Anotherpower.com Forum
Renewable Energy Questions/Discussion => Renewable Energy Q&A => Topic started by: WooferHound on November 05, 2018, 07:57:44 am
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I had found a few videos on YouTube about using High Power LEDs to make all kinds of lights. So I went on eBay and found this listing for LEDs from 1 to 100 watts.
https://www.ebay.com/itm/High-Power-1W-3W-5W-10W-20W-30W-50W-100W-White-SMD-LED-COB-Chip-Lights-Beads/122044236962?hash=item1c6a6744a2:m:mrwPJXkCqGpBSWx5zzsnzvA&var=421059306307
The prices were amazing, Shipping is free, and the seller was in California instead of China. Purchased a Lot of these and it only came out to $25 total. Be sure to click through to his Store and look at all of his LED products.
LEDs are powered at a certain Current, so a current limiter is needed to to use them. I found these Buck Converter Voltage Regulator/Current Limiters on eBay for $2 each, so I got 10 of them to play with. Perfect for powering LEDs from my 12 volt Solar Power system. They are rated at 5 amps but aren't stable above about 3 amps. The Output is a bit noisy so some additional filtering is helpful but not necessary.
https://www.ebay.com/itm/5pcs-XL4005-5A-DC-Buck-Step-Down-Voltage-Converter-Constant-Current-Power-Module/142632518904?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
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Small LEDs on the left are 1-3-5 watts. They look identical and I need to keep them in their packets until they are needed or they will get mixed up. The LED on the big heatsink top-right is a 10 watt. The Large LED bottom-right is a 20 watt. Buck Converter at the bottom.
I've been playing around with this stuff for about 3 weeks now and I'm very impressed.
First thing is, they get very hot. Assume that all the power that you put into them will come out as heat, a heatsink is required for anything over a minute. I have been gluing them down to heatsinks using 5-Minute Epoxy with very good results, the LED must be pressed down firmly to squeeze out the glue and get good thermal contact with the heatsink. I have had much better results using CPU Coolers, small heatsinks with a 12 volt fan attached. The fan gets the 12 volt directly while the LEDs are powered through the Current Regulator. Using a resister inline with the fan will slow it down and make it quieter. A small heatsink is fine for the 1 and 3 watt LEDs but a fan is needed for ratings 5 watts or more because the heatsink would need to be so too big.
The LEDs come in 4 versions of White . . .
Warm 3000-3500
Natural 4000-4500
White 6000-6500
Cool 10000-15000
I've tried the Warm and the Natural versions. The "warm" is a little green but nice and warm. The "Natural" is very nice and realistic. An order with some "Cool" versions will arrive in the middle of next week.
The LED Specs are . . .
1w - 3.5v - 350ma - 105 lumins
3w - 3.5v - 700ma - 270 lumins
5w - 6.5v - 700ma - 550 lumins
10w - 10v - 1000ma - 950 lumins
20w - 31v - 700ma - 1700 lumins
30w - 31v - 1000ma - 2750 lumins
50w - 31v - 1700ma - 4750 lumins
100w - 31v - 3500ma - 8500 lumins
They spread light 180 degrees from the face, but they are brighter with better color in the center area, They are rated at a 120 degree angle. The Higher power versions are harder to work with because of the 31 volts need to bring it up to Full Power. About the only way to use them is with a Boost Converter so I have decided not to mess with anything higher than 10 watts that requires 31 volts. It is easier to use multiple 5 or 10 watt LEDs to make the lighting and it's better light because it is spread out more.
The light coming from these things is a point source and it can hard on the eyes, If you look directly at them for more than just a glance, then you will see dots for hours burned into your eyes. Some kind of fixture needs to be used that will spread and soften the light and make it more appealing.
After playing with this batch of LEDs I put in another order for the ones that I liked, plus a few colors including Ultraviolet. Should be here in a few days . . . Can't Wait . . .
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Are you thinking of a bike lite with those...? Thought about rewiring this...super brite..
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Here are some more experiments that I made to learn more about these LEDs
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The first thing I made is pictured on the Left. I glued two 1w LEDs to a strip of aluminum. One was a Warm White and the other was a Natural White. This was to see what the colors look like and to see how much heat they produce. Powered from a 4 volt Lithium Ion 18650 battery with 2 ohm resisters inline. This got almost too hot too touch and is when I realized that I need some real heatsinks to use these lights.
