Busbar Thickness and Current Rating Explained

Introduction

How thick should a battery busbar be for a given current rating? This is one of the most common design questions among battery engineers and system integrators.

In this guide, we break down how busbar thickness, width, and material directly affect current capacity, voltage drop, and thermal performance.

Wellgo Battery, a trusted copper-nickel busbar manufacturer, provides insights based on engineering data and international standards — helping you design safe, efficient, and cost-optimized battery interconnects for EVs and energy storage systems.

What Is a Busbar and Why Thickness Matters

A busbar is a metallic conductor — typically made of copper or aluminum — that distributes current within lithium-ion battery packs, EV systems, or power distribution units.

The thickness of a busbar determines:

● The amount of current it can safely carry

● Heat generation (I²R losses)

● Voltage drop across connections

● Structural stiffness for vibration and welding

According to IEEE Std 80-2013, current capacity increases nearly linearly with cross-sectional area, provided temperature rise is managed.

Wellgo Battery engineers optimize busbar cross-sections using simulation models to ensure consistent current flow with minimal energy loss.

Relationship Between Busbar Thickness and Current Rating

The current rating (A) of a copper busbar can be approximated by the following empirical formula:

I=k×A0.75I = k \times A^{0.75}I=k×A0.75Where:

● I = current capacity (A)

● A = cross-sectional area (mm²)

● k = constant (0.8–1.0 for copper, 0.5–0.6 for aluminum)

Busbar Thickness (mm)	Width (mm)	Cross-Section (mm²)	Current Capacity (A, Copper)
1.0	10	10	50–60
2.0	15	30	130–150
3.0	20	60	230–250
5.0	25	125	480–500

Source: IEC 61439-1 Standard for Low-Voltage Busbars

Wellgo Battery validates every busbar design with actual current testing and thermal cycling to ensure compliance with IEC and UL standards.

 

Material Conductivity: Copper vs. Nickel vs. Aluminum

Choosing the right busbar material directly impacts current rating.

Material	Conductivity (% IACS)	Density (g/cm³)	Remarks
Copper (C11000)	100	8.96	Highest conductivity; standard for EV & ESS busbars
Nickel	22	8.9	Good corrosion resistance; used for surface coating
Aluminum (6061)	61	2.7	Lightweight, lower cost, but thicker for same ampacity

For lithium battery busbars, Wellgo Battery typically uses copper-nickel composite busbars, combining high conductivity with surface corrosion resistance — ideal for spot-welding and long-term stability.

 

Temperature Rise and Thermal Limits

Current flow generates heat proportional to I²R.

If the busbar is too thin, excessive temperature rise can lead to:

● Oxidation and plating degradation

● Reduced mechanical strength

● Thermal runaway risk in compact battery modules

For copper busbars, the safe operating temperature should not exceed 105°C for continuous current.

Wellgo Battery employs thermal simulation tools to verify temperature rise under load and optimize cooling pathways for EV modules.

Reference: SAE J2464 – Electric Vehicle Battery Safety Standard

 

Surface Plating and Contact Resistance

Surface coating improves connection performance and protects the busbar from corrosion.

Plating Type	Resistance (μΩ·cm²)	Benefits	Typical Use
Tin (Sn)	50–80	Low cost, solderable	ESS & general applications
Nickel (Ni)	20–40	Corrosion & wear resistance	EV & hybrid systems
Silver (Ag)	5–10	Best conductivity	Aerospace & high current

Wellgo Battery provides nickel-plated copper busbars to maintain stable low resistance after thousands of thermal cycles — ensuring consistent current flow over time.

 

Design Optimization: Width vs. Thickness

While thickness increases current capacity, it also raises cost and stiffness. Engineers often balance width and thickness to achieve target ampacity with minimal material waste.

A common ratio guideline is:

Width:Thickness=5:1 to 8:1\text{Width:Thickness} = 5:1 \text{ to } 8:1Width:Thickness=5:1 to 8:1Wellgo Battery uses finite element analysis (FEA) to simulate current density and determine the most efficient geometry for each battery busbar design.

 

Standards for Busbar Quality and Safety

To ensure reliability, battery busbars must meet multiple international standards:

● IEC 61439-1: Defines thermal rise and electrical clearance requirements

● UL 1973: Governs energy storage system safety and material testing

● ISO 9001: Quality management for manufacturing processes

● EU Battery Regulation 2023/1542: Material traceability and recyclability

Wellgo Battery complies with all major standards, ensuring traceable, RoHS-compliant copper-nickel busbars suitable for global OEM integration.

 

Real-World Example: EV Battery Pack Design

An EV battery pack rated for 300 A continuous current may use a 3 mm × 20 mm copper busbar (60 mm² cross-section).

To achieve similar performance with aluminum, a 5 mm × 25 mm bar (125 mm²) is required.

Wellgo Battery’s engineering team uses this ratio to design lightweight, high-current solutions while maintaining optimal cost per meter.

 

Quick Reference Table

Application	Typical Current (A)	Busbar Thickness (mm)	Recommended Material
Small ESS	50–100	1.0–1.5	Tin-plated copper
EV Battery Module	200–400	2.0–3.0	Nickel-plated copper
High-Power EV Pack	500–800	4.0–5.0	Copper or Cu-Ni composite
Industrial Inverter	800–1500	5.0–8.0	Copper or aluminum alloy

 

Call to Action

Need help choosing the right busbar thickness for your next project?

Customized Copper Nickel Busbars for Lithium Battery Solutions – Wellgo Battery — engineered for optimized current capacity, durability, and compliance with global standards.