automatable open call for heat w/240v heater controlled by Nest

andrewco

Hmmm...ok sonoff said that the dry contacts were both controllable and can control the line voltage circuit. I guess that's not the case.

ratio

Ok, things are starting to make more sense now. The 'aux contacts' ('S1' & 'S2") on the mini r2 are the input contacts, they get tied in to any (dry contact) manual controls you may have. The relay output itself is actually tied in to the high voltage internally—'LOut' will be connected to 'LIn' when the relay is turned on. It will not work for switching the low voltage call without extra parts, and it does not have a high-enough rating to switch the heating load directly.

The relay should go beside the RC840. You pick up line voltage before the RC840 contacts (so it's always energized) & use it to power a 240v relay like the RIB I mentioned, & use that to break the W just like the drawling you posted above.

andrewco

Ok. I guess sonoff saying I could control S1 & s2 was incorrect. I was just trying to find a single unit that had controllable dry contacts on it and could be powered by my nearby 240v power source. I could put in yet another relay but was hoping to avoid another device.

ratio

One thing to think about is that mini r2 '240 volt' rating is a European rating, meaning that it's still expecting the neutral to be at roughly ground potential. There's no guarantee that it is completely safe to operate with that terminal at a nominal 120 volts to ground like our 240 volt circuits.

andrewco

ok - so back to the drawing board. Need something that I can control with IFTTT (wireless automate) that can run off of 240v (not switch 240v) and can break the W wire contact (dry contact). Any ideas?

Zman

It is possible that the controller has "dry contacts". I can't determine that from the specs. Do you have a schematic from the manufacture

andrewco

I can't find it but I did a quick search and almost all implementations have S1 & S2 as switch input contacts as @ratio mentioned. I don't think these can be controlled - if so, they're probably be called something like C1 and C2 or such.

Jamie Hall

First off, let's get one thing very clear for you, as it seems to have escaped you entirely. That gadget requires 120 VAC to operate (actually 120 to 240, as it has a solid state power supply in it which can handle that range). It has a switch inside it which can switch 120 volt AC, up to a maximum draw of 10 amperes.

It won't operate on 24 VAC.

It won't switch more than 10 amperes current draw at 120 VAC.

I'm not actually sure that it will switch 24 VAC (some all solid state switches, which I suspect that is, won't correctly switch low voltages, even with what appear to be isolated -- "dry" -- terminals), which is what both your Nest and your heater require to be switched (that's that white wire).

Therefore.

It must be powered from a 120 to 240 VAC power source.

To be reliable, you have to use it to control a relay, which can also be powered from a 120 VAC source if you select the correct relay.

That relay in turn will make or break the 24 VAC heater control circuit from the Nest to the heater.

None of that is optional.

As I have said earlier, you are -- in my opinion -- taking an exceedingly complex approach to perform an exceptionally simple task.

andrewco

@Jamie Hall I completely understand that it needs to be powered. That was my earlier question. From an earlier comment the W wire doesn't carry 24 VAC hence the ability to use a dry contact for controlling it.

So based on how I'm currently controlling the heater with the Nest and the R840T, what's the best way to cut the call for heat (W) wire with smart control?

andrewco

Ok - it seems there was conflicting information. I had asked if the W wire actually carries 24 VAC and @Jamie Hall said "any switch (dry contact) will do" but then Jamie goes on to say the W circuit can carry 24 VAC which would seem would disqualify it for being control by dry contacts.

Jamie Hall

Oh dear. What I meant was that the control wire, depending on how the rest of the control circuits are wired, may have 24 volts on it if tested. Might not, too. What is important about that wire is that it completes an electrical circuit from one control terminal on the control, through the control devices, and back to the other control terminal on the control. Closed circuit, controlled device fires up. Open circuit, controlled device is off.

Neither the switch -- nor the Nest nor whatever else you might use to control -- is a power source. It is simply a way to close or open a circuit.

andrewco

@Jamie Hall right - I'm following you. Closing the W wire circuit closes the control circuit and since its a 24 VAC circuit could have 24 VAC running over it ;-) Therefore, it would be prudent to control that circuit with a device that potentially could handle 24 VAC. Instead of getting another relay that then in turn is controlled by my smart device (MINIR2), it would be great to have a single device that

a) can be powered by the local power source (240 VAC)
b) can control the W thermostat control circuit
c) is a smart device

Jamie Hall

It is entirely possible that the smart device can do it without a relay -- or it might even have a relay built in for the dry contacts. If it is known to have a mechanical relay, you're good to go. If it isn't, you can check if you have the device and a multimeter. First, check the resistance from each dry contact terminal in turn to both power feed lines to the device and to the ground (if the device has a ground wire). The resistance should be several megohms. Then plug it in, and check the voltage on each dry contact without anything else connected to the contacts and ground -- you may read a voltage, but it may vary -- and between the dry contacts (should be zero). Then, assuming we're good so far, measure the current from each dry contact to ground (should be zero) and between the dry contacts (should also be zero.). I you're still good, turn the device so it's on. Measure the voltages as before, and, if they are all still zero, measure the resistance between the dry contacts (should be close to zero if not zero). Now turn it off again, and recheck the voltages as before; if they're good, measure the resistance across the dry contacts (should be several megohms -- but if there' any voltage on either dry contact, don't try to measure the resistance -- it may fry your multimeter).

If it passes all of the above, it should work without the relay.

A bit more theory if interested. If it's a solid state relay (not mechanical), the switching is usually done by devices called triacs. Depending on exactly how the device is designed, these may have one of (or more than one of) three problems. They may have a residual voltage on the output from device's own power supply. They may not turn off completely -- and the off resistance may not be high enough to shut off your heater. Or they may fail to turn off at all, if the reverse voltage isn't high enough.