Controlling mains power with GPIO (In a compliant way)

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Handle9

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#2485380 18-May-2020 00:37

If you go with one of the major manufacturers (Schneider/Modicon, ABB, Rockwell/Allen Bradley, Siemens) you'll get decent legacy support for smart relay type products and can be done very quickly. If it was a Chinese product I'd be more wary.

The smart relay products are really cool now. These are designed for these types of projects (bring in a sensor, run into a compare block and switch something on or off on a schedule). Once you go to a "proper" PLC it's way more powerful but significantly more work to get going and for a domestic project the F around factor isn't really worth it IMO.

I've burnt waaaaaaay to much (of my employers) money on modbus integrations over the years. If it's booleans it's ok, if it's Floats, especially when some manufacturers seem to love reverse doubles without documenting them, kill me.

Disclaimer: I work for one of the major automation OEMs and have managed a lot of very large integration projects so take that as you will.

SirHumphreyAppleby

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#2485416 18-May-2020 09:21

Some great discussion happening over night. I thought the Geekzone community was going to let me down on this one.

What @SomeoneSomewhere has suggested is pretty much what I thought would be required. I.e. GPIO [-> relay] -> relay (with appropriate 'real' specifications and certification), with the first relay being required to provide the necessary coil voltage/current for the second relay.

The need for a tool to enter the enclosure with mains power wasn't something I'd considered, especially up in the roof.

With that in mind, my thoughts are to install a secured cabinet with at least two DIN rails, with the mains relays on one rail and the GPIO and intermediary relays on the second.

I'm not sure how Modbus would address scalability. The ad hoc nature of MQTT allows nodes to be configured to publish or subscribe to events based on a logical structure rather than a physical one.

I looked at PLCs a while ago and they definitely seemed to have a massive F around factor. Legacy support doesn't seem to be great in the domestic market for any sort of smart product. Didn't PDL have one a while ago?

dolsen

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#2485515 18-May-2020 11:45

At my house I use a mixture of zwave, DS/ Kogan smart switches reflashed with tasmota and one Sonoff for the towel rail (they are really good for that purpose with their timers / schedules / mqtt integration).

As the above are excluded by your requirements, have you looked at what can be done with the new(ish) PDL Iconic range with Bluetooth?

Not GPIO, but, may be able to do something with that? Would be able to get signoff and includes isolation by the use of bluetooth. Depends on what exactly you want to do though.

SomeoneSomewhere

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#2485590 18-May-2020 14:05

Modbus is kind-of more extendable in that your server can talk to more IO modules easily. If your RPi as acting as both the head end and the IO, this could get harder - you need a bank of pi.

You definitely want commercial grade gear, domestic grade smart home stuff is gone in five years.

There is a huge installed base of CBUS (but you can't really do anything outside that walled ecosystem), or you can get DALI relays and some kind of bridge to let an RPi talk to them.

pipe60

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#2485817 18-May-2020 19:11

I run a M340 PLC in our house there is not much you cant do with them,I use modbus tcp to the HMIs and to talk to the PLC in pump shed.

The Zeilo smart relays are worth a look but any thing with free software is a good starting point.

SirHumphreyAppleby

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#2485821 18-May-2020 19:13

dolsen:

have you looked at what can be done with the new(ish) PDL Iconic range with Bluetooth?

Not GPIO, but, may be able to do something with that?

I stumbled across these while looking for signs of the old PDL smart home product I'm sure they once offered. I think they are an okay solution for someone who wants very basic control of lights from a switch, but it's still a very limited product. I wouldn't install them as they use a proprietary system and ongoing supply and support is uncertain.

SomeoneSomewhere: Modbus is kind-of more extendable in that your server can talk to more IO modules easily. If your RPi as acting as both the head end and the IO, this could get harder - you need a bank of pi.

I'll only be using the Pis for I/O, but even if I were to install Node.js and NodeRED on there to do the things I will be doing myself in C, I'm confident the hardware is more than sufficient for the job. Most likely a PC Engines APU2 will be deployed for accumulating data and handling logic. That's another under-powered system by modern standards, but critically uses very little power and can be kept running for long periods during power outages.

I will be building a complete prototype system before I attempt to install anything, so I'll have plenty of opportunity to find any pitfalls in advance.

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Handle9

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#2485825 18-May-2020 19:29

SirHumphreyAppleby:

Some great discussion happening over night. I thought the Geekzone community was going to let me down on this one.

What @SomeoneSomewhere has suggested is pretty much what I thought would be required. I.e. GPIO [-> relay] -> relay (with appropriate 'real' specifications and certification), with the first relay being required to provide the necessary coil voltage/current for the second relay.

The need for a tool to enter the enclosure with mains power wasn't something I'd considered, especially up in the roof.

With that in mind, my thoughts are to install a secured cabinet with at least two DIN rails, with the mains relays on one rail and the GPIO and intermediary relays on the second.

I'm not sure how Modbus would address scalability. The ad hoc nature of MQTT allows nodes to be configured to publish or subscribe to events based on a logical structure rather than a physical one.

I looked at PLCs a while ago and they definitely seemed to have a massive F around factor. Legacy support doesn't seem to be great in the domestic market for any sort of smart product. Didn't PDL have one a while ago?

To answer your question on scalability Modbus is a truly open protocol with thousands of vendors selling products. You can have hundreds of devices on a network and once setup is very reliable. It has some very real limitations that more modern protocols like BACnet or Profisbus address (as well as introducing their own issues) but it is about as interoperable as it comes.

