Aluminium Busbar

Electrical grade aluminum busbar material also known as ec grade aluminum busbar. Compared to copper busbars aluminium offers a weight and cost save, but requires an increase in cross-sectional area of ~62%. Hence aluminium busbars need more volume for packaging.

The common grades of aluminum for electrical busbars:

1060

  • Good corrosion resistance.
  • High electrical conductivity
  • Typically formed by extrusion or rolling.
  • Good workability.
  • downside:
    • Low strength.

1100

  • Minimum of 99.0% aluminium.
  • Highest mechanical strength of 1000 series.
  • Excellent forming properties, especially in the fully soft, annealed temper.
  • Good thermal conductivity, hence often used in heat exchangers and heat sinks.

1350

  • Used as a battery busbar material.
  • Nearly pure aluminium with minimum weight percentage of 99.5% of aluminium.
  • Very good electrical conductivity.
  • Very good thermal conductivity.
  • Excellent corrosion resistance.
  • Tight controls are used on certain impurities that could adversely affect conductivity.
  • downside
    • Low mechanical strength.
    • Non-heat treatable

6063

  • magnesium and silicon as the alloying elements
  • good mechanical properties
  • heat treatable
  • weldable
  • good electrical conductivity
  • good bending properties

6101

  • Contains magnesium and silicon for high mechanical strength without significant reduction in conductivity.
  • Higher yield strength than 1350
  • Better creep resistance than 1350

Cross-Sectional Area

This depends on the current, electrical conductivity, maximum temperature and thermal environment that the busbar is in.

If you are replacing a copper busbar with an aluminium design you will need to increase the cross-sectional area by 62%.

Linear Expansion

Within the design you will need to consider the temperature swings and hence the expansion and contraction of any busbar so that you can look at loading and clearances.

In bolted joints thermal cycling of the busbar can lead to relaxation of the bolt force. Dagur Ólafsson et al [2] measured the bolted force relaxation for a copper and aluminium busbar that started with a pre-load of 40kN.

The clamping force relaxes at a higher rate for AA6101-T4 than for Cu-OF-04. From the original 40 kN, the clamping force in the Al lowers to 25.2 kN after 881 cycles while the force on the Cu lowers to 32.9 kN after 1236 cycles.

Ólafsson, D., Vilaça, P. & Vesanko, J. Multiphysical characterization of FSW of aluminum electrical busbars with copper ends. Weld World 64, 59–71 (2020)

The image below shows this in more detail.

Plot of the clamping force versus time for both the AA6101-T4 and the Cu-OF-04. The detail focuses on the period of about 13 min, between the 50th and the 60th cycles. The relaxation rates exhibited by the Al component are about the double of the busbar Cu end component. The relaxation rates of the clamping force are higher at start of the test, when higher clamping forces are present [2].

One option is to use copper ends on the aluminium busbar.

Bend Radius

The minimum bend radius is a function of aluminium grade and material thickness.

Aluminium GradeMinimum Bend Radius [mm]
1060
1100
13501x thickness
6063
61011x thickness (up to 12mm)
2x thickness (>12mm)

Plating

These are often plated or selectively plated at joint locations to reduce corrosion. Typically aluminium is plated with:

  • Silver
  • Tin
  • Nickel

Electrical Insulation

Insulation is normally applied as:

  • Dipped
  • Heat Shrink
  • Powder Coat
  • Wrapped

References:

  1. Busbar Design Guide, Mersen
  2. Ólafsson, D., Vilaça, P. & Vesanko, J. Multiphysical characterization of FSW of aluminum electrical busbars with copper ends. Weld World 64, 59–71 (2020)

2022 Tesla Model Y 4680 battery busbars

2022 Tesla Model Y 4680

The aluminium module P-group busbars are plated on the underside. This will be to reduce corrosion and improve the weld to the top of the cells.

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