Generally, normal switches are used at present to open or close an electrical circuit manually. Similarly, a Relay is one type of electromechanical switch used for connecting or disconnecting two electrical circuits. But a relay utilizes an electrical signal for controlling an electromagnet to fix or separate another circuit. Relays are used where a particular circuit or various circuits needs to control with a low-power signal. Relays are available in different types which are used based on the application like reed relay, distance relay, solid state relay, latching relay, overload relay, delay relay, automotive relay, timer relay, differential relay, and many more. This article provides brief information on latching relay-working, different types & applications.
What is Latching Relay?
A latching relay can be defined as; a two-positional electromechanical switch used to keep its position without providing a power supply to the coil. This relay is known as an impulse, stay, or bi-stable relay. This type of relay is used wherever consumption & dissipation of power needs to limit. This relay operates remotely, manually, through impulses, or with different control inputs. A latching relay is a great choice for an electrical component or device that needs to stay in a similar condition without requiring a constant power supply. The latching relay symbol is shown below.
How Does a Latching Relay Work?
The working principle of latching relay is to open or close its contact each time whenever a mains voltage signal is supplied to the terminals of its coil. The latching relay working is similar to a standard relay; but, there is no need for a power supply continuously to keep it strengthened. As an alternative, current impulses are utilized to activate & reset the relay by allowing it to modify its condition or location.
This relay uses a low-power control signal for switching a high-power electrical load. Because it uses power only throughout the switching action, the operation of this relay ensures the least power consumption. In addition, these relays are very useful in preventing temperature increase within both the circuit & relay coil, because it doesn’t work on a stable power supply. By using this relay, you can control electrical systems very effectively & it maintains the operation even after the supply is detached or in the occurrence of a power outage without causing overheating.
Types of Latching Relay
These relays are available in three types; magnetic latching, impulse sequencing, and mechanical latching.
Magnetic Latching Relays
This kind of latching relay is used as an automatic switch to control electrical circuits automatically like other kinds of electromagnetic relays. The condition of normally open & normally closed in this relay depends completely on the performance of the permanent magnet and also the relay’s switching condition can be triggered through a width of a pulse electric signal. The magnetic latching relay has some characteristics like stable performance, power saving, availability in small sizes, superior performance & its bearing capacity is large as compared to a normal electromagnetic relay.
This relay is separated into single-phase & three-phase. This relay’s highest contact switching current can reach 150Amps; the control coil voltage can be separated into DC12V, dc9v, and many more. This relay’s everyday electrical life is 10k times, mechanical life is 1000000 times approximately & voltage drop of its contact is below 100mVolts.
This type of latching relay is mainly used within IC card prepayment meters, centralized meter reading systems & in the reactive power compensation device’s composite switch. This relay is used with the combination of thyristors & is the major switching device within reactive power compensation devices for switching large current circuits, different household appliances & lighting control systems.
Impulse Sequencing Relay
An impulse sequencing relay or bi-stable relay is used to change the state of contact with each voltage input signal. These relays have high vibration & shock resistance. This type of relay upon power application decides which location the switch is in automatically & strengthens the opposite coil to activate or move it every time. These relays are used as wear equalizers and also turn ON/OFF a single device from single or many locations through a push button or single momentary switch at every station. For instance, a conveyor is started or stopped from various locations through a single button at every position.
Mechanical Latching Relay
Latching relays use a mechanical latch otherwise a permanent magnet typically for holding the contacts in their previous energized position without using continued coil power. So, this normally occurs by energizing a secondary coil. Afterward, holding contacts will remain locked in that position until the contrary coil has attained energy. These relays are particularly helpful in applications wherever power should be saved like a device operated by a battery or wherever it is popular to have a relay reside in a single position if power is disrupted.
Since this type of relay does not rely on a magnet, the locking strength will not corrupt ultimately or be unsuccessful through thermal cycling. Thus the contacts within the relay will be locked in the directed place until the contrary coil has been energized.
Latching Relay Circuit Diagram & Working
The latching relay circuit diagram is shown below. The designing of this circuit can be done with two push buttons like B1 & B2, DC supply, and latching relay. The connections of this circuit follow as;
- First, need to connect the relay with a DC supply & B1 push-button. Here, the push button is a NO (Normally Open) switch.
- After that, the common point of the relay must be connected with the source using a push button.
