1. DC Contactor Introduction

A DC contactor is a contactor controlled by a DC coil, capable of handling both DC and AC loads. Unlike an AC contactor, the core of a DC contactor does not experience eddy currents and is typically made of round soft steel or industrial pure iron. Since the DC contactor's coil is powered by direct current, there is no inrush current during start-up, and the core does not experience violent impacts, resulting in a longer lifespan. This makes DC contactors ideal for applications with frequent starting and stopping. Heisener, a leading online electronic parts and components supplier, offers a wide range of clamping diodes to meet the diverse needs of electronic circuit designers.

2. Working Principle of DC Contactor

DC contactors control the current in a circuit based on the electromagnetic principle. When the DC coil of the contactor is energized, a magnetic field is generated, pulling the movable iron core or armature toward the fixed iron core.

This movement causes the contacts in the contactor to close. When the contactor coil is energized, the coil current generates a magnetic field, causing the static iron core to generate electromagnetic attraction to attract the moving iron core and drive the contacts to move: the normally closed contact opens and the normally open contact closes, and the two are linked. When the coil is de-energized, the electromagnetic attraction disappears, and the armature is released under the action of the release spring, causing the contacts to recover: the normally open contact opens and the normally closed contact closes.

3. DC Contactor Failures

Overcurrent fault

Overcurrent fault can be divided into acceleration, deceleration, and constant speed overcurrent. It may be caused by too short acceleration and deceleration time of the inverter, sudden change of load, uneven load distribution, output short circuit, etc. At this time, it can generally be solved by extending the acceleration and deceleration time, reducing sudden change of load, adding energy-consuming braking elements, designing load distribution, and checking the line. If the inverter still has an overcurrent fault after disconnecting the load, it means that the inverter circuit of the inverter is broken and the inverter needs to be replaced.

Overload fault

Overload fault includes frequency conversion overload and motor overload. It may be caused by too short acceleration time, too low grid voltage, and too heavy load. It can generally be solved by extending acceleration time, extending braking time, checking grid voltage, etc. The load is too heavy, the selected motor and inverter cannot drag the load, and it may also be caused by poor mechanical lubrication. In the former case, a high-power motor and inverter must be replaced; in the latter case, the production machinery must be repaired.

4. How to Select the Right DC Contactor?

When selecting a contactor, several important factors should be considered:

Rated Voltage of Main Contacts: The rated voltage of the main contacts should be equal to or greater than the rated voltage of the load.

Rated Current of Main Contacts: The rated current of the main contacts should be at least 1.3 times the rated current of the load.

Rated Voltage of Coil: For simple circuits with fewer electrical devices, a coil voltage of 220V or 380V can be used. For more complex circuits or locations with a higher number of devices or safety concerns, choose a coil voltage of 36V, 110V, or 127V.

Number and Type of Contacts: The number and type of contacts should meet the requirements of the control circuit.

Operating Frequency: If the circuit has a high current or the frequency of operation (number of on/off cycles per hour) exceeds the specified value, select a contactor with a higher rated current. Failing to do so can cause contacts to overheat severely, potentially welding them together and causing phase loss in motors or other loads.