I want to replace my old, mechanical, bimetallic-based heather thermostat with a relay and a controller. It is the classic setup with just two wires that, when shorted, activates an electrovalve.
At first I presumed that it would work with up to 48 volts, but I did test the voltage at the contacts, and I see 220 volts. Checking in the community closet where the electrovalves are placed, I see that, yes, they work directly with mains'220 volts, and, according to the manufacturer, they draw about 7 watts (thus about 32 milliAmps).
I bough this board Módulo 2 relés 5V BricoGeek | BricoGeek.com (the classic one for arduino), but now that I see the true voltage, I'm afraid that it would be "not enough" in terms of reliability. Can I trust it, or should I use something more "rugged" and "professional"? Suggestions?
I'm looking for advise because I don't know if these "cheap" modules are rugged enough for a "serious" use when working with 220 volts, or should be used only in prototyping/learning environments.
You have a very light load, so such relays will cope. Just keep in mind that they are not designed to work in conditions of vibration and humidity.
In addition, the quality of these modules may vary
They will be placed at my living, so humidity and vibration is not a problem. Anyway, if there is a more professional option, I would feel safer... Any suggestion for an arduino-ready solution with guaranteed quality? (price is not a problem)
Why don't you want to buy a professional thermostat?
If you are not experienced with electricity, you should not use your homemade products in residential areas where other people may be harmed by them.
I'm too much experienced in electricity, that's the problem Now seriously, I'm experienced; the problem is, precisely, that I want to be sure that there won't be problems, so maybe that's why maybe I'm overreacting...
Maybe the best option is to add a safety relay in the heather closet, thus ensuring that only 24 volts arrive at home.
If you can bring the power circuit to the electrical panel as well as the signal, may be you could install a suitable controllable contactor in the panel ?
The relay module will be fine. If you're scared you can put a CB and a secondary contactor that is rated to a higher amperage. I use 48v contactors to run 415v 3 phase motors with no issues. You should make sure all your mains voltage is CB protected. The amps you're quoting are pretty measly though so the module should be fine for that purpose. I wouldn't use this type of module at work but for your home thermostat its fine. The main concern would be life expectancy, not fire. A rating of 10A will easily handle the milliamps you're working with.
The main problem with these (cheap) relay modules is often that the necessary creepage distances between 230V and the logic are not maintained. And that is a safety risk independent of any load.
I don't remember if anything changed, but in my time working with electricity, true voltage was V *1.41... 220V true = 310V.
But so much has changed in the last 50 years....
Since you have experience you can use a meager or Hi-pot to validate the relay's insulation resistance. Just keep the test voltages away from the electronics portion.
Those relay modules can not work with the highly inductive load of valve coils. You might need to use a 'contactor' style relay -- they are built to handle inductive loads. Alternately a relay made for air conditioning / heating (HVAC), but those HVAC type relays usually have a coil voltage that does not interface directly with microcontrollers.
Now seriously, I'm experienced; the problem is, precisely, that I want to be sure that there won't be problems, so maybe that's why maybe I'm overreacting...
