Home Automation - High Voltage side

[JohnW2]

In terms of using 5v relays to switch a 12v supply to the DIN mounted relay, how would this work in practice? The bit I cant get my head around is what exactly goes between the 5v output of the PCB relay and the 12v input on the DIN mounted relay??

You woudn't use a PCB relay which had a "5V output". You would use the contacts of a relay (which had a 5V coil) to switch a 12V power supply which then fed the 12V coil of a secondary relay.

My question regarding the dimmers may be a bit of a naïve one. I thought there may be 'intelligent' DIN mounted dimmer modules that could have, say, three circuits connected and I could send a message to an input that would control a specific load - is there such a thing?

Not that I'm aware of, but that means nothing, since I'm anything but an authority in relation to such matters. Others may be able to help.

Is that not now a DIYnot 'Home Automation' forum or something like that? If so, that would probably be the place to get informed answers.

Kind Regards, John

 

[endecotp]

In terms of using 5v relays to switch a 12v supply to the DIN mounted relay, how would this work in practice?

Relays driving relays? Don't do that. Just use your logic-level digital output to drive a transistor, and connect the 12V relay to the transistor.

The bit I cant get my head around is what exactly goes between the 5v output of the PCB relay and the 12v input on the DIN mounted relay??

A wire?

Do you know that there is a separate Home Automation forum here?

 

[JohnW2]

Relays driving relays? Don't do that. Just use your logic-level digital output to drive a transistor, and connect the 12V relay to the transistor.

That would certainly be better but I thouight (perhaps wrong!) from what the OP had said that the only output from his microcontroller was the contacts of (5V) relays.

Do you know that there is a separate Home Automation forum here?

Indeed. As you will have seen, I recently made that suggestion.

Kind Regards, John

 

[dunny]

Thanks for the replies so far.

I can do whatever is needed from the 5v logic level output so driving a transistor isn't a problem - I have only been using the 5v relays for prototyping. I had got it into my head (incorrectly by the looks of it) that one approach would be to use the 5v relay to switch a separate 12v load that would then feed the 12v relay.

I did notice that there is a home automation forum but I thought for the electric side of this it would be better covered here?

D

 

[JohnW2]

I can do whatever is needed from the 5v logic level output so driving a transistor isn't a problem - I have only been using the 5v relays for prototyping.

In that case, do as endecotp said - use the 5V logic output to feed a transistor which controls the 12V supply to a 12V relay.

I had got it into my head (incorrectly by the looks of it) that one approach would be to use the 5v relay to switch a separate 12v load that would then feed the 12v relay.

That's my fault, not yours. I thought you meant that all you had was the 'output' ('contacts') of 5V relays on the PCB - so I did, indeed, propose what you say here. However, as above, if you have the 5V logic outputs, then that's the way to go.

Kind Regards, John

 

[stillp]

Can't the 5V relays switch 230V? Why the intermediate 12V?

 

[John D v2.0]

Yes the home automaton forum is pretty quiet, but not all of the noise here is useful epic fail on keeping the thread clean...

Anyway regarding the main/logic separation, I'm going to do exactly this, and I'm going to have one enclosure with the mains relays in, and one with the electronics in. You need a good separation of mains and 5v, and the cables in the same enclosure to be insulated to mains voltage, so it's best to deal with that problem once.

Regarding driving a 5v output to drive a 12v relay the hardest part would be getting 12v in the first place if you're using a phone charger or a small battery to power it. I'm not sure what the problem with using 5v is unless you have a long run of cable? Keep it simple. some arduinos are only 3.3v nowadays, to save battery power, but if you're driving relays presumably you'll use a phone charger or something.

Good luck and keep us updated! I think I'll be following in your footsteps

 

[dunny]

Thanks. The 5v relays are on a separate PCB joined to the outputs of the microcontroller. There are also optically isolated 12v relays that can be directly driven by the 5v logic level outputs of the microcontroller but I think I prefer having DIN mounted relays instead. I can then mount the microcontrollers in their own enclosure and just pass in the output wires from the controller to the inputs of the DIN mounted relays. Is there any stipulation on the rating of the cabling between the micro-controller and the input of the 12v relays since it will pass into the enclosure of the main board?

D

 

[JohnW2]

Can't the 5V relays switch 230V? Why the intermediate 12V?

The OP seemed to favour 12V relays, although I didn't really understand the ("EMF issues") reason he gave. However, the main thing (I think) is to keep 230V away from the microprocessor's PCB.

Kind Regards, John

 

[John D v2.0]

I think as long as they're marked 300v on the insulations you should be fine. And make sure there's no exposed wire where you've stripped the insulation back.

 

[dunny]

Can't the 5V relays switch 230V? Why the intermediate 12V?

I understood from a post on here somewhere that using the 5v relays could suffer from EMF issues and 12v relays were therefore recommended. If this isn't an issue it would be pretty simple as the 5v relays can switch 230v / 10A.

EDIT - see this post:-

//www.diynot.com/diy/threads/home-automation-consumer-unit.445951/#post-3499778

D

D

 

[stillp]

EMF is a cabling problem, I think you probably mean EMC. I'm not aware of any general difference between 5V and 12V relays when it comes to either generating or withstanding interference.

 

[JohnW2]

EMF is a cabling problem, I think you probably mean EMC.

He might, but as I've said a couple of times, I'm not at all sure what he actually meant, and wondered whether he was perhaps talking about the (possibly) greater voltage drops in cables when using lower voltage cables. Mind you, that would make no sense if the 5V relays were actually in, or very close to, the microprocessor and, in any event, 'DIN-rail-mounted 12V relays' very probably require more current than a PCB-mounted 5V one - so most of those ideas go out of the window!

Mind you, as for EMC, aren't we talking about DC, not even significantly pulsed?

Kind Regards, John

 

[dunny]

EMF is a cabling problem, I think you probably mean EMC. I'm not aware of any general difference between 5V and 12V relays when it comes to either generating or withstanding interference.

I edited my post to show the link I had seen - Have I misunderstood the post on this thread?

EDIT - it was a post by bernardgreen about 8 posts down on the thread above.

 

[JohnW2]

I edited my post to show the link I had seen - I have misunderstood the post?

Are you talking about the reference in that thread to 'back EMF'? If so, that's an issue which has to be addressed with any relay driven by semiconductor circuity, no matter what coil voltage (5V, 12V or whatever).

Kind Regards, John