- We have to connect an additional push button which is NC (normally closed) through the DC line & latching relay.
The latching relay circuit is designed with two pushbuttons like B1 & B2 where push button1 is used for making the circuit & push button2 is used for breaking the circuit. Once push button1 is pushed, then the coil of the latching relay will energize & close the contact from A to B & C to D. When the relay coil is energized & closes the connection A & B, the supply stays to continue after releasing B1. The relay coil should be de-energized for interrupting the circuit. Thus, to de-energize the relay coil, push button 2 or B2 is used.
The push button B1 is the Normally Open button whereas the push button B2 is a Normally Closed button. So, B1 is open initially & B2 is closed. To turn ON the circuit, button B1 is pressed. Once this button is pressed, the flow of current will be there throughout the A to B. So this will make the coil of the relay strengthen. Here, the contacts are connected like A to B and C to D.
Once the B1 button is released, the relay coil will be energized & flow of current will be there constantly within the circuit. For disconnecting the relay circuit, we have to de-energize the relay coil by disconnecting the current path.
The B2 push-button in the circuit is used to turn OFF the relay circuit because the B2 button is normally closed. Once we press the B2 button, then it will adjust its stage to open. So, when we push the push B2 button, it will break the current path to de-energize the relay circuit.
Latching Relay Wiring Diagram
The latching relay wiring diagram is shown below. In this wiring. The most common use of latching relay is to control lighting in homes, residential complexes, offices, etc. This relay is used to control lighting by turning ON/OFF circuits when necessary.
The main benefit of using this relay in this wiring is that it allows simply for controlling lights from different locations which is helpful for convenience because these relays consume less power throughout the switching action. The main use of this relay in lighting circuits is great energy conservation, particularly whenever a system is large enough to cause vast energy losses.
Advantages & Disadvantages
The advantages of latching relay include the following.
- Latching relays play a key role in controlling the number of lamps than contactors of a similar nominal current.
- It takes less time in connecting the devices.
- It is not an expensive device.
- These relays save crossbar switches and conductors.
- These types of relays bring high comfort of control.
- It provides quiet constant operation as compared to a similar application with contractors.
- It conserves energy because energy is required mainly to adjust from the ON state to the OFF state or the OFF state to the ON state. So, no energy is required to keep the ON state.
- It allows the control of lights from various locations.
The disadvantages of latching relays include the following.
- Latching relays need extra wiring to form a latching circuit, so it is more complex as compared to a normal relay circuit.
- These relays consume more power as compared to normal relays because they need the power to set & reset the relay.
- These relays are expensive.
- The lifespan of these relays is limited because of the latching mechanism’s mechanical nature which can exhaust eventually.
The latching relay uses or applications are discussed below.
- Latching relays are used in Industrial counting & sorting systems.
- These are used in power supplies, refrigeration, anti-condensation systems & HVAC.
- These are used in cleaning equipment of industries like automated car-washing devices.
- These relays are used in automated food preparation & commercial coffee machines.
- These relay applications range from controlling lighting systems to electric motor control.
- This is used in motor starters wherever we don’t want to push the start button constantly.
- This relay is used in nearly all load switches.
- This kind of relay is used for controlling lighting by switching circuits ON/OFF as required.
- These relays are frequently used with metering applications such as prepayment.
- Magnetic latching relays were used in early computers to store bits.
Where is the latching relay used?
The latching relay is most frequently used in lighting systems to switch on/off circuits as required in offices, homes, residential complexes, etc. to switch circuits on/off as needed.
How does a latching relay reset?
The latching relay can be reset by providing reverse voltage through a push button.
What is the difference between a latching relay and a normal relay?
A relay is a type of switch that controls circuits electromechanically whereas a latching relay is a subtype of electromagnetic or electromechanical switch and it is used wherever the operator needs to control a large amount of current flow.
Does the latching relay hold all contacts closed even after power is removed?
The latching relay holds its contacts within position after power is removed.
Thus, this is an overview of a latching relay that is used to maintain its condition once the applied voltage is detached. So that the latching relay will stay in the ON/PFF condition until it is reset manually otherwise until power is detached. These relays are frequently used in applications wherever it is significant for an electrical circuit to stay in a particular condition, or even if the power supply is lost like safety circuits, alarm systems & backup systems. Here is a question for you, what is a magnetic relay