Increasing Reliability using SSR

Discussion in 'General Electronics Chat' started by bnilesh, May 5, 2011.

  1. bnilesh

    Thread Starter New Member

    May 3, 2011
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    Well I am new on this site. I am looking for upgrading the reliability of my developed distributed temperature control system. I had used SSR(solid state relay) for controlling the heaters. The SSR specification for o/p voltage & current are 330V AC, 16A. The actual load is resistive type not more than 8-10A @ 230V. Occasionally it was found the SSR were failing. These SSR are with internal snubber.

    The main problem is the failed SSR were found with closed contact which is not fail safe condition loosing control over heater. The electromagnetic relay has upper hand regarding this issue leaving contacts open in case of failure.

    I am planning to use electromagnetic realy in series with SSR with appropriate rating. The relay will be kept on normally opening the contact in case of SSR failure. Is there any other way out than this solution? Are their any design constraint for using electromagnetic relay in series with SSR?
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    None that I can think of. Use an SPDT relay's NC contacts so it only has to be energized when an SSR fails. How you're going to sense the failure might be interesting, I suppose your going to look at the input (control) and output to see if they don't match up?

    BTW: Do you have ample heat sinks on your SSRs? They generate a lot of heat when used with currents as high as you're using.
     
  3. bnilesh

    Thread Starter New Member

    May 3, 2011
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    Right you are. I will be sensing that by taking into consideration how far temperature goes beyond the set point. Also I am planning to monitor the load current which will give clear picture on control.

    Well I have used heat sink & cooling fan for avoiding heating problem. Anyway the SSR are being used to only 50% of their load capacity.

    But using NC contact will again will not be fail safe. Using NO contact with enegised relay in normal condition will make sure heater will be OFF in case of controllers power also goes bad.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    don't be mad OK.

    but what if you are <snip>

    Care to show us your SSR, I like to see it
     
    Last edited: May 5, 2011
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    R!f@@,

    Can you resolve your second line with your SIG? :(

    Ken
     
    Last edited: May 5, 2011
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    HUH !!.

    Is it about the crappy tech thing.

    I see there is some misunderstanding....I will clarify.
    By Crappy tech I meant OP might have done something wrong with the SSR mounting to the sink. OP said SSR is blowing. So it could be careless sinking methods...
    I just like to see how OP has done it.

    Is OP offended by my remark ?...if so. Sorry..I never meant it..u know...
     
  7. bnilesh

    Thread Starter New Member

    May 3, 2011
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    Well I see some misunderstanding at your end. First of all in the working unit proper heat sink & cooling provisions are made & the system has been rigorously used 24x7 periodically over months in last 4-5 years in industrial environment.

    The SSR are not failing regularly but sometimes it has been observed. Anyway what's the harm do you see in increasing the fail safe conditions? It is going to ensure power supply will not be delivered to heater in rare failure case of SSR.

    By the way it's wise people don't underestimate the others :)
     
    Last edited: May 10, 2011
  8. bnilesh

    Thread Starter New Member

    May 3, 2011
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    Anyone like to comment further ?
    Any comments & suggestions?
     
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