LED drivers and dimming questions

[yeldogt]

Lee Valley is selling an interesting small 12v LED fixture w/ adjustable beam that I think would be a good replacement for 8 12v incandescent MR-16's currently in my house. My question: Can I just drive these from the two standard 12v magnetic transformers already there?

The MR16's are 50w each -- one transformer runs 5 and the other 3. My memory is they are not the same size transformers. Both transformers are remotely mounted with low volt wires to the fixtures and Lutron Meistro dimers made for dimming magnetic transformers. For a few hundred bucks I could be rid of the WAC fixtures that I never really liked and these would fit into the same small holes - I'm painting the space.

LED's/drivers/dimmers -- confusing. With my new home project delayed we moved back into a house I have not lived in for the better part of 15 years. I have run into issues with both updating the old house and figuring how to control various fixtures in the new house --

I went looking for LED replacement MR16's bulbs -- they work .. but the current ones don't have the output of the old 50w incandescent.

 

[theoldwizard1]

A "real" LED runs on DC current. They do not require a lot of voltage, but need current control. The "correct" way to dim an LED is to pulse it on and off (faster that your eye can detect) and keep making the "off time" longer.

We have incorrectly related light bulb power consumption (50W) to the amount visible light generated (Lumens). A 50W Halogen creates a lot more lght than a 50W incandescent.

I think you will be happier if you stop trying to retrofit LED lamps into existing incandescent or halogen fixtures. Hell, I am still looking for oversized lamp harps so I can install compact florescent bulbs in the table lamps !

 

[yeldogt]

A "real" LED runs on DC current. They do not require a lot of voltage, but need current control. The "correct" way to dim an LED is to pulse it on and off (faster that your eye can detect) and keep making the "off time" longer.

We have incorrectly related light bulb power consumption (50W) to the amount visible light generated (Lumens). A 50W Halogen creates a lot more lght than a 50W incandescent.

I think you will be happier if you stop trying to retrofit LED lamps into existing incandescent or halogen fixtures. Hell, I am still looking for oversized lamp harps so I can install compact florescent bulbs in the table lamps !

Halogens are incandescent? The product LV is selling is a whole fixture with the LED module -- not just a bulb. The fixture uses 12v --

I have tried buying just the LED MR16 equivalent bulb -- they are 12v and designed to retrofit. I believe either a magnetic or electronic ballast will drive them -- mine were magnetic. They don't put out enough light (lumens).

It's all confusing -- some fixtures use the 0-10 controls .. and I understand I need a special dimmer for those. The 120v bulbs are all over the place -- fine for retrofitting when no dimming required.

 

[yeldogt]

So -- can't get an answer. I guess my only choice is to buy three and see how they work -- not what I wanted to do.

 

[cybrdyke]

I'll give you an educated guess...
The power supplies are regulating the current to the diode array to a specific amount.. The old magnetic transformers are not. I'm skeptical that they'll work at all, but even if they do, there would be no regulation of current and I wonder how long the diodes could last. I'm even more skeptical that you could "dim" the old transformers and have the new fixture behave appropriately.
That said, I've never had any issues finding LED MR16's that didn't blow away halogens by a mile. If you have 50w MR16's, then try something LED in the 10w range, like Philips or Green Creative. It's possible that you'll still have dimmer compatibility issues, though.
Good luck,
CD

 

[ddawg16]

Unless some things have changed...……..

A 12V AC transformer is just that....puts out aprox 12Vac RMS....give or take a couple of volts.

An incandescent bulb will work of either AC or DC. It does not care. To dim it, you don't reduce the current, you reduce the voltage. The bulb has a fixed resistance and reducing the voltage automatically causes a drop in current.

An LED bulb comes in two basic flavors. dimmable and nondimmable.

A non-dimmable bulb wants 12 or 24 Vdc and will keep drawing more current to maintain its brightness until it reaches its internal compliance voltage...then it will start to flicker and go out.

A dimmable bulb, as the supply voltage drops, the current going to the LED's drops....which reduces the brightness....until it gets to the point where the LED won't stay lit.

I have a dimmable setup for my pub. The power supply is a fixed 12 Vdc and I have a variable remote controller connected to the output. I went this route because I can also use the same PS if I want to keep some lights on a full brightness.

SuperBrightLEDS is a good web site to see all the options.

 

[Platonic Solid]

Found the fixture your talking about here: http://www.leevalley.com/en/wood/page.aspx?p=77330&cat=3,43349,72177 . Suggest posing your question to Lee Valley.

 

[yeldogt]

Found the fixture your talking about here: http://www.leevalley.com/en/wood/page.aspx?p=77330&cat=3,43349,72177 . Suggest posing your question to Lee Valley.

That's the fixture -- correct. What I'm trying to understand -- if it's 12 volt .. how will it care if its getting 12v?

Am I missing something? Are they not dimming as a voltage drop?

How is this fixture different than a 12v LED bulb -- do the bulbs have a driver to work with voltage drop vs current changes?

 

[yeldogt]

I'll give you an educated guess...
The power supplies are regulating the current to the diode array to a specific amount.. The old magnetic transformers are not. I'm skeptical that they'll work at all, but even if they do, there would be no regulation of current and I wonder how long the diodes could last. I'm even more skeptical that you could "dim" the old transformers and have the new fixture behave appropriately.
That said, I've never had any issues finding LED MR16's that didn't blow away halogens by a mile. If you have 50w MR16's, then try something LED in the 10w range, like Philips or Green Creative. It's possible that you'll still have dimmer compatibility issues, though.
Good luck,
CD

So what you are saying is the LED specific power supplies are doing more than voltage control?

