The space constraints that characterize electric vehicle systems place special demands on connectors that must handle high power and increasing data rates.
Giorgio Potenza • Harvin
There are six main systems directly related to electric vehicle (EV) propulsion. These consist of the on-board charger (OBC), the battery pack, the battery management system (BMS) which monitors various parameters of the battery pack, the traction inverter which converts DC from the battery into AC which powers the EV’s electric motor , the engine controller, which converts driver commands into changes in engine torque, and the DC-DC converter, which steps down the battery voltage for use in functions such as lighting, climate control, infotainment, etc.
All of these systems are characterized by a thermal and vibrational environment that can resemble that of conventional motor vehicles. The potential severity of these conditions makes all the mechanical systems that support them critical elements in determining the reliability of the entire vehicle.
With this reliability in mind, consider the electrical connectors found in typical EVs. Several attributes are essential for clutches in any automotive application. First, space is limited, so connector component sizes must reflect this reality while still offering high contact density. At the same time, clutches must be able to cope with the demanding automotive environment. They must show resistance when exposed to shocks, vibrations and high temperatures. Protection against ingress of dust and moisture is also required.
Another characteristic of modern electric cars is grid dependency. This forces network hardware to reliably handle high data rates even in harsh environments. For example, a radar sensor can generate data at a rate of 15 Mbps. The lidar sensor generates 100 Mbps of data, while the camera can reach 3500 Mbps. Clearly, signal integrity is a must despite the electromagnetically noisy environment in which these connectors will operate.
In addition, connectors need mechanisms to prevent connection errors during assembly. Finally, the increasingly competitive nature of the EV business means that connectors must be competitively priced and not add much to the overall material costs.
An example of a connector already specified for EV applications is the Archer Kontrol series. These connectors are designed to perform reliably in demanding industrial applications. They are 0.05″ surface mount connectors with 1.27mm pitch with SMT solders to further relieve PCB stress and location pins for precise placement during soldering.
Several manufacturers have designed Archer Kontrol into their EV drivetrains. These highly reliable board-to-board connectors are integrated into OBCs, motor controllers and traction inverters. Vertical and horizontal orientation options allow these connectors to fit into tight spaces.
These connectors also feature a 125°C rating to withstand the heat of the drive modules and vibration resistance – they are cycle tested at 10-2000Hz, 1.5mm, 198m/sec² (20G), for 12 hours. Because they can carry 3 Gbps data rates, they can easily support an Ethernet-based network in the car. Extremely durable gold/tin plated phosphor bronze contacts are used. These sockets are housed in rugged plastic housings with a UL94V-0 flammability rating.
Archer Kontrol connectors are fully sheathed (to prevent damage) and have built-in polarization to protect against misconnection. Stack height options are from 8 to 20mm and standard cable assemblies (150 and 300mm lengths) are available, with locks added to provide strain relief.
It is interesting to look at several automotive applications that now use these connectors. In a formula student car data logging system, the challenge was to minimize weight while meeting vibration requirements. And the components had to be readily available. The team ended up using Gecko connectors (G125 series) for signal pins, which provide a low-profile, two-row connection suitable for routing and connecting cables in areas where board real estate is at a premium. The car’s power connections were via Datamate Mix-Tek connections. They handle 3 A per signal contact (all electrically charged; 3.3 A per individual contact). They have a four-finger contact design to maintain electrical contact through strong vibration and shock and use beryllium copper contacts that can withstand ranges from -55 to +125°C.
Another automotive application involved sockets for insulated metal substrate (IMS) printed circuit boards. IMS boards are made with a copper circuit layer over a thermally conductive epoxy prepreg, with an aluminum or copper base plate. The layers are kept electrically isolated (no coated vias), so standard through-board sockets are unsuitable. This type of PCB 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 an upright socket located above the PCB with a surface mount connection to the PCB. Multiple sockets are assembled to pins on a patch panel. And the connectors were supposed to make it easy to connect two boards together.
The application uses the bottom-entry Sycamore Contact, a design that features three points of contact, providing continuity and strength once available only from two-piece kits. It should be noted that Sycamore connectors are available on tape and reel, while two-piece sets are rarely available. The Sycamore Contact is a one-piece SMT socket with a low profile of only 0.43mm maximum above the PCB. Available in top and bottom entry versions, it accepts 1 or 1.5mm diameter pins and is open-ended so there is no limit to the depth of the connecting pin. Manufactured from beryllium copper, the 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, keeping the solders away from the bottom layers of the module. A plated through hole is not required, only clearance under the socket to account for the length of the terminal pin. The final assembly is easy to connect to the opposing PCBs and terminal pins, making assembly during production quick and easy. If modules are damaged during testing, new modules can be quickly replaced without any soldering or crimping problems.
There are several other EV applications worth checking out. In one case, chargers for public parking spaces required a robust construction to handle long-term exposure to environmental conditions such as heat, cold and humidity. Ease of maintenance is also a factor, as is board-to-board distance. Here the Archer Kontrol connectors were up to the task and at the correct connection height. In another EV drive system, the control boards in the inverter required board-to-board connections that were durable and could operate over a wide temperature range while being competitively priced. Archer Kontrol connectors met the demand thanks to their high temperature characteristics and vibration resistance.