What is DC Contactor? Comprehensive Principle and Application

DC contactor acts as a switching mechanism in electrical systems. This way, you can enjoy complete control over the current within DC circuits.

Features of Contactors

What is DC Contactor

Figure 1 DC Contactors

Dustproof

The housing that holds the electrical contactor components within renders it dustproof. It does not allow a single dust particle to get inside. This facilitates the smooth turning on and off of your circuit.

Support Wide Temperature Range

You can install your DC Contactor anywhere you want. In high-temperature industrial or commercial vicinities. It can cope with the temperature ranging from -250C to 550C. Higher temperature does not affect the functioning or physical appearance.

High-Quality Materials

The materials that go into making the contactor are of high quality. Whether it is the outer frame or body or the components inside, they strictly align with the industrial standards and even surpass them when it comes to operation.

Rustproof

The higher humidity working support makes the contactor worth it. It can withstand humidity from 5% up to 95%. Rusting or corrosion phenomena cannot degrade the appearance and performance.

Types of Contactors for DC Switching

Certain types and forms exist for DC Switching. Uncover the facts on key type right below:

WHATS IS CONTACTOR?

By Design

The Contactor types based on design are:

Knife Blade

Knife blade DC Contactors have existed for a long time. These contractors mainly comprise a lever and a strip. Their actions result in an up and down movement.

This way, it facilitates the actual operation. Certain things have contributed to the end of its wide usability. Some major limitations include:

  1. Shorter service life
  2. No Safety
  3. Zero protection against dust or moisture
  4. Dual Breakage

DC Contactor knife blade

Figure 2 DC contactor knife blade

Manual

As the name reflects, you can use this DC contactor manually. It would help if you did this manually whenever you wanted to turn the circuit off or on. Although some things are better than the knife blade DC Contactor. Some of the plus points are:

  1. Added safety
  2. Ensure complete protection of inner components
  3. Compact form
  4. Offer higher current, especially in small spacing

Manual Contactor 25A 4P

Figure 3 Manual DC contactor

DC Magnetic Contactor

This type of DC contactor needs electromagnetic force to carry out the circuit off and on the operation. The current activates the magnets, which then switch the circuit on. No current means no dc contact functioning.

DC magnetic contactor

Figure 4 DC magnetic contactor

 Key notables of DC Magnetic contactor are:

  1. Automatic working, no manual or human force required
  2. High safety provision
  3. Negligible control current requirement for the effective operation

By Voltage

DC Contactor has the following categories on a voltage basis:

12v DC Contactor

The 12V DC Contactor comprises 1 pole. These contractors are suitable for coping with the 150 amperes of current. For instance, you can use them in engineering machinery, telecommunication systems, electronic control switches, and auto-electric winches.

BMC7-16 2P DC Modular Contactor

Figure 5 12v DC contactor

 With this contactor, you can judge the load, carry out smooth operations, and change the rotational direction.

DC Contactor 24V

24V DC Contactor, in general, comprises two poles. You can use them in applications requiring 300 amperes. Various household and commercial accessories require the usage of this 24V DC Contactor.

BMC7-16 4P DC Modular Contactor

Figure 6 24v DC contactor

DC Contactor 48V

The 48V DC Contactor, in general, comprises four poles. You can effectively control the circuits that are 120 Volts. With these contractors, you can completely control the slight inductive or non-inductive load types.

BMC7-25 4P DC Modular Contactor

Figure 7 48v DC contactor

These contractors benefit from railway applications, lighting, electric appliances, etc.

220v DC Contactor

The 220V DC Contactor mainly consists of 3 poles. It can offer support to accessories requiring up to 220 volts. Options exist to use them in 3-phase motors, isolation, charging stations, capacitor switching, etc.

BMC7-32 4P DC Modular Contactor

Figure 8 220v DC contactor

You can ensure the functioning and operation of bigger accessories on the go.

By the Number of Poles

On the pole basis, the DC Contactor has the following divisions:

Single Pole DC Contactor

The term single pole in single pole DC Contactor refers to a contactor comprising only one pole. It is highly applicable when you only need to deal with a single phase. Household accessories mainly employ this type of DC Contactor.

2 Pole DC Contactor

In 2 poles DC Contactor, you can use it where you need to deal with the two phases. Commercial places require the use of this DC Contactor widely. It can deal with 120 volts at ease. You can interrupt the dual phase instantly when you use a 2-pole DC Contactor.

DC vs. AC Contactors

Key items for your consideration are:

Structural

When de-magnetizing DC contactor, it produces an electromagnetic force. It does this through the utilization of a free-flowing diode. In AC Contactors, there is no diode exist. Rather it makes use of coils to power the equipment.

