A high-power inverter battery can be constructed using high-quality prismatic lithium cells but may experience issues with connection due to incorrect busbar design. This could lead to overheating, uneven current flow, poor fitting, and poor welding prepration. This, in turn, will impact battery performance and reliability.
Inverter manufacturers looking to construct lithium battery packs, there are several factors to consider when deciding on the correct laser welding type aluminum busbar. Current requirements, cell arrangement, busbar design, material characteristics, and the customer’s laser welding process must all be considered.
Factors to consider when choosing a bespoke aluminum busbar for prismatic lithium battery applications.
A laser-welding-type aluminum busbar is a conductive aluminum part created for a customer’s battery design and laser welding process. This is used to provide an electrical connection between 2 compatible prismatic lithium cells or certain terminals of the battery.
The size, shape, contact area, and finish of the busbar will be suitable and appropriate for the application and welding needs. Laser welding is performed by the battery manufacturer or their nominated welding service. The busbar itself is supplied by the manufacturer.
Why are the correct busbar designs required for high-power inverter batteries?
High-power inverter batteries can have high currents passing through them. If a busbar is chosen incorrectly, then there may be an additional resistance and local heat buildup.
Key factors:
Current carrying capacity
The busbar needs to be able to carry the expected current without overheating beyond the allowed limit.
For an inverter of a certain power, you can roughly calculate the DC current by:
AC Output Power divided by (DC Voltage x Inverter Efficiency)
For example, a 5000W inverter running from a 48V battery and with an efficiency of 90% will draw an approx. 116A when running at max output.
This is just an example of what size current we can expect. The actual current depends on a variety of factors such as voltage, load, efficiency, and transient loading.
The busbar should also be sized based on ambient temperature, cooling options, available space inside the enclosure, length of conductor, and local heating sources.
Heat Generation
There is always some resistance on all busbars; therefore, heat will be generated.
This can be calculated using:
Power Loss = I²R
The larger the current, the greater the importance of the resistance. There may also be an increase in resistance due to the connections. This can cause extra heat to be generated.
Selecting the correct grade of aluminum, section area, and connections can help to reduce the losses. The thermal properties of the busbar should also be taken into consideration.
Inductance
The shape of the busbar can affect the inductance. In high-speed power electronics, the layout of the positives and negatives can affect the parasitic inductance, voltage spikes, and EMI.
If possible, try to keep the positive and negative return as close together as possible to reduce loop inductance. The final design should also be checked to make sure it works with the electrical design of the inverter and switching characteristics.
1. Know your cell configuration.
Firstly, refer to the battery pack drawings and cell specifications.
You should know,
Cell dimensions and terminal positions
Series/Parallel connections
Length, width, thickness, and bends required
Distance between your cells and housing.
Spacing, insulation, and fixing requirements.
Do not assume that just because your cells have a certain capacity you will know what busbar you need. Two different batteries with similar capacity cells may need different busbar shapes depending on their layout and current requirements.
2. What grade of aluminum?
Aluminum is a lightweight material with good electrical conductivity, so it can be used in many situations.
However, different grades such as 1060, 1200, and 6061 are available.
1060 & 1200 are often used for their electrical conductivity.
6061 could be suitable if you have different mechanical requirements but will not have the same level of electrical conductivity.
Choosing the right grade will depend on the factors relating to electrical resistance, mechanical strength, forming, weldability, and customer requirements. Always confirm what grade and properties you have.
3. Correct Size
The thickness and width of your busbar will directly affect its cross-sectional area and therefore resistance. However, bigger is not always better.
Consider the amount of current you require, the temperature rise allowed, the space available, and the mechanical strength and weight. You may also have bends, holes, slots, and varying cross-sections, which can create hotspots.
It is preferable to have a qualified design review and thermal analysis.
4. Laser Welding Compatible
If you are looking for a busbar for laser welding, then you will need to ensure it is compatible with your customer’s welding process and terminal design.
Consider the following:
Weld area and overlap requirements
Thickness and tolerance
Cleanliness and finish
Alloy compatibility with terminal
Flatness and fit-up
Customers’ welding process and validation.
