Constant Resistance (CR) mode

In electronics and testing, Constant Resistance (CR) mode is a setting on electronic loads or a method of discharging a battery where the load behaves like a fixed resistor (R = V / I ). Unlike Constant Current (CC) mode, where the amperage stays the same regardless of voltage drop, in CR mode, the current decreases proportionally as the battery voltage drops.

Here is an overview of Constant Resistance in battery testing:

What is Constant Resistance Mode?

• Definition: The electronic load maintains a fixed ratio between input voltage and input current ( V/I is constant).
• Behavior: As the battery discharges, its voltage drops, causing the current drawn by the load to also drop linearly.
• Simulation: This mode simulates real-world resistive loads, such as heaters, light bulbs, or simple electronic circuits, making it ideal for testing battery life under these specific conditions.

Key Features and Applications

• Capacity Testing: CR is used to evaluate battery capacity, specifically assessing how much energy the battery can deliver under a set resistive load.
• Starting Conditions: CR is frequently used to measure the start-up behavior of electronic devices.
• Power Electronics: It is useful for testing devices with a defined source resistance, such as LED drivers or motor controllers.
• Startup Protection: When testing switching power supplies, CR mode is often preferred over CC mode because it allows voltage and current to ramp up together, preventing the power supply from overloading.

Advantages and Limitations

• Pros: Simulates real-world conditions (non-constant current) and allows for accurate measurement of peak loading conditions.
• Cons: Because the current drops as the voltage decreases, the test can be more complex to interpret than a simple constant current discharge, as the discharge curve is not linear.

Difference Between CC and CR Modes

Note: In the context of batteries, "CR" is sometimes confused with "CR2032" (a 3-volt Lithium Manganese Dioxide battery). However, in testing, it refers to the operating mode of the equipment.

Potential Confusions

• CR Battery Labeling: If you see "CR" on a battery (e.g., CR2032), it does not stand for "Constant Resistance." In the IEC standard nomenclature, "C" stands for Lithium Manganese Dioxide chemistry, and "R" stands for Round (cylindrical or button) shape.
• Internal Resistance: This refers to the battery's own opposition to current flow, which increases as the battery ages or discharges.

For precise testing, engineers often use specialized DC Electronic Loads that can be programmed to Constant Resistance mode.

Inverter-to-battery communication

Inverter-to-battery communication enables real-time data exchange (voltage, current, State of Charge - SoC) via protocols like CAN bus or RS485 for safe, efficient charging. It establishes a closed-loop system, allowing the Battery Management System (BMS) to control the inverter, which protects lithium batteries from overcharging/discharging.

• Closed-Loop Communication (Active): The battery BMS directly tells the inverter maximum charge/discharge current, voltage limits, and SoC.
• Open-Loop Communication (Passive): The inverter estimates battery status based on voltage, which is less accurate for lithium batteries.
• Physical Connections: Usually RJ45 cables (CAN/RS485) connecting the battery's BMS to the inverter's BMS/COM port.
• Data Exchanged:
  • State of Charge (SoC): Accurate percentage of battery capacity remaining.
  • Voltage/Current Limits: Prevents overvoltage and overload.
  • Battery Temperature: Adjusts charging based on temperature.
• Required Configuration: The inverter must be set to the correct protocol (e.g., Pylontech, BYD) matching the battery to ensure communication.
• Benefits: Increased safety, improved battery lifespan, and optimized charging.

Common Communication Protocols & Ports

• CAN bus: Standard for many lithium batteries (e.g., SMA Solar).
• RS485: Common for smaller or specific hybrid systems (e.g., FelicityESS).

• State of Charge (SOC): Allows the inverter to show an accurate percentage rather than just guessing based on voltage.
• Safety Limits: The battery tells the inverter exactly how much current it can safely accept (charging) or provide (discharging) based on its current temperature and health.Automated Control: Enables features like automatic generator starting when the battery is low or stopping the discharge before reaching a critical level.

• CAN (Controller Area Network): A high-speed, robust protocol common in modern lithium systems.
• RS485: Often used for older or more basic communication setups.
• Closed-Loop vs. Open-Loop:
  • Closed-Loop: The inverter actively adjusts its behavior based on direct data from the battery.
  • Open-Loop (or No Communication): The inverter operates based on its own preset voltage settings without direct feedback from the battery.

Setup Requirements

1. Compatible Cable: Often a standard Ethernet cable (CAT5/6), though pin configurations must match the specific manufacturer's requirements.
2. Protocol Matching: Both the battery and inverter must be set to the same protocol (e.g., selecting "Pylontech" or "Deye" protocol in the inverter menu).

Voltage Balancing Battery

mettere la foto cell_belance

Battery voltage balancing equalizes the charge across individual cells in a battery pack to ensure all cells have the same State of Charge (SOC), preventing overcharging/undercharging, maximizing capacity, and extending lifespan. It is essential for lithium-ion systems and can be achieved through passive (dissipative) or active (transfer) methods.

