The electrification of propulsion systems in electric vehicles (EVs) and hybrid electric vehicles (HEVs and PHEVs) is made possible by the presence of high-voltage batteries, battery management systems (BMS), power inverters, and powerful motors. All these high-voltage components are "floating," meaning that none of their power terminals are grounded to the chassis. Consequently, all high-voltage components and high-current carrying cables must be heavily insulated. The design and manufacture of EVs—as well as the associated charging points needed to power them—therefore require specialized equipment and procedures to ensure safety. And as more EVs enter service, their maintenance, repair, and recovery will also require similar equipment and procedures.
“Electric vehicles and charging points are demanding high-voltage environments for instrumentation and test equipment,” said Robert King, product manager for Reed relays at Pickering Electronics. “Due to their compact size, high insulation, and low leakage, Reed relays are well-suited for EV and charging point test applications where both safety and measurement accuracy are critical. Their mechanical contact path can switch AC or DC while helping to minimize leakage that could otherwise affect insulation measurements.”
This guide explains that electric vehicle power cables and high-voltage components are heavily insulated to protect against short circuits with any electrically grounded element and for safety reasons (since anyone working on the vehicle is likely to also be in contact with the chassis or ground). In addition to the need to measure high voltages (DC and AC), it is necessary to confirm the integrity of the insulation around high-voltage components and cables. High-voltage and insulation testing—both during product development and once they are in service—is also required for the charging points needed as the number of electric vehicles on our roads increases.
“Therefore, there is a need to develop instruments that can safely measure high voltages and perform insulation testing at charging points, and these instruments will require switching,” King added. “Reed relays can offer leakage currents of less than 1 nA and separation voltages of several kV in compact packages. The contacts of the reed switch are hermetically sealed, which helps protect them from contamination and oxidation compared to open electromechanical contacts.”
Reed relays offer an attractive solution because:
They are hermetically sealed, keeping dust and moisture away from the contacts;
they can withstand high switching and breakover voltages
have extremely low leakage, enabling accurate detection and monitoring; they are
galvanically isolated, helping to protect instrumentation electronics;
and they are fast, compact, and capable of performing millions or even billions of operations.
