Space constraints that characterize electric vehicle systems put special demands on connectors that must handle high power and rising data rates.
Giorgio Potenza • Harwin
There are six main systems directly associated with an electric vehicle (EV) powertrain. They consist of the onboard charger (OBC), the battery pack, the battery management system (BMS) that monitors various battery pack parameters, the traction inverter that converts dc from the battery into ac that powers the EV electric motor, the motor controller that translates driver commands into changes in the motor torque, and the dc-dc converter that steps down battery voltage for use in functions such as lighting, climate control, infotainment, and so forth.
All these systems are characterized by a heat and vibration environment that can resemble that of conventional motor vehicles. The potential severity of these conditions makes any mechanical systems supporting them critical elements in determining the reliability of the whole vehicle.
With that reliability in mind, consider the electrical connectors found in typical EVs. Several attributes are essential for connectors in any automotive application. First, space is limited, so the dimensions of the connector components must reflect this reality but still offer high contact densities. At the same time, connectors must be able to cope with the demanding automotive environment. They must exhibit resilience when exposed to shocks, vibrations, and high temperatures. Also necessary is protection against dust and moisture ingress.
Another feature of modern EVs is a reliance on networking. That forces networking hardware to handle high data rates reliably even in harsh environments. For example, a single radar sensor can generate data at a 15 Mbps rate. A lidar sensor generates 100 Mbps data while a camera can hit 3,500 Mbps. Clearly signal integrity is a must despite the electromagnetically noisy environment in which these connectors will function.
In addition, connectors need mechanisms to prevent mating errors during assembly. Finally, the increasingly competitive nature of the EV business means connectors must be competitively priced and not add much to the total bill-of-materials costs.
An example of a connector now specified for EV applications is the Archer Kontrol series. These connectors are designed to work reliably in demanding industrial applications. They are 0.05-in, 1.27-mm-pitch surface-mount connectors with SMT solder tabs for added PCB strain relief, and location pegs for accurate placement during soldering.
Several manufacturers have designed Archer Kontrol into their EV powertrains. These highly reliable board-to-board connectors have been integrated into OBCs, motor controllers, and traction inverters. Options for vertical and horizontal orientations enable these connectors to fit into tight spaces.
These connectors are also characterized by a 125°C rating to withstand the heat of powertrain modules and a resilience to vibrations—they are tested cyclically at 10-2,000 Hz, 1.5 mm, 198 m/sec² (20G), for 12 hr. Because they can carry 3 Gbps data rates, they can easily support Ethernet-based in-vehicle networking. Highly durable phosphor bronze contacts with a gold/tin finish are used. These contacts are embedded into rugged plastic housings rated to UL94V-0 against flammability.
Archer Kontrol connectors are fully shrouded (to prevent damage) and have polarization built-in to protect against mis-mating. Stacking height options are from 8 to 20 mm and off-the-shelf cable assemblies are available (in 150 and 300 mm lengths), with added latches to provide strain relief.
It is interesting to examine a few automotive applications that now use these connectors. In one formula student car data-logging system, the challenge was to minimize weight while also meeting vibration requirements. And components had to be available off-the-shelf. The team eventually used Gecko (G125 series) connectors for signal pins which provide a low-profile, dual-row interconnect, suited for stacking and cable mating in areas where PCB real estate is at a premium. Power connections on the car were via Datamate Mix-Tek connections. These handle 3 A per signal contact (all electrically loaded; 3.3 A per individual contact). They have a four-finger contact design to maintain electrical contact through high vibration and shock and employ Beryllium Copper contacts that can handle -55 to +125°C ranges.
Another automotive application involved sockets for Insulated Metal Substrate (IMS) PCBs. IMS boards are made with a copper circuit layer on thermally conductive epoxy pre-preg, with an aluminum or copper base plate. Layers are kept electrically isolated (no plated- through holes), so standard through-board sockets are unsuitable. This type of circuit board is common for applications that need heat dissipation such as EV power management modules and LED light clusters.
In the automotive application, the need was for a stand-off socket sitting above the PCB, with a surface-mount connection to the board. Multiple sockets assemble to pins on a mating panel. And the connectors had to make it easy to connect two boards together.
The application used a bottom-entry Sycamore Contact, a design that features three points of contact, providing continuity and ruggedness once only available from two-piece assemblies. A point to note is that the Sycamore connectors are available on tape and reel whereas two-piece assemblies rarely are. The Sycamore Contact is a single-part SMT socket featuring a low profile of only 0.43 mm max above the PCB. Available in top and bottom entry versions, it accepts 1 or 1.5-mm-diameter pins and is open-ended, so mating pin depth is not limited. Manufactured from Beryllium Copper, contacts are gold-plated for high conductivity and durability over a temperature range of -50 to +125°C.
In the automotive application the connector is assembled in an inverted orientation. The connection becomes an SMT PCB socket with the solder connections kept away from the lower layers of the assembly. No plated-through hole is required, just a clearance hole under the socket to allow for the length of the terminal pin. The final assembly is easy to mate with the opposing PCB and terminal pins, making subassembly during production fast and simple. If modules are damaged during testing, new modules can be quickly exchanged without any soldering or pressfit issues.
There are a couple other EV applications worth reviewing. In one case, chargers for public parking bays required a rugged design to handle long-term environmental exposure such as heat, cold and humidity. Easy maintenance also a factor as was board-to-board spacing. Here, Archer Kontrol connectors handled the task, and at the right mated height. In another EV drive system, control boards in the inverter required board-to-board connections that were durable and that could work over a wide temperature range while being priced competitively. Archer Kontrol connectors handled the need thanks to their high temperature ratings and vibration resistance.