OpenTherm VR33 and Vaillant ecoTEC plus 428

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  • bruce_miranda
    Automated Home Legend
    • Jul 2014
    • 2307

    #31
    If you have already invested in a VR33 and an OT interface then might as well use them.
    And you are right, ebusd needs a host.

    Comment

    • Vikings
      Automated Home Sr Member
      • Jan 2021
      • 55

      #32
      Thanks. Yes just need to work up the nerve to plug them in.

      Comment

      • bruce_miranda
        Automated Home Legend
        • Jul 2014
        • 2307

        #33
        Plugging the VR33 with its own OT jumper in place, while you still use terminal 4 to fire up the boiler will basically give you a Normal On Off system, but with a target flow of 90C. That target will never be reached because your boiler CH knob will clamp the max to whatever you have it set.

        Comment

        • Vikings
          Automated Home Sr Member
          • Jan 2021
          • 55

          #34
          That's all good. I'm planning to install with an easily accessible switch so I can swap between my OpenTherm interface and a loop across the VR33. That'll make it quick to swap out if I need to do any fault-finding.
          Am I right in thinking that if my device stops sending repeated commands at the required rate then the VR33 will drop to its 'off' state? i.e. target temperature minimum and therefore turn off flow?

          Comment

          • bruce_miranda
            Automated Home Legend
            • Jul 2014
            • 2307

            #35
            No idea what the fail safe of the VR33 is. All I can say is jumper out is 10C and jumper in is 90C (I think). I have only had the VR33 connected to an approved OT device.

            Comment

            • Vikings
              Automated Home Sr Member
              • Jan 2021
              • 55

              #36
              I installed the VR33 and with the connection looped all seems to be working fine. The diagnostics on the boiler also shows that it's detected an 'ebus controller'.
              I've not had any joy when I connected by Arduino to it so far. No reply detected. I'll need to do a re-test on my interface circuit to make sure it's working as it was meant to. The circuit I'm using is the 'master interface' half from the one shown here https://create.arduino.cc/projecthub...arduino-7818f5
              I suspect OpenTherm signals are going to be quite tricky to debug given the way they use combinations of voltage and current.
              I presume if feed temperature commands are getting through then I would see a change in the D.5 value on the boiler or perhaps D.9?

              Comment

              • bruce_miranda
                Automated Home Legend
                • Jul 2014
                • 2307

                #37
                D.9 is the all important value to watch. The beauty is you can have this value displayed on the boiler and watch it changing.

                Comment

                • Vikings
                  Automated Home Sr Member
                  • Jan 2021
                  • 55

                  #38
                  That's very helpful once again. Thanks.
                  I did see a very occasional small change in the set point but not matching the setting I was sending. I put a scope on the OT lines and I spotted the issue with my interface board. The rise time was far too long and it wasn't reaching a high enough voltage. It had been working when I had done basic level checks at DC but not at operating speed. When I copied the circuit design I had substituted a different optocoupler and it turns out to have a very slow switch off time - doh!
                  There will be a short delay while I produce a revised version of the board with the correct optocouplers. I'm quite optimistic that things will go a lot better once I've done that.

                  Comment

                  • bruce_miranda
                    Automated Home Legend
                    • Jul 2014
                    • 2307

                    #39
                    Are you really building this to save money or have fun. Because the cost of an OTG these days has dropped dramatically since more people started porting the original PIC design

                    Comment

                    • Vikings
                      Automated Home Sr Member
                      • Jan 2021
                      • 55

                      #40
                      It's a bit of both really. I also have a few other things on the same board as that particular Arduino is running several other sensors outside my house. I know I could stack the boards up but with the Ethernet board as well already the stack is getting big enough. Overall it saves me a little - although probably not much now I've had to do it twice!

                      Comment

                      • bruce_miranda
                        Automated Home Legend
                        • Jul 2014
                        • 2307

                        #41
                        Is your board cheaper than $15?
                        DIY OpenTherm Arduino/ESP8266 Thermostat Adapter

                        Comment

                        • Vikings
                          Automated Home Sr Member
                          • Jan 2021
                          • 55

                          #42
                          By the time I allow for postage etc then it works out very similar. That is a good suggestion though as that board is pretty small and so I could stick it underneath and bypass the OT part of my existing board. It will save me a bit of effort in redesign/build.

                          Comment

                          • bruce_miranda
                            Automated Home Legend
                            • Jul 2014
                            • 2307

                            #43
                            I used this for a while and that too was quite nice. Except that since these boilers are not natively OT, I figured there was nothing to gain beyond my eBus interface. So I sold it on here.

                            Comment

                            • Vikings
                              Automated Home Sr Member
                              • Jan 2021
                              • 55

                              #44
                              Originally posted by bruce_miranda View Post
                              Is your board cheaper than $15?
                              https://ihormelnyk.com/opentherm_adapter
                              Unfortunately it turns out he is in Ukraine and unable to supply these at present for obvious reasons. He was kind enough to refund my payment right away though.
                              I then tried ordering a similar board from https://diyless.com/ but that seems to be stuck somewhere in Ukraine too.

                              So I'm now back to getting some new versions of my own board with the correct optocouplers this time. Hopefully they will be here in a couple of weeks and I might be ready to test again.

                              Comment

                              • Vikings
                                Automated Home Sr Member
                                • Jan 2021
                                • 55

                                #45
                                I've built up my own revised board now with the 'correct' optocouplers and it now works perfectly!! I can set the boiler temperature and read back some data e.g. feed and return temperature.
                                Just need to finish writing the Arduino code to accept the temperature commands from my server now.

                                Comment

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