Principles

As the name reflects, AC Contactors uses AC. Usually, they have an iron core, which produces eddy currents and hysteresis loss. A lamination on the iron core prevents this from happening.

DC Contactors have no association with lamination. This is because the DC contactor faces no eddy current formation or depletion. Cast iron or steel goes into their manufacturing entirely.

Material used for Plating

To prevent contact plates from overheating, you will use a special coating with silicon steel.  While no such plating or lamination you need in DC Contactors.

Shape of the Iron Core

Cutting off the power in the AC circuit does not make the loop current zero. This contributes to the attraction and driving of the armature when open. On the other hand, in DC Contactors, you will not experience heating or eddy currents. This leads you to utilize entire metal in their construction.

Operating Frequency

In AC contactors, the operating frequency is always 600x per hour. Of course, this happens with a higher starting current.

However, when it comes to the DC design, the frequency is 1200x per hour.

Electrical Resistivity

The number of turns in the AC contactor is very few, with greater diameter and negligible resistance. It features a cylindrical shape to avoid heating, and there is a distance between them to facilitate heat escape.

In DC contactors, as there is no place for heat formation, it utilizes a thinner coil with maximum turns. Therefore they feature greater resistance. The thin coil formation results in better heat dissipation.

Room Requirement

AC Contactor does not have enough room requirement. You can place it anywhere you want if the place offers enough installation space.

This is not true regarding DC Contractors, and you need to ensure sufficient space for effective operation.

Extinguisher

Usually, the AC contactors come equipped with grid extinguisher. DC Contactors possess magnetic extinguishers within.

How to Choose Contactors for DC Switching

To make a suitable selection, you need to consider the following notables:

Current Inductance

The current inductance has a direct impact on overall breaking capacity. When induction occurs, the voltage rises, increasing the arc intensity. This contributes to the higher breaking capacity. For example, if the value of induction decreases from 15ms up to 1 ms, the ability for breakage increases by 300 percent.

Application Type

The application type helps you select the right contactor. If you need one pole or two pole contactor? The contactor you are going to buy can meet the load requirement. As there is one phase, two phases or three phase system exist. Each system requires a respective DC Contactor. For homepage applications, single or dual-phase contractors are good. While for the commercial and industrial sectors, the two or three-phase contactor is highly suitable.

Service Life

Several factors contribute to and decide the life of your DC Contactor. The service life directly relates to the application for which you are subjecting your DC Contactor. Mechanical application features no switching under load, while electrical application feature load switchings. For instance, in railway applications, the contactor may require to withstand more than 1 lac switching cycles. Therefore it is essential to choose a contractor with effective service life.

Maintenance Requirement

This point is crucial. Consider what maintenance requirements you need to follow if you can cope with the particular maintenance requirement you get with DC Contactor. In most cases, people don’t have enough time to perform the maintenance measures.

Direction of Operation for DC Contactor

It offer a dual operation functionality. The DC Contactor operates in a single order and can only cut off the current connection in one direction. On the other hand, the bi-directional DC Contactor can disconnect the current in both directions. Consider this while choosing your DC Contactor.

Main Components Of The DC Contactor

DC Contactor’s main parts are here for your reference:

1. Electromagnet/Coil

The source of the driving force within the DC contactor is the coil. The coil is present in the form of winding on a magnetic core. It mainly plays its part as an electromagnet. The coil comprises two components. One is movable, and the other remains fix. A spring is present on the movable portion.

The armature (rod) connects the moving parts. For a contact to occur, the force from the coil must exceed the spring’s tensional force.

On the other hand/vice versa, the disconnect takes place.

2. Contacts

The contacts carry current. Three kinds of contacts are present within the contactor:

  • Power contact
  • Auxiliary contact
  • Contact spring

The material that goes into the manufacturing of the contacts must have the following traits:

  • Superb arc resistance
  • Higher welding resistance
  • Resist Mechanical stress
  • High erosion resistance

The preferred material for low current application includes a mixture of silver cadmium and silver nickel. On the other hand, the higher existing applications require silver tin oxide as key composition material.

3. Body/Frame

The main role of the body/frame is to provide effective housing or closure to the internal components. It ensures protection from dust, dirt, oil, moisture, weathering conditions, explosion, etc. The body acts as a barrier and prevents direct contact.

components of DC contactor

Figure 9 Components of DC contactor

How does Contactor for DC Switching Work?

What is a Contactor? | Working Principles

The contactor for DC switching works in the following manner:

First, the current passes from the main circuit up to the contactor. This plays its part in magnetic core excitation.

