The Steps To Selecting The Relay You Need

Designing electrical and electronic systems and subsystems, either for a dedicated system or for production, is equal parts art and engineering. The creativity leading up to the engineering is arguably the fun part. But the engineering of your system or subsystem is what makes your product or system function, perform well, and do what it’s supposed to do throughout its design lifetime. That’s why engineering is critical.

This criticality reaches down to the selection of components and how they fit – either stand-alone or on a manufactured board. Attention to the specifications of individual components is crucial to product performance, lifecycle, and safety. Selection of a component that carries out a simple function, and has been around forever, is no less crucial, as is the case with relays. Choosing or operating a relay outside of its specifications can not only lead to product or systems failure, but also to serious safety considerations for operator personnel.

With each of the two basic types of relays available: electromechanical (EMR) and solid state (SSR), you go through a related qualification process. For SSRs, however, the number of steps is a bit longer.

When selecting either an EMR or an SSR, the initial steps include:

  1. Identify the mounting type. Do you need a panel mount for a stationary electrical system, DIN Rail for an equipment rail inside an enclosure, Plug-in for ease of replacement, or PCB for ease of manufacture?
  2. Next you need to identify the required load voltage rating and type. What is the maximum voltage to be switched (AC or DC)?
  3. Third step is to identify the required load current rating, including the average load current, (current that the system is drawing over a period of time), and the surge (or in-rush) current, which is the maximum current draw of a device when first powered-on (or any sudden rise in current for a short period of time above rated or normal value).
  4. Decide on the required control voltage and type. Either AC or DC and the control voltage range.

Steps 1 through 4 above are the same whether you are planning on using an EMR or an SSR. The final step to take if you are using an EMR, is:

  1. Identify the required circuit/switching arrangement. Decide on the number of poles or circuits to be switched, and whether it is a normally open, normally closed or changeover switching configuration.

Once you’ve determined the parameters of the device needed, you can identify an EMR that matches your maximum load range, maximum surge current, load type, control voltage, type and mounting requirements.

Now, if you plan on using an SSR, you’ll need to follow two additional steps, which include:

  1. Identify the load type. Decide between an inductive (Random Turn-on SSR), or a resistive (Zero Crossing SSR).
  2. Identify the type of SSR required for your application. Decide between standard, or special application: phase angle control, burst fire control, or soft start capability.

Once you’ve decided on these additional parameters for the SSR you need, you can identify one that matches your maximum load voltage, maximum surge current, load type, control voltage, type and mounting requirements.

At this point, for an application using an SSR, you will also have to determine the amount of heat that needs to be dissipated from the device and select a suitable thermal management solution to make sure the parameters of the device are not affected by heat build-up from resistance.

Keeping these steps in mind can help you navigate the process of selecting a relay for your design. You can make the process even easier by reaching out for assistance to the qualified technical personnel at a professional franchised distributor.