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Types of Latching Relays, Their working and Application

Electronic latching relay
Electronic latching relay
Resource: https://www.youtube.com/watch?v=CjiaPfmk2rE

Depending on your specific application, you can choose from the different types of latching relays available. In this guide, we will explore the types of relays that you can buy today, how they work and their potential applications. This will help you choose the best latching relay for your project.

Latching Relay Meaning

The term “latching” describes how a latching relay works, which is to latch and maintain a state once triggered. A latching relay, therefore, is a relay that retains its set or reset condition after the trigger is removed. This allows for the relay to remain in a closed or open state without being constantly energized.

The latching relay working makes it suitable for use in a range of electrical circuits, from the lighting systems of buildings to the electronic systems of hospitals, telecommunications firms, and so on. These relays are also installed in the metering systems of different equipment.

Different types of latching relays use different methods to accomplish their switching action, such as magnets, interlocking parts and single or double coils. These variations result in five basic designs of the latching relay, which are explained in the below section.

Mechanical latching relay
Mechanical latching relay
Resource: https://www.youtube.com/watch?v=rcA8XKtbbq4

Types of Latching Relays

The different types of latching relays are based on their latching mechanisms, the number of coils, and whether an electronic system is used to operate its working and operation. In light of that, we will discuss the following types of this device: Mechanical latching relay, magnetic latching relay, electronic latching relay, single coil latching relay, and double coil latching relay

1. Magnetic Latching Relay

The magnetic latching relay is the most common type of this device, with application in many different settings or systems. Just as its name implies, the relay uses a magnet to latch its contacts in either a closed or open state. This can be a permanent magnet or electromagnet. The magnetic latching relay operation is explained below:

Permanent Magnet Latching Relay

In a magnetic latching relay that uses a permanent magnet, the magnet pivots above a U-shaped electromagnet — and can stick to either end of the electromagnet’s core. The pivoting magnet is also connected to (and operates) the relay’s armature

  • When a trigger voltage is applied coil, the core magnetizes
  • The core then pulls the permanent magnet toward its one side
  • This closes or opens the relay’s contacts, latching them together
  • When the current is removed, the permanent magnet remains in
  • To reverse the latching directions, a reverse pulse needs to be applied
  • This is either a reverse voltage or voltage applied to a different coil

Residual Magnet Latching Relay

Another type of magnetic latching relay operates on the basis of a residual magnetic field. Although the same principle applies, the working of this relay is different from that of the permanent magnet type.

  • The relay’s core is made from a material that offers a high remanence
  • When input voltage is applied, the core attracts the armature
  • Upon removing the trigger voltage, the armature remains stuck to the core
  • This is due to the residual magnetism of the core
  • To unlatch the relay, a reverse pulse is applied. This can also be a pulse to a second coil that will cancel out the residual field

2. Mechanical Latching Relay

The mechanical latching relay does not use a magnet to latch its contacts. Instead, it relies on a physical locking mechanism. The mechanism can vary depending on the specific design, but it typically involves a ratchet gear and cam.

  • The contacts of are actuated by a lever and spring combination
  • These are, in turn connected to the locking mechanism
  • This causes the coil and core to become magnetized
  • The armature moves, causing the contacts to either open or close
  • The ratchet lock latches the new relay position until a trigger pulse is applied

The mechanical types of latching relays are not so common today and their place is largely being taken by the electronic types. Reasons for that include their bulkier construction that makes them take up more space, as well as their slower operation that makes them not suited for some applications.

3. Electronic Latching Relay

An electronic latching relay is a type of magnetic latching relay that also uses an electronic circuit consisting of semiconductor components to switch between latching states. This relay is used in applications that require a fast changeover, such as switching of power supplies.

  • The electronic latching relay uses the magnetic core and coil setup
  • When voltage is applied to the coil, the core becomes magnetized
  • This moves an armature to close or open contacts, depending on the direction
  • The armature remains attracted to the core, either by residual magnetism or a permanent magnet
  • The electronic circuitry will then, when needed, provide the pulse to unlatch the armature

Electronic latching relays are generally smaller than mechanical relays. They’re also fast acting, and easy to control from a remote location, which makes them more applicable in today’s automated electrical systems and equipment.

4. Single Coil Latching Relay

This is also called a 1-coil latching relay. As its name indicates implies, 1-coil or single coil latching relay uses only one coil to latch and unlatch its contacts. To achieve that, the relay must change the polarity of the coil current, that is, reverse the voltage applied to it. So it’s also often called a single pulse latching relay.

These types of latching relays are usually used in applications where frequent and fast switching is needed; by applying only one pulse, both a latching and an unlatching operation are performed. It also has lower power consumption than 2-coil relays since it only uses one coil.

5. Double Coil Latching Relay

This relay is also called a 2-coil or dual oil latching relay. As opposed to the single coil latching relay, dual coil relays use both a latching and an unlatching coil. The way this type of relay works is similar to that of the single coil relay but two pulses are applied, one to the latching and another to the unlatching coil.

The 2-coil latching relay can be a mechanical or electronic type. When it’s an electronic type, you get more features and capabilities, just as described earlier. These include fast action, smaller size, and ability to easily use it in complex automation systems.

Conclusion

Different types of latching relays are used in many different applications. While each type has its own unique operation, they all provide a reliable way to switch electrical contacts and control circuits with minimal energy consumption. Depending on your specific use, you may want choose from permanent magnet, residual magnet, and electronic latching relays.

William
William

I am William, Electrical Engineering Author. Dedicated to writing technical articles on Timer Relay, Monitoring Relay, Surge Protection Device and other electrical devices. With 7 years of writing experience, I am committed to providing accurate and in-depth expertise to my readers.

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