• Increased battery life: By protecting the battery from operating outside its safe operating area, the BMS can help to extend the battery's life.
• Improved battery performance: By ensuring that all cells in the battery pack are balanced, the BMS can help to improve the battery's performance.
• Enhanced safety: The BMS can help to prevent battery fires and other safety hazards.
• Reduced warranty costs: By protecting the battery from damage, the BMS can help to reduce warranty costs.

Know about lithium cell models?

 

lithium cell model

Lithium cells come in a wide variety of models, each with its own specific designation. Here are some common examples:

Common Shapes and Sizes

• Cylindrical Cells (like AA or AAA batteries, but bigger):

  • 18650: 18mm in diameter, 65mm long. Common in laptops and flashlights.
  • 21700: 21mm in diameter, 70mm long. Used in electric cars and power tools.
  • 26650 & 32650: Even bigger cylinders, for things that need a lot of power.

• Pouch Cells (flat and flexible):

  • Fit well in slim devices like smartphones and tablets.

• Prismatic Cells (boxy):

  • Rectangular blocks are often used in electric cars and large battery packs.

What those extra numbers and letters mean

• They give you more details about the cell's performance, like how much energy it can store and how quickly it can release. For example, in "18650-30Q", the "30Q" tells you about its discharge rate.

Finding the right battery

• Always check the manufacturer's information for the most accurate details about a specific lithium cell model.

How moisture infiltrate Lithium-ion battery Packs?

Moisture on Lithium-ion Cells

 Moisture can infiltrate lithium-ion battery packs through several primary mechanisms:

• Condensation: When warm, humid air encounters a colder surface within the battery pack (such as the cells or enclosure), the moisture in the air transitions into liquid water. This phenomenon is particularly prevalent in environments where temperature and humidity levels fluctuate significantly.

• Leaks: Imperfections in the battery pack's casing, including cracks, faulty breather plugs or inadequate seals, can create pathways for external moisture to penetrate. These vulnerabilities can arise from manufacturing defects, physical damage during transport or usage, or the natural wear and tear associated with the battery pack's lifespan.

• Coolant Leaks: In battery packs equipped with liquid cooling systems, leaks within the coolant lines can introduce moisture into the pack. Coolants often contain water or possess hygroscopic properties, meaning they readily absorb moisture from the surrounding air.

• Manufacturing Process: While less frequent, moisture can be inadvertently introduced during the battery pack's manufacturing process if proper drying and sealing procedures are not strictly adhered to.

The presence of moisture within a lithium-ion battery pack can have detrimental consequences:

• Diminished Performance: Moisture can corrode the internal components of the battery pack, leading to an increase in internal resistance and a subsequent reduction in energy capacity.

• Safety Hazards: Moisture can interact chemically with the battery's constituents, generating heat and potentially culminating in fires or explosions.

• Accelerated Aging: Moisture can expedite the aging process of the battery pack, resulting in a shorter overall lifespan.

To mitigate moisture ingress, manufacturers employ a variety of strategies:

• Hermetic Sealing: Utilizing high-quality seals and gaskets to establish a moisture-tight barrier.

• Desiccants: Incorporating moisture-absorbing materials within the battery pack to minimize the impact of any residual moisture that may enter.

• Regular Inspections: Conducting periodic inspections to identify and address any potential leaks or damage.

• Controlled Manufacturing Environments: Maintaining a low-humidity environment throughout the manufacturing process.

By comprehending the pathways through which moisture can infiltrate lithium-ion battery packs and implementing effective preventative measures, manufacturers and users can contribute to ensuring the safety, performance, and longevity of these critical components.

Thermal adhesives in lithium-ion battery packs

Thermal adhesives - Thermal management in lithium-ion battery packs

Thermal adhesives play a crucial role in lithium-ion battery packs, especially in electric vehicles (EVs), by facilitating efficient heat dissipation and maintaining optimal operating temperatures. Here's a breakdown of their applications in lithium cell connections.

1. Cell-to-Cell Bonding:

• Heat Dissipation: Lithium-ion cells generate heat during operation due to internal resistance. Thermal adhesives between cells create a thermally conductive pathway, allowing heat to spread evenly and dissipate more effectively. This prevents localized hot spots that can accelerate battery degradation and compromise safety.

