AC Power and/or Relay interface

  • I am looking for a way to put an MySensors Relay actuator behind a wall switch. I read a lot of information provided here (special thanks goes to @sundberg84 for all his research and sharing his findings and results) and also studied some power supply designs found on the web ( and also some commercial products).

    I learned a lot and feel like I demystified the architecture of power supplies a bit, so that I am now a lot more comfortable with AC mains electronics in theory. I think the recommended design for Safe In-Wall AC to DC transformers is safe enough to use and as far as I have seen it is even more secure (at least by design, schematic is another topic) than a lot of commercial products out there.

    But nevertheless I am still concerned because of missing certifications and the fact that assurances might decline to pay in case of an accident. That's why I am currently looking for another solution. My dream solution would be something that deals with everything AC related and provides an low voltage output (as well as an digital input for controlling an embedded relay).
    I am pretty sure there is nothing like that, but asking doesn't hurt.

    I also like the Sonoff devices. I'd consider them also, if they would be using an Atmega instead of an ESP8266 and if they were smaller in size. But on the other hand using a custom software would again break the certification...
    Also the Livolo switches are nice for tinkering, but missing an interface I could use, I think this is also not a solution for the certification issue.

    Maybe here is somebody who has seen something like that or who has another suggestion.

  • Mod

    What's the problem with esp8266? If you want really small relays you need to look at zwave products

  • @gohan There is no problem. I like the devices very much, but I'd like to have something not WiFi based for that purpose.

    Why Z-Wave? Do you know a Z-Wave device, that serves low voltage output and is externally controllable?

  • You can find that in any electronic shop, it is called phone charger or just 5v power supply. If You want to put it behind the wall switch You have to search for flush mounted power supply, but it is hard to find realy small one that will fit with another device.

  • @rozpruwacz Thank you for your suggestion. I already searched for that for hours (if not days). Most results are either uncased (so not certified) or/and quite expensive.
    The best thing I could find was the Recom RAC03. But the price (and again the missing certification, not sure) make it not suitable.

  • @exilit said in AC Power and/or Relay interface:

    Recom RAC03

    I'm no expert in consumer electronics certification but i think that this is the same as HLK module. I'm talking about something like this:

  • @rozpruwacz Wow, that looks great. Still missing the relay for my dream product 🙂 but that's a starting point. Do you know more of that? Like I said, I searched that for days and didn't find anything similar.

  • @exilit said in AC Power and/or Relay interface:

    Recom RAC03

    oh, You are talking about this ?

    if so then yes this is exactly what I mean and actualy this item looks very good 🙂 about the price I believe that maybe you could find something half the price but not less ...

  • Mod I think this could be an option

  • @gohan Thanks, but I believe Z-Wave will be expensive. And apart that I would really like to run MySensors (Not mandatory, but currently my goal).

  • @exilit said in AC Power and/or Relay interface:

    like to run

    from my personal experience: more You do yourself the cheaper unit price but You spent on it more time - so You have to calculate how much Your time costs.
    The other issue with making something to fit into wall switch is that it has to be small, so this requires more custom design -> so more made by yourself -> then it won't be certified. Or You choose small but very expensive parts.
    Personally I wouldn't buy cheap power supply, this is the most important part of the device.

    So if You have good knowledge how to design safe power supply just do this and don't worry about certification, If You design it well then it will not cause your home tu burn 🙂

  • other solution would be, considering that there are thick cables in the walls to handle large currents, to run only low DC voltage instead of high AC voltage for the lighting, but it would require to use low voltage (12V DC) led lights everywhere. And this might be a problem, because there is very little bulbs operating on 12V DC axept of led strips and some halogen replacement bulbs.

  • @rozpruwacz said in AC Power and/or Relay interface:

    If You design it well then it will not cause your home tu burn

    🙂 Yes you are most probably right. But if it does, I will not only lose my house, I will also be bankrupt and homeless.

    But seriously: This is what I was thinking for some time also. Especially because I have seen In-Wall device that are way unsafer than the ones on this forum using the HLK. But for some reason I'm very unsure for the last few days...
    So if there is another solution I think I still would like to take that. If not... well, I will do it myself and hope that my house does not burn. Maybe I put a CE sticker on it... 😄

  • Mod

    You wanted small device that is also certified and the smallest solution I know are Zwave devices. I don't think you can find a certified product running on atmega controller with mysensors and be also certified

  • @gohan I know the requirements are very specific and hard to find. I am just searching for ideas.

  • Mod

    It is just a matter of choosing commercial or DIY, that means certified or not certified 🙂

  • @rozpruwacz said in AC Power and/or Relay interface:

    @exilit said in AC Power and/or Relay interface:

    Recom RAC03

    oh, You are talking about this ?

    if so then yes this is exactly what I mean and actualy this item looks very good 🙂 about the price I believe that maybe you could find something half the price but not less ...

    Yes, that is what I was talking about. Half the price sounds good.
    But to be honest, I think the one you posted suits it better. The Recom power supply's use cases seem to be the same as the HLK module.