The item in the center is an emergency light I made with a single LED with a good heatsink. It does not have a switch and powers up when a battery is inserted. It will run for about 5 hours on a 4 volt 18650 battery. I tried this one outside at night to see if this 1w LED would be useful on the Bicycle and was pleasantly surprised at how well it works, it lights up the whole area. The 1w LEDs are 3.5v at 350ma so I would only want to use 1 with the single battery on the bike.
The light on the right-hand side was built yesterday. It's built on top of a 2100mah Lithium Cell Phone battery. It has a single 1w Warm White led glued to a small heatsink, then glued to a big nail. Everything is glued together with 5-minute Epoxy. It has a Slide Switch and a 1/8 inch plug to be used for charging the Cell Battery. Best for emergency lighting but it was more of a fun little project
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The most useful thing I made was this cute little battery powered Gooseneck Lamp. It has Two 18650 batteries for 8 volt power, and it uses a 3w LED which is 3.5v 700ma. Inside the chassis box is a Buck Converter to regulate the power to the LED so it stays the same brightness and color as the batteries drain. It will last over 6 hours on charged batteries and the 3w LED makes it wonderfully bright. Really nice to use when working close to some small projects and need good lighting.
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Should get my new LED order in the mail tomorrow. I have already started assembling a couple of things that I will use those LEDs for.
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Looks like you are having lots of fun Woofer.
I like the cute little light on the aluminium box.
We use 12 volt lights in our house, a mix of LED bulbs and LED dichroic lamps.
The new 12 volt LED bulbs are great, I find a 7 watt LED bulb is great as a reading lamp, general lighting.
Keep on experimenting,
Pete
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I remember buying LED lights ~1 watt in the early 2ks
At one time I checked they were $40+ I finally got one for a flashlight once they dropped to about $25
That flashlight works flawless to this day. It's been through 3, 6v lead acid batts in its life, but the led is still going strong.
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For the last week I have been using this little lamp I made to that will light up my computer desk which is also a small workbench a lot of times. It is attached to a lighted magnifier. The wiring is temporary for now but I use this light all the time now.
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Basically it's LEDs glued to a CPU Cooler that has been mounted inside of a small 3 inch PVC pipe ring. Two power feeds, one for the LEDs from the buck converter, and another feed from the 12v solar power to the fan through an 82 ohm resister so it is slow and quiet.
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There are four 1w LEDs glued into the 4 corners so the light will come from a wide area and soften the shadows that will be created from it. Two LEDs are Warm White and the others are Natural White, wired into a series/parallel arrangement, making it 7 volts at 700ma or 4.9 watts.
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I have so much of this LED stuff going on that I have decided to build a box with 4 buck converters in it to power some more lighting that is planned after the Mail runs today with another pile of LEDs to play with.
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The picture above was taken using this light and the camera white balance set to Incandescent. You can see the Soft Shadow effect from the box.
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Hi Woof, I also have one of those magnifier lamps. I took the flouro tube out of mine and installed LED's. I bought some that were three leds on a strip and they had plugs that allowed them to be paralleled. They came with sticky backs so I just stuck them around the inside of the lamp where the tube was, junked the mains parts and connected it to 12 volts. Works great, probably not as bright as your newer LED lamp though.
Great to see someone having fun
Pete
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Well . . . I thought about it too much and decided not to make a box full of Buck Converters, instead I made some individual boxes that are attached directly to the lighting that they control.
The box on the left has 2 buck converters in it which will control 2 lights on the Lighted Magnifier pictured above, including the PVC Tube Light also in the story above. The other light will be on the Back Rail supporting the magnifier and will face up toward the ceiling for some indirect uplighting. There are a couple of Air Holes drilled in the box for cooling but it doesn't really get warm.
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The Box on the right has a single Buck Converter in it and powers a couple of white LEDs that light my Computer Keyboard from above. Two normal 20ma LEDs in series so only 20ma total. Then I tried to set the buck converter to 20ma there was an odd flashing effect. Tried several things to fix it and it finally worked OK at 20ma with a 1000mfd capacitor across the output.
I was having trouble with some projects using the Buck Converters around fans where I could see a slight strobing effect, indicating noise and flashing. Was also getting a high frequency tone through my 12 volt sound amplifier. I have found that a 470mfd capacitor across the LED will stop those problems.
