Help needed replacing Thermomax controller unit

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  • Shtukka
    Junior Member
    • Sep 2018
    • 7

    Help needed replacing Thermomax controller unit

    Hi all, I'm at a dead end so hoping there's some experts here who might be able to help.

    Moved into my current home 3 years ago with solar PV and solar thermal. The Thermomax SMT-300 controller for the thermal has gone kaput and I think it needs replacing. It must be 10-15 years old now, and when powered on emits a buzzing noise just like in this video (not mine, but it shows the problem) https://www.dailymotion.com/video/x2lt3gi Until recently, my unit behaved like in the video - it would buzz if the power was cut off before seeming to fix itself after 5-10 minutes. However, it no longer fixes itself! There's no troubleshooting in the manual I found online so I'm not assuming it needs replacement. But cannot find the same part and have no leads on how to find something similar I could drop in.

    With that, my options seem to be: Call up a local specialist company and pay a big wedge of money for them to supply a replacement - unless they have a very similar model I suspect they'd have to change the sensors, so with parts and half (?) a days labour I'd guess I won't see much change from £1,000
    Accept that it's just not economically worthwhile replacing and leave it. (Don't know if that means it'll blow up next summer!)
    Any suggestions or leads on replacement parts?
    Cheers.

  • LucMan
    Solar Fanatic
    • Jul 2010
    • 624

    #2
    The buzzing you hear is a power relay trying to pull in.
    The repair could be as simple as spraying a little WD40 on the hinges on the relay if it is an open style relay. If enclosed style you will need to pry off the plastic cover then spray it. This could get the system up and running.
    The other issue could be that the relay coil voltage is low. If that is the case replacing the controller will be required.
    The sensors may not need replacing if they are the same type used on the replacement controller.

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    • Shtukka
      Junior Member
      • Sep 2018
      • 7

      #3
      Thanks LucMan. I'll try the first idea, but very likely I'm on door number 2, and that's my problem - I'm looking for leads on how to get a replacement controller of the same type.... Thermomax SMT-300 seems to have gone out with the dinosaurs.

      Comment

      • Mike90250
        Moderator
        • May 2009
        • 16020

        #4
        have you contacted them ?

        Thermo Technologies
        Solar@ThermoTechs.com
        9009 Mendenhall Court Suite E
        Columbia, Maryland 21045
        Voice: (410) 997-0778 Fax: (410) 997-0779
        We welcome your comments and suggestions.
        Please send them to: Webmaster@thermotechs.com
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

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        • LucMan
          Solar Fanatic
          • Jul 2010
          • 624

          #5
          There should be no problem finding a replacement, it's only a differential controller. What does it have 2 sensor inputs and power out to the pump?
          Goldline, IMC instruments, Tekmar are just a few off the top of my head. I don't know if they make 220v 50 hz models for the Euro market.
          Last edited by LucMan; 10-11-2019, 11:08 PM.

          Comment

          • Shtukka
            Junior Member
            • Sep 2018
            • 7

            #6
            Thanks Mike 90250, I'll try those details. I'd drawn a blank to date on even getting sensible-looking contact detail for Thermomax. ta!

            Comment

            • Shtukka
              Junior Member
              • Sep 2018
              • 7

              #7
              Oh, and Lucman, thanks again for those pointers: it's a 3-sensor unit (Collector, Return, Tank). My worry is that I have no idea if the sensors are compatible.

              Comment

              • LucMan
                Solar Fanatic
                • Jul 2010
                • 624

                #8
                Most likely pt 100, pt 1000, or 10K thermisters. If you have an ohm meter you can check the resistance at any given known temperature and compare it with the pt charts.
                pt 100 = 100 ohms at 32 F, pt 1000= 1000 ohms at 32F, 10K= 10,000 ohms at 77F. The charts are available online for download

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