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I've put a PID on my 2-group hx

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  • #16
    Been reading along with this Robusta, and a great thread it is too!
    Agree with yours and Mal's suggestions. Maybe whats needed is to try a few locations and test the outcomes.
    Have you a Scace II device? Or can make one up? Other suggestion would be Temp strip on Boiler at / or below water level, plus an InfraRed temp reader, to test temp points along the way.

    I can relate to where you find yourself....And what is often needed here is 2 or 3 mates a few beers one arvo, good n bad suggestions,
    till Old Mate 'Boofa' comes up with the laughable idea that is immediately jumped on by all and sundry....till ...someone pipes up and says you know that might just work ....
    So in the spirit of Boofa, here is a few more suggestions....
    1/ Henkel ( Loctite) have a heat conductive copper based metal repair adhesive commonly available at Auto shops.
    2/ The TC looks similar to heatsnob - so may be a 'common' either 5 or 6mm dia x 1mm pitch thread. Easy to obtain either dye's to drill / cut your own thread in a piece of solid copper round. Braze this to copper plate for a greater surface area then affix to boiler as you've prev said near to but below upper water level.
    3/ I reckon easiest is - take said solid copper round fitting you've just made up and braze it to the PressureStat pipe near to the take off from the boiler, whilst drilling a small hole in the pipe once brazing is done.
    I take it the TC is waterproof ?
    Heat rises so this is likely to be the 'highest' temp point in the machine's setup.
    GL

    PS Just saying it wasn't me you might have been 'debating' the merits of a PID'ed HX all those years ago !

    Comment


    • #17
      EspressoAdventurer, thanks for the suggestions. Once I find the ideal spot on the boiler to affix a thermocouple I'll give more thought to the means of adhesion.

      Probing with my multimeter thermocouple I found a huge discrepancy between its readings and the PID's. SO I used the PID's adjustable settings to calibrate up.

      I've found a tiny ledge on the bottom of the boiler where it bolts onto a support bracket. So I've wedged the TC bolt into that little ledge. Temporarily of course.

      Through oh so fun trial and error I found a set point of 94C would take the pressure gauge to 1 bar during heat up.

      BUT---within seconds pressure drops, to 0.5 bar. Too cold for brewing and probably steaming 2 lattes.

      You can then increase the set point, to 98-100C, and it idles nicely under 1 bar.

      But if you have that 98-100 set point from cold, it will blow the overpressure steam valve.

      So more pulling up a front row seat with glazed eyes tomorrow.

      Comment


      • #18
        Work is the food on which this glutton feeds. Instead of trying to solve the immediate problem, I look for another.

        As mentioned, the PID is 240VAC, and I deliberately wired it to take its power from position 2 (heating) on the barrel switch.

        But if you want to tinker with its settings that means doing so while the element is on. And that's not always desirable.

        Wiring to position 1 (water regulation only) may not be desirable either, because the PID will be sending power to the relay--though of course it won't be closing the heating circuit. But relays have a finite number of cycles. Probably nothing to worry about.

        Anyway, I proceeded to do what should have been a 5-minute job. Remove the drip tray, remove the switch box cover, move two PID wires to the No 1 circuit.

        Three hours later....

        The two small bolts clamping the power chord wires to the switch were so damn tight it took 90 minutes EACH to unscrew them.

        My wife had to hold the barrel onto a block of wood while I used screwdrivers and a hammer as impact drivers. All the while mindful not to smash the plastic switch. Rewired, all worked.

        Then...back to the PID control.

        A bit of calibrating and fiddling and I settled on 94.5C as a good idle setting. I say setting, not actual degrees, because it's an exterior surface reading, not actual water temp, which of course is much hotter.

        The problem still remains, and it has me stumped. A couple of degrees before reaching set point, boiler pressure hits 1 bar and will keep dangerously rising without intervention.

        Intervention is to open the steam wand and release enough steam to stop that rise for a few seconds until set point is reached and the heating stops.

        Getting over that hump, it then idles beautifully. The 2 groups come to temperature, and pressure remains absolutely steady at 1 bar.

        Comment


        • #19
          Thermocouple has gone back to square one, near the element end of the horizontal boiler, and below halfway up mark.

          I'm not so sure now placement is the problem.

          the sight glass water level is behaving like there's a poltergeist inside it. Though water level is set at a shade under halfway, and the autofill system works...At some point in the heating cycle the level rises to the upper limit mark. Without any additional water having entered.

          And it can jump around, up and down erratically, 10-20 mm at a time. Without anything being touched.

          Would that faux high level be pressure, over the water in the boiler, pushing down on the water surface, which in turn forces water up the sight glass? What else could it be.

          Secondly, is the boiler full of hot air?

          While I regularly service the vacuum break valve...is it possible that it's closing too early, trapping in air which is causing excessive pressure during the PID heating cycle...overstepping 1 bar despite temperature setpoint not having been reached?