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I have been working a lot lately and haven't done much with the LED lighting, although I have been experimenting with the High Power Colors that arrived in my last package.
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Here is 1w Blue and Red Together. Getting ideas for Nightlights here
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This is 1w Royal Blue. A really interesting color between Blue and Ultraviolet
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And this is a small circuit board with sixteen 5mm Ultraviolet LEDs soldered to it
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I also have several projects started which will provide strong White Light. This is a test of a triple-brightness lighting fixture being constructed to mount to the ceiling over my computer desk/workbench. It has a 5 watt LED for the Low level and four LEDs that total 10 watts for the high level. so it can be switched to 5/10/15 watt levels. It sure is bright and competes with Sunlight coming through the window.
More to Come . . .
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Hey Woof!
I have installed and repaired many outdoor 100w led floodlights of the Chinese persuasion and they use the case as a heat sink and use thermal paste under the led and screw it down. The led’s are the same like the 20w you show in the pic. I have used a thermal glue to attach waterproof Dallas temp sensors to my inverter and find it works quite well. I just bed the sensor in a glob of it and masking taped it in place for 24 hours. Not as fast as epoxy but I feel like it conducts heat better. Of course the fixtures I installed had a flaw in that the case had minimal fins on the back and the entire surface area was only 10”X10”. This may be why they failed so often or power surges lightning. I did install a a high quality surge protector on the parking lot lighting system and failures have slowed.
I wonder if you were to epoxy a 100w led to a heat sink that it may begin to melt the epoxy? There are scew holes so maybe consider drilling holes. I designed and built a dump load for my windmill and drilled holes in the heat stink, thermal past under the resisters and small screws.
Like your projects. Keep on keeping on bud!
SN
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Hey Woof!
I have installed and repaired many outdoor 100w led floodlights of the Chinese persuasion and they use the case as a heat sink and use thermal paste under the led and screw it down. The led’s are the same like the 20w you show in the pic. I have used a thermal glue to attach waterproof Dallas temp sensors to my inverter and find it works quite well. I just bed the sensor in a glob of it and masking taped it in place for 24 hours. Not as fast as epoxy but I feel like it conducts heat better. Of course the fixtures I installed had a flaw in that the case had minimal fins on the back and the entire surface area was only 10”X10”. This may be why they failed so often or power surges lightning. I did install a a high quality surge protector on the parking lot lighting system and failures have slowed.
I wonder if you were to epoxy a 100w led to a heat sink that it may begin to melt the epoxy? There are screw holes so maybe consider drilling holes. I designed and built a dump load for my windmill and drilled holes in the heat sink, thermal paste under the resisters and small screws.
Like your projects. Keep on keeping on bud!
SN
Those 100w LEDs get scary hot. We have some store-bought LED floodlights in our theater that we use as worklights. Last week I looked at them closely and there were only small ripples on the back for a heatsink. I placed my hand on the back and it was burning hot. I don't see how these can last very long working at a temperature that high. Those high power LED modules that hook directly to the 120vac mains, Flash hugely at 120hz, I would use them outdoors but would never work under them. I have seen a lot of YouTube videos about Construction and Teardown of powerful LED fixtures and I always feel that they don't pay enough attention to the heat.
I have given a lot of thought to the possibility of the Epoxy Glue melting, but I have decided to only use LEDs that are only 10 watts or less because they all work well with 12 volt power using Buck Converters to control the current. The heat is very easy to manage using these LEDs and if I need more light I'll just use multiple pieces until I get what I need. I have tried a 10w LED on a substantial heatsink before and it still got too hot to hold onto but the glue seemed to be OK. I have a small fan that I will add to it later to make it usable.
Here is a small 10w fixture that I made yesterday afternoon. The LED is glued to a CPU cooler. The fan has an 82ohm resister in series to the 12v side of the buck converter to slow it down and keep it quiet. Then it is all glued to a PVC ring to help control the light and will give me a way to mount & aim it later.
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I ran it for a coupla hours and the heatsink stays cool to the touch, not warm at all. The backplate on the LED had a hint of warmness, The electrical connections were warm, but the LED case was too hot to touch in a couple of areas. I was very satisfied with the cooling.
These LEDs put out an amazing amount of light using only 10 watts of electricity, 10 volts at 1 amp. I think they were rated at 1150 lumens.
