Heating control with Raspberry Pi

Cerdito

I have the following heating setup in my house as per this diagram

1. Gas boiler controlled by a wall panel (on/off/timer)
2. Hot water heater (immersion) controlled by timer/on/off control

I would like to remotely control both systems using a raspberry Pi while leaving the existing control panels in place. I have drawn a schematic of how I think it will connect. The main questions I have:

1. Will this work as drawn or can it be done better?

2. What would happen if the 5V relay had switched on the boiler/immersion and it was also switched on by the existing timers i.e. two live feeds active?

3. How would I add LEDs to show that the GPIOs were switched in the on position?

Steve

Cerdito wrote: »

1. Will this work as drawn or can it be done better?

It looks like it would work fine as long as the relays are rated for the load they will be switching.

2. What would happen if the 5V relay had switched on the boiler/immersion and it was also switched on by the existing timers i.e. two live feeds active?

The proposed system is optimistic so either or both can call for heat.

3. How would I add LEDs to show that the GPIOs were switched in the on position?

It would depend on the relay board and whether the relays are optoisolated from the GPIO lines. Would need more info to answer that.

Stoner

Steve wrote:

It would depend on the relay board and whether the relays are optoisolated from the GPIO lines. Would need more info to answer that.

Great reply Steve.

Regarding LEDs could you not use other IO and and a very simple bit if code to switch on

Bruthal

The 5v relay is unlikely to be able to switch the immersion directly.

It looks like the relay will also either have the boiler or immersion on, with one or the other always on, if the relay is a standard no/nc 2 way relay.

Chet T16

The Pi has 3.3v outputs so it won't drive those relays. Solid state relays should work from 3v and up and I think most have optoisolation built in.

antoinolachtnai

The basic idea is fine. But buy a relay board. This will provide the opto-isolation and usually has LEDs. It will also sort out the problem with the 3.3v.

I hate to recommend a particular relay board. You don't know what they're going to be like when you actually get them. It is quite important that they have cuts in the board to make sure there is an air gap between the mains voltage and the low voltage. So this isn't a recommendation, it's just an idea of what's out there.

http://www.dx.com/p/4-channel-5v-12v-relay-module-w-optocoupler-blue-expanded-version-452854#.WOIKURjGzdc

You connect it to the pi with some jump leads and off you go. You can test everything before you get mains involved. It is very important to go to the trouble of boxing everything up properly.

In principle you might be able to control a small immersion with a 10A relay. In practice I advise you not do this. I would suggest you buy a contactor, which is a safe way to do this. It is basically a high-amps relay, boxed up to be safe and to deal with the various bad things that can happen to a relay. This will cost a a few bob (probably more than the whole rest of the setup) but is worth it for the peace of mind. You can also buy a solid state contactor, but it will cost more. You can get cheap contactors from the far east, for sure, but why take a risk with high amps and high voltage? This is especially the case if you don't have a lot of knowledge and experience.

Get enough relays to control what you actually want to control. I don't know exactly what you are trying to do on the diagram. You seem to have two things connected to one relay.

What are you going to use for software?

Cerdito

Thanks for the recommendations and comments. My design has come on a bit since I posted last. I put together this diagram:



Using a Pi Cobbler to connect the GPIOs to my breadboard. Using a 5V 10A relay board in the kitchen as the boiler control is only 3A.

For the immersion I'm using a 40A rated Solid State Relay with heatsink. I have two DS18B20 temperature sensors, one in the living room and one external one routing out through the attic.

The software I intend to use is PiTherm. I thought about programming it myself in Python and using WebIOPI but I can't afford the time (new baby!!).

antoinolachtnai

Who needs an outdoor sensor when you have the Internets?! You could put the extra sensor on your hot water cylinder.