• Structural Support: Adhesives provide mechanical bonding between cells, enhancing the structural integrity of the battery pack. This is particularly important in cell-to-pack designs where individual cells are directly integrated into the battery pack structure.

• Electrical Insulation: While primarily designed for thermal conductivity, these adhesives offer electrical insulation, preventing short circuits between adjacent cells.

2. Cell-to-Cooling Plate Bonding:

• Efficient Heat Transfer: Thermal adhesives bond cells to cooling plates or heat sinks, which are essential components of the battery thermal management system. The adhesive facilitates efficient heat transfer from the cells to the cooling system, maintaining optimal operating temperatures.

• Uniform Contact: The adhesive ensures uniform contact between the cell and the cooling plate, maximizing the heat transfer area and efficiency.

3. Module-to-Pack Bonding:

• Thermal Management at the Module Level: Battery packs with modular designs, and thermal adhesives are used to bond individual modules to the pack structure. This helps manage heat dissipation at the module level, further enhancing overall thermal management.

• Structural Integrity: Adhesives contribute to the structural integrity of the battery pack by bonding modules together and to the pack housing.

Key Considerations for Thermal Adhesives:

• Thermal Conductivity: The primary requirement is high thermal conductivity to ensure efficient heat transfer.

• Adhesion Strength: The adhesive provides strong bonding to maintain contact between components under various operating conditions.

• Electrical Insulation: The adhesive should be electrically insulating to prevent short circuits.

• Chemical Compatibility: The adhesive must be chemically compatible with the cell materials and other components in the battery pack.

• Long-Term Reliability: The adhesive must maintain its properties over a wide temperature range and throughout the battery's lifespan.

In conclusion, thermal adhesives are essential for effective thermal management in lithium-ion battery packs. They facilitate heat dissipation, enhance structural integrity, and contribute to the overall safety and performance of the battery system.

 

DFMEA Process in Lithium ion battery?

DFMEA Cycle

DFMEA is a structured approach to identifying and assessing potential failure modes in a product or process design. 

By proactively identifying and addressing these potential failures, organizations can improve product reliability, reduce costs, and enhance customer satisfaction.

Key Steps in a DFMEA:

1. Define the System: Clearly outline the system or product being analyzed, including its functions and intended use.
2. Identify Function: List the primary functions of the system or product.
3. Identify Potential Failure Modes: For each function, brainstorm potential ways in which it could fail.
4. Identify Potential Effects: Determine the consequences of each failure mode on the system or product and the customer.
5. Assess Severity: Assign a severity rating to each potential effect, indicating the seriousness of its impact.
6. Identify Potential Causes: For each failure mode, identify the root causes that could lead to its occurrence.
7. Assess Occurrence: Assign an occurrence rating to each potential cause, indicating the likelihood of it happening.
8. Assess Detection: Determine the likelihood of detecting each failure mode before it reaches the customer. Assign a detection rating.
9. Calculate Risk Priority Number (RPN): Multiply the severity, occurrence, and detection ratings to obtain the RPN. A higher RPN indicates a higher risk.
10. Develop Action Plans: Prioritize the highest-risk failure modes and develop action plans to mitigate or eliminate them.
11. Implement Corrective Actions: Execute the action plans to address the identified risks.
12. Re-evaluate: Periodically review the DFMEA to identify new risks and update the analysis as necessary.

Benefits of DFMEA:

• Proactive Risk Management: Identifies potential failures early in the design phase.
• Improved Product Quality: Reduces the likelihood of product failures and defects.
• Enhanced Customer Satisfaction: Delivers more reliable and durable products.
• Cost Reduction: Prevents costly recalls and field repairs.
• Regulatory Compliance: Helps meet industry standards and regulatory requirements.
• Continuous Improvement: Fosters a culture of continuous improvement and risk mitigation.

By systematically applying DFMEA, organizations can significantly improve their products and processes quality and reliability.

Lithium-ion battery DFMEA Analysis (Design Failure Mode and Effects Analysis)

Here's how the DFMEA process is applied to lithium-ion batteries:

1. Define the Scope:

• Clearly define the system or subsystem being analyzed (e.g., the entire battery pack, a single cell, the battery management system (BMS), etc.).
• Identify the functions and requirements of the system.

