With the growing number of electric vehicles the demand towards wire harness is becoming more challenging. High-voltage cabling is still an area where OEMs are investigating electro-thermal behavior and high-voltage components of wiring harness for hybrid and electric vehicles. In the interview with Dipl.-Ing. Christophe Holyk you will find out more about high voltage wiring harnesses and the challenges of dimensioning the components. Read the interview here: http://bit.ly/_Interview_Holyk

1. “Itis usualto say thatthe useof aluminiumcablescould allow weightand cost
reduction when thinking aboutlow-voltbattery cablesbutthis assessmentis
notalwaystrue forshielded cables.”
Automotive IQ spoke withDipl.-Ing.,Christophe Holyk about high voltage wiring harnessesand the
challengesofdimensioningthe components.Mr. Holyk also clarifiedthe pros and cons ofusing
aluminiumand discussedstandardization issuesforthe industry.
Editor’s note:At the time of this interview, Mr.Holyk wasa doctoralcandidatein the R&D department
forhigh voltagecabling at Mercedes-Benz. Currently,heis employed with Daimler.
What are you working on at MercedesBenz?
Currently, I'm doing a doctorate in engineering sciences (electrical engineering) in the R&D department
for High-Voltage cabling of Mercedes-Benz. I investigate the electro-thermal behaviour and sizing
methodsof the High-Voltage(HV) componentsforwiring-harnessesof hybridandelectricvehicles.
My research activities are focused on the dimensioning of electrical cables, connectors and fuses. I work
on the development and validation of several dimensioning models for these components by
performing simulations and experimental studies. Actually, very few dedicated design tools for
engineers on this topic are available, several dimensioning methods for such problems still exist in the
literature butneedtobe reviewedandvalidated.
The aim of my contribution is to determine the thermal-heating and current carrying capacity of these
components as a function of the operating conditions, geometry data and material properties to enable
furtherweightandcostreductionof the HV wiring-harness.
In low-volt wiring-harnesses, the size of small cross-section cables is in most cases constrained by
mechanical specifications whereas in HV wiring-harnesses the cable size is first constrained by thermal
specifications and then by mechanical specifications such as bending-radius. In the context of growing
power requirements and decreasing available space, thermal management and size optimization are
becomingthe maintopicsof researchto improve the designof HV wiring-harnesses.
You and your team also make some special tool to be able to create the wiring harnesses?
We don’t develop the design tools directly in our department. We use different tools and databases to
design the routing of cables and create wiring layouts. We are therefore very interested in their
capabilitiesandthe wayto optimize them.

2. Concerning the development of tools for the electro-thermal design of the wiring-harness, we work in
continuous cooperation with the University of the Bundeswehr in München which conducts research
activities for the development of computation methods and tools for the determination of the current-
carrying capacity of automotive cables, connectors and fuses. A representative from this University will
alsobe presentatyourconference.
There’s quite a lot of discussion around high-voltage charging systems for vehicles and obviously with
EVs and hybrid electric vehicles, high-voltage solutions are important. Why are high-voltage wiring
harnesses particularly important for these vehicles? What are the most challenging aspects you’ve
experienced?
In EVs and hybrid electric vehicles, the HV-components are generally distributed over the entire vehicle
and thusthe HV wiring-harnesstakesamajorrole to connectand supplythemwithelectrical energy.
One challenging aspect is the routing of the wiring-harness over the car. The HV-components have to
be positioned in the vehicle depending on available space and chosen power-train architecture. Then,
the possibilities for the cable routings are limited and the designer has to follow several specifications,
rules and standards concerning a wide range of domains such as: mechanical, thermal, Electromagnetic
Compatibility…In additiontothat,manufacturingcostandmaintenance mustalsobe considered.
So you understand this step is quite difficult to discuss in details. Concerning the topic where I am
involved, dealing with the thermal modelling, simulation and measurement of wiring-harnesses, the
determination of the operating conditions in the vehicle is the main challenge. (e.g. current,
temperature,heat-radiation,andheat-convection)
Especially in hybrid vehicles, the range of ambient temperature over the motor compartment and the
vehicle substructure is wide. To perform a proper dimensioning it is needed to assume realistic
scenarios of operation to check the thermal behaviour of the wiring-harness. This is achieved through
the definition of electrical load profiles and area of ambient temperature along the routing paths, which
are then use to compute the temperature over time and space of the components of the wiring-
harnesses. The definition of the cross-relation between ambient conditions, load profiles and power-
traincapabilitiesisthe greatestchallengeforperformingaproperdimensioning.
So some of the challenges then are with packaging in needing to be able to curve around some of the
things that are in the engine and also the thermal management issues. In that case, are there any
material preferencesthatyou have to manage that challenge,andalso the voltage drops?
Cables in HV wiring-harnesses are generally made of copper conductor insulated with a silicon sheath.
Silicon material allows long-time operation of the cable up to 180 °C and enables to transmit the
required electrical energy despite the wide range of temperature existing in vehicle. In addition to that,
this material has the advantage of allowing short-time overload without causing prior aging of the
insulation sheath. Other insulation materials still exist and might be also used depending on the
applicationrequirements.
Copper is chosen as conductor material because it has a lower resistivity than aluminium. Basically, the
resistance of the conductor has to remain low to limit voltage drops and power losses in the HV wiring-
harness.
It is usual to say that the use of aluminium cables could allow weight and cost reduction when thinking
about low-volt battery cables but this assessment is not always true for shielded cables. In the case of