first of all, I’m not sure if this fits more here or in the hardware category - so sorry if it’s OT
I am trying to ESPHome-ify my boiler and am stuck at chosing a way to control the relays.
The schematic should be simple enough (I guess)
I’m going to use two DS18B20 Temperature sensors (for redundancy … don’t worry - even if everything fails, there’s still a thermal cutoff for safety), and a simple relay (no SSR, because I don’t have enough space/airflow for a heatsink)
the heating coil draws up to 1500W (~230V ~38Ω) so a relay which is ratet 10A sould be plenty - I think this one should do the job. Now at 5V it draws 180mA - so I plan to switch it through a transistor… but I can’t figure out what properties that transistor should have… or is there another way to switch it?
it’s hot water for showering - it’s in a bathroom (so not a central device for the whole house). It only used for the shower and the sink in this bathroom.
Of course it has its own temp control - this is how it worked the last couple of years. But first of all, why not integrate it into home Assistant?! And secondly, its bilt in controls are messed up … I didn’t mention this before, but the whole device actually consists of two tanks “connected in series” in one boiler - so there are two temperature sensors, two heating rods, therefore two relays, and some electronics that control all of it. Now here’s the catch - even though there’s two of everything, the electronics turn off BOTH heaters, as soon as one reaches the desired temperature - this results in one tank (the one closer to the water-output) reaching the desired temperature as intended and quite fast (because it gets the pre-heated water from the other tank) but the other barely reaches 35°C, because it has to heat the fresh and cold water from the water-input but gets turned off, as soon as the other, generally hotter tank reaches the desired temperature. I always kind of wondered why the water gets cold so fast, even though it’s a decent size boiler… so recently I put in two temperature sensors (for another project - not because I wanted to figure this out) and found out the reason by accident…
Now I would like to replace the electronics (which drove me crazy from the very beginning - the display regularly fails, and occasionally it wouldn’t heat for no apparent reason until I power cycle it). It was a very cheap boiler but fits perfectly in the designated space, which is why I put up with it so long and now I would like to upgrade it and reveal its full potential so to speak
yes and no. I like Contactors for motors high amps but Boilers a relay can be ok 10A …my boiler is 20 to 21 amps so I used contactor with a Shelly to switch the contactor. Shelly Pro was not available at the time.
What I have done. I have 1 boiler with 2 coils. One coil at the top and one coil at the bottom. The design of the controls is top coil must be satisfied before bottom coil will be switched on. Idea is really for off peak power to save $$. Top coil heats about 50 lt and the bottom coil will heat the whole unit 200 + lt. So at night off peak power we turn on the bottom coil to heat everything through HA automation… the top coil is on 24/7 so we will always have hot water regardless but it only heats up a small amount 50 lt. This is saving us a lot of $$$. We then have a manual push button to turn the bottom coil on as if more people are using the shower we can cope with demand on that day. We can also turn the bottom coil on through HA switch. That night the HA automation kicks in and will turn the bottom coil off next day resting it.
I say all of that because you could adopt the same logic saving $$ having 2 tanks. Closes tank to the outlet on 24/7 and the other one on a timer for off peak power.
Q: What is your desired temp? above 60°C is recommended to prevent legionnaires’ disease.
To your original questions
You could use a relay but in your case I would go with Shelly Pro2 or if you would like power monitoring go with Shelly Pro2M.
If you use your existing controls to heat up the coil closes to the outlet running 24/7 and just disconnecting the inlet tank coil and control just one tank coil you could go with Shelly Pro1 or power monitoring Shelly Pro1M
If you need something smaller you could go with the Plus series but they are lower in Amps so just check it suits you… they are more cost effective to.
All the Shelly’s are local control no cloud, no account needed. Connects to HA easy, self discovery…
Your temp sensors could use ESP32 but I think the Shelly plus series can add a temp sensor to them but not 100% sure.
I already have a couple of Shelly devices - but didn’t know about the Pro series - they look very interesting - especially since they have an ethernet jack! Will definitely keep them in mind for the future!
However, for this project, I would like the boiler to work completely independently. So all of the controls should be locally done by ESPHome (or whatever), even if HA goes down (which it hasn’t for over a year now, since I switched hardware - keeping my fingers crossed).
Well I’ll be damned … there’s an official temperature sensor addon for the Shelly 1 (not Pro though) … so getting two of these (the 1s are also rated for 16A) and programming them each with ESPHome to be thermostats, would actually be a lot simpler than building my own PCB and everything!!!
Thanks for giving me this idea!
I’m trying to do a similar thing. However, I don’t have a night tariff, but a small photovoltaics system. Now I’m building a Dimmer that feeds all the excess power (around noon it’s quite a bit actually) into the boiler - it’s still very much work in progress, but the results look promising.
Yes - I did consider that. Which is why I plan to heat it to 70°C, right after there’s no more power from the PV system - should only be like 10°C left, so using a bit mains power is absolutely worth it
If you use the Shelly app or your browser to log into it you will all be set the shell and you can turn off wi-fi and HA… it will still work including time clock. Check your other shellys go to settings / device & services click on a shelly go to “1 Device” under device info click “visit device”… all there stand alone if you like.
@Farnsworth I was reading your other post (DIY Boiler Solar Energy Storage) and ended up here! (Thanks for sharing btw).
I’m looking to do the same: dump excess PV production in a boiler but limit the boiler so it doesn’t pull from the grid if the PV produces less than the rated power of the element.
Issue is: I was thinking of purchasing an old “dumb” boiler for this purpose, but they are all too big for the space I have to put one. I came across several models that seem to have the dual tank setup, and that are only 30cm deep, which I could fit in the space.
And then I read your post!
How did you control the two tanks with the DMX controlled dimmer? Did you use two dimmers or?
So I ended up replacing the boilers electronics with two Shelly 1 - one for each tank. For temperature sensors I used DS18B20 (well - the cheap chinese knock-offs you get from Amazon … they work well enough). The elegant solution would have been to buy the official adapter and temp-senors, but I went the DIY way and directly connected them to the Shelly 1. CAUTION - that means that there is mains power on the sensor (I don’t care since everyting is securely contained within the boiler and grounded)
On the Shellys I run ESPHome with a thermostat configuration, so the boiler is able to operate completely by itself, if for any reason it loses connection with Home Assistant. Thhat pretty much just means, it turns off if it gets too warm.
As for the dimmers, I only use one for both. It’s not the best way to do it, because the boiler has 2500W, but the dimmer can only provide 10A (2300W). That means I have created a Node Red flow that determines which of the boilers is on and dimms it accordingly. In hindsight, that’s an overly complicated solution.
The better solution would have been to use two dimmers. Maybe even not use shellys at all, but use the dimmer (which itself is powered by ESPHome too) as the termostat itself.
For the future (when I expand my PV system) I plan to do it that way. I want to get one really big layered storage boiler with multiple heating elements at the very top. For example there are 6000W 3-phase heating rods, that you can also operate in 3x 230V @2000W mode - and I’m planning to use 3 dimmers for those. I believe that would be a lot less complicated than having one dimmer and switches.