2. Identify Potential Failure Modes:

• List all potential ways in which the battery or its components could potentially fail. Examples include:
  • Cell Level: Internal short circuit, electrolyte leakage, thermal runaway, capacity fade, overcharge, over-discharge.
  • Pack Level: Poor thermal management, inadequate electrical connections, BMS failure, mechanical damage.
  • Material Level: Degradation of electrodes, separator breakdown, current collector corrosion.

3. Determine the Effects of Each Failure Mode:

• Describe the consequences of each failure mode on the battery's performance, safety, and reliability. Examples include:
  • Reduced capacity, loss of power, overheating, fire, explosion, shortened lifespan.

4. Assign Severity Ratings:

• Assign a numerical rating (typically on a scale of 1 to 10) to each failure mode based on the severity of its effects. A higher rating indicates a more severe consequence. 

5. Identify Potential Causes of Each Failure Mode:

• List all the possible causes that could lead to each failure mode. Examples include:
  • Manufacturing defects, material impurities, improper handling, extreme temperatures, mechanical stress, and electrical abuse (overcharge/over-discharge).

6. Assign Occurrence Ratings:

• Assign a numerical rating (typically on a scale of 1 to 10) to each cause based on the likelihood of it occurring. A higher rating indicates a higher probability of occurrence. 

7. Identify Prevention Controls:

• Describe any existing design features or controls that are in place to prevent or detect the failure modes. Examples include:
  • Safety vents, thermal fuses, BMS functions (overcharge/over-discharge protection, temperature monitoring), and quality control measures.

8. Assign Detection Ratings:

• Assign a numerical rating (typically on a scale of 1 to 10) to each control based on its ability to detect the failure mode before it has a significant effect. A higher rating indicates a lower probability of detection.

9. Calculate the Risk Priority Number (RPN):

• For each failure mode, calculate the RPN by multiplying the severity, occurrence, and detection ratings:
  • RPN = Severity x Occurrence x Detection
   
• The RPN provides a quantitative measure of the risk associated with each failure mode.

10. Develop Recommended Actions:

• For failure modes with high RPNs, develop and implement corrective actions to reduce the risk. These actions may include:
  • Design changes, material selection, process improvements, and additional controls.
     

11. Take Action and Re-evaluate:

• Implement the recommended actions and then re-evaluate the RPNs to ensure that the risk has been adequately reduced.

Lithium Batteries Failure Cause and Effects:

                                                             Lithium-ion battery DFMEA Analysis (Design Failure Mode and Effects Analysis)

What are the do's and dont's to keep Lithium Ion battery Safe & Healthy?

 

Lithium Iron Phosphate (LiFePO4) cells arranged in parallel to increase capacity; 3.2V 700AH

The industry follows some dos and don'ts for the safe operation of LFP(Lithium Ferrous Phosphate) or any other lithium-based batteries, which are as follows.

Do's:

1. Store at Ideal SOC: Always store lithium batteries or EV batteries at an ideal state of charge (SOC) between 40% and 60% for longer periods.

2. Hazardous Safety: Keep the batteries away from hazardous materials, such as fire, oils, explosives, and similar substances.

3. Adequate Ventilation: Ensure adequate ventilation if storing more than one lithium battery in a single location.

4. Optimal temperature: Store lithium batteries at an optimal temperature range of 20°C to 45°C.

5. Optimal Charge: Charge the EV battery or vehicle to 100% SOC at least once a week to calibrate the Battery Management System (BMS) for SOC correction.

6. Physical Verification: During general service checks at the dealership, inspect for any dents or rust underneath the tray of the lithium battery.

Don'ts:

1. Avoid Using Incompatible Chargers: Do not charge lithium-based batteries with chargers meant for VRLA or lead-acid batteries. Always use the charger provided by the original equipment manufacturer (OEM), or ensure that any alternative charger is equipped with the appropriate charging methodology for lithium batteries.

2. Optimal State of Charge (SoC): Lithium-ion batteries should be stored at 50% to 60% of their state of charge for long durations (2 to 4 months). Additionally, it's important to top up the charge every 6 months if the battery is not in use.

3. Charging Speed Matters: Avoid ultra-fast chargers, as they can impose high stress on the battery and reduce lifespan. While occasional fast charging is acceptable, it’s always preferable to use slow charging methods.

