DC Motor direction control by two relay H bridge

DC Motor direction control

Small size permanent magnet  dc motor have two armature winding terminal for connection. Normally they are connected to positive and negative of dc supply and motor start in one direction. To change the direction it needs to interchange both wire. This is manual way of changing direction. To control motor with push button or joy stick it requires to use two relays contacts in H bridge configuration. Further we can use solid state IC based H bridge for controlling dc motor. It can also be interfaced with micro controller.

In H bridge configuration we use two relays R1 and R2 which have minimum of two change over contacts. Change over contact have three point ie 1 Common 2 NO contact and  3 NC contact normally it is shown on body of relay which terminal no is connected to which point. All relays have two point normally marked as a and b for coil connection. Relay comes in different ac and dc coil voltage. Relay may also have different no of contacts with different current and voltage rating. The voltage and current rating is to be selected as per load requrement. Coil voltage is selected as per control circuit voltage. Here we will use 12 volt coil. Conection of 12 v supply and motor is as shown in diagram.

Positive of battery is connected to NO contacts of relay R1 and relay R2. Negative of battery is connected to NC contact of relay R1 and relay R2. Motor positive is connected to common of relay R1. Negative of motor is connected to common of relay R2. These four contacts and motor in the circuit form a shape of english later H thats why it is known as H bridge configuration. We use two push button to give supply to relay R1 and R2. When push button 1 is pressed relay R1 picks up. Hence positive supply goes to positive of motor through NO contact of relay R1 and negative supply goes to nagative of motor with NC contact of  relay R2 and motor start running in forward direction. Similarly when push button 2 is pressed relay R2 picks up. Hence positive supply goes to negative terminal of motor through NO contact of relay R2 and negative supply goes to positive terminal of motor throgh NC contact of relay R1 and motor start running in reverse direction. Motor remains stopped when button are not pressed.

The circuit given below can also be used if you have set of 2 NO contact in relay. This circuit can be used for double the voltage than circuit given above..

If you feel any doubt pls ask in comment. thanks for visiting.


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