I went down the route of using a Tesla T-Smart replacement Immersion thermostat. Not that expensive, easy to replace with no draining and there’s now a custom component for HA (on these forums)
You definitely need to use a contactor for this application. A 3kW immersion will draw about 13 amps, and while that is within the spec of the Sonoff, it’s a lot of current to run through a small device and that will probably generate a lot of heat.
Ideally, I would recommend one that has a manual override switch included.
Thanks for the suggestion. Should have said I already have tank water temp available in HA and immersion thermostat works great to set 60C. The heat pump does most of the hot water heating so T-smart would be a bit wasted.
Thanks, yes I’m coming to same conclusion. I use a tplink smart plug for granny lead ev charging at 10a and it works well but immersion is 30% more and hard wired. The tplink gets a little warm and it’s in the open air. The Wi-Fi switches are much smaller and would be in an enclosure so heat definitely a concern.
Smart plug has switch for manual override although I’ve never needed it as reliability has been good.
Only issue was recovery after power outage - my house network takes a while to come back and the Tasmota plug gave up - fixed with Tasmota Wificonfig mode 2.
Hi, I would love to replicate this. Could you please provide a brief overview of the steps involved in connecting the contactor to the Tasmota smart plug? Any specific instructions or tips would be greatly appreciated
Really interested in how you have tank temperature in HA? Did you replace thermo with something smart? Or is this because your have Tesla immersion and can get temp out from this?
I get the hot water temperature from my heat pump via the MELCloud Integration.
There’s a temp sensor on the hot water tank that feeds into the heat pump control system so that heat pump knows when water has reached set temperature. That and lots of other data feeds into the Melcloud so can be seen on the Melcloud app on my phone.
Fortunately a clever fellow wrote an HA integration so that same data can get into HA.
I am going for multiple (3) Dallas temperature probes using the 1-wire approach and an esp32 running esphome at different heights on the hot water tank. I have discovered having a probe at only one height will not give you much useful information unless the boiler is on and there’s some convection inside the tank.
edit : this will surely apply to the t-smart setup unless it comes with some wires and extra probes for you to attach.
I got it all working and it’s brilliant. I can use the sensor at the bottom to limit the set point (e.g. 53 degrees all week to save energy but then use 61 on each Saturday as an anti-legionnaires/anti-bac measure). And I now know from the data the last 10 degrees takes just as long as the first 40 degrees when heating (simple reasons why etc.) … so this is definitely an energy saving.
I found the sensor I have in the middle (maybe it’s 2/3rds up) is perfect to use as a trigger to re-heat the tank ad-hoc e.g. if it drops below 43 in my case.
I set up a nice dashboard with water threshold controls (set point and ad-hoc trigger threshold) and schedules as well as a README/FAQ in markdown so that I cannot be accused of not explaining things.
I used the linear calibration features in ESPHOME to modify the middle and top sensor readings somewhat, to bring them in line with the bottom sensor which is inserted in a hollow tube inside the tank.
