Are electromechanical relays (EMRs) better or worse than solid-state relays (SSRs)? In terms of functionality, they both switch a signal based on an input to the relay.
Solid-state relays have fewer moving parts and are quieter. Thus, they may not be susceptible to vibrations, but they will wear out based on number of executions and heat. Also, costs may be higher initially, but if you look at the comparison of savings—replacement frequency and the amount of real estate in the cabinet, then the cost becomes a wash. Why? If I can build a smaller cabinet and the machine is smaller but does the same thing, then is the cost worth it?
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Performance-wise, SSRs may be faster than EMRs, and SSRs also have a longer service life. Solid-state relays have low power consumption but high heat. Thus, consider if the cabinet needs more space for air flow, in comparison to size. Maybe it depends on the number of relays being used.
A bank of solid-state relays will require less space, but, if you only have three or four relays, maybe the justification is not there.
Sound and vibration are other considerations. SSRs won’t bounce on vibration. They also won’t weld shut if a spring breaks. Thus, what is the machine application, and where is the machine going to go?
Considering safety, is it important to switch the relay off when at an ac load point of zero current? Inductive loads may have current and voltage signals 90° out of phase. This means peak current and peak voltages are reached at different times. Solid-state relays can switch on zero Amps. Fast operations may work better this way.
Spares are the next question. Does your customer already stock the spare or have a relationship with the contact manufacturer? As an equipment manufacturer, these are the small requirement questions that can be asked to show the customer that you care and that you are thinking about the design not just as part of your build, but in relationship to the customer. Also, SSRs have little lights normally, so troubleshooting is easier.