As a result, the magnetic field produces by the electromagnet/coil. This starts armature motion and closes the contact.

Later the current start moving through contacts up to the load. On the other hand, when there is no current in the circuit, de-energization occurs. This represents zero magnetic forces. Doing so, the troops on the spring increase and draw the armature backward, causing the circuit to open. This way, the subsequent turning OFF and ON takes place.

DC Contactor working principle

Figure 10 DC Contactor working principle

DC Contactors Vs. Relays

A Plethora of differences exists when it comes to DC Contactors and Relays. Some of the key differences that you should note include:

  1. The load-bearing capacity of the DC Contactors is much more in comparison to the relays. You cannot use the relay for more than 15 amperes of load. While contractors serve higher loads anywhere 150A, 300A, 600A, etc.
  2. DC Contactors come in a single configuration, so they always remain open. Whenever they experience a current, they switch it on. This is not the case with the relays. They come in dual configurations, including the NC and NO.
  3. Regarding protection, the relay cannot compete with the DC Contactors. They ensure complete safety and security in case of a cut-off. This is what makes them worth it to high-power applications.
  4. The weight of the contactor is far more than the Relays because they can cope with higher power requirements. The switching speed of the contactor is slower when you compare them to relays. You will experience more cost with the contractors because of more turns (consume higher power).

Relay

Figure 11 Relay

Common Causes of Failure in Contactors for DC Switching

Many things contribute to the failure of your DC Contactor. Some of the key reasons include:

Overcurrent

When the current exceeds the desired limit, it damages your contactor components. You can also experience a short circuit.

Temperature Boost

The higher temperature causes the internal components to change their physical appearance or form. This, in the end, adversely affects the overall functioning of the DC Contactor.

Improper Installation

Improper installation means poor connection to the poles or terminals. This will prevent the DC Contactor from performing at its peak potential. It will also end up in quick failure.

Aging

Another factor that causes the failure of your DC Contactor is aging. Due to sufficient usage, the product has performed to its fill and has no more capacity to continue functioning. This causes your DC Contactor to fail.

Fluctuating Voltage

The successive rise and fall in the voltage contribute to the damaging effect on key contactor components. This renders the DC contactor failure.

High Current DC Contactor vs. High Voltage DC Contactor

A higher current DC Contactor is highly suitable when switching high currents. The current can be anywhere from 100A up to 600A. For instance, 100A DC Contactor. The applications of high-current devices include welders, power supplies, transistors, superconductors, etc. Please note where the current is high, the voltage will be lower and vice versa.

When the end purpose is to switch the high voltage, then you can employ a high-voltage DC Contactor. For instance, 1000V DC Contactor. The applications for high voltage DC Contactor include electrospinning, medical imaging, electron beam generation, water treatment, etc.

DC Contactor Wiring Diagram

The actual wiring diagram of the DC Contactor is as follows for your consideration:

Applications

You can utilize the DC Contactor in multiple fields. Some of the key areas for DC Contactor include:

DC Drive Contactors

These DC Contactors are truly beneficial when it comes to driving systems. Especially the system whose speed is adjustable. You can say a DC motor or other driving system.

DC Switching Contactor

A wide variety of applications exist when it comes to DC Switching Contactor. Some applications are electric loads, lighting, capacitor banks, thermal evaporation systems, etc.

Solid state DC contactor

The name derives as these contractors do not contain any moving component within. Instead, they make use of electronic parts and semiconductors. The key applications are DC motors, water pumps, heater control, etc.

DC Air break contactor

It is beneficial when it comes to switching higher currents. The key applications include ventilation systems, air conditioning, evaporators, etc.

Electric vehicle DC contactor

The key function of the electric vehicle DC Contactor is to switch off or on the power lines within the car. It is highly desirable in electric and hybrid vehicles.

Quick FAQs

1. Why does DC Contactor fail?

As mentioned above, the key failure reasons are:

  • High Current
  • Bad Installation
  • Wrong DC Connector selection
  • Harsh operating conditions
  • Higher temperature fluctuations

2. Does the load affect the DC Contactor capacity?

Yes, the load has a great influence on the overall capacity of the DC Contactor.

Each DC Contactor can bear a particular load. Exceeding the parameters will lead to the failure of your DC Contactor.

Conclusion

You now have in-depth insights on working, types, benefits, components, selection considerations, applications, and more about DC Contactors. This information will help you make the best selection or deal with DC Contactor effectively.

Enjoy complete protection and safety with a DC Contactor in your electric network system today. Please share your thoughts in the comment section or seek assistance by emailing us. We would love to help you out.