White Paper: Automotive

High-Performance Starter Contactor Design


Shifts in the vehicle market are forcing changes in internal combustion engine (ICE) starting technology. Most substantively, the advent of start/stop engine technology requires a much longer operating life for the starting system components. This is a challenge for the high-current contactor. In this device, the contacts are subjected to arcing on both closure and opening, causing contact wear, and distributing arcing-related debris into the unit. As a result, the contacts have a limited lifetime. As the starting current is increased, the lifetime of the contacts is dramatically reduced.

Starting current is highest immediately upon closure. This inrush current peak can be more than five times the steady state current during the start sequence. This is true even in the smaller-displacement ICEs that are becoming more common and will predominate in the future. The trend in ICE technology is toward lower displacement and higher performance. This has resulted in higher-compression engines that are oversquare (bore is larger than stroke). Both conditions can potentially raise the required starting torque. Another market driver that unintentionally raises the inrush current is the move to lightweighting. This industry shift has resulted in changes to the configuration of the starting systems to remove excess cable length and reduce the overall resistance of the starting circuit outside of the motor.

A customer approached TLX with a requirement for a starter contactor needing the following key characteristics:

  • 950A inrush handling

  • 175A steady state current handling

  • 30,000 cycle durability

  • 1m/5-minute water immersion survival

  • Replace an incumbent part weighing 120g

Their original part failed at inrush currents above 600A and had no immersion protection. That piece utilized a copper contact system, and the high-risk failure mode of contact welding was realized during early testing with the actual vehicle powertrain. TLX undertook the development of an improved contactor to meet the key requirements while maintaining a minimum part mass.

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