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What is SPDT relay ? everything explained


Relay is an electronic control component, usually used in automatic control circuit. It is actually a “circuit breaker” that uses a smaller current to control a larger current, so it plays a role in automatic regulation, safety protection, and conversion circuits.In this article today we will introduce one of the relays-SPDT relay.

What is a DPST relay?

A switch with a single input and two remarkably dissimilar outputs is known as an SPDT or single pole double throw switch. The two dissimilar or unlike circuits are controlled by using a SPDT switch by a similar single input. It can be operated manually or by an electromagnetic coil. Double Pole Single Throw is also known as DPST. It is used to switch 2 different loads. It can also be used as equivalent to two SPST switches which are NO and NC namely ‘normally open’ and ‘normally closed’. When a voltage is applied NO DPST connects 2 loads whereas a NC DPST relay disconnects the two loads when voltage is applied.

What is relay SPDT type?

Single Pole Double Throw relays are referred to as SPDT relays. SPDT relays are those that have a single set of Form C, break before make or transfer connections. A common terminal is attached to one of the other two in an SPDT relay. But at the same time, they never connect to both of the terminals. The relay has five connections in total, with two of those connections being for the coil.

Where is SPDT relay used?

The SPDT relay is mostly used in the electric motors, high voltage switches such as parking lights, horns and headlights are also controlled by a SPDT relay. Low-power electronic circuits were employed to manage high-power applications with the help of SPDT relay. It is also used in LED series and parallel series.

What is the difference between SPST and SPDT relay?

A SPST relay has only one pole and one throw. The product has a single on position, which regulates one. In contrast, an SPDT relay has a single pole and two throws. One is regarded as ordinarily open (NO) and the other as generally closed based on the pole’s default position (NC) in a SPDT relay. The switch may be an On-On or On-Off-On kind.

How does a SPDT relay work?

A SPDT relay operates switches by making one common pole to the other two poles. Assume an SPDT relay that has a common pole of “C” and separate poles of “A” and “B.” When the coil is not electrified or active, the common pole “C” attached to the pole “A” (NC) s in the resting state.

Since the coil is not being supplied with DC voltage, the terminal T is connected to Contact 1, enabling current to flow through Fan 1 but not Fan 2.When terminal T is now connected to contact 2 and DC voltage is delivered to the coil, the current no longer flows via fan 1 but rather through fan 2 which can also be seen as below.

How do you test a SPDT relay?

The simplest way to check if either SPDT relay work or not is to use a multimeter. Then set the multimeter to ohms and measure the resistance by rubbing the leads against the magnetic coil pins. If the values which it returns are between 50 and 120 ohms, then it means that the relay is working fine. A poor magnetic coil winding and the need for a new relay are indicated by being out of range or open.

How many pins does a SPDT relay have?

The five pins on an SPDT relay are identical to those on a DPST relay. They both look the same from outside. The coil ends that are stored inside the relay are represented by two pins A and B. A little rod on which the coil is wrapped is magnetized whenever electricity flows through it. The NC (Normally Connected) pin is always connected to the COM/POLE.

How many terminals are in SPDT relay?

A SPDT relay consists of 5 terminal points namely NC, NO, COIL, COIL and COM.
How-many-terminals-are-in-SPDT-relay● NC
This switch is generally off. To turn on the relay while it is not getting power, you must connect the device to this terminal.

● NO
This is normally open switch. You attach the gadget to this terminal so that it will be powered by the relay when it is activated.

This is the coil’s beginning.

This is the switch’s opposite end. In order to power the coils, voltage is provided to these terminals.

It is the common of the relay. If the switch is closed and the relay is turned on, COM and NO are in continuity. COM and NC are connected if the switch is open and the relay is off. You must connect the initial component of your circuit to this relay terminal.

Which terminal of a SPDT relay is the normally open terminal?

The normally open terminal in the SPDT relay is the NO terminal. When the relay receives the required voltage, the output will be located there and turn on. When the voltage is insufficient or null, output will be open and no voltage will be received.

What is 4 channel 5V SPDT relay module?

What-is-4-channel-5V-SPDT-relay-moduleIt has the ability to switch up to 4 circuits with the help of digital signals from microcontroller. Each relay may be connected for both NO Normally Open and NC Normally Closed operation and operates similarly to an SPDT.

What is 12V SPDT relay?

The term “12V DC Relay Single Pole Double Throw” (SPDT) switch refers to a switch with a single input that may be switched between the two outputs and linked to. It is generally controlled by a magnetic coil; multipurpose relays are electromechanical switches.


This SPDT relay article should have allayed your doubts and perhaps even taught you something new. On the IBE website, you may read more articles about electronic components, access information about PCB and PCBA.

If you are looking for component manufacturers and PCB assembly manufacturers, then IBE is a good choice for you. IBE is a one-stop PCBA manufacturer and provide all the service from PCB fabrication, PCB design, electronic components procurement, DIP/SMT and packaging, which will greatly save you time and costs.

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