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Shows how a DC motor can be operated using a relay. The operator can start the motor by pressing the Normally Open (NO) pushbutton and stop the motor by pressing the Normally Closed (NC) pushbutton.
This circuit uses a Relay to switch the motor ON/OFF. A Relay is an electro-mechanical switch that can be toggled by energizing its Coil. While a voltage is applied to the Relay Coil, the Relay Switch will change position. As soon as the Coil Voltage is removed, the switch will return to its initial position.
One useful trick for wiring relay circuits is using the Relay switch to Latch on the coil after the NO pushbutton is no longer pressed. This enables the motor to be switched on and stay on. The NC pushbutton then acts as a stop button as it is placed in between the relay switch and coil. This breaks the circuit and stops the motor power supply.
Lastly, the diodes within the circuit have been used to stop back EMF within the circuit. Without the diodes, the circuit operates in a similar way. However, as the motor is stopping, it temporarily becomes a generator. It's generated back EMF is fed backwards into the circuit and causes problems.
Real hard wired control systems consist of several Relays that are interconnected and work together to operate several devices simultaneously. These types of systems are still widely used. However, are being replaced by industrial PLC controllers as they are easier to work with and maintain.
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