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DPDT switch

Double Pole Double Throw DPDT Relay

The DPDT relay (Double Pole Double Throw) is quite interesting and can be used in various scenarious, including for changing the direction of a motor as you can see in the picture below. It has 2 terminals and 4 connectors and you can look at the DPDT relay as the equivalent of 2 Single Pole Double Throw SPDT relays.

Change motor direction with DPDT relay

change motor direction with DPDT relay

As you can see in the schematic the 12V battery (or use other voltages) is connected with the plus at terminal T1 and minus at terminal T2. The contact 1 and 4 are connected together as 2 and 3 are too.

Without voltage applied to the coil the battery plus is connected to contact 1 (and 4) and minus to 3 (and 2) therefore the motor is turning in one direction (let’s say clockwise). When voltage is applied to the coil then the relay switches and now T1 (plus) is connected to contact 2 (and 3) and T2 (minus) is connected to 4 (and 1) therefore the motor is changing the direction of rotation.

Switch between 2 different Loads with DPDT switch

DPDT relay

In this second application we can use the DPDT switch to choose between 2 different load and have a visual indication of what load is connected. In our case (figure 1) when there is no voltage applied to the coil the fan and green LED are turned ON . When we apply voltage to the coil (figure 2) the relay switches its contacts and now the light buld and red LED are turned ON.

 

Related product: Electromechanical Relay

6 Comments

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  • AKP678

    What is the use of Transistor in Double Pole double Throw relay? what will happen if it is not used?

  • V.Sambath kumar

    Hi Marian,

    Very good article good idea.

    Regards V.Sambathkumar.

  • Alun Jones

    Appreciated article – well explained.

  • Mike Miller

    I have a door that I want to open and close with a 12 volt arduino solar relay. It gives a 12+ voltage from one terminal for Light and 12+ voltage from a different terminal when Dark.

    I have a mechanical DPDT switch that works now but would like to replace the mechanical with a relay. Do you have a DPDT relay that has no normally closed or open but is controlled or toggled by a pulse plus voltage on two different terminals?

    Thanks, Mike Miller

    • V.Sambath kumar

      Hi Mike Miller,

      Here is a simple circuit i designed for you using 2 nos dual contact
      relays and 2 nos scrs. check my attachment .

      Good Luck,

      Regards
      V.Sambathkumar.

  • Gort Newton

    Nice article, explains things well.

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