MQTT is a much more modern standard and isn't really built for large scale industrial/commercial automation. If I want to build scheduler groups or mass update setpoints it's a PITA where something like Profinet or BACnet is built for it. It really depends on what you want to invest / achieve.

IMO you have three real choices.

1. Roll your own solution, which appears to be the way you are going. Cheap, fun and pretty much unsupported by anyone who isn't you. Guaranteed to require ongoing support and a PITA when hardware becomes unavailable. Domestic grade hardware so it'll die in a ceiling in 5 years.

2. Use "Smart" domestic products. Cheap, you get modern tools to use. Gear comes and goes, getting spare parts will be a PITA. Not that flexible. Will dies in a ceiling in 5 years.

3. Use a "real" automation platform. More expensive, tools/protocols aren't as easy to use but will be supported for many years and there is usually an upgrade path for hardware and software. Will likely be much more reliable that 1 or 2 and require very little ongoing support. Not cheap compared to 1. or 2.

SirHumphreyAppleby

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#2485846 18-May-2020 20:12

Handle9:

1. Roll your own solution, which appears to be the way you are going. Cheap, fun and pretty much unsupported by anyone who isn't you. Guaranteed to require ongoing support and a PITA when hardware becomes unavailable. Domestic grade hardware so it'll die in a ceiling in 5 years.

I think that's a pretty good summary. The exception being that I won't be relying on any particular hardware/software vendor.

Removal of smart features from the system will also be quite simple.

Eitsop

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#2485893 18-May-2020 21:01

SirHumphreyAppleby:

niallm90:

Can you link what relays your talking about? Are they a fully enclosed package or do you plan to put them in a box?

The panel mount relays are here...

https://nz.rs-online.com/web/p/solid-state-relays/1450568

I don't think these are suitable for more than a couple of circuits due to the switching current requirements.

In terms of cost, a 24V coil relay similar to below is cheaper and easier to source, even if you need to add another power supply.

https://nz.rs-online.com/web/p/non-latching-relays/8886871/

Any need for an enclosure is one of the compliance requirements I am hoping to establish with this thread.

So you saying you could have

- RPI

- RPI Hat Relay https://nicegear.nz/product/raspberry-pi-relay-board

- 24v Power supply between RPI Hat & Solid State relay https://nz.rs-online.com/web/p/din-rail-power-supplies/1368308/

- Solid State Relay https://nz.rs-online.com/web/p/solid-state-relays/9225194/
- plus SS Heatsink https://nz.rs-online.com/web/p/solid-state-relay-heatsinks/9222123/

Obviously in a electrical box. And this would control a HWC okay?

SomeoneSomewhere

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#2486572 19-May-2020 18:39

With SSRs and significant load, you need to be really, really, really careful with cooling. If you're at more than 1/3 of the rated capacity or have several in a box, you will probably want forced cooling. Beware that even when you're looking at the derate for 'ambient temperature', this doesn't include the amount that your enclosure heats up due to their own heat. I have seen banks of them melt plastic.

We usually use DIN mount ones like this. They're also nice in that the low voltage plugs in separately.

Another option, if you use the panel mount ones, is to mount them to a metal box and then mount a heatsink to the outside - this is sometimes called 'cold plate' and avoids issues with dust inside your box.

For a hot water cylinder which doesn't need to be switched frequently, just get a contactor like this. Save the SSRs for stuff like infrared radiant heating where you might want it to switch every minute or two, or lights that you want to flash.

You could also use a transformer instead of using DC. Costs a little more but will last for decades - who wants to replace a power supply because it's in a hot box in a hot attic? 24VAC contactors are also easier & cheaper to get hold of.

Eitsop

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#2486595 19-May-2020 19:13

It’s all harder than it should be.
we should be able to something like this

https://www.aliexpress.com/item/4000302967772.html

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Eitsop

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#2486602 19-May-2020 19:30

Think I will wait until snider electric wiser products come to nz

https://www.se.com/fr/fr/home/smart-home/wiser/energy-management/

andrewNZ

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#2486621 19-May-2020 20:21

attewell:
It’s all harder than it should be.
we should be able to something like this

https://www.aliexpress.com/item/4000302967772.html

Wouldn't touch that with a very long pole.

As with many Chinese products, the claimed specs are generous at best.
I don't believe there is any way you can switch the current they claim in the size device they have.

Handle9

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#2486627 19-May-2020 20:26

andrewNZ:
attewell:

It’s all harder than it should be.
we should be able to something like this

https://www.aliexpress.com/item/4000302967772.html

Wouldn't touch that with a very long pole.

As with many Chinese products, the claimed specs are generous at best.
I don't believe there is any way you can switch the current they claim in the size device they have.

You don't think 10kVA is possible in such a compact form factor? Surely no Chinese manufacturer would rebadge their product into 5 different current rating without upgrading the internal components? They would never supply safety test reports to whatever spec the customer wants overnight either. 🤣🤣🤣

SomeoneSomewhere

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#2486671 19-May-2020 21:28

This product has NO overcurrent protection.

Hmm. Certainly not a circuit breaker.

Assuming you weren't using it as either a circuit breaker or device for isolation (which it fails on numerous grounds before even getting to the 'must comply with X standard' stuff)...

You can get contactors around that size. This is a double-pole 63A version, at twice the size. Delete one pole... single pole units just aren't really made. Not sure why.

Fitting electronics into the same space would be fun, though.

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