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

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  • I've put a PID on my 2-group hx

    Part 1

    Yes, it's probably sacrilege. Yes, I've argued that a PID on a pressurestat-controlled single boiler heat exchanger machine is unnecessary. And it is. So why have I done it to my bullet proof 2-group commercial Grimac?

    I like digital readouts. The Sirai pressurestat is probably more than 20 years old, and while still performing well, is getting on a bit, with below-par contacts I've cleaned a couple of times now. And to adjust temperature is a bit of a pain, partly dismantling the machine covers to reach the pressurestat.

    I put a lot of thought into the project. Out of necessity. No guides to follow. No instructions. No wiring diagram for the Grimac. Anyway, I bought an inkbird PID, 240v, with an overkill 40 amp solid state relay.

    I'll detail the how in another post. For now, it's taken 1 1/2 days solid work, and there's some more to be done.

    It's working, and we had our first espresso and latte tonight. Is it superior to the Sirai pressurestat control? Doubt it. But it's fun. Easy to adjust. And nothing blew up. Click image for larger version  Name:	20220308_202642.jpg Views:	50 Size:	280.4 ** ID:	904619

    More to come.

  • #2
    Nice work. I’ve got a half finished mod to add a PID to my Expobar Minore 2 (dual boiler but no pid). So I’m interested in the details…

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    • #3
      Part 2

      THE CHALLENGES.

      How would a PID be wired in. How would it interact with the existing pressurestat and Gicar control box?

      For a simple machine, the Grimac has a hell of a lot wiring. All bundled in neat looms so it's difficult to see where they lead to.
      Then there's the very industrial barrel switch with 8 wires and 3 positions: off, water control on, boiler element on. Yikes! Why all those 8 wires? Where do they go?

      You could argue that if these questions spring to mind you're out of your depth and shouldn't go any further. But I was confident that with some exploration and my fair knowledge of electricity and electronics the answers would be discovered.

      I thought it logical that the electrical components could be divided into 2 distinct function . Those which controlled the flow meters, water level, touchpads and 3 solenoids being 1.

      The second function controlled the heating element. They are quite separate circuits.

      That was a huge relief in then knowing how to proceed, which circuits to dismiss and on which to concentrate.

      The pressurestat obviously had to be removed from the circuit and replaced with the PID and solid state relay. But where to connect the new wires? Where to mount the thermocouple?

      The (solid state relay (SSR) comes with a big heat sink, which limits the available spaces within the Grimac to mount it. Lots of thought and dry fitting went into that.

      So those were the challenges. The second lot of challenges, being the implementation, and the third ones, being the operation. Those posts to come.

      Pictures are of the barrel switch, and pressurestat wiring.

      Attached Files

      Comment


      • #4
        I dips me lid to you Robusto ! Very interested to hear all your trevails ..... the good the bad and the ugly!
        As you've had the guts and the motivation to give it a crack.

        Both you n Dishchucker may recall the banter here ala 2010ish when a Q would consistently crop up -
        Re : ' Hey I once had a Ms Lucy and then I PID'd it , it was fantastic, So Im thinking of PID'ing my new shiny HX blah blah'

        Well the toos and the fro's went back n forth...yes / no....yes / no.
        Well I agree that it can only be an investment well worth while!

        Any thoughts to Pimping this Grimac further?
        Saturated Head one side And a 'Pompa' on the other Head?, Gear Pump or better still a Variable Speed / Pressure Pump,

        Whilst on this build.....Have you taken an accurate temp reading of GH and all the way back to the Boiler?

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        • #5
          Hi EspressoAdventure. No, I haven't taken the pimping further -- I'm snowed under with other more pressing things to attend to (including the central heating). My advice hasn't changed since we argued about putting a PID on a HX way back then. And that's don't do it. As a temperature controller, totally unnecessary. The pressurestat system is ingenious and works so damn well. When combined with the engineering of these machines with their E61 groups, thermosyphoning etc, it's all you need

          So if it's pimping and a project you need, yep, by all means do the PID. But you won't get superior results.

          As to the group head temperature... I have placed thermocouples inside the bolts on the front of the groups, and get readouts on two digital thermometers. I posted on that project about a year ago here..

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          • #6
            Part 3

            THE INSTALLATION

            The PID is an Inkbird ITC -100 VH There are a few models, for different relays, thermocouples, 240VAC, or 12VDC. I chose the 240 volt over the 12v ( ITC-100 VL--L for low I'd imagine) because I wanted it to operate when I switched my coffee machine on...rather than have to turn on both the machine and then a separate 12VDC power source for the PID. It will take its power from the machine's 240v power.