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I wonder how some of these high-power LEDs would go with NO heatsink, stuck between two sheets of glass with a decent circulation of some of these "engineered fluids" they use for immersion cooling of electronic components (read: super high density datacentre computing stacks).
In effect, liquid-cooling and being able to make them very small and quite importantly, silent and cool...
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Hi Ross!
How are ya? I’ve seen guys submerging desktop computers in mineral oil and the Fans actually kept all the components quite cool well under oil. The temps were monitored using an app in windows. They did have to add external cooling pump and cooling heat sink as the tank heated up. Then the aquarium started leaking and that was the end of that. Maybe a frame with double pane glass like you say and a cpu cooler system using mineral oil might work. Hmm wonder.
SN
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I have used 12 volt LED's for years now as home lighting. The main problem I have found is that the capacitors in the converter circuits die. Mostly in the dicroic lamps. It seems that sending all the heat upwards to where the electronics are is not such a great idea.
It also seems that electrolytic capacitors are not always what they used to be. Some of the capacitors I have come across coming out of China are only half the weight of older better known products.
Oil cooling has been used in power transformers for many years, the tubes on the outside of the tanks are there for convection cooling.
keep having fun Woofer
Pete
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I’ve seen guys submerging desktop computers in mineral oil and the Fans actually kept all the components quite cool well under oil. The temps were monitored using an app in windows. They did have to add external cooling pump and cooling heat sink as the tank heated up. Then the aquarium started leaking and that was the end of that. Maybe a frame with double pane glass like you say and a cpu cooler system using mineral oil might work. Hmm wonder.
Not oil. Certainly not oil. It does a nice job cooling, but it has more downsides than up.
Google Novec, or Novec 1230. Your components come out of Novec clean and dry.
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I finished the last project that is pictured a few posts up. Bent up a 14ga thick strip of sheet metal to make a Yoke to mount the 10w LED light onto allowing it to be aimed with both Pan & Tilt.
These 10w LEDs are about a 75w incandescent-equivalent providing wonderfully usable light over a large area. This will get placed on top of my computer desk about 6 feet over the floor where it can be swiveled to where the light is needed.
Works great aimed up at the ceiling for indirect lighting. Measured at .8 amp from the 12 volt solar power.
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Finished another project this morning that was posted above as a three level brightness test of a light having capability of 5/10/15 watt settings.
The bell housing is from an old incandescent fixture that has been gutted. The U shaped yoke was bent from a small piece of sheet metal. The top housing is from another old incandescent light. Everything is wired with Ethernet cable because it has 4 pairs of wires in it. Three pairs used coming up from the switches, all four pairs used between the Buck Converters and the main Housing.
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Three buck converters are mounted in the Top Housing. Two for the Low (700ma) & High (1400ma) settings and a third for some colored Mood lights (350ma) on the side of the fixture.
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The center LED is a 5w for the Low level, the 4 LEDs on the outside are 2.5w times 4 totaling 10w for the High level. The fan on the back of the CPU Cooler runs through an 82ohm resister for quietness on the low 5w setting but runs at full speed on the high 10 & 15 watt settings.
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When I was designing this I knew that there would be extra wires in the Ethernet cable that is being used. So Red & Blue LEDs were added to the side to point up at the ceiling and to the side for the wall, to be used as Mood or Party lighting.
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At the risk of showing you how messy my computer desk/workbench is, here is the fixture mounted to the ceiling on the high 15w level. Gosh this is hugely bright for 15 watt light. The buck converters have red indicator lights on their PCBoards and they show up through the ventilation holes in the top housing. You can see the 10w light from the previous post, on the very top of the desk on the left under the lamp shade.
Tonight I'll get a picture of the colored lights operating. I will be drinking some local Craft Beer so I will be in the mood for sure.
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Now I have Plenty of lights for the area that has 12v Solar Power, so I'll be focusing more on 120vac fixtures for other areas around the house.
The mail today came with 10 more Buck Converters
and an interesting selection of LEDs including . . .
10x 3w Ultraviolet
and an assortment that has 20x 5mm LEDs in ten colors, 200 in all
plus a couple of sets of 1w high Color Temperature white LEDs in the 6k and 10k range
I should point out that these White LEDs are rated to 80 CRI (Color Rendering Index) relating to the quality of light. If Sunlight is coming through the window to compare to, the Sunlight kicks the LEDs ass about light quality. The LEDs seem a bit green and lacking in red. Food looks OK under it, but not great like an incandescent or Sunlight.
