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Running house LED lights on AC

Braeden Hamson

Feb 18, 2016
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I don't know whether to classify this idea as hairbrained or not half-baked. Regardless, I'm not taking this very seriously. So if you'd like to have a bit of fun, read on.
I've been thinking a great deal about the power lost in the LED lights I have in my house. They all contain AC-DC power supplies. Each one loses about 5-6W on conversion. I have about 12 or so in my house so I lose 68 W, which is negligible when my air conditioner takes 1800W. But us engineering types are never satisfied. The actual LED module runs at 60 V, 10 6V LEDs in series AFAIK. So here's the hairbrained part, what if I took a 120V to 30V transformer, you wire 5 of the LEDs one direction and 5 the other. You'll get the first 5 turned on between 0 and π of the AC wave and the other 5 will be on from π to 2π. No need for AC-DC conversion and the whole thing will be much more efficient. Now you may say, it will be half brightness. True, but we're pulsing the LEDs meaning we can over drive them to make them brighter. As is common in cars. The only drawbacks I can see is a lack of current limiting. What have I overlooked? I hope to learn a little more about "das blinken lights" in the process.

-Thanks for putting up with this post :p
 

kellys_eye

Jun 25, 2010
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There's no such thing as 100% efficient - other than bank profiteering - so the 'energy saving' side of LED lighting is all about comparisons. Losing 68W is better than losing 268W if you used filament lamps (so they say).

The lighting circuit of any household is (usually) totally independent of the other circuits which means you could disconnect the feed and apply whatever DC voltage you needed to run ALL the lights ALL over the property. Use an efficient constant current source (for example) and you could reduce the losses significantly.
 

duke37

Jan 9, 2011
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If you use two LEDs in inverse parallel on AC then they can be overrun a little since they will be resting for half the time.

Where do you get a 6V LED?

A current controlled supply can be quite efficient and more efficient than a resistive dropper.
 

dave9

Mar 5, 2017
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It might help if you gave us a link to similar, if not the exact lights you have. A 60V, 10 x 6V LEDs, seems similar to some standard E26 ~ 10W bulbs I've taken apart. Those are definitely not losing 5-6W on conversion, more like a 85% or higher efficient SMPS so they are losing under 2W.

You wrote "took a 120V to 30V transformer", but where is this magical transformer that achieves much more than 85% efficiency? A very carefully designed SMPS could get in the mid- 90's % efficiency but that's not a lot for the effort, and you have to build another one everywhere you have a light or create a low voltage power distribution wiring system for the lights, all to replace bulbs that come with their own PSU for under $5 each?

It seems like all you're really doing is wanting to get rid of PSU diodes and use the LEDs as the diodes, but then you wanted to use a linear transformer alone which is down closer to 60% efficient, maybe a bit more if a more expensive transformer?

Why would you be pulsing them? The human eye can see 120Hz. Maybe not everyone but "enough" people can. You'd want capacitor filtering so not so much pulsing any longer.

Maybe I am not understanding what you meant as it seemed a simple concept that I possibly over-simplified?

AC to DC conversion is not that inefficient. Full bridge rectifier is ~1.4V drop out of 100-something VDC (depends on capacitor size vs load), around 1% loss.
 

dave9

Mar 5, 2017
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The lighting circuit of any household is (usually) totally independent of the other circuits which means you could disconnect the feed and apply whatever DC voltage you needed to run ALL the lights ALL over the property. Use an efficient constant current source (for example) and you could reduce the losses significantly.

?? Maybe in Scotland the lighting circuit is separate, but it is not this way in the US. In the US it is most often a circuit shared with the wall outlets in the same room at a minimum, except in areas like bathroom or kitchen where there might be some outlets on a separate ground fault circuit.
 

(*steve*)

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it is not this way in the US

He did say "usually". In many respects the odd two phase electrical system in the US is weird (and unusual) :)
 

kellys_eye

Jun 25, 2010
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The UK wiring system has the lighting on a separate circuit (6A) and also separates the upper and lower floors such that if the lower floor RCD trips the lower floor LIGHTS don't go out (they are powered via the upper floor RCD).