4. Regular Charging: Users should charge the battery to full at least twice a week and ensure that the state of charge does not drop below 20%. Both high and very low SOC can damage lithium battery cells.

5. Temperature Considerations: Do not charge the battery in extremely cold temperatures. 

By following these guidelines, you can ensure safer and more reliable operation of lithium-based batteries.

 

What are IP Ratings?Types of IP ratings

                                           

What are IP Ratings?

IP rating or Ingress Protection Rating are the indicator which defines the protection of electrical or Mechanical enclosures Components from the external Intruders like Water,Dust,Oil splash etc...

or simply IP Ratings shows how any enclosure is protected against Water and Solids.

The IP rating has a two digit number after a letter IP X X (X)--->optional

IP - Ingress Protection

X - Solids ( Dust,sand etc..)

X - Liquids ( Moisture,Oils,Water etc..)

X - Pressure (Optional)

Note: The Higher the number after IP ,the better the Protection.

IP Ratings

What is Insulator, Insulation Resistance and How to measure IR in Batteries ?

   Figure 1: Insulator in the High Voltage Transformer

Insulator: A material which blocks movement of electric current due to high resistance. The high resistance is due to the higher band gap from Valance to Conduction band.

Insulation Resistance: The insulation resistance is a method used to detect any power leakage inside  HV components (Battery,Inverter,Motor etc).

In this process we will be applying High DC Voltage (500V or 1000V) with miniscule amount of current and resistance is measured.(Typically 550MOhms).

If the component has insulation fault then the resistance value showing in the IR Tester or Megger will  be low and Vice Versa,

                                   

       Figure 2: Showing no insulation Fault (OK)         Figure 3: Shows insulation Fault(Faulty)

Process to Check Insulation Resistance (IR):

1. The above Figure 2 & 3 shows Insulation Tester or Megger to check the Insulation resistance.

2. It has 2 probes one is RED to check the insulation by giving appropriate voltage either 500V or 1000V and the other BLACK probe is a common ground.

3. The IR meter has a (Test ) button, also the test probe too has a push button (Test) to pass the voltage.

4.The common ground probe need to touch the HV component ground or the body ( Typically the HV systems body metal structure is the ground ).

5. The red probe need to touch the LIVE part of the system, in case of batteries it will be battery terminals ( Negative or Positive Terminals).

6.Then the TEST button shoud be pressed, we will get the result (as shown in the above image).

To read more about Batteries -- Click Here

What are Lithium ion Batteries & How LFP batteries work?

                               

                                       Figure 1: 48V LFP battery fixed inside a cabinet.

What are Lithium ion Batteries ?

Lithium ion batteries are the rechargable batteries which has Lithium as cathode active material.

There are different types of Lithium ion batteries like LFP,NMC,NCA etc, All these comes under Lithium family batteries and each one has its advantages and disadvantages.

These batteries having better features compared to other lead acid or VRLA batteries because of the Power electronics components avaialbilty to control each and every parameters of the battery.

For example the monitoring section reads and monitor all real time data's from individual cells and sensors connectd in it, means Voltage of individual cells,battery pack,total voltage,cell temperature,Over current or Under current etc...., each and every parameters of the battery including SOH and SOC also tracked using in-build BMS(Battery Monitoring System).

The Lithium ion batteries have high energy density, means the amount of energy stored per unit volume is higher than the traditional Lead acid batteries hence the size of the battery is smaller.

The Li-ion battery can store as much as twice of the power Lead Acid batterycan hold and also environmentally friendly but these batteries are susceptible to 100% discharge so max 90% discharge is recommended.

Working of LFP battery?

                                                   

                                              Figure 2: Shows movement of Ions & Electrons

Like anyother LMO (Lithium Metal Oxide ) batteries, the working of LFP is similar and the only change is the usage of cathode metal oxides.

Incase of LFP the cathode is Lithium (Ferrous Phosphate) Li-(FePO4), for NMC battery the cathode is a mixed of Lithium (Nickel Manganese Cobalt Oxide) Li(NiMnCoO2).

The Negative electrode of Lithium ion battery is graphite/graphene and the positive electrode is lithium iron phosphate, The electrolytes such as LiPF6(lithium hexafluorophosphate) is used.,The Seperator used in the LFP batteries can be Polyethylene (PE) , Polypropylene (PP).

