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Replacing Electromechanical Relay with Solid State Relay

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  • Replacing Electromechanical Relay with Solid State Relay

    hi

    I've searched high and low for any discussion on this topic, but I couldn't find anything.

    Does anyone know whether it is advisable or not to replace the electromechanical relay that powers on/off the boiler heating element, with a suitably rated Solid State Relay (SSR)?
    I spoke to the guys that service my machine about this, but none had heard of it being done, or whether it was advisable at all. All the commercial machines they had on the shelves awaiting service had electromechanical relays. They felt that whilst they couldn't see any reason why you couldn't use a SSR, there must be some reason why they've never seen one implemented.

    cheers

  • #2
    Because an SSR requires an low level DC voltage input to tell it what to do whereas a pressurestat simply opens and closes an AC circuit with no external voltage control. You would need a source of DC voltage to be supplied to the SSR when the element needs to turn on and off. The requirements to make this work would not be cost effective for mass manufacture, as you will read.

    A way to implement this idea though, and is something I want to have a go at one day on my Wega if I get the time, is to replace the pressurestat with a pressure transducer, connect it to an Arduino onto which you load a program to output a DC voltage (to switch the SSR) when the trasnducer resistance is between X and Y values. This could be adjusted to be extremely precise.

    However, going to that much work and expense, it's probably be better to just install a PID. Does basically the same thing except instead of pressure as the variable, it uses temperature. Going the transducer/Arduino route would be mad though, certainly would be unique.

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    • #3
      Originally posted by noidle22 View Post
      Going the transducer/Arduino route would be mad though, certainly would be unique.
      I think that that is the mechanism that the Slayer uses...

      Comment


      • #4
        I've not seen too many Slayers around the place so I reckon it would still be unique haha

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        • #5
          Lots of SSRs around of suitable rating that operate with a 240V AC Input...

          Mal.

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          • #6
            Originally posted by versatile View Post
            They felt that whilst they couldn't see any reason why you couldn't use a SSR, there must be some reason why they've never seen one implemented.
            I guess if they mainly service commercial machines, they've probably used commercial quality pressurestats for boiler temperature control. Lots of prosumer models use SSRs as standard these days, as do the more up-market commercial machines...

            Mal.

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            • #7
              Can't you just wire up the output of the existing pressure stat to trigger the ssr and the ssr does the high current switching.

              Cheers

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              • #8
                Originally posted by artman View Post
                Can't you just wire up the output of the existing pressure stat to trigger the ssr and the ssr does the high current switching.
                Cheers
                It might be slightly more involved than that but as Mal says if you use an SSR with an AC input voltage trigger, it would work.

                Something like this would probably do the trick
                https://oceancontrols.com.au/SSR-110.html

                Actually I think I might get one and give it a try in my Dalla Corte Mini as the latest versions have some sort of SSR/Triac assembly doing the current switching of the steam boiler element just like this.

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                • #9
                  One thing to keep in mind with an SSR is that you will need to attach the unit to a surface that supplies some heat sinking capability, particularly inside a hot coffee machine. Also, when they do fail, I have had a lot of them short internally, so you will need to bear this in mind with regard to what it is controlling, and have adequate safeties in place.

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                  • #10
                    Originally posted by MattyRay View Post
                    One thing to keep in mind with an SSR is that you will need to attach the unit to a surface that supplies some heat sinking capability, particularly inside a hot coffee machine. Also, when they do fail, I have had a lot of them short internally, so you will need to bear this in mind with regard to what it is controlling, and have adequate safeties in place.
                    Thats why I said, it might be slightly more involved than that :-)

                    Artman this post shows the internals of a current model Dalla Corte Mini and is a good explanation
                    http://coffeesnobs.com.au/brewing-eq...tml#post543339
                    Photo 2 shows the SSR current switching device (they refer to is as a Triac module)
                    Photo 3 is an overall view of the machine, The module is located at the base of the machine below the boiler to keep it cool and regarding safety failure there is a high temp cutout thermostat in series with the steam boiler element wiring (beige cylindrical thing with the red button on it)

                    MattyRay, I hear you on the SSR failure thing I work in Air conditioning and one well known manufacturer used to use them to start and stop the Indoor fan on some of their ducted airconditioners. If a customer called and said "I've turned my air conditioner off at the wall control but the Indoor fan seems to keep running and I can't get it to stop" meant immediate alarm bells as the Indoor fan SSR had failed. When those SSR's failed they tended to "half short" and would pass half of the AC sinewave through the AC motor, left too long they would burn out the Indoor fan motor.
                    Obviously that manufacturer hadn't paid much attention to failure modes!