Laser welding can be sensitive due to the reflective nature of aluminum, oxide layer, and thermal properties. Ensure compatibility with your team carrying out the welding. This should be validated with the correct testing.
Just because it is laser welding type doesn’t mean it will be compatible with all laser systems.
5. The manufacturer can follow your drawing.
When looking for bespoke busbars for your battery, it is important to have a manufacturer who can manufacture them to your specific requirements.
Ensure they can be manufactured to your size, holes, slots, bends, and edge finish. Having the dimensions checked will ensure they fit into your cell layout and the weld area is as required.
Adinath Enterprises manufactures copper and aluminum busbars according to your drawings. We can cut, punch, bend, drill, and do other finishing processes to your exact technical requirements.
Lighter Conductors:- The use of aluminum can reduce the weight of interconnections when compared to copper designs with equivalent electrical resistance.
Correct Electrical Properties:- When sized correctly, busbar resistance and conductor losses will be under control.
Flexible Design:- The custom size and formed design can be applied to a number of prismatic cell designs.
Welding Compatible:- Contact areas can be specified so that the surface finish is suitable for the customer’s validated laser welding process.
Consistent Fit:- The busbars are manufactured using drawings and dimensional checks to ensure there is consistency across production batches.
Depending on the alloy type, shape, quality of manufacture, and application.
Current is not just about the size of the conductor :- The current rating depends on many factors, including temperature rise, cooling, housing, and conductor shape.
The contact area can affect the heating :- This can be dependent on the contact shape, terminal type, and joint resistance.
Not considering different aluminum grades :- Conductivity, strength, and formability will differ between alloys.
Not checking for fit :- Incorrect bending, hole positions, and tolerances can cause issues when assembling your battery.
Prototype testing should be carried out to ensure correct sizing, electrical performance, thermal performance, and weld quality (if required).
To give manufacturers an idea of what you require, include:
Cell make, model, and terminal details.
Battery voltage and expected current (both constant and high).
Busbar drawing or CAD.
Aluminum grade and thickness (if applicable).
Laser welding interface requirements.
Insulation, plating, or surface finish (if applicable).
Quantity of prototypes and full volumes.
If you are still designing your product, provide any details you have. This will allow the manufacturer to look at your drawing and ask any questions about the manufacturing process.
1. What aluminum busbar would be suitable for a high-power inverter battery?
This will depend on current temperature rise, cell arrangement, available space, grade, and connection requirements. It should always be checked that the final size is suitable for the application.
2. Why do we use prismatic lithium cells in inverter batteries?
They have a compact design and structure, which can make it easier to design the battery pack. However, the design will depend on the cell specifications, thermal management, connections, and enclosure requirements.
3. What is a laser-welding type ready aluminum busbar?
A conductor made from aluminum that has been manufactured to suit the customer’s laser welding requirements. The welding will be done.
4. Is aluminum a better material to use for inverter battery busbars?
Not always. Aluminum is a lighter material, but copper will generally have higher electrical conductivity. However, the correct material will depend on the resistance, weight, available space, mechanical requirements, and overall design cost.
5. How do I work out the current rating for my aluminum busbar?
You will need to look at the expected current, conductor size, material type, temperature, cooling, enclosure, and temperature rise. A generic table cannot be guaranteed to be safe.
6. Can aluminum busbars be bespoke for different prismatic cells?
Yes. A manufacturer can make busbars to your drawings. This means they can be a specific size, width, and thickness with holes, slots, and bends. It will depend on what the manufacturer can do.
7. What should I check when approving a busbar prototype?
Check the size, fit, grade, finish, resistance, temperature rise, and if it is suitable for the joining process. Laser welding validation should be done by the welding team.
Several factors will be considered when deciding on the best aluminum busbar for your high-power inverter batteries. These include cell layout, conductor resistance, heat dissipation, grade, and joining.
A laser-welding type aluminum busbar can be used to help achieve your particular battery interconnect requirements with prismatic lithium cells in your inverters if the busbar is manufactured to specification.
If you need a bespoke aluminum busbar for your battery requirements, then get in touch with Adinath Enterprises. We can help you with your drawings, material type, size, and manufacturing needs.
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