At first glance, selecting a busbar when designing a lithium battery pack seems easy – you know the current, you know how the cells are connected, and you need a piece of copper or aluminum to connect the battery cells together. However, selecting a busbar is not just about matching the current to the thickness of the busbar.
Many factors affect the size of the busbar, including current, cross-sectional area, materials, temperature rise, available space, connection pattern, and the actual battery pack design.
For busbars that are meant to be used for laser welding, it is paramount that the geometry of the busbar is compatible with the terminals and the welding process.
It is for this reason that a busbar that looks perfectly good on paper may still end up giving you overheating, voltage drop, or mechanical or assembly issues in the finished battery pack.
This guide will help you determine how to go about the busbar sizing of your battery packs and tells manufacturers what to keep in mind before requesting custom busbars.
Busbar size calculation involves determining the correct width and thickness of a busbar depending on the current that it will carry and the environment where it is going to work.
When talking about battery packs, the calculation must also involve the arrangement of the cells, the length of the conductors, the material of the busbar, the thermal conditions in which it will be used, connection points, and what space is available for installation of the busbar.
As for a starting point, the formula is:
Busbar Cross-Sectional Area = Width Ă— Thickness
For instance, if a busbar is 20 mm wide and 2 mm thick:
20 mm × 2 mm = 40 mm²
However, this value does not help to understand whether a busbar is appropriate for the specific battery pack since the allowed current does not depend just on area.
If busbars aren’t the right size, it can be a weak point in a high-quality battery system.
Current flowing through a conductor causes resistance to create heat, and higher resistance will cause a higher voltage drop, which will have implications for the efficiency of the system.
Poor sizing of busbars can lead to the following:
Too high a temperature increase
Higher energy losses
High incidence of voltage drop
Unreliable connections
Heating of terminal connections
Degradation of the materials used
Difficulties meeting the necessary requirements
On the other hand, making busbars excessively large is not a solution either.
Busbars that are too large will increase production costs, weight, size, and difficulties of production.
There is no single busbar size suitable for all batteries. The practical calculating consists of finding the following inputs:
1. Find Maximum Constant Current
The busbar size must be calculated from the maximum continuous current value. The nominal battery current value must not be used without taking into account the level of actual operating conditions, including:
Constant discharging current
Constant charging current
Peak conditions
Average operating time
Connecting cells in parallel
Temperature
Cooling method
Once again, a busbar with a carrying capacity of 100 A during the whole time of operation should be considered differently from the one rated for only a few seconds.
2. Calculate Necessary Cross-Sectional Area
The basic formula is:
Cross-Sectional Area = Width Ă— Height
For example, if the necessary area is estimated to be about 30 mm², different combinations can provide the same area.
For instance:
15 × 2 mm = 30 mm²
10 × 3 mm = 30 mm²
20 × 1.5 mm = 30 mm²
While all options have the same electrically geometric cross-section, the difference is in their mechanical behavior. The choice of the configuration will depend on the available battery-pack place and bending needs.
3. Choose the Busbar Material
Copper and aluminum are two frequent choices for battery busbars.
Copper busbars are more preferable than aluminum busbars for compact dimensions with high conductivity.
Aluminum busbars are lighter than copper ones and are better choices for electric vehicles (EV) and energy storage projects because of their low weight and material efficiency.
The material chosen involves different weights, conductivity, resistance, thermal performance, surface processing, and other manufacturing features.
It is inappropriate to replace a copper busbar with an aluminum one with the same dimensions without knowing how it will perform in practice.
4. Take into Account Temperature Rise
The amount of current that can be passed through a busbar is not just an unchanging quantity measured for a specific busbar size.
The rise in temperature depends on many factors, such as:
Temperature of the surrounding environment
Orientation of the conductor
Air flow
Enclosure conditions
Busbar distance
Surface area
Continual current
The duty cycle
Number of conductors installed next to each other
Cooling method
Because of that, busbar sizes may serve as initial reference points only.
Most of the time, you will see queries like “current carrying capacity of copper busbar,” “busbar ampacity,” “200 amp busbar size,” or “busbar size table.”
These queries provide good starting points, but there’s a downside.
Basically, a given busbar does not have one rating.
For instance, let’s take two identical copper busbars measuring 25 x 3 mm each.
The busbar located in a wide-open space will perform differently than the one placed in a small container that limits heat dissipation.
As a result, sizing a busbar requires more advanced specialists who can take into consideration electrical and thermal loading.
In case of battery packs, the same rule applies to each module.
A busbar size table can simplify selecting busbars.
However, do not choose production busbars only based on the information provided in the table.
Use the table to narrow down your selection by checking up the information, for example:
Current → Cross-section → Material → Temperature rise → Geometry → Connection → Application
The final product should pass tests with regards to conditions under which it is going to operate.
There is a new design aspect connected to laser welding methods.
The busbar can be manufactured as a component that is appropriate for the laser welding process for prismatic lithium batteries, taking into account its geometry and material.
However, for an effective construction of the busbar, it is necessary to follow the welding requirements as well as the terminals of the cells.
The design aspects include:
Cell spacing
Terminal location
Busbar width and thickness
Welding area
Places of bending
Geometry of the holes or slits
Conditions for electrical isolation
Distance between the conductive elements
Tolerances
Sequence of the assembly of the battery module
Thus, it is obvious that a designed busbar has more possibilities compared to the ready-made one.
