DC Contactor vs AC Contactor: All You Need to Know 

If you frequently use electrical equipment, you may already be familiar with power contactors. They are electrical appliances with the capacity to activate or deactivate electrical circuits using a unique relay. Power contactors are classified into two types based on their applications, features, and capabilities. Compared to switches, power contactors are used for applications requiring higher current flows and frequently have multiple contacts, such as electric motors. 

Power contactors are primarily divided into two types based on their applications, features, and capabilities: AC Contactors and DC Contactors. 

Even though they both have the same goal, they differ in a number of ways. Let’s look at both of them. 

Common Grounds

If you frequently use electrical equipment, you may already be familiar with AC and DC power contactors. They are electrical appliances with the capacity to activate or deactivate electrical circuits using a unique relay. 

Compared to switches, these power contactors are used for applications requiring larger current flows and frequently have several contacts, such as electric motors.

In terms of functionality, the contactor is used to isolate, cut off, or draw in the electrical circuit. In terms of contacts, AC and DC contactors are essentially identical, but different coil designs and voltages are employed.

Differences: DC Contactor vs AC Contactor

Below are the key differences based on the various specifications between DC and AC contractors. 

Structure

When the coil is de-energized, the DC contactor uses a free-flowing diode to release the electromagnetic force that has accumulated in the inductance. 

The free-wheel diode structure is not utilized by the AC contactor. Instead, it makes use of shade coils to keep the power in the equipment running effectively and laminated iron cores to stop heat loss.

Principles

The AC contactor operates on alternate current principles and has an iron core, which causes eddy current and hysteresis loss. The iron core is laminated with silicon steel plates to prevent this.

DC contactors do not require such lamination to compensate for loss because there is no generation or depletion of eddy current. As a result, DC contactors can be made entirely of cast steel or iron.

Plating Material

In order to avoid overheating, AC contactors must also have silicon steel plating. Direct current does not generate heat, so the iron core in DC contactors does not require this lamination.

Iron Core Shape

When the power supply current is zero, the induced current of the short-circuit loop cannot be zero. Its magnetic current attracts the armature pair, overcoming the armature’s release tendency and ensuring that the armature is always driven when it is opened. 

Because the short-circuit ring greatly reduces noise and vibration, it is also known as the vibration absorbing ring. Because the iron core in the DC contactor coil does not generate eddy currents and does not have a heating problem, the iron core can be entirely cast steel or cast iron, usually u-shaped.

Operating Frequency

The maximum operating frequency of the AC contactor is approximately 600 times per hour, and the starting current is very large. The DC contactor can operate at a maximum frequency of 1200 times per hour.

Electrical Resistance

The coil of an AC contactor has few turns and low resistance, but it also generates heat, so it is usually made into a thicker, shorter cylindrical shape. To keep the coil from burning, there is a gap that allows heat to escape. Because the DC circuit‘s coil has no inductance, the number of turns is large, as is the resistance and copper loss. To maintain good heat dissipation, the coil is usually made into a thin cylindrical shape.

The Number of Coils

Both AC and DC contactors can be distinguished based on the number of coils. The DC contactor has more coils than the AC contactor, which has fewer coils. Two-phase winding coils should be used in series by the contactor if the primary loop current is too high (i.e., greater than 250A). Despite the DC relay’s enormous coil reactance, its low or even negligible current power consumption.

Ample Clearance

A shading coil on the AC contactor distinguishes this device from other AC contactors by allowing the device to be placed almost anywhere as long as there is room for operation. During the assembly process, there must be enough clearance around the DC contactor to ensure proper operation.

Built-in Extinguishers

AC Contactors have grid extinguishers; DC contactors have magnetic extinguishers within them. 

Emergency Replacement

AC contactors can be used in place of AC contactors during emergencies. But the duration of the action is limited to two hours (because the heat dissipation performance of the AC coil is worse than that of the DC coil, which depends on the structure of the AC coil). It is best to connect the resistor in series with the AC coil if you need to use it for an extended period of time. The AC contactor, on the other hand, cannot take the place of the DC contactor.

Current and Hysteresis Loss

The iron core of the AC contactor is what causes hysteresis loss and current loss. To reduce current and hysteresis loss and stop the iron core from overheating, the iron core is combined with a silicon steel sheet, and its magnetic field is modified. As a result, the AC contactor’s iron core is typical of the e-type. 

The electromagnetic coil generates an alternating current driving force on the armature when alternating current flows through it. Both the magnetic current in the coil and the actuation force on the armature are zero when the alternating current is zero.

As per Faraday’s law of electromagnetic induction, an emf is also induced in the armature core of DC contactors when it rotates in the magnetic field. Despite the tiny produced emf, the body experiences a substantial current flow as a result of the core’s low resistance. Eddy current is the name of this current. Eddy current loss is the name for the power loss brought on by this current. 

Why DC and AC Contactors Cannot Be Substituted for One Another?

Provided that the rating of the AC contactor is at least 5 times or preferably 6 times than that of the DC contactor. This is primarily due to the DC voltage and its current’s steady-state nature. 

DC is typically used for transmission at lower voltage levels, levels that are common, and very high levels. You can check these items from the leading supplier. 

Conclusion

Knowing the key distinctions between an AC contactor and a DC contactor will help you choose more easily which one you need.

Contactors are essential devices for circuit control and have additional safety features. As with any electrical device, it is critical to find one that meets your needs and functions properly. You also want more design and utility options, as well as professional support. These factors assist you in identifying a suitable gadget that promotes safety and provides good value for money.

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