Some of these LED systems require the power supply to be before the dimmer -- this makes controlling from a typical switch setup impossible.

The bulb I bought -- is just the bulb .... its a 12v bulb designed to retrofit into an existing mr16 fixture that previously had an incandescent bulb.

EDIT: CYBRDYKE -- the bulb is a 3000k 5w SORAA. Bought it about a year ago -- I see they have many more and 7.5w now. In my new build I'm doing about 40 small plastered in recessed fixtures. Getting LED module units were at least $600. I was able to buy about 45 MR16 fixtures and trim for less than $100 each -- frankly, I like the halogens .. but If I can get suitable LED bulbs .. I will.

 

[MattT]

That's the fixture -- correct. What I'm trying to understand -- if it's 12 volt .. how will it care if its getting 12v?

Am I missing something? Are they not timing as a voltage drop?

You're missing the difference between AC vs. DC. Those fixtures you're looking at are rated for steady DC voltage. If you supply them with the AC waveform from your existing circuit there's no telling what they might do.

 

[cybrdyke]

How is this fixture different than a 12v LED bulb -- do the bulbs have a driver to work with voltage drop vs current changes?

Yes, LED bulbs have a driver in the base that converts voltage and regulates current.
CD

 

[Platonic Solid]

yeldogt - I actually think the fixture will work just fine with your 12V transformers, but I have no first hand experience with MR16s to back that statement up.

 

[cybrdyke]

yeldogt - I actually think the fixture will work just fine with your 12V transformers, but I have no first hand experience with MR16s to back that statement up.

I've never seen a 12v LED replacement product that didn't come with a driver (internal or external), or one that was designed to run on a 12v magnetic transformer. If it was OK, they would be a huge hit in the track lighting world. CD

 

[yeldogt]

You're missing the difference between AC vs. DC. Those fixtures you're looking at are rated for steady DC voltage. If you supply them with the AC waveform from your existing circuit there's no telling what they might do.

The transformers are 12v DC

 

[yeldogt]

Yes, LED bulbs have a driver in the base that converts voltage and regulates current.
CD

but if the fixture is 12v dc and my magnetic transformer is providing 12v DC .. what's the fixture converting ?

 

[Platonic Solid]

I'm assuming the bulb/fixture includes simple current regulation either as an integrated component on the array PCB or a mini buck driver like this one.

 

[Bert_]

but if the fixture is 12v dc and my magnetic transformer is providing 12v DC .. what's the fixture converting ?

Led's need regulated current, not voltage.


Platonic is probably right that they (the fixture) has a simple current regulator built in.

 

[yeldogt]

I've never seen a 12v LED replacement product that didn't come with a driver (internal or external), or one that was designed to run on a 12v magnetic transformer. If it was OK, they would be a huge hit in the track lighting world. CD

I did not understand that the 12v LED replacement bulbs for the halogen MR16's had a driver inside the bulb.

With all of the MR16's in use I guess it surprised me that the 50w equivalent LED bulb I bought was so bad --- I see that many more have come out in the past year.

 

[cybrdyke]

I'm assuming the bulb/fixture includes simple current regulation either as an integrated component on the array PCB or a mini buck driver

Led's need regulated current, not voltage.


Platonic is probably right that they (the fixture) has a simple current regulator built in.

Why would you assume this if the manufacturer is telling us that we need to buy a power supply to go with the fixture? The output of the power supply is regulated from within it. There is nothing in the fixture data that says that it's ok to run it without the power supply or on a non-regulated 12v supply.
CD

 

[Platonic Solid]

I see that all of the power supplies offered are "constant voltage".

 

[yeldogt]

Maybe this is my fault because I'm talking about both "bulbs" and "fixtures" at the same time -- The Lee Valley item is an entire fixture that includes the LED module -- no replaceable "bulb". It's a 12v lighting fixture.

I currently have small fixtures with a 12v MR16 halogen bulb ... now, I could just replace the bulb. But -- not liking the whole fixture ... was thinking of replacing with the LV fixture.

So, I'm trying to understand what the fixture is looking for other than 12v ... is 12v dc .. 12dc? The MR16's are tied together run by a transformer --- like landscape lighting would be

On another front: Retrofitting 120v bulbs into existing fixtures that have dimmers is problematic -- I have found that my electronic Lutron dimmers don't operate the bulbs .. even the Nova style Lutron dimmers don't work. It's easier for me to just keep the 120v incandescent bulbs and all the controls.

What's confusing today. Years ago with low volt lighting you simply matched the dimmer to the transformer (magnetic or electronic) -- the bulb did not care what drove it .. but, the transformer did care about the dimmer. Magnetic low volt dimmer with magnetic transformer -- no problems.

Now its all over the place -- some of my 120v JUNO 2" LED fixtures look to have a magnetic ballast/transformer/ power supply (whatever you want to call it) .. and they can be driven with a typical dimmer. The cheaper 120v stuff all seems to have separate power supplies that require special dimmers.

There is no way to wire many of these fixtures using a wall dimmer as they require the dimmer after the power supply. The dimming occurs on the low volt side not the 120 side.