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Here is a pic of the Red/Blue Mood Light working
Nice interesting shades of Lavender
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Got another coupla projects finished . . .
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The first is an Ultraviolet Flashlight (black light). It's a 3.5v 700ma UV LED running on a 4 volt battery with a 1 ohm dropping resister and a switch. This UV LED is 3 watts and is very effective at making fluorescent materials light up without throwing too much visible purple light out. Should run about 3 hours with the 2200mah Lithium 18650 battery.
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The next project is for lighting up my computer keyboard. I used some small LED flashlights, replaced the original LEDs with some extra bright 5mm LEDs, and Folded some metal parts to make a small light that is easy to aim where it's needed. Removed the batteries and wired the 2 small fixtures in series for a small 6v 20ma load. Powering these from a buck converter that is barely able to control a little 20ma load. These are mounted over both sides of the monitor lighting the keyboard from above.
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Last is a project for running a spotlight for my job in a theater. We use Spot Sights to line up on the target before fading the intensity up. Here is what it looks like to look through the small Heads Up display on the Unit.
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These Telrads use two AA batteries. I cut out the batteries and powered it with a 5v phone charger. It has a 2v red LED for the target sight, but I added more LEDs to light up the area where I sit to run the spotlight. Now on the side facing down at my lap, I have 2 pairs of 5mm LEDs, individually switched for White or Blue.
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Been playing with LEDs some more and made a coupla more small projects. They use only colored LEDs and are intended to be more like Art than useful lighting. These are running on wall-wart transformers
One of the devices was going to use 5 different colors in Series. It was assembled, but the Red LED wasn't working. Replaced that LED twice and discovered later, both LEDs tested good. The Bottom Plate on these LEDs are designed to dissipate excess heat onto the surface they are mounted on. After some testing I found that all my LEDs are electrically isolated except the Red & Deep Red ones. So the surface was cleaned and I applied a thin piece of Cellophane tape, then glued the LED down and all was fine.
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Here are the 2 new Projects.
On the left is the 6 color Rainbow effect that was causing the problems mentioned above. The 5 colors are: Deep Blue, Blue, Green, Red and Deep Red. They are all 1w LEDs wired in series and add up to about 14.5 volts with current set to 350ma, powered Using a 19vdc wall-wart power supply.
On the right is a simple 2 color effect that uses 1w Deep Blue and Deep Red LEDS. These LEDs total 7 volts in series and are set to a current of 350ma using a 9vdc wall-wort power supply.
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The Rainbow Effect about 5 inches from the wall. This reveals that the intensity of light isn't very evenly distributed from the individual LEDs, but it still looks great in person. The deep colors aren't presented well by a camera or computer monitor. It gets fairly warm to the touch, but not hot. I had added some small heatsinks to the inside of it to help out some.
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This is the Deep Blue and Red effect at 5 inches from the wall. Once again you can see the rough light distribution but still looks super cool. Gets warm but not hot.
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Today I woke up with a hangover and decided to do something Easy. So I ended up making 5 Nightlights. Two have Natural 4500k White, then 2 more white ones that are Warm 3000k and Blueish 10000k. The fifth one is Colored Blue. I found some old incandescent nightlights and Used the Clear lens covers on these LED remakes. They are all powered with a 5v wall-wart charger, Glued together using 5-minute Epoxy. The heatsinks are 1x3 inch sheetmetal strips bent to fit the wall-warts.
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They all use a 1w LED glued to the sheetmetal with a 4.7 ohm 1w limiting resister. These lights use almost 2 watts and get warm to the touch when running. The resister gets rather warm too dropping 5v to 3.5v at 350ma. In fact, the short thick resister lead transfers a lot of heat and it is heating up the LED too much. If I make anymore nightlights I'll make the lead much longer to keep the heat farther away from the LED.
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I bought a pound of solder at a Hamfest and it's not very good. I is a rosin core solder but it takes a high heat to make it work right and makes a crust on the soldering tip that is hard to remove even with a wet sponge. Got some new solder on order.
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Sounds like you bought the newer no, or low lead solder. In my opinion the stuff sucks for general hobbyist use.
