Relays are electrically operated switching devices, used to gain control over processes and circuits. Based on their principle of operation they are classified into two types: Solid-state relays and electromechanical relays. In this article let us discuss each one of them, their differences and similarities.
Comparison of electromechanical and solid-state relays
|In these relays, electromechanical force is generated by the relay coil on the application of voltage. This force pulls the armature and closes the relay contacts
|SSRs do not have electromagnet or any moving contacts in it. Instead, it consists of semiconductors and optocouplers within. When a voltage is applied to the input section of the SSR, current flows through the optocoupler and triggers the TRIAC at the output section, and the TRIAC starts conducting.
|An electromechanical relay consists of the following parts:
1. Electromagnetic coil
|A Solid-state relay consists of the following sections:
1. Input circuit
3. Output driver circuits
4. Semiconductor switching devices.
|An electromechanical relay uses physical contacts for switching.
|An SSR uses semiconductor devices such as TRIAC, Thyristors, MOSFETs and transistors.
|Relay contacts gets eroded during prolonged switching.
|SSRs do not have mechanical contacts.
|Heat generated by these relay are little and can be neglected.
|Semiconductors inside the SSR generated large amount of heat. Therefore heat sinks are required for heat dissipation.
|These relays produces noise while switching.
|No switching noise.
|Fluctuations in coil voltage causes chattering of contacts in an electromagnetic relays.
|No chattering due to the absence of mechanical contacts.
|On-load switching of relay contacts can result in arc formation.
|No arch formation.
|The inductance of electromagnetic coil may cause voltage surges while switching.
|No risk of voltage surges in solid-state relays.
|Electromechanical relays has a life time of few million mechanical switching.
|SSR lasts longer than electromechanical relays.