There are so many things to think about in any busbar bolted joint design. Hence it is useful to look at examples and experience.
One of the most comprehensive resources in this field is the “Copper for Busbars Guidance for Design and Installation” by the Copper Development Association [1].
The Electrical Power Engineering Reference & Applications Handbook [3] gives recommendations for bolt size, washers and torques for busbar joints.
Bolting Patterns
Holes should be placed in-line along the length of the joint, offsetting the holes increases the resistance by increasing the disturbance of the current flow.
Copper Development Association [1]
Pressure Uniformity
Too high tightening torque or too small pressure distribution can lead to distortion of the busbars and reduced contact area [4].
This post has been built based on the support of and sponsorship from: Quarto Technical Services, Eatron Technologies and About:Energy
Another technique for reducing contact resistance is to cut a longitudinal slot in both busbars. This relieves / reduces the localized contact-pressure differences and instead increases its uniformity across the contact area.
Storm Power Components [2]
The Copper Development Association [1] state that this approach can reduce the contact resistance by 30 to 40%.
Beneficial effect of sectioning was associated with a more uniform stress distribution between the keeper and conductor that assured a larger contact area at the conductor-connector current carrying interface [6].
The electrical engineering portal [4] gives ideas for nuts, bolts and washers to reduce likelihood of thermal and vibration loosening of bolted joints.
It should be noted that the thermal and vibration inputs into the joint can be both linear and rotational. Or a combination of those.
There are may sprung and serrated washer options.
The Nord-lock washer stretches the bolt and prohibits further rotation.
Busbar and Joint Enclosure
The Toyota Prius Gen 2 Battery has short copper busbars between each module. Below you see a WeberAuto [5] image where the black plastic cover over the module terminal posts is being removed.
In the next image you can see the details of the busbar and fixings (different example of a Prius pack). Although signs of corrosion, you can clearly see the nut and washer spreading the load. Plus the orange plastic surround to protect the engineer.
A regular repair on these battery packs is to strip out the bus bars and replace the connecting plates and nuts on each battery module. Corrosion can be caused because the air used to cool the battery comes from the cabin that can be hot, cold, moist etc. When rebuilding always use a drop of Stabilant 22A on the nut/stud.
Andy Latham, Salvage Wire
Image supplied and copyright of Salvage Wire.
We would like to extend this examples page, please do share examples: images and descriptions where possible: nigel@batterydesign.net
References
- Copper for Busbars Guidance for Design and Installation, Copper Development Association
- A Comprehensive Guide to Jointing Busbars: Which Method is Best?, Storm Power Components
- Recommended practices for mounting buses and making bus joints, Electrical Power Engineering Reference & Applications Handbook
- Shaping and connecting rigid busbars in low voltage switchgear, Electrical Engineering Portal
- 2016 – 2022 Toyota Prius Li-Ion Battery, WeberAuto, YoutTube
- Braunovic, Milenko. (2001). Effect of connection design on the contact resistance of high power overlapping bolted joints. Components and Packaging Technologies, IEEE Transactions on. 25. 220 – 229. 10.1109/HOLM.2001.953215.
See also: Cell Joining Techniques