  • @exilit the one i posted is much bigger and 12v, so You need buck converter. This makes it harder to fit atmega board, but maybe You will :). for sure there is more 12v flush mounted power supplies and they are cheaper because they are used for led lighting. The cheaper ones will propably draw more power, they will be powered 24/7 so it is important that they draw at lest less than 0.5W.

  • @exilit what voltage are you needing?

  • @Black-Cat Ideally 5V or 3.3V. But in the end it doesn't matter too much, as converting it down wouldn't be too difficult. Do you know something?

  • @exilit For Z-Wave control the only device I am aware of that uses those voltages is a Z-UNO. You would need to build your own controller but it's not difficult.

  • @Black-Cat I'm a little bit confused. This does not address my issue, does it?

  • Mod

    @Black-Cat He is looking for an in-wall relay and a small power supply.

  • @gohan the smallest PS that I know of that is enclosed is 62.55128mm (LWH)
    available in 3.3v, 5v DC
    There should be local distributors in the required region.
    If the OP can do without an enclosed PS then there are smaller such as
    this step down shield. Supplies-Connectors/Transformers/AC-DC Supply-240vAC-5VDC

    There are many different relay's on the market, googling will turn up something that fits the requirement.

    Sorry about the Z-Wave confusion.

  • @Black-Cat said in AC Power and/or Relay interface:


    RAC03-05SCR/277 is smaller

  • @Black-Cat said in AC Power and/or Relay interface:

    If the OP can do without an enclosed PS

    I can do, but I am specifically looking for something that simplifies (in a sense of "assurance-safety") the whole High Voltage side. The products posted by you are really nice, but unfortunately do not address my request. 🙂

    Like I said before, I am aware, that the product I am searching for might not yet exist. (wondering why 😕 ) But maybe somebody has seen something like that.

  • Mod

    @exilit said in AC Power and/or Relay interface:

    (wondering why )

    I'd say because they don't want people mess with the product so they usually sell product with their own SW solution. It is like rooting a mobile phone, in case of problems you are out of warranty and in case something happens they are out of liability

  • @gohan Well, for most companies you are probably right. But have a look at ITEAD with their Sonoff products... They are already quite open and also seem not to do a lot against people tinkering with it. They sell good products which are adoptable if needed/wanted. And people obviously like it and large communities originate from that which create even better products.
    So I think there is a market for those products.

    That's what I mean, I'd like to see products where I don't have to void the warranty because I don't need to open it.

    I imagine something like the following:

    I think that would be awesome.

  • For good AC-DC solution look at MeanWell and their IRM range, For example, IRM-05-5

  • Mod

    @exilit also ITEAD has a warranty sticker that you need to break if you want to reflash the relay. Could be a good idea what you proposed, maybe you can start a kickstarter campaign 😄

  • So I did this recently, I have two ESP8266 Wemos based switches and 2 MySensors based in production right now with more MySensors on the way. They encompass the following from AliExpress:

    Arduino Pro Mini & NRF24L01
    220/110V to 5V Transformer -
    WS2812B Single LED -
    2 Small Tactile Buttons -
    Relay -
    Dupont cables to make the switch and box separate.

    3D Printed Switch and Rear Box

    I created a switch and the box that goes in the wall in TinkerCAD. On the switch side, there is a little WS2812B led which i use to show states, and a little startup sequence to know its up and connected to the MySensors gateway. There are two buttons both behind the switch, one is pressed by the switch itself, the other is a reset switch which connects ground to the reset pin. This is in case it needs to be reset or something. I did this 2 piece approach for being able to take off the wallplate, pull out the switch, connect up the FTDI adapter and upload new code in the case of the MySensors nodes. For the ESP8266, those are OTA.

    I am printing the latest version of the box and switch now, I will upload pics when they are done.

    Here is the one in my garage, white means light is off (so you can find it in the dark), green is on. There is a red light coming from behind the switch which is the relay light, I dont care much in the garage so you can see it. On the inside ones, I used a small piece of heat shrink to cover it. Also, the pictures just do not do it justice at all, the light blurs out the camera and you cannot see the switch very well nor the power icon behind the LED.


  • @gohan said in AC Power and/or Relay interface:

    maybe you can start a kickstarter campaign

    I did not thought about that, but that sounds like a good idea :simple_smile:. Maybe it's worth thinking about it.

  • @Brian-Morris Great project, looks good. But I think also not what I am looking for.

  • Np. I saw the "I am looking for a way to put an MySensors Relay actuator behind a wall switch." description. My project is a switch and relay in 1. Are you talking about just putting a MySensors node with a relay behind a working normal light switch?

  • Adding the imgur album.

  • @Brian-Morris i Think wat i am really looking for is a tinkering-friendly Device that can deliver some low voltage power as well as a possibility to switch higher voltage devices.

    The point is that - as far as I know - tinkering with low voltage is uncritical (with respect to assurances and power providers) but everything related to mains power needs to be certified and/or should only be installed by people qualified to do so. So what I would like to see is a device that can be controlled easily and at the same time is safe to use.

