I’m not an electrician, so take this with a grain of salt, but I believe 20 amps should be enough with your 3.6kw load (which is about 16 amps), but I opted to get a contactor that is 25 amps, just to be on the safe side.
It’s on a 20amp spur so 20 should be plenty but I may well use a higher current contactor as the price difference isn’t much!
Just built one using a shelly1 and a 40A contactor to control my water heater.
A replacement for a 30A load switch from insteon that croaked.
Contactor and case from Amazon, shelly1 from Allterco
CONTACTOR 2 POLES 40A 240V (2 Pole 40 Amp 240 Volts)
I added a push button and indicator light as well.
Thanks All
I’ve gone the route of a Sonoff TH16 + 25amp 2 pole contactor and enclosure as that covers my need for a temperature sensor, Alexa control and ability to handle 3.6kw storage heater, total cost £55
I would be a bit wary of the Sonoff TH16. I had one connected to my immersion heater whilst we were having building work done recently, and the builders failed to switch back on the water leaving the tank dry. The Sonoff burned out, I think because the wire terminals are not very robust (flimsy push-type rather than screw terminals), and very nearly started a fire.
Same thing happened to this guy:
https://support.itead.cc/support/discussions/topics/11000012976
Probably worth avoiding for high load applications, despite the power rating.
I’m just using the Sonoff to switch the contactor so there will be very little load, I had read about the Sonoff and that’s the main reason I am not attempting to use it to supply the actual load current, technically I could have supplied 3.6kw but I wasn’t going to risk it!
You wouldn’t happen to have a write up of any kind on this would you?
Not really, no formal writeup. Somewhere I have a half-a$$ schematic that I can post.
The thing about the contactor I bought is that it is bristling with push-on connector blades that makes the connections to the push button, indicator lamp and shelly1 super-simple.
A schematic would be awesome! Keeping the HW heater off during peak times would cut down on the electricity bill a lot I think.
I don’t know your background, so I will caution you to be very careful with this. I have been using my shelly-controlled contactor for several months now and it has been working fine
FWIW, when I first moved into my house, the electric water heater had its own meter, so I could tell how much I was spending on hot water; about $60/month in the early 80s in New England.
I put a “Little Grey Box” mechanical timer on it and my bill was cut in half. So your bill should see a similar reduction, if you choose to run the heater about 8 hours/day.
Mine runs that over 2 4-hour blocks.
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This is perfect! Thank you, I’ll post back with my results
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FYI, the Shelly1 should be set up as a latching relay, with the switch mode as a push-on / push-off.
The button offers a manual override, should you want to control the appliance outside of its regularly scheduled times.
I have similar situation, only I try to power my electric heater that draws 2400w. Could something like that be done with sonoff basic and contactor?
Yes, it doesn’t matter which HA-supported switch you use for the contactor. You only switch the contactor coil. The power circuits are connected to the contacts of the contactor.
Nice, thanks!
Do you meybe know any contactors on aliexpress that are any good for 2400W heater?
I was looking at this one:
25A and 230V is 5750W. Sufficient reserve.
Well, i placed an order on those, it should be safer and more reliable than 16A relay.
Just curious if you have any feedback on this contactor; reliability/quality? Thx
This Aeotec switch works beautifully for my pool pump, has been going strong for a while now.