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Solid State Relay Advantages Applications and Updates

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Solid State Relays Advantages vs. Electro-Mechanical Relays and Load Contactors

   Architecture differences between solid state relays vs. electromechanical relays provides the basis for why a Solid State Relays are a better choice in many applications than an Electro-Mechanical Relays. VB Controls’ solid state relays and solid state contactors will be used as the norm for this comparison. Solid State Contactors and Industrial Solid State Relays are sufficiently similar to refer to both as Solid State Relays.

Solid State Relay Architecture

   A solid state relay can be divided into sections; Control input, isolation, trigger or drive, solid state switched output, and output noise suppression.  All of the components in Solid State Relays use electronics with no moving parts, hence the title Solid State. Solid state relays must be selected for AC or DC control input and AC or DC switched output. Solid State Relay Control Inputs have a wide voltage range with small current draw and Solid sate relay Isolation is optically-coupled, with no reliance on magnetic fields.  AC solid state relays have a trigger circuit that delays the Control Input to synchronize Turn-On to the next zero crossing of the AC line. AC Solid state relays use SCR technology, which transition to the Off-State only when the AC line current drops to zero. Thus, AC Solid State Relays change output state at the AC line’s lowest energy points. Next, AC solid state relays have a snubber circuit to suppress electrical noise on the AC line. VB Controls’ DC solid state relays have a DC to DC converter to power up the Drive Circuit and use a MOSFET or IGBT device for output switching. DC Solid state relays change output state almost immediately after the control input.

Electromechanical Relay Architecture

   An Electro-Mechanical Relays or Contactors can be broken up into its components: magnetic coil, fixed output contact(s), and mobile contact(s) on an armature with spring return. Since Electro-Mechanical Relays have moving parts its more prone to fail and it also creates arcing. When sufficient current flows through the coil, the coil’s magnetic field moves armature which physically breaks or makes connection between the moving contacts and the fixed contacts into the “energized” state. Each relay coil is made to draw sufficient current at a fixed voltage. When coil voltage is removed, there is a flyback or magnetic reversal which helps the return spring move the contacts back to their “normal” state. Many of these devices use mercury to extend contact life. Electromechanical relays and electromechanical contactors are simply referred to as electromechanical in this comparison. This comparision continues on the bottom of our home page.

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