What is a DC Contactor?

Previously, we have discussed contactor, mainly focusing on AC contactor. Today, let's delve into DC contactor and understand the key differences between AC contactor and DC contactor.

contactor - Crucial Safety Barriers in the New Energy Industry

A DC contactor is an electrical device used to control the current flow in a DC circuit. Unlike AC contactor, DC contactor need to address the issue of arc extinction in DC circuits. DC contactor typically consist of one or more contacts, which can be controlled to make or break the circuit either through electromagnetic force or manual mechanisms. When in the closed position, current can freely flow through the contacts, while in the open position, the current flow is interrupted.

Composition of DC Contactor

DC contactor mainly consist of three parts: the electromagnetic system, the contact system, and the arc extinguishing device.

The electromagnetic system of a DC contactor comprises a core, coil, and armature, often adopting a plunger-type structure with angular movement.

DC contactor have main and auxiliary contacts.

The arc extinguishing device of DC contactor extinguishes the arc by stretching and cooling it. Due to the absence of zero crossing in DC arcs, extinguishing DC arcs is more difficult compared to AC arcs, often resulting in strong arcs that can damage contacts and cause delayed disconnection. Therefore, the arc extinguishing device in DC contactor is generally more complex than that in AC contactors.

Principle of DC Contactor

When the coil of the contactor is energized, it generates a magnetic field, attracting the armature via electromagnetic force, thus causing the contact action. The normally closed contact opens, and the normally open contact closes, both in a linked manner. When the coil is de-energized, the electromagnetic force disappears, and the armature releases under the action of a release spring, restoring the contacts to their original positions.

Differences Between AC contactor and DC contactor

DC contactor typically have higher insulation strength because the current in DC circuits cannot easily change, thus requiring better insulation measures.

AC contactor can use simple iron-core coils to generate a magnetic field since AC current continuously changes direction, eliminating the need for strong insulation measures.

The main differences between AC and DC contactor are as follows:

1).Different control objects:

AC contactor mainly control AC electrical equipment, while DC contactor primarily control DC electrical equipment.

2).Different core structures:

The coil of an AC contactor carries AC, leading to eddy current and hysteresis losses in the core during operation. To reduce eddy current losses, the core of AC contactor is made of insulated silicon steel laminations and is often E-shaped. The coil of a DC contactor carries DC, so there are no eddy current and hysteresis losses in the core during normal operation, and the core does not heat up. The core of DC contactor can be made of solid cast iron or cast steel and is often U-shaped. To eliminate the vibration and noise generated by the electromagnetic attraction, AC contactor embed short-circuit rings on the end faces of the static core, while DC contactor do not use short-circuit rings.

3).Different arc extinguishing systems:

AC contactor use arc-splitting devices to break long arcs into short arcs, while DC contactor use magnetic blowout devices to stretch and cool the arc. This is because DC arcs do not cross zero, making it much more difficult to extinguish DC arcs than AC arcs, often resulting in strong arcs that can burn contacts and cause delayed disconnection. Therefore, the arc extinguishing device in DC contactor is generally more complex than that in AC contactors.

4).Different coil turns:

The coil of AC contactor has fewer turns, lower resistance, and less copper loss, while the coil of DC contactor has more turns, higher resistance, and more copper loss. The main component that generates heat in a contactor is the coil. To ensure good heat dissipation of the coil, it is usually wound into a long and thin cylindrical shape, with a very small gap between the coil and the core to dissipate heat with the help of the core.

Different operating frequencies:

The operating frequency of AC contactor is typically up to about 600 times/hour, while DC contactor can operate at up to 1200 times/hour.

Application of contactor in Charging Station Industry

DC Contactor:

DC contactor are one of the key components in DC charging stations. They are mainly used to control the output switch of DC charging stations, realizing the transmission and disconnection of electrical energy. DC contactor feature fast response, high reliability, and low power consumption, ensuring the safe operation of charging stations.

DC contactor are installed between the software of the battery system of electric vehicles and the inverter power supply. They act as protective devices when the system software stops operating, connecting when the system software is operational, and safely isolating the energy storage technology system software from the vehicle circuit system when the vehicle is turned off or common faults occur, effectively cutting off the power supply circuit. They are also used as power control components in other auxiliary control circuits.

AC Contactor:

AC contactor in charging stations are crucial components that connect the power supply to the vehicle charging interface. Their role is to disconnect or connect the AC power supply. When a vehicle needs to be charged, the AC power supply is connected to the vehicle charging interface via the AC contactor to supply power to the vehicle battery. After charging is completed or in case of a malfunction, the AC contactor automatically disconnects the AC power supply to ensure the safety of the charging process.

The reliability and response speed of AC contactor directly affect the charging efficiency. The shorter the time taken to connect the AC power supply during charging, the higher the efficiency, and the shorter the time taken to disconnect the AC power supply, the higher the charging efficiency.