                    Comment


                    • #11
                      Originally posted by ausdb View Post
                      Thats why I said, it might be slightly more involved than that :-)

                      Artman this post shows the internals of a current model Dalla Corte Mini and is a good explanation
                      http://coffeesnobs.com.au/brewing-eq...tml#post543339
                      Photo 2 shows the SSR current switching device (they refer to is as a Triac module)
                      Photo 3 is an overall view of the machine, The module is located at the base of the machine below the boiler to keep it cool and regarding safety failure there is a high temp cutout thermostat in series with the steam boiler element wiring (beige cylindrical thing with the red button on it)

                      MattyRay, I hear you on the SSR failure thing I work in Air conditioning and one well known manufacturer used to use them to start and stop the Indoor fan on some of their ducted airconditioners. If a customer called and said "I've turned my air conditioner off at the wall control but the Indoor fan seems to keep running and I can't get it to stop" meant immediate alarm bells as the Indoor fan SSR had failed. When those SSR's failed they tended to "half short" and would pass half of the AC sinewave through the AC motor, left too long they would burn out the Indoor fan motor.
                      Obviously that manufacturer hadn't paid much attention to failure modes!
                      Thanks ausdb, some good info there.

                      I used to replace them regularly on commercial toasters, which had a very high internal temp, particularly when the cooing fan had failed :-) Having said that, for the OP, I would be more than happy to use one in my machine, and am in fact contemplating doing just that with a PID temp control, provided the safeties are appropriate.

                      Cheers!

                      Matt

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                      • #12
                        As Matt says...

                        Attention must be paid to protecting the SSR from self generated heat losses. Proper siting, adequate heat-sinking, application of a suitable thermal interface compound and the selection of an over-rated device will go a long way to building in reliability and safe operation.

                        Most prosumer quality espresso machines already have built-in safety measures to protect against the event of a shorted p/stat or SSR, in the form of a mechanical Safety Pressure Relief Valve. Over temperature sensing could also be used in the control side of things but I haven't seen this implemented in any of the prosumer machines I've checked out. Of course, the venerable Silvia has an Over-Temperature Thermostat mounted on top of the Boiler (no Safety PRV fitted), so something even as simple as this could be utilised, if so desired as an additional safety element. There are better and more sophisticated measures that could be used though...

                        Also remember please, that working on 240V AC equipment is illegal in some states unless you are both suitably qualified and licensed. In any event, at the very least you should have your handiwork inspected and tested by a qualified and licensed person before plugging it in and using.

                        240V AC can and does KILL...

                        Mal.

                        Comment


                        • #13
                          This is certainly a problem for a electronics wiz to solve

                          I'm no electrician by any means, but IMHO why dont you consult an electronics expert and see if you'd get somewhere.....

                          Hope this very simple piece of advice helps the OP,

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                          • #14
                            whats all the fuss about?

                            Click image for larger version

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                            This is not posted for people to think the fitment as shown can be copied as is and all will be ok...because it may well not and non qualified people should not be attempting to modify electric fitments inside electrical equipment.....The fitment and wiring is specific to and is current factory spec on the machine pictured (a BFC Unico Splendor).

                            In machines where there is little room due to their compact size I think this is much better than "traditional style" miniature pressurestat assemblies. However in machines where there is more room, I would instead use the small sirai.

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                            • #15
                              Originally posted by ausdb View Post
                              Something like this would probably do the trick
                              https://oceancontrols.com.au/SSR-110.html
                              Keep in mind when looking at these types of modifications the manufacturers limits on the devices.
                              The above SSR is quoted as: Operating Temperature: -20 to 80degC

                              Pretty easy to find it's operating well outside of spec next to a 125C boiler!
                              (and will either melt, die, short, none of which is a desirable outcome)

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