maretodoric
Posts: 13
Joined: Wed May 01, 2019 12:59 pm

Simple Thermostat ON/OFF Control Wiring

Fri Aug 23, 2019 4:33 pm

Hello everyone,

Not sure should this go to beginners or Projects, or here, so i do apologize. But i am a beginner so I'm posting here.
Basically, i would like to build so the Pi would send ON or OFF signals through thermostat wires onto central heating (wood pellet fireplace), just based on command that i will type in terminal. I do not need it based on room temperature or similar.
Currently i have radio transmitter and receiver, something like this:

Image

The receiver part (bottom left corner) is connected to central heating via two thermostat wires (literally one cable, two wires). The lower right unit is like the top one, it sits in room where temperature needs to be monitored and if temperature drops bellow certain point, it will trigger the receiver to send the signal to power on the central heating via before mentioned two wires. If temperature goes above, it would shut it down.
My question is, could i just connect those two wires to some GPIO pins on Raspberry pi and i could control ON/OFF signal through it, or i need a resistor or transistor in between or similar.
I would connect Pi to central heater without the unit in the picture,

Sorry for silly question but I'm not familiar with thermostats or cables that they are using so i do not know if there is any specific voltage, current, or is it just based on simple switch "technology" if i could say it like that.

I would develop everything else, communications to GPIO, remote control... I just need help with wiring schematics. Again, without temperature sensor. ON/OFF would be controlled manually (or by automation if i build it with help of IFTTT) through RPi.

Thanks in advance.

kflmiami420
Posts: 53
Joined: Thu Mar 21, 2019 6:54 pm

Re: Simple Thermostat ON/OFF Control Wiring

Sat Aug 24, 2019 7:56 pm

...
Last edited by kflmiami420 on Mon Aug 26, 2019 1:50 am, edited 1 time in total.

Andyroo
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Location: Lincs U.K.

Re: Simple Thermostat ON/OFF Control Wiring

Sat Aug 24, 2019 9:01 pm

I would not risk it with your level of knowledge as any error could fry the Pi, break the controller, burn the house down through incorrect controls or even kill you as mains voltage is deadly.

I would look at capturing the signal sent via IR or Wireless between the units - lots safer for your health...
Need Pi spray - these things are breeding in my house...

maretodoric
Posts: 13
Joined: Wed May 01, 2019 12:59 pm

Re: Simple Thermostat ON/OFF Control Wiring

Sun Aug 25, 2019 12:03 pm

Andyroo wrote:
Sat Aug 24, 2019 9:01 pm
I would not risk it with your level of knowledge as any error could fry the Pi, break the controller, burn the house down through incorrect controls or even kill you as mains voltage is deadly.

I would look at capturing the signal sent via IR or Wireless between the units - lots safer for your health...
So, you're saying that voltage going through wires to thermostat relay on central heater is actually too high to cause possible fire or death? Didn't actually realize it's that bad.

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rpdom
Posts: 15052
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Simple Thermostat ON/OFF Control Wiring

Sun Aug 25, 2019 12:28 pm

Many (but not all) heating systems use the full mains voltage on the thermostat. So you could be switching 110 or 240V depending on where you live.

Other systems use 24V, which is safe to switch.

maretodoric
Posts: 13
Joined: Wed May 01, 2019 12:59 pm

Re: Simple Thermostat ON/OFF Control Wiring

Sun Aug 25, 2019 1:45 pm

My heating system doesn't seem to be using any direct power at all on thermostat link.
Check this from my furnace manual, It's on Serbian so I'll try to translate that.
Capture.PNG
Capture.PNG (121.81 KiB) Viewed 409 times
Upper picture:
KOTAO = Furnace
ELEKTRONIKA = Electronics, that one was easy, lol.
SOBNI TERMOSTAT = Room thermostat

When it's connected like on picture 55 (Slika 55) it's not using room thermostat, otherwise, it can be connected to room thermostat like on picture 56.
I'm guessing based on schematics on top picture, this needs to be connected to NO and COM ports, so I'm guessing relays ?
Relay needs to be connected to RPi and thermostat wires to it's relay.

So based on one of links @kflmiami420 sent and based on this schematics from my furnace manual, this is what I'm thinking. Correct me if I'm wrong, please.

I should purchase something like this:
Image

- I should connect the 5V from GPIO PIN4 to VCC pin on module
- Connect IN1 (Relay 1) pin from Module to GPIO PIN 11 (BCM17)
- From IN1 Relay, connect NO and COM wires to thermostat wire terminal , one that has a label of TERMOSTAT on pictures 55 and 56?

If that is correct wiring that awesome! The rest of the programming should be easy on my part, as long as i get the wiring correct.
I wanted to disassemble current thermostat that i have and that is connected to furnace just so i can see the wiring , but the guy who installed it somehow glued it all together, i cannot take the cover off.