BMS Configuration

 BMS (Battery Management System) configuration involves setting up parameters like cell count, battery capacity, chemistry (e.g., LiFePO4), and safety thresholds (voltage, temperature, current). It ensures safe charging/discharging, balances cells, and defines communication protocols (CAN/RS485) to maximize battery life.

Key Aspects of BMS Configuration

• Battery Pack Structure: Defines the series (S) and parallel (P) arrangement (e.g., 4S1P for 12.8V LiFePO4, 16S for 48V systems) to match the cell count.
• Voltage Parameters: Sets the Maximum (Overvoltage), Minimum (Undervoltage/Cutoff), and Balancing voltages for individual cells and the total pack.
• Current Limits: Configures maximum continuous charge and discharge current limits to protect the FETs (Field Effect Transistors).
• Temperature Protection: Defines operational ranges for high/low temperatures to prevent thermal runaway.
• Balancing Strategy: Sets the voltage threshold at which active or passive balancing begins to equalize cells.
• Communication: Configures CAN bus or RS485 for communication with inverters, chargers, or monitoring software.

How to Configure a BMS

Most modern BMS units (e.g., JK, Daly, Seplos) are configured via Bluetooth app or PC software.

1. Connect: Link the BMS to a phone/PC and use the default password (often "1234" or "123456").
2. Define Cell Type: Select LiFePO4, Li-ion, or LTO.
3. Input Basic Data: Enter the exact number of series cells and battery capacity (Ah).
4. Set Protections: Adjust over-voltage protection (OVP), under-voltage protection (UVP), and current limits based on the battery manufacturer's datasheet.

Types of BMS Topologies

• Centralized: A single controller is connected directly to every cell via a wiring harness. It is cost-effective and compact but creates complex wiring for large packs.
• Modular/Master-Slave: Several secondary controllers manage cell modules and report to a primary master controller. This is common in electric vehicles (EVs).
• Distributed: Each cell has its own mini-controller, connected by a simple communication bus. This is highly scalable but more expensive.

Common Configuration Settings

When setting up a BMS (often via Bluetooth apps or CAN bus), you must define several critical limits:

• Cell Count (S/P): Defining the number of cells in Series (S) to set total voltage and Parallel (P) to set total capacity.
• Voltage Thresholds: Setting the Over-Voltage Protection (OVP) and Under-Voltage Protection (UVP) levels to prevent fire or permanent damage.
• Current Limits: Defining the maximum continuous charge and discharge current the battery can safely handle.
• Balancing Logic: Configuring when the BMS should equalize the charge between cells (e.g., only when charging or when a specific voltage difference is detected).

Essential Tools

• Configuration Software: Many modern systems like the JK BMS or Victron Energy use smartphone apps or PC software to adjust parameters in real-time.
• Communication Protocols: Smart BMS units often use CAN bus or RS485 to "talk" to inverters or vehicle controllers.

Temperature Cycling of battery

Temperature cycling of batteries involves repeatedly exposing cells to high and low temperatures (e.g., to -40°C +72°C) to test safety, reliability, and lifespan. Extreme cold causes ion sluggishness and capacity loss, while high temperatures accelerate degradation, causing chemical reactions that increase capacity fade and internal resistance. 

Key Effects of Temperature Cycling

• High-Temperature Cycling (>40°C): Drastically accelerates aging, reduces cycle life, and can cause rapid capacity fade, especially if charging occurs at high temperatures.
• Low-Temperature Cycling (<0°C): Causes, electrolyte breakdown, lithium plating, and increased internal resistance, leading to potential dendrite formation and safety risks.
• Thermal Fatigue: Repeated fluctuations cause physical stresses on internal materials, such as electrode layer separation and solid electrolyte interphase (SEI) layer rupture.
• Capacity Fade: Both, extreme high and low temperatures decrease the usable capacity, with  potentially reducing performance much faster than room temperature (e.g., 
   SOH vs  SOH after 400 cycles).

Temperature Cycling of battery

• High-Temperature Cycling (e.g., >55°C): Significantly accelerates degradation, increases internal resistance, and causes rapid capacity loss due to faster electrolyte breakdown and electrode structural changes.
• Low-Temperature Cycling (e.g., <-20°C): Causes severe capacity reduction, increased internal resistance, and lithium plating on the anode, which can lead to hazardous internal shorts.
• Thermal Management Importance: Active cooling is essential, as every   rise above  can double the rate of degradation, reducing cycle life.
• Safety Risks: Repeated cycling can weaken structural integrity, leading to premature thermal runaway, especially in unevenly heated battery packs.

Testing Objectives

• Safety Standards: Evaluating behavior in extreme environments to ensure reliability.
• Life Prediction: Assessing capacity loss after multiple cycles to estimate real-world performance (e.g., in EVs).
• Performance Optimization: Determining the optimal temperature range to minimize cell-to-cell variance in packs.