Power battery copper busbars play a crucial role in electric vehicles and energy storage systems. They are responsible for transferring electrical energy between battery cells, modules, and motors, ensuring power connection and voltage acquisition within the battery pack.
Key design considerations for copper busbars in power batteries
(1) Integrated Functions: Power battery copper busbars highly integrate functions such as power connection, temperature sensing, and signal transmission within the battery pack.
(2) Material Properties: Hard copper busbars typically use pure copper, which has good conductivity and durability.
(3) Design Considerations: The fixing and installation of copper busbars in the battery distribution box must be reasonable to prevent deformation and damage.
(4) Electrical Performance: High-voltage copper busbars in electric vehicles are likened to a "vascular network," directly affecting range and charging capability.
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Design Requirements for High-Voltage Connector of Power Battery System
1. Appearance and Dimension Requirements
(1) The connector body should be flat, without sharp corners, burrs, or cracks;
(2) The electroplating layer should be free of peeling, cracks, blistering, stains, and other electroplating defects;
(3) The end welding/pressing layer should be intact and free of delamination;
(4) The insulating sheath should be orange, with a flat appearance, free of obvious scratches, deformation, and other defects, and should not have obvious color differences compared to products of the same type and batch;
(5) The dimensions of the connector body and insulating sheath should meet the drawing requirements and ultimately meet the assembly requirements of the power battery assembly.
2. Cross-sectional Selection Requirements:
The effective cross-sectional area of the connector should meet the rated/peak current carrying capacity requirements of the power battery system, while also satisfying mechanical reliability and process convenience requirements.
3. Installation and Fixing Requirements:
After the connector is assembled into the power battery system, effective fixing must be ensured. Refer to the following:
(1) When the bridging length of the rigid connector is ≥180mm, design fixing points;
(2) When the bridging length of the flexible connector is ≥150mm, design fixing points.
Common connector fixing structures include, but are not limited to, the following: cable ties, buckles, and special plastic parts.
4. Mechanical Reliability Requirements
(1) Theoretical Analysis: Stress and fatigue strength analysis is required.
(2) Requirements: The connecting strip must have intact mechanical properties, bolt residual torque ≥60%, no local fractures, intact insulation layer, no wear, and intact end weld/press layer without delamination.
5. Electrical Insulation Protection Requirements
(1) Insulation Resistance Requirements
Test Method: At room temperature, apply 500VDC or 1.5 times the nominal voltage (whichever is greater) between the connecting strip body and the insulation sheath, and wait for a stable reading.
Requirement: The minimum instantaneous insulation resistance during the measurement phase must be ≥0.1KΩ/V, and the minimum instantaneous insulation resistance calculated during the measurement phase must be ≥1kΩ/V.
(2) Breakdown Voltage Strength Requirements
Test Method: At room temperature, apply a 2500VAC 50~60Hz voltage between the aluminum busbar and the insulation layer for 1 minute;
Product Requirements: No insulation material breakdown or arcing should occur during the test.
6. Surface Treatment Requirements
Main surface treatment methods include: nickel plating, tin plating, and nickel sheet lamination. Performance and characteristics are as follows:
(1) Nickel Plating
a. The nickel plating layer has high stability in air. Due to the strong passivation ability of metallic nickel, a very thin passivation film can be quickly produced on the surface, resisting corrosion from the atmosphere, alkalis, and certain acids;
b. Can be used as a protective decorative coating;
c. Uniform thickness.
(2) Tin Plating
It has corrosion resistance, colorfastness, non-toxicity, easy welding, softness, and good ductility, but is easily scratched. It should not come into contact with hand sweat or be stored in damp places, otherwise it will easily discolor.
(3) Applying Nickel Strips
A 0.1mm (or other thickness) pure nickel strip is applied to the surface of the high-voltage flexible connector.
Advantages: The surface is not easily oxidized at high temperatures during welding, and the product is resistant to polishing and cleaning;
Disadvantages: The conductivity of the nickel strip and the connector is inconsistent, affecting the overall conductivity of the product. Design and selection should be based on specific product usage requirements.
7. Temperature Rise Requirements
Test Method: At 40℃, apply a 1C current to the entire battery pack (or connect the connectors in series within the battery pack) for 40 minutes.
Product Requirements: The surface temperature of the connector must not exceed 80℃.