Headache about migrating dimmable halogen spots to LED spots

Hi folks,

Need help again from the electrical guys in this community...

In my living room there are 7 (12V) halogen spots that can be put on/off and dimmed via 3 separate physical push buttons. With a short click the spots go on/off and when I long press it, the spots will be dimmed (first long click the brightness increases, second long click the brightness decreases, third time the brightness increases again, and so on ...).

It has been working fine for about 20 years, but now suddenly 2 spots died. So the wife gave me a female hint that it is now time to migrate to LED's. And according to here this 'cannot be that difficult' :wink:

My current wiring diagram looks like this:

I was wondering if I could just remove the transfo, and replace my 7 (12V DC) halogen spots by 7 (230V AC) LED spots. Since the lady of the house is all her life working at ikea, she already bought yesterday a box of Ledare bulbs:

My dimmer is a Niko R5AH250V and seems to operate with triacs for phase control (their manual also contains an english section).

Would be awesome if I can keep using this dimmer, because:

  • Then I don't need to change my wiring
  • The electricity of my house has been checked and certified in the past, so want to change it as less as possible
  • When my Node-RED fails (or when I have left this planet) an average electrician can fix it for my family in case of problems.

That is the reason why I have no interest at all to switch to Ikea Tradfri or something like that...

Of course it would be nice if I could add something (e.g. some device from Shelly) afterwards, to create a fourth virtual push button, to make all functionality available via Node-RED also. So any ideas about that are also welcome...

Thanks already to all the community members, that are ready to save my marriage again (for a couple of weeks at least :wink: )!!


According to the tech sheet the minimum load is 50 W/40 VA, so the led load would need to be above 50w, Also older dimmers are not always compatible with LED loads, using transformers and 12w leds would remove the uncertainty of if the dimmer can run the LED load.
Shelly's are good but from experience the dimmer2 does not like low loads with no neutral wire, just to warn you i recently installed 6 dimmer2's for a customer, 3 had bypasses and no neutral, all 3 failed within weeks. The ones with neutrals are going strong with no issues with the lowest running a 8w lamp.

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Hi Bart,
It sounds as if the "good lady of the house" has already made the decision for you.

As you said two of the spots had died I can deduce that all the spots are wired in parallel.
Regarding the three buttons you mentioned in your write-up... how do they work?
If they are wired in parallel, then that would mean the lights will only go "off' if ALL buttons/switches are off.
Or do the buttons have a push-on, push-off toggle action?

What you are thinking of doing (removing the transformer and substituting "mains" bulbs for the old 12V bulbs) sounds as if it should work. You need to check the rating of the dimmer - how many watts it can handle.
I suspect it should be OK as the LED spots are probably rated at 5W each times 7 = 35W.

@E1cid makes a good point about the dimmer operating with a lightly loaded circuit.

If you had problems with the dimmer not driving a light-load, you could probably replace one of the LED spots with a mains driven 50W old-fashioned GU10 bulb. (I've got plenty here if you need one.)

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Are the LEDs advertised as Dim-able? Some are and some aren't.

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It says dimmable in the image supplied by Bart.

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That's ok then. It isn't easy to see on my screen, I had to blow the image up.

It's very doubtful that your existing dimmer will work ok with LEDs, and you may need to look at an alternative solution.
Even if you get your load up to 50W, it's likely that the lights will flicker and be generally unstable

Like @E1cid I've replaced my dimmer with a Shelly dimmer2, and we control it totally by voice commands using node-RED & smarthome.
But as E1cid has said, the Shelly should really be wired with a neutral wire.

Also I thought GU10 bulbs are 240v not 12 so will def need a new dimmer

Ah my electric special force commands are there when you need them on the home battlefield :+1:
Thanks to all you guys!!!

I see in the specs that the Ledare spots have a rated power of 7.5 W, so the total load is 7*7.5 = 52,5W. Did I understand you correctly, that I should buy other dimmable LED's (of 12W) to make sure my old dimmer keeps working fine?

Now I need to rewind :exploding_head:
Do you mean I can keep my 12V transformer and use 12V dimmable LED spots? Probably I misunderstood this completely...

I have faked to the outside world for more than 10 years, that I am allowed to make decisions in my own home. But now everybody on this blue planet knows that this is not the case :wink:

I think I am getting nuts...
Aren't those Ledare LED's 230V AC? I don't think that they operate on 12V?

It are good old wall mounted push-buttons. When you release them, they go back to their original state. So as long as you click them, the contact keeps closed. And when you release them, the contact is opened again.

Damn, I had a bad feeling that somebody in this community would suggest that feedback...
So the new LED dimmers work in another way I assume, compared to my old dimmer?
Damn again....

Had a look at the Shelly dimmer2 this morning also. But I had a lot of uncertainties about it:

  • Do I need one dimmer per LED spot. Because perhaps it needs to be near my spots? My transformer is located at my loft, which is about 8 meters away from my LED spots. Don't know if that is too far away (for radiation of the wires or whatever other reason).
  • Can one dimmer handle all my 7 spots?
  • Can I operate such a dimmer also using simply by my 3 existing physical push buttons? Because I really would like it to keep working without Node-RED...

If I could replace somehow my old dimmer&transformer setup by a Shelly dimmer2, that would indeed offer me a lot of extra features.

