What is the function of a contactor? Although there are many different types of contactors on the market, their overall function is the same. Today, let’s take the high voltage DC contactor as an example to explain it further.
What is a high voltage DC contactor?
A high voltage DC contactor is a circuit switch with protective functions, primarily used in electric vehicles, charging stations, and energy storage systems to enable the safe connection and disconnection of high-voltage circuits. As electric vehicles continue to evolve and become mainstream in the automotive market, one of their core components—the power battery pack (PACK)—has also matured significantly. As a key electrical component within the power battery PACK, the performance of the high voltage DC contactor directly affects the vehicle’s fundamental operation and electrical safety.
In the electrical circuit of a power battery PACK, high voltage DC contactors serve the fundamental functions of carrying the operating current and isolating voltage and current. In the event of a vehicle fault, the contactor plays a critical role in cutting off the fault current to ensure personnel safety. Major manufacturers are continuously upgrading the materials and manufacturing processes of high voltage DC contactors to enhance their current withstand and breaking capabilities, thereby extending their electrical lifespan.
👉 Learn what a high-voltage DC contactor is? Check out this article.
Types of High Voltage DC Contactors
The biggest difference between high voltage DC contactors and traditional AC contactors lies in their use of specialized sealing technology. The contact points are enclosed within a sealed chamber, isolated from external air, to achieve higher voltage withstand capability. This design makes them particularly suitable for switching various DC loads in the power industry.
Take the Porsche Taycan, which uses an 800V high-voltage platform, as an example. This model is equipped with eight high voltage DC contactors—including three main contactors, two pre-charge contactors, and three high voltage load contactors—one to two more than traditional 400V models.
Internal Working Principle of High Voltage DC Contactor
This is another article explaining the working principle of a DC contactor.
Precautions
In an electric vehicle’s power system, a high voltage DC contactor must reliably break current in the main circuit. Unlike AC systems where arcs naturally extinguish at the zero-crossing point of the sine wave, DC arcs require additional arc suppression techniques. When interrupting a high voltage DC circuit, the contactor generates a persistent arc across the contacts. If not extinguished quickly, this high-temperature, high-voltage arc can lead to contact welding, arc leakage, or even explosive failure of the contactor. Therefore, effective arc suppression is vital to ensure system safety and contactor longevity.
Beyond the contactor’s internal magnetic blowout structure, the contact separation speed is also critical. Faster separation stretches and cools the arc more efficiently, making it easier to extinguish. However, when a flyback diode (also known as a freewheeling diode) is used in the coil circuit to protect against voltage spikes, it slows down current decay in the coil. This can reduce contact break speed, negatively impacting arc suppression and shortening the electrical life of the contactor.
The flyback diode plays an essential protective role. When the contactor coil is de-energized, it suppresses the inductive kickback voltage caused by the coil’s inductance, preventing damage to sensitive control components. It’s important to note that there are two common wiring configurations for high voltage DC contactors on the market—non-polarized and polarized. Polarized contactors include an internal flyback diode and must be wired with the correct polarity; incorrect connections can result in permanent damage.
BSB’s BSBC7 series contactors offer an optional PWM economizer circuit, which includes a built-in reverse surge absorption circuit, eliminating the need for external surge protection devices. This enhances system protection while maintaining high-speed contact response for better arc suppression.