Solid State Relays

Discussion in 'General Electronics Chat' started by SLK001, Jan 29, 2016.

  1. SLK001

    Thread Starter Well-Known Member

    Nov 29, 2011
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    Has anyone ever done a teardown of a solid state relay like this?

    s-l400.jpg
    Is it anything other than a triac on a heatsink in a glorified package?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    It typically also has an opto-isolator IC to isolate the input signal from the AC and generates a zero-crossing turn-on gate signal to the Triac to minimize high current transients and EMI.
     
  3. WBahn

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    Mar 31, 2012
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    And doing a teardown would probably leave you as much in doubt as to what's in there as before you started.
     
  4. tracecom

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    Apr 16, 2010
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  5. WBahn

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    Do you mean page 3?
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I see it on P5.
    Max.
     
  7. SLK001

    Thread Starter Well-Known Member

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    The picture was generic (I just grabbed it off eBay). I was just curious about what was inside the block diagrams. Looking at the datasheet you guys pointed to, it says that the rated current is for a resistive load, but the current for an incandescent light (also a resistive load) can only be 25% of the rated current.
     
  8. tracecom

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    Tungsten filaments have very low resistance when cold, and thus very high inrush currents. Apparently, the SSR will not tolerate those inrush currents even for a very short time.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    It can tolerate them fine for a few turn-on cycles, and maybe even a few dozen or a few hundred cycles. But these things are rated for hundreds of thousands of cycles, and all of those little jolts add up.

    ak
     
  10. cmartinez

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    Jan 17, 2007
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    That sort of ssr is usually built using two SCR's connected back to back (and not a triac, so as to make them more reliable), and triggered using an opto isolator.

    But as has already been said, I doubt you'll be able to discern anything if you try to pry them open... you'd only see a mess since they're completely encapsulated in hard resin.
     
  11. WBahn

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    Ah, I see it now. I didn't see the page numbers at the edges (I only looked at the bottom) so I was referring to it as being on the third page of a five page document. But the pages ARE numbered, they are just numbered, 3, 4, 5, 28, and 29.
     
  12. WBahn

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    Where does it say that the current for a resistive load can only be 25% of the rated current?

    It says that the rated current is FOR a resistive load. For an incandescent light you need 4x the nominal current of the light.
     
  13. WBahn

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    Or were you just pointing out that an incandescent light is also a resistive load?

    Yes and no. As others pointed out, it's a resistive load whose resistance at turn-on is a lot lower than the nominal resistance when on. Hence the necessary derating.
     
  14. crutschow

    Expert

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    Isn't 1/4 equal to 25%? :confused:
     
    tracecom likes this.
  15. SLK001

    Thread Starter Well-Known Member

    Nov 29, 2011
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    I did some quick math to get 25%! And that was for an incandescent load, not a resistive load (but an incandescent load is a resistive load - kinda). If you could ramp the voltage to an incandescent load, you might be okay, but since these are only ON of OFF, the inrush current would eventually kill them.
     
  16. MaxHeadRoom

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    All the ones I have used, Opto22 etc have a current rating of X10 rated for 1 cycle.
    Max.
     
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