Solid State Relay

In the previous posts we have discussed the use of relays in an electrical circuit. Now it is time to have a look at a relay with no moving contacts; the Solid State Relay. As with all the components you intend using, you need to make sure that you match the equipment to the switching capability, load and frequency of switching

Before we look at where we would use the Solid State Relay, let’s spend a bit of time looking at how it works.

As mentioned before, the Solid State Relay has no moving contacts. Solid State Relays uses semiconductor switching elements, such as thyristor, triacs, diodes, and transistors. The other very interesting thing is that they use optical semiconductors, called photo-couplers, to isolate input and output signals. Photo-couplers change electric signals into optical signals and relay these signals through space, thus fully isolating the input and output sections. This all happens at very high speed.
The fact that it switches without the use of moving contacts means that you can expect a much longer life from them and there is no risk of welding contacts.

With the advances made with these relays, you have a wide variety of choice which ranges from very small units with an integrated heat sink to the traditional relay that you need to mount on a heat sink. Consult your supplier to establish which unit would suit your application the best.

So, in which applications would you opt for a Solid State Relay?

  • The first consideration is the Load. These relays can switch high current loads. Make sure you select a suitably rated unit. When you are going to turn electric heating elements on and off, avoid using a contactor. The Solid State Relay will be far better suited to this application
  • Number of switching operations. Let’s say you have a solenoid that will be turning on and off up to 20 times per minute. The conventional relay will work but will fail given the duty it is performing. Again, this is where I would recommend the use of a Solid State Relay

These are just two applications but you will soon see how effective these units are and how you can incorporate them into your circuits. Sometimes I get asked which brand I would recommend but I believe you should work with the brand you prefer. There are a number of brands available and most of them are very good, so it really comes down to personal choice for me.

If you want me to expand a bit more on the actual operation of Solid State Relays, please feel free to send me an email or leave a comment. That brings us back to the last bit of the post namely:

Think Safe, Work Safe and be Proud of what you do