            Click image for larger version

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            First, unplugged the machine from power. Then removed all the side, rear and top panels off the machine for access.
            I made drawings of the wiring on the barrel switch, and the pressurestat (PS).
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ID:	904752 WIRING NOTES

            Next, with my multimeter set on on ohms, I probed the distribution of power from the position one of the switch (water control), and position 2 (heating).

            The PID would be connected to the barrel switch position 2 circuit, just as the existing PS is.

            I was going to removed the PS completely. Which meant removing the steam pipe from the boiler to the PS, and capping the outlet on the boiler. However, it proved too difficult to get a 12mm compression cap. So I disassembled the PS, took out the contacts, and left it connected, spring and all, and thus sealed to the boiler.

            But all the wiring to and from it I disconnected.
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ID:	904750RATHER LONELY PRESSURESTAT, IT'S ONLY FUNCTION TO SEAL THE PIPE FROM THE BOILER

            The positive and negative wires feed the input side of the PS. When steam pressure is low, the contacts close and electricity flows to the output side to the boiler.
            When pressure builds to the set point (under 1 bar) the diaphragm is pushed up, actuating a spring which forces the contacts open and electricity stops flowing to the terminals of the boiler's heating element.

            This switching on/off on/off will now be done by the PID pulsing a 40 amp solid state relay. But instead of being ON for about 20 seconds, and off for about 2 minutes when the machine is up to pressure and idling, the switching will be pulsed, half a second-- if that-- ON, then off for a few seconds, rinse and repeat.

            I connected the four blue negative wires together in a terminal strip bolted to the inside frame of the machine. The black and red positive wires which went from the barrel switch to the PS are connected together on one terminal of the SSR. The other red and black wires which went from the output side of the PS are connected to the other terminal of the SSR.

            Click image for larger version

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ID:	904749TERMINAL STRIP FOR ALL NEUTRAL WIRES

            When the PID senses a temperature drop via the thermocouple, it sends a low 12 volts dc pulse to the SSR, the SSR electronically switches 240 Volts ac power from one set of red and black wires, to the other set which goes to the boiler.

            The PID needs a 240V positive and neutral, which I took them from the barrel switch's number 2 heat position. Each terminal on the PID is numbered so it's easy to follow the wiring diagram as to which wire goes where. The PID also has a 12volt DC output which connects to the clearly marked low-voltage DC side of the SSR.
            Click image for larger version

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ID:	90474840 AMP SOLID STATE RELAY LOW-VOLTAGE TERMINALS PROMINENT, HIGH-VOLTAGE ONES AT INSIDE END.

            I found a spot for the SSR and its big heat sink on the rear bottom frame of the machine. It doesn't really heat up anywhere near as much as expected. Pretty cool actually, since it draws 10 amps vs it's rated 40 am

            The only other connection is the thermocouple. This boiler was never designed for them. It has no well into which to screw in or insert a thermocouple. And the supplied thermocouple has a threaded bolt on the end. Tricky. For now, I used a wire tie and a cable tie to support the thermocouple on a pipe near the boiler. The actual bead rests against the boiler. Far from ideal, and a work in progress.

            So far, for me this whole project was really a Proof Of Concept. If it worked, well and good. If not, I'd order a new PS, install that, and call it a lesson learned.

            More on that in the next instalment.



            Attached Files

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            • #7
              PART 4

              HOW IT OPERATES

              I turned the Grimac to position 1, and the PID did nothing. Good. That's what I wired it up to do--or not do--in that position.

              Then, the moment of truth. Turned the switch to position 2. The PID came to life. No smoke, no breakers tripping, nothing exploded.

              I arbitrarily pulled a number out of the air and set the PID set point to it. About 50 degrees I think. I watched the actual temperature display rise and rise, as the red LED on the pid stayed solid, indicating power was going to the boiler uninterrupted.

              so, with the thermocouple just brushing up against the boiler somewhere above halfway up the boiler, how do you know what the set point temperature should be?

              You don't. So you keep a careful eye on the steam pressure gauge. It's usual position in years of use has been a low of about 0.65 and an idle of 0.8 bar. So I didn't want pressure to go beyond 1 bar.

              I also have a digital thermometer with a thermocouple on each group.