So I need the left setup:

I think this will not be a problem in my case.

Hi Bart,
I think you may have misunderstood my poor English / sentence construction about replacing the bulbs.
You are going to remove the old 12V spots and the 240V-to-12V mains transformer and replace that part of the system with a set of mains driven LED spots.

Hope that clears it up?

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That is an awesome diplomatic way of saying that my non-natve english really s*cks :joy:

The transformers would need to be dimmable and work with a minimum wattage of the new 12v led lamp, most are 20w min (UK) but there are 0w min versions, You could also try using 1 transformer(50va-100va) to run all 7 lamps, but you may find the volt drop to cause uneven lighting.

I would probably try removing the old halogen 12v transformers, change the lamp holder to gu10 an try the new lamps. If there are issues with the dimmers it should show up very quickly, i.e dimmers not dimming smoothly, led's flickering at lower dimming levels. You may get lucky and have no issues.
The worst that could happen is the dimmers fail.
If that happens just switch to shellys, which can be fitted at the light (must be a permanent live) if the switch has no neutral.

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Yes, older dimmers used leading-edge voltages to dim incandescent lamps, whereas LED dimmers use trailing-edge voltages.
Most dimmers over a few years old use the former.

Just choose the most convenient location as distance doesn't really matter (except for the wifi signal). Some users mount them behind the switch in the wall, but also in the ceiling. You need to look at your existing wiring.

Yes, one Shelly will handle all of them (up to a combined load of 200W)

No, not really. You won't need 3 switches, 2 will do all of the necessary functions, and probably a good opportunity to try one of these - Shelly - Shelly
You can of course use both physical switches AND node-RED, so you can use the switches and also dim the lights using your phone or voice commands, without leaving the sofa.
By introducing node-RED, you can do much more. For example, to slowly dim the light over 10-15 minutes, or increase it in the morning on a schedule to wake you up.... etc..
The transformer will need to go, as the proposed system would be 250V throughout.

Yes, don't use the right setup (with or without a bypass resistor) otherwise you are introducing problems :wink:


I think Bart means 3 switches wired in a two way and intermediate configuration, i.e switches at different door ways.
The answer would be yes, and if you jiggle the wiring you could use both switch inputs of the shelly, that is if dutch 2way wiring is the same a UK. You could even make the second switch input a scene controller, to set preconfigured scenes in the room (short press, long press, 1 press, 2 presses etc)

For info, i use Click Mode Grid Module 10A 2 Way Retractive | Toolstation switched cheap and good quality and interchangeable in the front plate. Click also do them in stylish chrome,brushed nickel etc and still reasonably priced, they are also under name Scolmore

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Yes indeed, you are absolutely correct. I should have mention that...
I have 3 push buttons in the room (one at each door), that can be used to turn the 7 spots on/off or dim them (via long press):


After re-reading all the above feedback, it feels like I should remove my old dimmer and transfo. And replace it by a Shelly dimmer2...

So I can connect all my 7 LED spots to a single Shelly dimmer 2 device:

I could also buy a Shelly dimmer 2 din-rail holder (for one or two dimmers):

But after googling quite a bit, it is still not clear to me how the Shelly dimmer 2 works in combination with physical buttons. The dimmer allows 2 physical buttons to be wired to it, in case the dimmer is configured to operate in dual mode:

  • SW1: button for dimming
  • SW2: button for brighten

But I only use SW1 for all my buttons. I "assume" I can wire my 3 push buttons to SW1 like this:

But in my case all 3 buttons are being used for the same purpose (on/off/dimming), depending on via which door you enter into the room. It is still not clear to me how the Shelly dimmer 2 responds to short clicks and long clicking. Would be nice if any body could explain it! Because the Shelly should handle my 3 physical buttons autonomous, even if my Node-RED system would be down...

Definitely not like that the switch on 240v connect from sw1 to live. not to neutral. We do not want and load popping sounds.

You can leave you switches alone as they should be incorrect configuration as is, as that's how the old switches worked. Just connect one switch wire to a live from same circuit and other to sw1.

The configuration for only using sw1 is -
One short click, shelly will turn on where last turned off (unless configured otherwise).
Press and hold it will dim up
Press and hold again it will dim down.
One short click and it will turn off.

The shellys are very configurable, with a clean easy interface.

Ok I have updated my wiring diagram:

If it is possible to explain in short to a noob why you would expect a popping sound, don't hesistate to share it here :wink:

Could you explain a bit more in detail what you mean with "alone"?

Really? That is awesome. Just what I need :champagne:
Then I will convert my setup to use Shelly...

Thanks a lot for all your time to respond to my noob questions about this!!!!!

I need quite a lot of other Shelly devices. So - for the first time in my life - I am going to wait and hope that they have some kind of black friday deals.

The sound of a 24Ov electronic circuit short circuiting when you press a switch and the internal circuit board says most violently no.

Alone meaning untouched, as your existing switches will be in parallel all ready as they are momentary/retractive switches, assuming your original dimmer is wired as wiring diagram 1, 2 or 3 from the manual.

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This morning I had no idea how to get started, and now it is all clear.
Thanks a lot everybody for thinking out loud, and solving my problem :+1: :+1: :+1: :+1: :+1:

@E1cid - I know diagram 2 will work with incandescent lamps, but are you sure it will work with an LED load?