MG Chemicals 60/40 is my go to I guess. It might be a bit more $ compared to some you can get, but it is worth it to me to have consistency.
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I am about halfway finished with another Art project which will project 120 Fast Color Changing RGB LEDs onto the wall or Christmas tree or anything else.
There is a 12 x 11 grid of LEDs, minus 3 from each corner so the image will have some roundness.
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Color Changing LEDs are dependent on a certain Voltage on the input and the current limiting is done by the microcontroller onboard each RGB LED. These LEDs are rated 3.0-3.4 volts and I'm giving them the full 3.4 volts to insure best brightness. All 120 LEDs are wired in Parallel. It took over 2 hours to get the PC board made.
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These LEDs Flash 2 to 5 times a second and do fast color fades too. I took some pictures but since the LEDs are flashing, about a third of them will be off at any instant. This ends up being a very Busy and Exciting display that can't be captured in a photograph.
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This is being powered from my 12v solar power right now, but I will be using a 120vac powering a 6vac transformer to make an 8.5vdc power supply feeding a Buck converter to get the needed 3.4v to feed the panel. Measured the Current draw from the buck converter to the panel and it averaged about .9 amp at the 3.4 volts, so it's a little more than 3 watts to the LEDs.
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It works really good and is really bright, showing up real good in bright light. Unbelievably busy Dancing Patterns. Changing the Focus makes some great effects and it will be built to make the focus easy to adjust. I've gutted an old Meteor Liteflower disco light and will be placing everything inside of that.
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The Buck Converters that I'm using to control Current to my LED projects don't work very well below 100ma. It drives the converters PWM frequency too low and will flash the LED if there are no capacitors on the output. I'm working with all kinds of LEDS right now and need low currents a lot so I've started to use the LM317 variable voltage regulators wired into Current Limiting mode.
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This requires a resister to set the output current and here are the values needed to set the current on the LM317
Ma -- Ohms
20 - 62.5
40 - 33.3
60 - 20.8
80 - 15.6
100 - 12.5
120 - 10.4
140 - 8.9
160 - 7.8 1/4w
180 - 6.9 ^^^^^^
200 - 6.3 vvvvvv
220 - 5.7 1/2w
240 - 5.2
260 - 4.8
280 - 4.5
300 - 4.2
320 - 3.9
340 - 3.7
So this works OK up to about 160ma, then the resister values need to be too precise and it starts generating heat. My buck converters work great above 120ma and these LM317 regulators work great below 120ma. I also discovered the CL2N3-G regulators. They are hardwired to 20ma and work up to 90 volts which can be very useful.
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I've been doing a fair bit of late with some battery-powered LED applications, a bit like you Woof.
I've come to the conclusion that series linear regulation is a dead-end.
It does have the benefit of simplicity, I'll grant it that. But that's about its only benefit.
The wasted heat is power your battery is giving up that SHOULD have been used in making light.
So either you get less light output for you battery, or less run-time.
I've been making some indicators. These are 4 x 1W LEDs, I believe very similar to the ones you are using.
The PCB acts as a bit of a heatsink, but I'm also not driving them to their full power, to reduce heat and extend life.
(http://general.rossw.net/trainlights/smartindicatorv2.0/IMG_3881.jpg)
The HUGE difference here is that with this circuit, I can run 4 or more white LEDs (or any other colour!) at high brightness, off a SINGLE 18650 CELL. (It'll work from about 1.8V to 5.5V). The boost converter uses a very small value resistor (I'm using 2.2 ohms) to set the current, so there is almost no heat or waste power in the resistor. Under a thermal camera, the only part of this board that gets detectably warm is the inductor, and even that is only about 4 degrees above ambient.
In the interests of power conservation, I would urge you (and anyone else dabbling with power LEDs) to skip the series resistor, and/or linear regulator solutions, and go straight to a switch-mode converter using a very low voltage sense (feedback) control. The one I'm using tries to maintain 0.25V across the feedback resistor.
Additional benefits they bring to the table is a "brightness" input pin that can be driven by PWM, or by an analog input, to dim the LED from basically nothing to 100%, with virtually NO LOST POWER. Nothing gets warm. 92% or 96% or something of your battery power gets to the LED, none of this "dropping lots of volts (at full LED current)" nonsense.