Charging:

While Charging,the lithium atoms leave the metal oxide structure and ionize into Li+ ions under the release of an electron. In this process Li+ ions diffuse to the negative electrode(anode). 

At the surface of the graphite particles the Li+ ions and electrons recombine with each other forming neutral lithium atoms and are reintercalated into the molecular structure of the graphite.

When no more ions will flow, the battery is fully charged and ready to use.

Discharging

During discharge, lithium atoms oxidize by forming Li+ ions and electrons, whereas Li+ ions move to the positive electrode diffusing through the electrolyte and the separator. The electrons flow from the negative electrode to the positive on the external circuitry, where the resulting current flow can be used to run any type of load.

 At the positive electrode the electrons recombine with the Li+ ions and are stored in the molecular structure of the cathode active material,

When all the ions have moved back, the battery is fully discharged hence it needs charge again.

How Batteries Works ?

What is a Battery?

Figure:1

A Battery is a device which can converts stored chemical energy to electrical energy, the battery consists of single or multiple electrochemical cells connected in series which can be charged or discharged.

As per figure 1, Generally a battery works from the movement of ions through electrolyte & electrons movements in the external load from cathode to anode and Viceversa for Charging & Discharging.

Cathode is a Positive electrode

Anode is a Negative electrode

Electrolyte is a medium in which ions travel from one electrode to other.

Seperator is a material which placed inbetween anode and cathode which physically seperates them still facilitates ion movements while charging and discharging.

Unlike Anode and cathode in power electonics components where Diodes anode is Positive and cathode is Negative, the Battery Anode is Negative and Cathode is Positive.

Types of Batteries:

1.Flooded Batteries ( Wet Batteries)

2.Non Flooded Batteries (Dry Batteries)

1.Flooded Batteries ( Wet Batteries)

  

Figure 2: Panasonic Lead Acid Battery               Figure 2: Lead Acid Battery internal Cell connections

Lead Acid batteries like the ones we are using in our Bikes,Cars,Autos,Heavy Vehicles,Generators  for starting an engine are Flooded batteries.

These batteries are easy to construct and are cheap to manufacture, The electrolytes are 35 to 40% sulfuric acid & 60 to 65%% distilled water.

Since we need to refill the electrolytes and also the chances of leakage of electroyte was observed in these batteries hence it is called as Flooded or Wet batteries.

2.Non Flooded Batteries (Dry Batteries)

These dry batteries are the advanced Lead Acid Batteries which donot need refilling of electrolytes,

Examples like Gel and AGM batteries.

AGM - Absorbent Glass Mat Batteries 

• These Gel or AGM batteries have different electrolyte compared to Wet batteries, 

• In Gel battery the electrolyte is a sulfuric acid in gel state.

• In AGM batteries the electrolyte stuffed in between fibre glass mesh which absorbs and holds the (water & Sulfuric acid) and acts like a sponge or cushion and will allow only required amounts of electrolytes to pass for the ion movements.

Since these batteries doesnt need topping of electrolytes it is called as Dry batteries.

Lithium Ion batteries are also a Dry battery. 

Click To know more about Lithium-ion battery.

Memory Effect in Batteries

 Memory Effect:

These are observed mostly observed in NiCd Batteries and the battery loose its maximum energy capacity because of  repeated charging after only partially discharged. 

It Means : Battery is not fully discharged instead but charged to full repeatedly.

This effect is also known as battery effect,lazy battery effect or battery memory.

This effect was first observed in Satellites where the solar power was used to charge the NI-Cd battery and since satellites in the orbits revolve round the earth it has to go behind the earth and doesn't get any sunlight for some time and it has to use battery power for its operation.

The batteries utilizes suns power at day and battery power at night but it wont utilizes complete energy, hence the battery is getting discharged only 30% SOC and recharged to 100% for thousand of times, the NI-Cd remmembered it ( In Chemistry terms ), and the remaining 70% of the battery capacity was lost.

How to Mitigate Memory effect: 

1. The Memory effect can be mitigated by discharging the battery completly untill the battery ceases to function, then charge it to 100% SOC.

2. Try to discharge the battery pack completly and charge it to full atleast once in a month.

Fortunately Lithium based Batteries are not subjected to memory effects or Lithium batteries have no memory effects.