It has to be a pretty efficient (and safer) way of doing things!
 

BobK

Jan 5, 2010
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Where do you get the info that you are losing 5 to 6W on conversion? That sounds unlikely. A typical 60W LED bulb only uses about 7W and I don't think 5 to 6W is wasted, unless you are counting the efficiency of the LED itself, which is about 20%.

Bob
 

Braeden Hamson

Feb 18, 2016
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Where do you get the info that you are losing 5 to 6W on conversion? That sounds unlikely. A typical 60W LED bulb only uses about 7W and I don't think 5 to 6W is wasted, unless you are counting the efficiency of the LED itself, which is about 20%.

Bob
I took apart an LED light an measured the current and voltage to the actual LEDs inside and I measured the current going into the from the wall.
 

Braeden Hamson

Feb 18, 2016
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There's no such thing as 100% efficient - other than bank profiteering - so the 'energy saving' side of LED lighting is all about comparisons. Losing 68W is better than losing 268W if you used filament lamps (so they say).

The lighting circuit of any household is (usually) totally independent of the other circuits which means you could disconnect the feed and apply whatever DC voltage you needed to run ALL the lights ALL over the property. Use an efficient constant current source (for example) and you could reduce the losses significantly.
I meant 100% power conversion, because there is no power conversion. I shouldn't have phrased it like that though.

Funny you should mention a DC system for your house. I'm currently writing a paper about that for my writing class, which is why I was thinking so much about light efficiency. This would be even better if you had a solar panel and battery set up.

You're right though, I'm realizing how efficient filament bulbs are. if you were to go through the trouble of implementing this system it could all be undone by running one incandescent bulb.
 

Braeden Hamson

Feb 18, 2016
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If you use two LEDs in inverse parallel on AC then they can be overrun a little since they will be resting for half the time.

Where do you get a 6V LED?

A current controlled supply can be quite efficient and more efficient than a resistive dropper.
I took apart an LED light and measured the voltage across one LED inside, it was 6 volts. Pretty good source of bright little LEDs if you ask me.
 

dave9

Mar 5, 2017
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I took apart an LED light an measured the current and voltage to the actual LEDs inside and I measured the current going into the from the wall.
You took apart what specific light? You measured how for the LEDs and how from the wall?

I suppose it is possible, there are some terrible generic designs coming out of China, but I do not think the results are accurate if you measured for any current model major brand light.

You're right though, I'm realizing how efficient filament bulbs are. if you were to go through the trouble of implementing this system it could all be undone by running one incandescent bulb.
Depending on what you mean, that isn't necessarily true. Any savings from LED bulbs is a savings and those which are still incandescent for whatever reason, are just the same baseline consumption, not "undone" at all by improving the efficiency of other lights.

I don't understand why you are taking a simple and great way to save power and trying to make it difficult and unworkable? If the idea you had was more efficient in a cost beneficial way, that is how light bulbs would be designed already. Bulbs are already pulsed at a driver frequency deemed unnoticed by most if not all consumers to eek out a little bit more light for the build cost, but what you have, probably in KHz instead of Hz range.

If you really want to abandon the standard bulb and shoot for efficiency, pick the most efficient LED (at whatever moment you want to do it) and use more LEDs at lower drive current with massive heatsinking from salvage aluminum. Considering the time spent and misc costs, standard major brand LED bulbs look pretty attractive to me.

They didn't have the same options 10 years ago but today is another day. The lifespan of some bulbs is questionable but that's a whole different can of worms, determining lifespan versus a homebrew creation that needs a larger sample size and years of testing to validate a lifespan expectation. I do not think it would be hard to exceed major brand bulb lifespan but at a real, monetary cost.

There is no question in my mind that given enough effort and build cost, a more reliable and efficient lighting system can be built, today, and probably forever considering the factors at play. The question that remains is what specific problem does DIY solve now? Artistic, maybe. Using parts you already have, maybe. Improving the common light bulb? It's already been done. Eeking out more efficiency for a space exploration vehicle, yes that's a noble target.
 