Just to demonstrate the point - in your above linear option, you're going to drop 1.25V across your resistor 100% of the time. So lets work at 100mA (where I have mine set). If you have 4 LEDs at 2.3Vf that's 9.2V across the LEDs. With your battery full and sitting at say, 12.8V, that's 3.6V you have to drop across the regulator. 1.25V across the resistor (125mW) and 235mW across the LM317, for a total of 0.36W wasted as heat from your total of 1.28W drawn from the battery.
As the voltage goes up, the worse this gets. At 13.8V, it's 4.6V to drop, 460mW wasted from 1.38W drawn from the battery.
The converter option with 0.25V sense would be about 0.99W drawn from the battery with 0.07W wasted as heat for exactly the same LED output!
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I'm in full agreement. Buck converter is THE way to go for driving LEDs.
Linear (and by "extension", simple resistor), as Ross pointed out, is very wasteful at anything above trivial power levels.
"Plain" PWM is riddled with problems as well, and typically still requires the use of some sort of "absolute ballast" to limit current, so while it provides a means to control brightness, it doesn't do it very well (as mentioned, flicker can get really obnoxious) and I'm a firm believer that it's also harder on the LED dies because of the rapid thermal cycling... Even at higher frequencies (yes, law of averages helps there but it's still repetitive "heat and not heat").
Buck conversion (or boost as well, just not quite as common because of the voltages involved) gets around many of the problems associated with either and/or both.
Flicker and thermal cycling are reduced because conversion inherently requires the use of a cap at the output to catch the pulses, and converting rather than dissipating takes a lot of the losses out of the mix, yielding more efficiency. Current limiting is trivial to implement in most chips designed for SMPS (eg buck conversion) and what results is a stable consistent drive for a wide range of input with minimal waste.
For anything more than pretty much indicator LEDs, I personally will never use any other method ever again having seen the benefits of conversion up close for myself.
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I was trying to point out that the Buck Converters that I'm using don't work very well when set to currents less than 100ma and I'm using the LM317 regulator mainly to power ordinary 20ma LEDs. I'm about to build a small light for my computer keyboard that will require 60ma and I'll use an LM317 for that. There are two 20ma LEDs in series that light up my computer desk that need a LM317 to control them. Earlier I posted about making nightlights with 5v wallwarts and a 5 ohm resister. sure it's wasteful but it was still bright and only used 2 watts which is half the power used by the usual 4w incandescent bulb normally in a nightlight. I plan to get a large number of those 20ma CL2N3-G regulators for many future small projects.
For anything over 100ma the buck converter is the only way to go.
So after all that, I am making a Test Box using four LM317 regulators to give me 4 different current levels for testing LEDs and powering Prototype projects. There will be a terminal strip on top that will provide 4 individual outputs at the following current Levels
20 ma - regular LEDs
25 ma - laser diodes
310 ma - 1w LEDs
640 ma - 3w, 5w and 10w LEDs
When finished this will greatly speed up my project builds and testing new LED orders that I receive. It will be powerd from a Cigarette Lighter plug from my 12v solar power
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I finished my Test Box for experimenting and making LED lights. Has a Cigarette Lighter plug for the input, then then 4 handy Current Limited outputs for testing and prototyping new projects. I've already used it to sort out the color of some LEDs that got mixed together while working on my solar bicycle light project.
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Got a buncha new stuff in the mail and testing 4 items out in the center of the picture. . .
-- 5 CPU cooler heatsink fans, $2 each. Got these specifically for using 10w LEDs and they do a great job keeping everything at almost room-temperature while staying quiet running full speed.
-- 3 Blue LEDs 10 watt $2.50 each. One of them is glued to the heatsink in the center. The colored 10w LEDs are brilliant as all the energy is directed into the one color.
-- 3 PWM motor speed controllers, $2 each. Being used as an LED Dimmer these work wonderfully down to about 5% brightness then off. The PWM frequency is 10k.
-- Got a lot of Reflector units in various sizes, some with a lens. These seem to double the brightness of the LEDs while directing the light.
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Building a 20 watt LED Lighting Fixture From Scratch
I've been building small lighting using LEDs and decided to make something that was more powerful and could be considered bright enough to work under.
It uses four 5 watt LEDs with two Buck Converters. A fan was added later because there was too much heat being produced. Not as bright as four florescent tubes 4 feet long, but plenty of light to work under. gets fairly warm but still cool enough for long life.