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How does a DPDT Relay Work?

Author: Apogeeweb
Date: 27 May 2022
dc motor



Ⅰ Types of Relay

    1.1 What is a SPDT Relay

    1.2 What is a DPDT Relay

    1.3 The Symbol of DPDT Relay

Ⅱ 12V SPDT Type Relay

Ⅲ SPDT type Relay Pins Configuration

Ⅳ How does a DPDT Relay Work?

Ⅴ How to Connect DPDT Relays in the Circuit

Ⅵ Uses of a DPDT Relay

Ⅶ How to Connect a DPDT Relay in a Circuit



A relay is a switch that is controlled by an electrical circuit. It has a sequence of input and control signals because it is a circuit. It operates by receiving an input signal from connected input power sources that function as normal switches. This article will show you how to wire dpdt relays in a circuit. It will also assist you in comprehending how the dpdt relay operates and its applications.

Quick DPDT relay component introduction and demonstration

 Types of Relay

Electrical Relay Switches of many varieties are available on the market.

  1. SPST – Single Pole Single Throw
  2. DPST – Double Pole Single Throw
  3. SPDT – Single Pole Double Throw
  4. DPDT – Double Pole Double Throw

However, the most commonly utilized Relays are SPDT Relays and DPDT Relays, both of which function as electromechanical switches.

1.1 What is a SPDT Relay

A single pole double throw (SPDT) relay has two coil terminals and a common terminal, followed by two switching terminals N/O (Normally Open), N/C (Normally Closed) (Normally Close)


If there is insufficient DC supply in the coil terminals, the relay displays the idle situation, which is represented by the common terminal attached to the N/C terminal. When the coil receives the needed DC supply, it becomes magnetically energized, and the magnetic flux force attracts the common terminal lever, which is composed of iron and connects to the N/O terminal, causing the N/C to open.

1.2 What is a DPDT Relay

A dpdt relay is an electromagnetic device used in electric motors. It is also known as a Double(D) Pole(P) Double(D) Throw(T) relay. There are two inputs to a dpdt. Furthermore, each piece of data has two outputs.

This DPDT Relay has two coil terminals, two independent common terminals C1, and C2, and two Normally Open (N/O1, N/O2), and two Normally Close (N/C1, N/C2) terminals. It makes two different connections and controls the coil with a single control signal.


If there is no bias at the coil, the relay remains in an idle state, with common terminals connected to N/C terminals. When DC bias arrives at the coil, it magnetically energizes and attracts common terminal levers, forming a connection between common terminals and N/O terminals. The N/C terminals now become open and work with their pairs.

1.3 The Symbol of DPDT Relay


Let's look at the DPDT Relay connection diagram to better comprehend its operation.


The coil of the relay is connected to a battery series with a switch designated S1 in this diagram. Two distinct circuits are linked by two distinct input and output pairs. Battery1, LED1, and LED2 make up Circuit 1. Circuit 2 is made up of batteries 2, LED 3, and LED 4.

When switch S1 is turned off, the relay's coil is not energized, so LED2 and LED4 are turned on since they are linked to NC terminals, but LED1 and LED3 are turned off.

When the switch S1 is turned on, the coil of the relay is activated, which turns off the LED2, and LED4, and turns on the LED1, and LED3.

DPDT relays are found in sophisticated electronic circuits and gadgets.

The DPDT relay is highly intriguing and may be utilized in a variety of scenarios, including altering the direction of a motor, as seen in the illustration below. It has two terminals and four connectors, and it is equivalent to two Single Pole Double Throw SPDT relays.

 12V SPDT Type Relay


This is a 12V SPDT relay (Single Pole and Double Throw). Normally, I utilize these types of relays to manage alternating current loads. The specifications for the relay are displayed on the top. This relay can be controlled using 12VDC, which is the voltage utilized to energize the relay coil. This voltage is fully isolated from the voltage supplied to the relay's Common and typically closed or normally open contacts.

It can handle AC load currents of up to 7Amps at 250VAC, 10A AC loads at 125VAC, and 12A AC loads at 120VAC. This relay can also manage DC loads with a voltage of up to 28VDC and a current of up to 10Amps.

 SPDT type Relay Pins Configuration

Even if you use a 5v Relay, the pin configuration of these sorts of relays is the same.


This relay has a total of 5 pins or contacts, with 3 on one side and 2 on the other. The center of the three contacts on the left side is the common contact, while the other two are coil contacts. On the right, there are two contacts, NC and NO. The normally closed contact is NC, and the normally open contact is NO. The coil connections are electrically insulated from the Common, Normally Closed, and Normally Open contacts. In other words, no physical connection exists between the coil contacts and the other relay connections.

Connect 12V and GND to the coils relay coil connections to test this relay. Because the relay coil has no polarity, it makes no difference whether the side of the coil is connected to the 12VDC and which side is connected to the GND.

 How does a DPDT Relay Work?

When manual switching is unavailable, a relay-insulated coil automatically flips changeover switches. As a result, it functions as a control circuit. When electricity is applied, relays frequently use components that resemble transistors to carry the electrical loads. However, there is a type known as electromechanical relays. These relays are simple to understand.

The relays use low voltage to convert the electromagnet into a magnetic field. It also contains a contact switch for controlling the magnetic circuit. When the maintained course is within the magnetic field, the relay mostly operates as if a button is flipped with the contacts in place.