EDIT: Just to add something from the manual
"Thermostat link must not have direct power! Thermostat link is pure contact, without dynamics. Due to that nature, it should not be connected via additional power supply otherwise it may come to short circuit or it could fry other components."

PhatFil
Posts: 1345
Joined: Thu Apr 13, 2017 3:55 pm
Location: Oxford UK

Re: Simple Thermostat ON/OFF Control Wiring

Sun Aug 25, 2019 1:52 pm

YES BE CAREFUL !! A quick google of "Unitec sq3 rf" provides a manual
https://www.elementa.rs/files/55275-a.pdf

while i cant read it the picture on page 2 does strongly suggest your 2 thin wires carry 230v A/C at 50-60 hz

maretodoric
Posts: 13
Joined: Wed May 01, 2019 12:59 pm

Re: Simple Thermostat ON/OFF Control Wiring

Sun Aug 25, 2019 2:04 pm

That is confusing.. Yes..
Though device manufacturer that i currently use is Bergen , but the device looks the same on the outside that's why i posted that picture. I'm still trying to find the exact model that I am using so i could find it's specifications.
But if it does transmit full current and my furnace manual says it should not be used, than damn, i was tricked. It's wonder how it even works.

pcmanbob
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Location: Mansfield UK

Re: Simple Thermostat ON/OFF Control Wiring

Mon Aug 26, 2019 7:28 am

The manual you need to read is the one for your boiler , that will tell you if your controls are 24v or 110-230V,

if you have no electrical training I would still advise you do not make any changes to your boiler control systems, as an error could still read to your boiler failing or being left in an over heat situation.

You may also be breaking the laws in your country or invalidate any building insurance you may have.

if you really want to go ahead with this project you need to seek qualified/profession help to make sure your project is built correctly and safely installed.
We want information… information… information........................no information no help
The use of crystal balls & mind reading are not supported

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rpdom
Posts: 15052
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Simple Thermostat ON/OFF Control Wiring

Mon Aug 26, 2019 8:01 am

pcmanbob wrote:
Mon Aug 26, 2019 7:28 am
The manual you need to read is the one for your boiler , that will tell you if your controls are 24v or 110-230V,
I have the user and service manuals for my boiler. I don't believe they mention what voltage the optional external thermostat works at, but inside the boiler is a label that says "All connections are at Mains voltage".

I don't have an external thermostat on mine, just the valves on the radiators. The boiler has an internal thermostat to set the water temperature, so it won't over heat.

It does have a simple internal time switch, which I have disconnected and put a Pi driven relay across the contacts. The Pi has been happily controlling my heating through that for about six years now without any problems.

The boiler has a series of internal safety features, so I'm not worried about the Pi causing any issues.
if you have no electrical training I would still advise you do not make any changes to your boiler control systems, as an error could still read to your boiler failing or being left in an over heat situation.

You may also be breaking the laws in your country or invalidate any building insurance you may have.

if you really want to go ahead with this project you need to seek qualified/profession help to make sure your project is built correctly and safely installed.
Agreed.

maretodoric
Posts: 13
Joined: Wed May 01, 2019 12:59 pm

Re: Simple Thermostat ON/OFF Control Wiring

Mon Aug 26, 2019 2:51 pm

Exactly.

In my case, it has protection if water temperature goes over 80 degrees celsius. It will shut itself off after some period of time if temperature doesn't drop or keeps rising. And it also has few operation modes that will keep that from happening. I will set the max temp on furnace itself, and when it approaches that temp, it will lower the mode of operation (it will start inserting lower amount of pellets so the temperature will drop) and it should idle at set max (should not even reach 80 if i don't set it to 80).
So thermostat is just On/Off. Literally nothing else.

It doesn't even pay to have this thermostat that i currently have set at for example 23 degrees room temp. If that temperature reaches, thermostat will power the furnace off, but in fact, it will remain in low power mode for 10 minutes unless receives ON signal from thermostat. And because of that, temperature will not drop bellow 23 degrees set on controller unit and furnace will shut itself completely off, turning off the fire by cutting oxygen levels to it. Then when temperature really drops, it will start the furnace again.

But at that point, it's not even recommended to turn it on unless cleaned and it consumes more pellet during start operation that it would by just operating at max temperature set at furnace itself.

Ridiculous system. That is why i would at least like to make it work by remotely turning it on/off.
But. if this cannot be handled or if there could be risk. I will try to avoid.

Other thing that i could do is accepting Andyroo advice and to capture the Wireless signal sent by my controller unit to thermostat receiver, and cloning that signal so that Pi can send it instead of controller.
However, i do not think that would be an easy job too, since they operate at 868MHz frequency. And i could only find 433MHz transmitter and receiver modules for Pi.

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