Dimming Leds for home lighting?

[Sosijdog]

Hi there guys, and Merry Xmas!

I am building a new house and would like to install Leds for backlighting as well as conventional down lighters and wall lights.
I want to install a 3 gang dimmer switch on the wall to control these lights (Wall, ceiling, leds).
Now I am aware Leds can be dimmed and also that conventionial dimmer switches are not suitable for doing this but I would ideally like a single switch plate with 3 dimmer controls on it rather than 3 seperates...

So my question is this:
Can I get a PWM unit that my conventional dimmer switch can be wired into to control these leds rather than buying a seperate dimmer control for them?


PS. Yes, I did look through the past threads on dimming leds.... nothing really answered my question....


Thanks in advance guys!
Stevo.

 

[audioguru]

LEDs are not bright enough for home lighting and their light is in a narrow angle and is an extremely glaring tiny dot.
Powerful LEDs are also extremely expensive.

Compact fluorescent light bulbs use low power and shine their light all around in a big enough glow to not cause glare. They are inexpensive and some can be dimmed.

 

[Sosijdog]

Aha, I should have mentioned it will be an led strip about 2m long with a shed load of leds so that shouldn't be a problem.
They will have their own transformer to step down the voltage from 240v AC to 12v DC.

I just need to know if a regular dimmer switch can be used to drive a PWM to do the dimming or does it have to be a special stand alone dimmer switch.

Taa very much.

 

[audioguru]

A regular dimmer cannot be used with a transformer-reduced-voltage power supply. An LED lights and turns off instantly.

An incandescent light bulb has a huge thermal mass that takes a long time to heat and cool so it averages power very well from the low frequency mains from an AC dimmer.

The very low frequency from an AC dimmer will allow an LED to burn out on the peak of each of its very low frequency cycles and the visible low frequency blinking on and off will be awful.

 

[MrAl]

Hi there S,

If you are using 12v DC then you can dim the LEDs on the DC side rather than the AC side.

As audioguru pointed out, regular dimmer switches dont fare too well with transformers. In fact, back in the 1980's i was determined to do this myself and actually did, but the transformer makes a groan which is not very nice and i didnt check to see if anything was going wrong but i suspect there were. Transformers made for 60Hz line dont like high frequency switch transients at all. It could lead to overheating but i never ran it that long to find out, and although lower duty cycles probably wouldnt overheat i never bothered to find out.
Theoretically there are better ways to dim an AC signal that even a transformer would not argue with, but i am not sure if they make these kind commercially available. They involve pulse with modulating the line frequency, not merely turning it on once at a set angle like the run of the mill dimmers do, but actually modulating the line frequency using PWM with a frequency of a couple kilohertz or more. To the transformer, it looks like a reduced voltage sine at the line frequency. If you had an application that absolutely had to work on the primary of the transformer then we'd have to think about this and possibly design one that would work efficiently. For now i'll assume you have more control over the setup than that.

Dimming on the DC side is very reasonable however. Using a PWM circuit you can dim one or a thousand LEDs and it will work for years. The transformer provides the 12vac (or whatever you have) and the rectifiers and filter caps turn that into somewhat smooth DC, then the PWM circuit modulates the DC into a pulsing pattern that either cuts back the brightness or allows full brightness with the max setting. The PWM frequency is kept high enough so that the human eye notices no blinking of any kind except in the extreme case of turning the head quickly.

 

[Sosijdog]

Hey Mr Al,

Thanks for the info! Thats what I needed to know.
Could I possibly buy a PWM and fit it to the back of a 3 way switch (just using one of the 3 control knobs to trim the PWM itself for 12vdc control)?
If this could be done, what kind of PWM should I buy? Are there any best suited for lighting or would one for motor control be any use? (Am thinkin ebay here, there are a few on there.)

Cheers again,
Stevo.

 

[MrAl]

Hi,

Well im still not sure if you are still trying to control the line voltage or the DC voltage.

I was actually thinking that you'd have to build it up yourself using electronic components, unless someone else here knows where to buy one.

 

[Reloadron]

Since this is a nice clean install in home improvement given a choice I would likely buy over build. A Google of LED Dimmer will bring up dozens of hits like this one. One very big advantage is you get a complete package enclosed in a nice standard size for mounting in a standard wall box. I don't know your location but many are carried by home improvement stores like Lowes as well as home lighting stores. They are designed for a wide variety of LED and CFL lighting applications. Personally I doubt I could build one and get it in a standard box for what I can buy an off the shelf solution for.

Ron

 

[Sosijdog]

Hi Ron,
I agree with you that to buy would be better but thats the problem - I cant get a single switch plate with 3 dimmer knobs on it to control 3 different sets of lights because one of those sets is the LEDs. Conventional dimmers wont work for this.
I can get 3 single dimmers but, for purely cosmetic reasons, I would liked to have it on the one switch plate. The one you have posted is simply a single switch plate and I can get those no problem.

MrAl - I want to control the DC voltage. Many companies offer dimmer switches for dimming LEDs that control the DC side. However, they only seem to come in single switches. I have seen 3 gang switches which claim to be LED compatible but do they, or can they, work with regular filament bulbs?

Cheers.

 

[Reloadron]

I see what you mean. While there are 12 VDC LED dimmer switches that use PWM, like these, they are single gang and three of them would require a 3 gang box.

Ron

 

[4pyros]

What about a RF remote control for your lights? I have seen many for LEDs.

 

[MrAl]

Hi Ron,
I agree with you that to buy would be better but thats the problem - I cant get a single switch plate with 3 dimmer knobs on it to control 3 different sets of lights because one of those sets is the LEDs. Conventional dimmers wont work for this.
I can get 3 single dimmers but, for purely cosmetic reasons, I would liked to have it on the one switch plate. The one you have posted is simply a single switch plate and I can get those no problem.

MrAl - I want to control the DC voltage. Many companies offer dimmer switches for dimming LEDs that control the DC side. However, they only seem to come in single switches. I have seen 3 gang switches which claim to be LED compatible but do they, or can they, work with regular filament bulbs?

Cheers.

Hi,

The only way to know for sure is to check the manufacturers web site or whatever they offer as documentation. There are too many possibilities to give a blanket solution for all such devices. I've seen dimmers that can only dim down to about 50 percent for a bulb, but others (better) that can dim all the way down to very nearly out completely. They look almost the same too. Maybe you can find writing on the box it comes in if you go to a store to check them out.