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Pnp npn1/14/2024 It is a purely electronic device There are no moving parts in this relay type because the mechanical contacts are replaced by power transistors, thyristors or triac’s.Ībsence of any movable part makes the relay highly reliable, long lasting and reduced electromagnetic interference. The solid-state relay has no moving parts. To overcome the difficulty of this relay, another type of relay called solid state relay was developed. Also, they are electrically noisy with the contacts suffering from contact bounce that might affect the electrical circuit to which they are connected. This results in an open circuit condition and no circuit current flows through the relay.Īfter some time, the moving parts of electrochemical relay will wear out and fail or the constant arcing and erosion may make the relay unusable. As soon as the contacts are open, the resistance between the contacts becomes very high. Relay contacts are constructed using conductive pieces which allows the current to pass through them when comes in contact. Ex- Never attempt to supply a 10A load with two relay contacts in parallel that have 5A contact ratings each. One important point to remember about using electrical relays is that “It is not advisable to connect relay contacts in parallel to handle higher load currents”. Note: These terms “Normally Open” and “Normally Closed “or Make and Break Contacts refer to the state of the electrical contacts when the relay coil is “de-energized”, i.e., no supply voltage connected to the relay coil. This voltage is capable enough to damage any semiconductor device such as a transistor, FET or micro-controller used to operate the relay. The induced reverse voltage value is very high as compared to the switching voltage. This is due to collision of magnetic flux with the coil. When the current is turned “OFF” in the coil, a large back emf voltage is produced. The relay coil is generally made from coils of wire.Īs the current flows through the coil, the self-induced magnetic field is generated around it. The biggest problem with relay coils is that they are “highly inductive loads”. These magnetic fluxes are used to mechanically operate the relays contacts. This coil converts electrical current into an electromagnetic flux. One of the more important parts of any electrical relay is the coil. In normally “ON” position the switch contacts are pulled towards the inductive coil. Now, in the normally “open” position, the contacts are closed only when the field current is “ON”. One pair of contacts is called Normally Open (NO) or make contacts and another set which are called Normally Closed (NC) or break contacts. Relays are configured in two modes namely “Normally Open”, or “Normally Closed”.
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