Direct current (DC) contactors are electrical devices used in various industries to control and switch direct current electrical circuits. These products are engineered to handle the unique characteristics of DC power, which maintains a steady flow and consistent voltage level.
DC contactors are particularly great for the EV market because of their ability to carry high currents and voltages.
How DC Contactors Work
DC contactors serve as electrical switches that are used to control the flow of current in a circuit by opening and closing a circuit path. These switches are turned on by applying an operating voltage across two external contacts. This energizes an internal coil, creating a magnetic field that attracts or repels an internal connecting contact. This results in the function of an electromechanical switch.
Why DC Contactors Fit the EV Market
- Ability to Handle High Currents & Voltages: DC contactors are built to switch very high currents and voltages. They can carry more than 500 Amps and are rated upwards of 2,000 Volts. In order to achieve this, there are several unique design features built into these DC contactors. For example, the housings are built out of resin or ceramic and hermetically sealed. Inert gasses, such as hydrogen, fill the inside arc chamber. This helps prevent oxidation, helps quench arc current, and keeps resistance low and stable. The IP67 sealed housings keep the gasses inside and prevent arc leakage, thus proving to be a great safety feature as well.
- The Magnetic Arc Blow-Out Feature: Another feature is known as magnetic arc blow-out. Permanent magnets inside the arc chamber create a magnetic field across the contacts, driving and stretching the arc current outward, helping to extinguish it faster. Arc current is created when contacts are opened and not good for the contacts, so these magnets in combination with the gas help increase the life of the contactor.
- The Coil Economizer: The coil economizer is a feature that reduces coil power and heating after the contactor is energized. It takes a great deal of power to close the switch of these powerful contactors, but once closed there is not much needed to keep it closed. So electronics such as PWM (pulse width modulation) help reduce this power and heat as well.
EV Applications for DC Contactors
Contactors can find a home in a variety of areas in the EV world. Applications for high voltage DC contactors in the EV space include charge and pre-charge contactors, main and auxiliary power contactors, battery disconnect units, charging stations, battery packs, and energy storage systems.
What to Keep in Mind When Designing-In DC Contactors
- Rated Insulation Voltage & Operating Current: When choosing a contactor it is first important to define the application requirements, considering the rated insulation voltage and rated operating current. Problems may arise when specifying the current as it is dependent on the contact resistance, material, input voltage, and contact force. When properly specified, depending on the operating conditions, the actual current value can deviate without damage being expected.
- Inductance of the Circuit: In addition, the inductance of the circuit is important as it can influence the breaking capacity. There should also be considerations for the risk of a short circuit. If the DC contactor is not appropriately matched to the main fuse then damage to the contactor may occur.
- Service Life Requirements: Finally, the service life requirements depend on the application. Certain contactors provide specialized capabilities for the automotive/battery industries, offering no-load switching cycles. On the other hand, for industrial applications, they are designed to handle switching cycles under defined loads.
Chief & DC Contactors
Chief is Altran Magnetics’ value-added distributor. We offer design-in services, pigtails, kits, and custom mounting solutions to bring your program to market fast. For more information about DC Contactors and how Chief can help mitigate your design challenges, please contact us or shop DC Contactors on our web store.