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kellys_eye

Jun 25, 2010
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The LED versus Filament light argument has been raging for years. The fact is that a filament lamp puts HEAT into your environment that has to be 'replaced' if you use an LED lamp in its place.

A few 100 watts is a significant contribution to warmth in any room - ok you might get used to having a slightly cooler environment but if you have to switch a heater on just to take the chill off a room then you negate all the savings that using an LED light source is supposed to give.

Obviously this doesn't apply to everyone but in temperate climates like the UK we need some form of home heating 'on' almost 6 months of the year.

It would be an interesting exercise to do a 'closed environment, whole-year study' of energy consumption in a household with LED or filament lighting just to see how much (or not) the heat from such filament lamps actually provides to the residents.

Mathematically, if a room 'needs' 750W to maintain comfort and you remove 200W by changing to LED then that 200W MUST be returned by some other means........ else the room is colder. Simple.
 

(*steve*)

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Fortunately we have means of getting 200 watts of heat energy into a room without expending 200W :)
 

Braeden Hamson

Feb 18, 2016
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I don't understand why you are taking a simple and great way to save power and trying to make it difficult and unworkable?

:D That's what people say to me when we work on group projects. I always like to add bells and whistles. I'm killing that habit I promise.

I have no plans to actually go through with this, its all in good fun. I was just poking at established ideas, seeing if anything dropped out of it. It's kind of beating a dead horse trying to squeeze a few watts out of as you say a great way to save power. I was just wondering why every single LED light AFAIK uses a AC-DC converter. You'd think there'd be some Dollar Basement version without it, but as someone pointed out its flicker. As well as a host of other things.
 

Braeden Hamson

Feb 18, 2016
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The LED versus Filament light argument has been raging for years. The fact is that a filament lamp puts HEAT into your environment that has to be 'replaced' if you use an LED lamp in its place.

Mathematically, if a room 'needs' 750W to maintain comfort and you remove 200W by changing to LED then that 200W MUST be returned by some other means........ else the room is colder. Simple.

That's a very interesting point, the first thought in my mind is that most bulbs are in rescesses in the ceiling. So I'd think that most of the hot air generated by the light would sit up inside the recess. Also, I'm not sure those enclosures are insulated.
 

Tha fios agaibh

Aug 11, 2014
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first thought in my mind is that most bulbs are in rescesses in the ceiling. So I'd think that most of the hot air generated by the light would sit up inside the recess. Also, I'm not sure those enclosures are insulated.
Yes, Most ceiling can lights are poorly insulated. They have holes for ventilating the heat generated by an incandescent lamp into attic space.
Unfortunately, they also ventilate conditioned air in the room which wastes a lot of energy. Perhaps more than the led inefficiencies you speak of?

It's admirable to want to make lighting more efficient, but we'd be better served if we can make air conditioning (usually largest load) even slightly more efficient.
 

Braeden Hamson

Feb 18, 2016
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Yes, Most ceiling can lights are poorly insulated. They have holes for ventilating the heat generated by an incandescent lamp into attic space.
Unfortunately, they also ventilate conditioned air in the room which wastes a lot of energy. Perhaps more than the led inefficiencies you speak of?

It's admirable to want to make lighting more efficient, but we'd be better served if we can make air conditioning (usually largest load) even slightly more efficient.
That's also something I've been thinking about. If only I had a vent along the top of my ceiling as I have a sloped ceiling. This is how some houses were built before electricity, they had tall towers on top with shutters. Opening those shutters would create what I think are convection currents, and pull air through. I think people are bringing this back into designs.

Of course, I think the ideal set up is to have an partially buried house, earth is a good insulator. This also has the added bonus of making neighborhoods look like The Shire.
 

Tha fios agaibh

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I went around my house with my Ir camera and was horrified buy the leakage around the ceiling can lights. It looked similar to this google picture.

Screenshot_2018-08-09-22-37-22-1.png

Add up all these leaks and imagine the energy lost.
 
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