Because of the operating principles of a household switch, it will always remain in the state you left it. If you turn it on, it will remain on until you turn it off, and vice versa. A relay coil, on the other hand, operates differently since its basic activities need electromagnetic actions. The electrical switches are relaxed when the magnet present is in a field during deactivation. It says that if the current ratings are off, the external circuit will switch on; else, the device would fail.

A dpdt relay is a type of relay with two poles. As a result, this double pole can toggle the circuit on both sides. Furthermore, the dpdt has a double throw. Because of the double-throw, the course may simply switch between wires rather than just control output by turning it on and off using electric power systems.

 How to Connect DPDT Relays in the Circuit

A dpdt is an electromagnetic relay that contains a solenoid wrapped in an insulated wire coil. This device features some connections as well as a reasonably moveable iron armature motion. It also has a magnetic flux of a low reluctance path that is emitted by an iron yoke. Not to mention the standard circuit conditions it possesses.

 Change the direction of a motor with a dpdt relay.


 (Circuits that explain the operation of a dpdt relay in a motor.)

We're using a 12v battery and various contact sets based on the circuit design's printed circuit board. Similarly, any continuous power battery can be used in the relay coil connection. We also link the contacts in parallel. The power source's positive end will be connected to the T1 terminal, while the negative end will be connected to the T2 terminal. We also have DPDT contacts 1 and 4 connected, as well as DPDT auxiliary contact sets 2 and 3.

When no trigger voltage is applied to the single coil, the positive end of the battery is connected to T1. This will then be related to contact 1. Furthermore, the opposing end will connect to T2 and make contact with 2. These contacts that link to T1 are known as positive-guided contacts. It causes that motor to rotate clockwise.

When we provide trigger voltage to the single-coil, the automotive relay switches automatically. As a result, the contacts in the circuit track alter, resulting in contact resistance. T1 from the battery's +Ve terminal connects to contact 2, whereas T2 from the negative terminal connects to contact 4. As a result, the motor's rotational orientation is reversed anticlockwise.


(battery icon showing the positive and negative ends.)

Switch between 2 different loads using dpdt switches.


(circuits that explain the switch between two different loads)

The coil terminals link to a fan from the first circuit's contactor coil, as well as green and red LED lamps. The lighting loads are the bulbs. The green LED and fan turn on when no direct current is provided to the coil form. When a current is applied to the coil, as in circuit 2, the coil current switches the relays. As a result, the red LED and light bulb are turned on.

 Uses of a DPDT Relay

Used to separate two electronic circuits in an industrial motor starter. Then, in the presence of a magnetic field, it magnetically joins them.

When the electronic switch is relaxed, we utilize them in electronic gadgets as well. This connects electronic circuits that use a low contact currently to others that use a larger contact current.


an electric motor

 How to Connect a DPDT Relay in a Circuit

Terminal Pins

A Double Pole Double Throw Relay comes with 8 terminal points.

The terminals are COIL, COIL, COM, COM, NO, NO, NC, NC.


This correlates to the following in the relay:


Terminal Descriptions

  • COIL- The COILterminal is located here. These are the terminals to which you apply voltage in order to power the coils (which then will close the switch). Polarity is irrelevant. One side receives positive voltage, while the other receives negative voltage. It makes no difference which order you use. Polarity is only important when using a diode.
  • NO- This is a switch that is normally open. When the relay is energized, meaning when the COIL receives adequate voltage, this is the terminal to which you connect the device that you want the relay to power. When the relay is not powered, the device linked to NO will be turned off, and when the relay is powered, it will turn on.
  • NC- The Normally Closed Switch is what it sounds like. When the relay does not receive power, connect this terminal to the device you want to power. When the relay is not powered, the device linked to NC will be on and will turn off when the relay is powered.
  • COM- This is the relay's common. COM and NO have continuity if the relay is powered and the switch is closed. COM and NC have continuity if the relay is not energized and the switch is open. This is the relay terminal to which you connect the initial part of your circuit.

Now that we understand what each terminal pin represents, we can connect it to a circuit and use it to perform a real-world operation. To light up LEDs, we'll connect a Double pole double throw relay to a circuit. When the relay is not turned on, both the red LED and the DC fan illuminate. When the relay is turned on, the red LED and fan switch off, and the green LED and DC motor turn on.

This is the circuit below:


Because the relay is rated for 12 volts, it must be powered on using 12 volts. It may function with a lower voltage, but 12V is the minimum it should receive. This connects to the COIL terminals on either side. Even if you switched the power supply's positive and negative voltages, it should still work.

The relay's COM terminals are connected to the first half of the circuit. This terminal can be left open if there is no first part of the circuit. In this scenario, the 5-volt power supply and the 9-volt power supply are used to power the LEDs, as well as the DC fan and DC motor.

Even when the relay is not energized, the NC terminals receive power. This means that as long as the 5-volt power source is turned on, the red LED and DC fan will be activated.

Only when the relay is energized do the NO terminals receive power. When the relay receives 12 volts of power, it switches from the NC to the NO position. The red LED and DC fan has now been turned off, and the green LED and DC motor has begun to work.


A dpdt relay is widely used in electronic devices. It regulates the circuit to ensure that no current is wasted.

We hope that this article shed some light on the dpdt relay. If you enjoyed it, please read more of our articles. Please contact us if you have any more questions!

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