          But how could that be?

          Comment


          • saeco_user
            saeco_user commented
            Editing a comment
            Does the sight glass level change when boiler pressure is regulated by the old pressurestat?

        • #20
          Saeco, I don;t think so, it's not something I kept an eagle eye on, just the occasional look to make sure the level was right.

          Comment


          • Dimal
            Dimal commented
            Editing a comment
            Could be that you may have a partial blockage of the orifice at the top of the Sight Glass...

        • #21
          Might be seeing progress with the over-pressure while still heating to set point.

          I removed the vacuum break valve. It was probably due for a new o-ring and clean anyway. It seemed to be operating the way it should, but a service wouldn't hurt.

          So cleaned the piston and seat with steel wool, new o-ring, put it back into service...and
          temperature from relative cold came up to set point WITHOUT exceeding 1 bar boiler pressure. Happiness.

          So far so good, because that is by far the main obstacle.

          But having reached set point, pressure proceeded to drop away and group temperature was way too low. Even after idling some considerable time. A higher set point to try maybe? Will I press my luck?

          Since it's best to do these tests from cold, I'll continue tomorrow.

          Why this worked with a cleaned vacuum break valve, I don't know. It wasn't sticking before, so it opened and shut when it should.

          Comment


          • #22
            May have been coincidental re: the vacuum break valve.
            What are your P.I.D. settings Robusto? May need tweaking...

            Comment


            • #23
              Mal, it certainly may have, especially considering it's more common for these valves to fail to seal.

              Settings last night were: PID set point 60.5C. Temperature calibration offset +8 degrees.

              This morning against my better judgement and proper practices I changed too many variables. I decreased the PID temperature offset by 5 degrees to bring the reading for the cold boiler in line with room temperature. This has the effect of having to heat for longer to reach set point.

              I also increased the set point from 60.5 degrees to 65. This compounds the above.

              So as the boiler warmed up, with many degrees still to go to set point, the pressure went above 1 bar and I switched everything off and went back to the old settings: 60.5 set point, +8 degrees C offset.

              Now waiting for things to cool down before trying again.

              Comment


              • #24
                Another very frustrating day. I'll spare you the details, but wow! I had no idea silicon heat transfer paste could have such an incredible affect on a thermocouple bead.

                I found a copper nut, oversize unfortunately and smeared some paste inside and around it. I had the silicon paste left over from mounting a new computer chip years ago.

                I pressed the TC into the nut and both against the boiler. The thermocouple measurement shot up 30 degrees Celsius!

                Experimenting with new, higher PID settings now.

                Comment


                • #25
                  Ah, yes... Thermal Interface Compound is a given but sorry I forgot to mention it mate.

                  What I was actually asking re: the P.I.D. settings, is the actual individual setting of each of the Proportional, Integral and Derivative parameters. It will give us some idea of the current behaviour of the Controller/Boiler. Which Inkbird controller model have you used would help too, if known...

                  Mal.

                  Comment


                  • #26
                    Hi Mal,
                    The PID is an Inkbird ITC-106VH driving a 40A SSR (I gave the model details in #6)

                    After auto-tune-- the self learning mode-- the settings are P=50 I-30 D-8.

                    It seems to be working well now, but will probably need tweaking when I am satisfied of its consistency.

                    Then we move on to a permanent thermocouple installation to the boiler.

                    For that, the plan is to take the one and only copper nut I have, which is slightly oversize to the thermocouple bolt, and a steel nut I have, which is the right size and thread, and solder them together.
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                    The copper nut is then soldered to the surface of the boiler. The TC is screwed into the assembly, add some heat transfer paste on the bead

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                    And hopefully it all works. Having a greater thermal mass on the TC bolt will no doubt require some adjustment of the settings.

                    That's the plan.

                    Comment


                    • #27
                      The extra mass of the copper nut, etc won't make any measurable difference when you compare its mass with that of the boiler and water. Sorry for missing the details you posted in post#6, comprehending what I see isn't always what it once was...

                      Anyway, will check on the controller to become familiar with its particular idiosyncrasies for future reference.

                      Cheers mate,
                      Mal.

                      Comment


                      • #28
                        Mal: "comprehending what I see isn't always what it once was..."

                        You're not alone in that respect!!

                        There are many YouTube videos about this PID, almost all used for home brewing...brewing alcohol, not coffee.

                        Comment


                        • #29
                          Originally posted by robusto View Post
                          There are many YouTube videos about this PID, almost all used for home brewing...brewing alcohol, not coffee.
                          Ah, good to know. Must be a reasonably reliable unit...

                          Mal.

                          Comment


                          • #30
                            Hard to get a reasonably priced project box in which to place the PID so I'm building one from an 8mm thick plywood sheet from an old wardrobe.
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                            It's a pain to work with because the surface ply splinters soon as you look at it.
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                            Almost finished, but I might try again with better quality wood.
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