The challenge:
- Provide a meaningful weight, size and cost reduction for cross-linked ISO-6722-1 power cables at a major North American Automotive OEM.
Project background:
With the growing complexity of automotive power, control and sensor systems on today’s modern vehicles, wire and cable harnesses are the 3rd heaviest and costliest item behind the engine and chassis. Heavy components get a lot of attention from the engineering disciplines at the automotive OEM’s because every ounce adds up and the totality of lighter components significantly contributes to better overall fuel efficiency. Plus, if a component can also be smaller while being lighter, then that space savings is a prized benefit due to the ever-shrinking real estate under the pretty exterior of a new car.
The challenge:
To determine if a smaller 150°C cable could effectively replace a larger 125°C cable while still meeting the electrical power and other requirements of the application (flexibility, fluid resistance, etc.). Could it be done at a lower cost, and was the weight and cost savings enough to justify the engineering effort to prove the concept and the re-tooling needed to make it a reality in their production.
Copper conductors are sized based on many concerns. Current flow over a conductor creates heat, so the first aspect typically reviewed is the conductor size in relation to desired current draw and the temperature rating of the wire. A larger conductor has lower resistance and thus will generate less heat, and a higher temperature cable will be able to handle higher heat and not melt or otherwise become compromised.
But deeper analysis is required. Is the current flow consistent or does it fluctuate? If it fluctuates, what are the expected cycles and duration? Can a life cycle be replicated for testing? What is the ambient temperature of the end-use environment? Is it constant or does it fluctuate? Is there air flow to help dissipate the heat? If so, does the air flow change or is it consistent? What cable insulation material is used? Is there risk of melting? Out gassing? Is the cut-through resistance strong enough? What will the cable do in an overload condition? How long is the cable length? Is voltage drop a concern? These are just a few examples of many cable design considerations.
The solution:
Working together with R&D, Engineering, Operations and Sales, Champlain determined that the best insulation material to use was our EXRAD® 150 HVFX Irradiation Cross-linked polyolefin. EXRAD® HVFX offered the best balance of thermal and mechanical robustness, flexibility and fluid resistance, plus it met the ISO-6722-1 global automotive standard used by most automotive OEM’s. The incumbent cable size was 35.0mm2 so Champlain made samples of 25.0mm2 EXRAD® HVFX to use for comparison. Champlain then conducted tests to compile data on thermal resistance, ampacity charts, fuming curves, flex, cost, etc. and presented to the customer. The customer also purchased samples for their own side-by-side evaluation of the incumbent cable which included some of the same tests, but also cut-through, thermal cycling, processing (cutting and stripping) and other testing on connectorized cable assemblies. This process of sampling, testing and documentation was over two years in the making.
The Results:
The customer accepted the test results which showed that a 25.0mm2 EXRAD® 150 HVFX irradiation crosslinked power cable not only physically outperformed the incumbent 35.0mm2 chemically cross-linked cable, but also provided a significant cost and weight savings. EXRAD® HVFX was the best blend of cable size, weight, performance and price for the application.
By the numbers: Reducing from 35.0mm2 to 25.0mm2 reduced the copper weight by 30%, and reduced the cable area by 38%. Although the cost savings vs. the incumbent product was not available to us, the savings justified the associated engineering effort and tooling costs. The customer has reduced other sizes as well based on the success of this effort.