Difference between electromechanical relays and solid-state relays

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.

Difference between electromechanical relay and SSR

Electromechanical relaysSolid-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 contactsSSRs 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
2. Armature
3. Contacts
A Solid-state relay consists of the following sections:
1. Input circuit
2. Optocoupler
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.
Electromagnetic relay
Electromechanical Relay
Constructoin of solid state relay
Solid-State Relay – SSR
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