Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
If you mean SSR as in solid state relay, the advantages are
-no moving parts
-longer operation. can survive an indefinite number of switches - electromechanical relays tend to wear out eventually due to moving parts
-no sparking. this also leads to longer life
-very fast switching times. Because these relays are controlled by an infrared LED, the switching speed is measured in microseconds.
-they can be much smaller than electromechanical relays
SSR have also disadvantages when comparing with normal, mechanical relays ..
One of them is the leakage current, which in some circumstances may, for example, cause a fluoro light to “glow” even if the SSR is OFF ..
Plust to IanP I will add that SSR dissipate power, and request adequate heatsink, at full load can be 40W of dissipation. Relay dont have that problem if contacts are adequate for job.
When we sum SSR with heatsink I dont think he is smaller then relay, but this depends on controlling power (current) in circuit. Plus is good to use isolated SSR, we dont want some elctroshocks when heatsink is touched.
When you look better in auditor (back window) you will notice that relay last longer then SSR (if properlz dimensioned and choosed).
SSR can be used if you need frequent On/Off switching, and if you need silence in device operation, or if you need some power-current adjusting (dimming).
Another advantage of SOME SSR's is that they will not switch off until the AC current goes to zero. This can be helpful if you are switching inductive loads as it will eliminate the voltage spike that you would get if you turned off the same load with a mechanical relay when there was current through the load.
On the other hand relays have problem with contacts, especially if they are overloaded with current, or is used more than the permissible voltage. Relays usually have determined current for NC and current for NO state of contacts, just as frequency of switching.
I assume you are referring to AC current switching. One disadvantage to SSR is their on state voltage drop of 1.5v to 1.8v. As current requirements get higher they require large heat sinking. For example 30 amps rms current requires 50 watts of heat sinking.
Another factor is switching split phase 240 vac (U.S. type residential feed). Generally both hot lines should be switched on 240 vac devices for safety reasons. For a double SSR relay this just doubles the heat dissipation requirement.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