Adinath Enterprises produces copper and aluminum busbars in accordance with requirements and drawings of the customers. The company produces aluminum busbars, which are already ready for welding on prismatic cells of lithium batteries.
Only relying on current rating
Current should be the first variable considered, not the only one in the calculation.
Using a one-size-fits-all busbar size table
A sizing table can differ significantly from the vessel’s actual characteristics and cooling and working conditions.
Not considering voltage drop
For very long or high-current busbars, voltage drop and resistance should be taken into account.
Not choosing shape before gauging the thickness of the busbar
It can be possible to select a thicker busbar that matches the calculated current, but the hardware can have problems in a bend or a terminal of a cell.
Designing the busbar after designing the battery
Busbars should be taken into account while designing modules instead of treating them as add-ons.
Disregarding tolerances needed for production
Even a precise CAD drawing needs repeatable tolerances to be made.
When planning the design of a busbar, it is essential to provide your manufacturer with the following details:
Code of battery
Cell type and size
Design of the cell
Peak rated current
Maximum current value
Charge current
Material of busbar required
Dimensions of the busbar
Terminal dimensions of the cell
Layout of the busbar
Requirements for the hole positions
Requirements for manufacturing
The surface treatment required
Insulation factors
Production requirement
In case of the ongoing design process, some manufacturers can provide feedback on design from their end.
Generally speaking, the design of the battery modules is rarely identical for all batteries.
Even if two batteries use almost similar formats of the battery cells, the demanded busbars can vary due to several factors:
Client position
Pins from terminals
Required current
Size of the module
Welding connections
Frame specifications to restrict the use of jigs
The use of customized busbars provides an opportunity to follow the specifications of the battery configuration rather than to apply standard elements to a battery design.
1. Consider the actual current draw when determining size.
It isn’t enough to use nominal voltage and battery capability alone to size.
2. Design for the real thermal environment.
A busbar operating in an enclosed module must be designed differently from a busbar operating in open air.
3. Match the busbar to the cell terminal.
Sizing is only a part of the equation; correctness in mechanical condition and connection must be ensured.
4. Make sure the welding area is clear.
If the busbar is designed for laser welding application, the welding zone must be suitable for the battery manufacturer’s welding method.
5. Provide a complete drawing.
Providing a proper drawing will eliminate confusion regarding holes, bends, dimensions, tolerances, etc.
6. Perform final validation.
Making prototypes and verifying thermoelectric properties of the product will justify high-volume production endeavors.
If you are trying to get a quote for a custom battery busbar, you don’t need to have the ideal size of the busbar beforehand.
A manufacturer can take your requirement, cell model, battery configuration, measurements, and drawings in order to come up with an appropriate production process.
For example, Adinath Enterprises can analyze customers’ drawings regarding the requirements for parameters such as material, measurements, the angle of bends, holes needed in the busbar, surface finish, and the feasibility of production.
That is why the process is much easier than trying to just ask for the “busbar for 100 A” or “busbar for 200 A” without giving any other information about the application.
How is the size of the busbar determined?
To find the necessary busbar size, first determine the current needed, then calculate the cross section by multiplying the width by the thickness. You then need to factor in possible issues with the conductor material, the rising temperature, installation method, and voltage drop.
What is the formula for busbar size?
The basic geometric equation says the following:
Cross section of the busbar = width multiplied by thickness.
However, this won’t allow you to establish the exact size needed, because current is not the only factor needing consideration.
What is the size of busbars suitable for 200 amps?
There cannot be just one size suitable for 200A busbars. This depends on various factors like material used, acceptable temperature rise, how it is installed, how it cools off, and the general design requirements.
Which is better: copper or aluminum for battery busbars?
Neither has an undeniable advantage here. Copper has a higher conductivity, while aluminum is much more lightweight. The correct choice will depend on battery design, weight requirements, and way of connection.
Is it possible to utilize aluminum busbars for lithium battery packs?
Definitely. In battery applications where weight and electrical characteristics are significant factors, aluminum busbars are quite popular. The quality of material and its dimensions, terminal interface, and welding requirements must be compatible with the battery design.
What is a busbar fit for laser welding?
A busbar fit for the laser welding process is a product designed with the necessary dimensions, geometry, and material. This means that the busbar does not have to undergo laser welding by the supplier.
Is it possible for Adinath Enterprises to produce custom battery busbars?
Sure. Adinath Enterprises develops busbars made of aluminum and copper as per the order this can include aluminum busbars fit for laser welding to be used for the production of prismatic cell lithium batteries.
Sizing the busbars is not simply about choosing a value from a current ratings table.
Instead, creating a working battery pack demands consideration of the current, the cross section, material, temperature rise, voltage drop, shape, the terminals, the welding area, and the tolerances.
In this regard, the situation is more complicated for compact lithium battery packs, as here the busbars have to be designed to both carry the current and fit the mechanical features of the pack.
If you have a drawing, specification sheet, or current demand, you should find a manufacturer that specializes in making busbars, and that will help you turn your design into a final product.
Are you looking for a custom copper or aluminum busbar that can be welded by laser and fit into your battery pack? Contact us at Adinath Enterprises, and let’s discuss what your project will look like.
For any query, please call us, email us or fill the form and wewill contact you shortly.
+91-9899772424
+91-9899335858
abhinavjain2001@hotmail.comÂ
info@adinathenterprises.com
