The latching relay is — most often — the better choice for controlling electrical functions, especially when power consumption must be kept to a minimum. What are the reasons for that and how do latching relays work? We will explain this and more in this article, so let’s begin.
What is a Latching Relay?
A latching relay is simply a type of switching relay that keeps its last condition or position, even after the activating signal has been removed. In other words, it remains either “On” or “Off” without the power supply. That’s why it’s called a latching relay; its position latches in once activated.
As you can easily tell, the latching relay switch is a great choice when you require an electrical device or component to remain in the same condition without needing a continuous power supply. These include remote control systems, industrial automation, communication, and applications that involve power equipment.
Owing to its memory switching action (stays in the last position) and pulse operation, the latching relay goes by several other names. These include the following:
- Memory relay
- Bi-stable relay
- Stay relay
- Impulse relay
Latching Relay Diagram
The latching relay diagram above shows the parts and electrical connections of the relay. As you can see, the typical latching relay uses a mechanism consisting of an electromagnet, an armature, spring and a set of contacts.
The relay’s activating current flows through the coil, as shown, which sets up a magnetic field. This, in turn, moves the armature to make or break the contacts. More about the latching relay working later. For now, let’s see its purpose in an electrical system.
Latching Relay Function
The main latching relay function is to allow the use of a low-power control signal to switch a high-power electrical load. Because it also only uses power during the switching action, the latching relay operation ensures minimal power consumption.
Additionally, latching relays are used to prevent a rise of temperature in both the relay coil and circuit. This is because it doesn’t operate on a constant power supply like other relays do.
So, with the latching relay switch, you can effectively control electrical systems and have the relay maintain the operation even after the power supply is removed or in the event of an outage—all this without causing overheating or excessive power consumption.
How Does a Latching Relay Work?
The latching relay operation is basically the same as that of a standard relay; however, there is no need for a continuous power supply to keep it energized. Instead, current impulses are used to trigger and reset the relay, allowing it to change its state or position. Here is how a latching relay works in more detail:
Latching Relay working Principle
A latching relay working is based on one of these three common mechanisms: mechanical latching, permanent magnet, and residual magnetism.
- Mechanical latching: a mechanical latching relay uses a ratchet-cam mechanism to provide the locking action, in addition to a coil and armature set up.
The ratchet and cam are connected to the armature. When an electrical current is introduced, the ratchet and cam moves to lock the contact in position until another trigger pulse is applied.
- Permanent magnet: these types of latching relays use a permanent magnet to provide the locking action. The magnet rests atop a U-shaped core and coil. Upon energizing the coil, the magnet is attracted (and sticks) to one end of the core.
The magnet then remains in this position until another pulse is applied, either to a second coil or as a reverse of the initial pulse.
- Residual magnetism: this latching relay switch has a coil and armature/contact, but no permanent magnet. It relies on residual magnetism to keep the contact in either an open or closed position after it has been energized.
This works due to the fact that the magnetic field created by the current passing through the coil will remain until there is an opposing force to reverse it. To remove the residual magnetism, a reverse pulse is applied.
Latching Relay Circuit
The latching relay circuit is relatively simple and consists of a power supply, the latching relay switch, and the system to be controlled. When the switch is turned on, current is sent through the relay which then energizes its coil.
The work of the latching relay circuit is to enable the switching on/off of a system. Note that the latching relay connection can basic, with only a few components, or complex and involving a complex, industrial automation system.
What is a Latching relay Used For?
For many applications, the latching relay is an invaluable device, enabling the switching of circuits from a remote location, as well as the ability to maintain a state in which a circuit will remain either on or off even after power loss. Some common latching relay applications include:
- Automatic counting and metering systems
- Lighting control systems
- Industrial process automation
- Safety interlock systems
- HVAC and air conditioning controls
- Telecommunication switching networks
The application of latching relays in place of regular mechanical switches helps to reduce the number of operations required, as well as to increase reliability and lower power consumption. Latching relay applications also eliminate the need for 3-way switches, for example, or cross-bar switches. In general, their use offers these advantages:
- Reduced power consumption
- Low heat generation
- Simplified switching circuits with fewer components
- Fast operation and reliability even in a power outage
Latching Relay Price
If you’re looking to buy latching relay units for your system or business, you most likely have a budget in mind. But how do you tell how much you’re likely to spend? Knowing the approximate price range of latching relays can help you narrow down your options and make right decisions.
The latching relay price will largely depend on their size, power rating, number of contacts, and brand. Smaller relays may cost anywhere from $20 to $50, while higher-powered units can be much more expensive. The price of latching relays also varies depending on the number of special features.
For large orders, you may be able to negotiate a lower price with your supplier. When buying in bulk, contact manufacturers directly to inquire about their discounts and other specials. Most often, companies will offer discounted prices for larger purchases.
The latching relay is a great choice for applications that require a continual switching action without needing a constant power supply. By understanding how latching relays work and the advantages they offer, you can determine if this type of relay is right for your system; because, as we have seen in this article, latching relays offer a range of benefits for many applications.