  • @exilit said in AC Power and/or Relay interface:

    @Brian-Morris i Think wat i am really looking for is a tinkering-friendly Device that can deliver some low voltage power as well as a possibility to switch higher voltage devices.

    The point is that - as far as I know - tinkering with low voltage is uncritical (with respect to assurances and power providers) but everything related to mains power needs to be certified and/or should only be installed by people qualified to do so. So what I would like to see is a device that can be controlled easily and at the same time is safe to use.

    LV is a voltage above 110VAC or 50VDC, this is the critical test.
    Below 110VAC or 50VDC it is ELV and does not require the mandatory testing.
    For a device as suggested to be made, it would need to undergo testing, then further reporting and certification in many different world wide regions before it could be sold on the market.
    It is a very expensive and time consuming effort (been there and done that)-I doubt that any money could be made on developing a device such as this (it's still a good idea, don't get me wrong, but I doubt it has a commercial application otherwise it would have been made.)
    The least expensive way of controlling Line Voltages remotely that I would use is to use a Z-Wave device. Depending on the region you are located this will cost you between 40-maybe 85 local currency units. Use OpenHab as your controller software then you have control from your sensors and Z-wave control of your Power relays.
    Problem solved.

  • @Black-Cat Thank you for your input, I really appreciate it. Sounds like you have some experience with the whole topic of certification. Apart from being time consuming and expensive, do you think it would be possible to certify a device that allows to switch LV (Low Vortages?) by exposing an ELV (extra Low Vortage?) Interface?
    Or does any Device interfering with the LV device have to be certified also?

  • @exilit This will depend on the region for certification.
    Where do I start?
    Generally, most if not all devices will come with Test Reports for that region. i.e. The EU has an overall requirement, but there may be local variants that need to have an aspect of the device that needs a specific test report.
    Once you have that report you can apply to a Certifying Authority for the issue of a Compliance Certificate (more cost). The Certifying Authority may (and usually does) find another aspect of the report that has not been covered, so occasionally you end up back to Step 1. Just as an example, the last Series of electricals I had certified took 18 months of back and forth communication between the Reporting Authority and the Compliance Company.
    It burnt a huge hole into the budget, not only because of the cost, but also the delay in bringing products into the market.
    There may also be different Equipment Levels, ie Level 1, 2 or 3. to contend with.
    The device will have to comply with the requirements of these levels. In our region Level 1 is the most stringent and applies to all devices that the Consumer can come into direct contact, ie Switches and so forth. The level will determine the complexity of the reporting required. Devices that are designed to be installed by an Electrician in a switchboard and treated differently. (usually Level2)
    You could argue that this device is for professional use and will be installed by a Qualified Electrician in a Electrical cabinet of some description, but it's really drawing a long bow when you manufacturer it yourself. On the other hand if you make it and use it yourself (don't tell anyone just in case it fries and burns the house down) then you have what you want.
    Is your head aching yet? Mine did and still does at times, however I can sleep soundly at night knowing that we have taken all possible precautions and the devices are as safe as they can possibly be and if the issue lands in Court then I can waive the necessary paperwork to prove that we were not negligent.
    To simply answer your question:
    Any device that uses LV will require some type of Test Report and Certification if you intend to manufacture and supply these for sale.Just be using a signal or ELV to control LV does not offer a way around the requirement.
    However as you can now probably see, it's just not that simple.
    I hope this helps, it not complete but you need to do a look of research of the requirements relation to the Certifying of Electrical Equipment in your region and make the correct judgment. As a Start look up Standard IEC 60669 and all the parts that come with it as a generally primer.

  • @Black-Cat Wow, thank you for all the information, that really sounds almost impossible.
    I will definitely try to get some information regarding IEC 60669.

    So if I got you right there will be one test report in the end which will cover all the different tests required by the different certifying authorities.
    There are two things I still not understand.

    • Is it possible to certify a device so that it can be extended (through a defined interface) by self made hardware without loosing the certification?

    • What do you mean with the part about doing it myself? I think just not telling anybody would be difficult, as the assurance would like to know what caused the fire and therefore would do some research to find out. Or are you talking about the case when it is a Level 2 device and I only connect it myself?

    I hope you understand what I mean. It's difficult for me to write down this part.

  • @exilit One test report should cover it. I say should as it is really up to the Certifying Body to determine it any further reports are necessary. These could be FCC (radio frequency reports), LVD, CISPAR or statements that report the use of certain products used in the manufacture and disposal of the PCB, Components, Solders etc.
    Certifying is a very comprehensive process and I think that any advice I give you really is only an opinion as requirements will vary.
    My feeling is that you should obtain professional advice from a Electronics Engineer who has all the answers to the questions you ask before proceeding any further.
    In answer to your points, you should be able to obtain certification on a device that has an additional interface, however, the device that interfaces may also need certification or may already have it.
    Doing it yourself I meant as a a DIY project, oddly if you offer it as such then there appears to be no obligation on your part to seek reporting or certifying advice.
    Sell it as a kit and buyer beware.

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