25 February 2021

Solid state relay advantages and disadvantages

SSR stands for the solid-state relay, it is a relay that is a substitute for the electromagnetic relay. It referred to as an optocoupler due to its construction. It consists of a light source and a light sensor. This type of relay mainly used to provide isolation than switching high current. So here this article gives the advantages and disadvantages of the solid-state relay to better understand this topic.

Advantages of the solid-state relay:

  • Solid-state relay has a very high lifetime.
  • It is insensitive to vibration.
  • It is smaller in size.
  • SSR offers to switch time than EMR.
  • The chance of noise pollution is almost negligible due to the absence of direct contact with moving parts.
  • The output resistance remains totally constant even after they have multiple uses.
  • It offers a very fast response usually about 1 microsecond ON and 0.5 microseconds OFF.
  • It is highly durable.
  • There is no coil in the design which can introduce back EMF  into the circuitry.
  • It shows less sensitivity towards external factors like shock, vibration and magnetic field, etc.
  • Some variants can work as low as 1.5 Voltage direct current(DC), unlike electromagnetic relay which requires at least 3V DC.
  • It offers low power consumption due to fewer current requirements.
  • As there is a complete internal separation between input and output terminals, it can be used to switch high voltages.
  • SSR offers long-run use as there is no contact moving parts thus less susceptible to wear and tear of the machinery.
Disadvantages of Solid-state relay:

  • It offers non-linear voltage-current characteristics.
  • Sometimes its output exhibits a polarity-sensitive nature.
  • Sometimes voltage transients result in spurious switching.
  • There is leakage current at the output even if the relay is in OFF mode.
  • For this, relay, the gate charging circuit there exists a requirement for the isolated bias supply.
  • It is a fixed value voltage drop on output due to internal impedance. Hence it is less efficient.
  • It cost is very high.
  • It generates waste heat during On mode. This is proportional to the voltage drop.
  • It is triggered by brief voltage spikes on the input side device, unlike the electromagnetic relay.
  • It is more vulnerable to surges and also they spikes in the current which is switched on the output side, unlike the EM relay.