The selection of protection boards for lithium batteries is crucial to the safety, lifespan and performance of the batteries. The following are the specific selection methods and key points:
I. Method for Selecting Protective Boards
The protection board is the "safety manager" of lithium batteries. Its main function is to prevent overcharging, overdischarging, overcurrent and short circuits, and to balance the voltage of the battery cells. The following dimensions need to be paid attention to when making a choice:
1. Clarify the core parameters
Compatible battery type
Lithium battery types: ternary lithium (3.7V per cell), lithium iron phosphate (3.2V per cell), lithium titanate, etc. The protection board needs to be matched with the battery type (the charging and discharging cut-off voltages of different materials are different).
The number of series and parallel connections: Select the corresponding channel protection board (such as 3 series, 4 series, etc.) based on the number of series connections (determining the total voltage) and parallel connections (determining the total capacity) of the battery pack.
Current parameter
Continuous discharge current: It should be greater than the maximum working current of the equipment (for example, if the peak current of the electric vehicle motor is 30A, the continuous current of the protection board should be ≥35A).
Instantaneous peak current: It is typically 2 to 3 times the continuous current when dealing with short-term high-current scenarios (such as motor startup and impact of power tools on loads).
Charging current: It needs to match the power of the charger (if the charger outputs 5A, the charging current of the protection board should be ≥5A).
Voltage parameter
Overcharge protection voltage: The voltage for a single lithium ternary cell is generally 4.20±0.02V, and that for lithium iron phosphate is 3.65±0.02V.
Over-discharge protection voltage: For single-cell ternary lithium, it is generally 2.5-2.75V, and for lithium iron phosphate, it is 2.0-2.5V.
Balancing the starting voltage: When the voltage difference of the battery cells exceeds the set value (such as 0.02V), the protection board activates the balancing function to prevent the battery cells from being unbalanced.
Ii. pay attention to the protection function
Basic protection:
It must be equipped with overcharge, overdischarge, overcurrent and short-circuit protection. Some high-end protection boards also support temperature protection (with built-in or external temperature sensors).
Balancing function
Passive balancing: It consumes the energy of high-voltage cells through resistors, making it suitable for low-current scenarios. It has low cost but low efficiency.
Active balancing: It transfers energy through inductors/capacitors, suitable for high-current scenarios. It is highly efficient but costly, and is mostly used in power batteries.
Communication function:
If real-time monitoring of battery status (such as voltage, current, temperature, and remaining capacity) is required, a protection board with CAN bus or I²C communication interface can be selected (suitable for scenarios such as energy storage and electric vehicles).
Iii. Materials and Craftsmanship
PCB board: Prioritize FR-4 fiberglass board (heat-resistant and corrosion-resistant), and avoid cheap paper-based boards (prone to aging and short circuits).
Component quality: MOSFETs, resistors, capacitors and other components should be selected from brand products. Inferior components are prone to overheating and burning out.
Welding process: The weld points of the protective plate should be full and free of false soldering. For large current paths, thickened copper foil or nickel plating treatment is required to reduce internal resistance (excessive internal resistance will cause severe heating).
Ⅳ. Adapt to scene requirements
Low-power scenarios (such as power banks, flashlights)
Choose a protection board that is small in size and low in cost, with a focus on overcharge and overdischarge protection. The balancing function can be simplified.
High-power scenarios (such as electric vehicles, energy storage systems) :
A high current protection board (with a continuous current ≥50A) is required. It must be equipped with active balancing and temperature protection. It is recommended to choose an intelligent protection board with a BMS (Battery Management System).
Special environment:
In high-temperature environments (such as outdoor energy storage), high-temperature resistant components (operating temperature -40 ℃ to 85℃) should be selected, and in humid environments, moisture-proof treatment is required.
V. Brand and Certification
Give priority to choosing protective boards from well-known brands, as their quality and after-sales service are more guaranteed.
Certification requirements: Lithium battery protection boards must pass safety certifications such as UN38.3 and IEC62133. Products for export must comply with the regulations of the target market (such as EU CE and US UL).