              Anyway, there was a bit of experimentation with both the temperature set point and thermocouple position on the boiler. It overshot well above 1.5 bar at a couple of settings, and wouldn't bring the steam gauge to speed at others I tried.

              I've settled on placing the thermocouple near the bottom of the boiler and close to the heating element end. And the setpoint ar 87.5 degrees

              Inputting settings for P, I and D is a pain. So I set the PID to self-learning autotune to save me grief. It's a fast learner.

              It's all working very well. Love pulling up a chair and taking a front row seat. In the first stages, I sat on the lounge too to see the numbers and dials. So I used binoculars to ensure the pressure wasn't going too high.

              It doesn't.

              More to come, including what's left to be done, and how PID control compares to pressurestat control.







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              • Dimal
                Dimal commented
                Editing a comment
                Love your style Robusto...

            • #8
              Part 5

              STILL TO DO LIST


              The priority now is to put the PID in a suitable box. Jaycar's weren't high enough. I'll try Bunnings or a craft shop, but I might end up having to make my own from plywood, with holes for aeration, and spray it grey to match the machine. I might mount it on a side panel, or just sit it alongside or even underneath the machine on the counter top.

              The wiring from the PID to the machine I'll cut to a uniform and proper length. I've only used scrap bits of cable to see if everything works a this stage.

              The thermocouple needs a more permanent and positive touch of the boiler. As it is now, if it drops off, the boiler will keep heating and heating until catastrophic things happen.

              Suitable silicone or JB Weld might do it, or, I'll JB Weld or solder a nut or two to the boiler (on the surface of course) into which the thermocouple can screw.

              Then...my wife can reclaim her dining table, and benchtop which are now full of assorted and scattered tools.

              (Have you seen those TV shows when someone is building a robot from scratch, and the only visible tool is a screwdriver?)

              The cost? $55. That's for the PID, 40 amp SSR with heatsink, and thermocouple. Labour? -- I'd say all up about 20 hours, many of them just working out the existing wiring and dismantling.


              Still to come: Was it worth it? How does it compare to the regular pressurestat?








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              • #9
                The thermocouple needs a more permanent and positive touch of the boiler. As it is now, if it drops off, the boiler will keep heating and heating until catastrophic things happen.
                An ideal location to position the t/c, would be to drill a 3mm hole laterally into the boiler end flange (where there is plenty of material) at a height that replicates the water level in the boiler, minus about 20mm. You can then fix the t/c bead permanently into place using any one of many thermal epoxy adhesives available.

                Would be a very tidy and reliable way to do this.

                Mal.

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                • #10
                  Thanks Mal, yes, that position is ideal. But I'm loathe to drill into the boiler. I suspect the threaded bolt at the bead would rust, being steel, and dissimilar with the copper.

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                  • #11
                    Not into the Boiler per sé, but laterally into the edge of the Boiler Flange only deep enough to allow fixing of the t/c. Lots of material there and once fitted (with thermal epoxy) will last practically forever and will not give any cause for galvanic corrosion concerns. No bolts are involved.

                    Mal.

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                    • #12
                      Click image for larger version

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ID:	905050 Unfortunately Mal, my boiler has round-over ends, no flange.

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                      • #13
                        Ah, sorry mate. Thought it used a typical commercial machine design for the boiler.

                        Still worth considering using a dab of thermal epoxy to secure the t/c to the boiler. Just lightly sand the location first and then hold it in place using adhesive tape as a temporary measure while the epoxy cures. I think a "bead type" t/c would be easier to work with. An adhesive something like the one in image attached below from Mektronics would be fine...
                        Attached Files

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                        • #14
                          Thanks Mal, I'll look into that adhesive.

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                          • #15
                            Still experimenting with the ideal location to surface mount the cumbersome thermocouple on the boiler. It was working well until this morning when the water temp at idle seemed too low.

                            It's not an easy matter of turning up the PID set temperature.

                            If the set point, and TC location aren't happy together, the steam pressure will get dangerously high many degrees C before the set point is reached.

                            Then, if this hurdle is stumbled across, when the machine starts idling, the water temperature is likely to be too low.

                            I'm thinking the TC bead needs to be mounted on a part of the boiler which gets hot quickly. If placed on a relatively cooler spot, the water keeps heating and heating even though the heating element has already brought the steam to pressure.

                            Tomorrow I'll use the temperature probe on my multimeter to search for the hot spot and see how we go.







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