Repurposing CPU coolers for indoor LED lighting.

Orum

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I recently built another PC, and as Intel insists on including a stock CPU cooler (heatsink + fan), I now have a second CPU cooler that's going unused. I'd rather they not go to waste, I was thinking about instead using them for LED indoor lighting. I would love to replace my CFL lamp with something more efficient, and hopefully dimmable as well.

The coolers are made for 95W and 77W TDP CPUs, and are essentially identical except for some minor differences in the fin design. Each features a copper insert at the base, 28mm in diameter, which is then shrouded in radiating aluminum fins. I've uploaded an image of the two coolers (top of one and bottom of the other, fans are identical).

A few things are holding me back before I order, so I came here seeking advice. They are:
  1. How should I attach the LEDs to the heatsinks? Obviously they'll have thermal grease between the emitter's base and the copper core of the heatsink, but I'm afraid that that won't be enough to hold it on securely, especially once it gets hot. Perhaps some wire between the fins to tie it down? I don't want to use anything too permanent.
  2. Will I need active cooling, or can I get away with passive? I currently have a 13W and 26W CFL in my lamp, and though I typically only use the 13W, it's nice to have them both on in some occasions. From my quick googling, it looks like 13W CFLs output around 800 lumens, and the 26W is roughly double with 1600 lumens. So, to get the same output with 2 LEDs, I'd need ~1200 lumens/LED, but I'll take anything close to that (+/- 300 lumens/LED). Will the heatsinks alone be enough for cooling LEDs with that output or will I need to plan on running the fans as well?
  3. Which LEDs in particular, or perhaps more importantly, where to get them? I've browsed around DealExtreme for some time now, but it appears most of their LEDs are a cool white (I definitely prefer a warmer white, i.e. 3500-5000K), and those that are warmer don't have very high output.
  4. What to drive the LEDs with? I'm in the US, with 120VAC mains. Ideally I'd like adjustable output (voltage, not PWM) to dim the LEDs, and if I need to drive the fans as well, I'd also need a second (ideally adjustable) output as well. Any commercial products I should look at (including fixed voltage options)? Of course, whatever I drive it with will have to be fairly efficient, or else I'd have to put the regulator on the heatsink instead of the LED :ironic:.

I'll be sure to update this thread once the build is underway, but right now I just need to figure out what to order. :thinking:
 

Optical Inferno

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This may be an opportunity to look at the Cree MT-G or MPL with a Tyco holder. The holder needs three small holes drilled into the heatsink but secures the LED to the heatsink with no solder. You can also buy reflectors from Ledil that match the LED and fit into the Tyco connector. This will prevent custom circuitboard design and reduce the cost of the custom build.

The heatsink you have should work passively but always test before committing to the total build.

As for power, try an off the shelf Meanwell power supply.

All these parts can be purchased from places like Digikey, Mouser, Newark. Good Luck.
 

Norm

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I think at all costs you want to try and cool passively, I for one don't want to listen to computer fans in my living room, it's bad enough in the office.

Norm
 

The_Driver

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The 95W rating of those coolers is the absolute mxaimum. Normally when a cpu is idling (most of the time) is produces muuuch less heat. At 95% the fan will be blowing full power (another 6W). You can calculate though how much heat you can produce without using fans with this heatsink. The sorface area of the fins is very important for this.

Regarding the mounting options:
The best thing you can do is solder an emitter directly onto the copper core, but this is difficult and requires a custom pcb. A more realistic method is using emitters on stars and screwing those done (with set screws or better even torx screws) and arctic silver in between. For optimum efficiency you could use 3 or even 7 XM-Ls. You could also use one of the big bridgelux leds, which are made for this kind of thing.
If you want "quality" light use an led with a high cri rating (90 or more) and no less than 3000K. These leds wont be nearly as efficient as cool white ones though.
 

blasterman

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CPU heatsinks, unless you happen to be using one of the huge old fashioned ones that used to run with P3s are designed for active cooling only. You can run them without a fan, but because of their thin fins they are very inefficient and moving heat away from the central plate and they'll over heat quickly. 10watts is about the limit I'll use with a solid copper CPU sink with no fan.

Most of the newer fans are pretty darn quiet, and below audibility if mounted on a bookshelf or something. If they are still too loud use a 6volt walwart to drive them.

I use standard Epoxy to mount LEDs. Bolting the led to the heat sink is the most efficient way, but I don't have a machine shop. It's the width of the gap that matters most, and in this respect fancy thermal adhesives are rip off.

Inventronics drivers have the easiest built in dimming, but are more expensive than Mean Wells. Dimmable bucks are the easiest to use, but require a fixed voltage supply. Many easy ways to do dimming.
 

idleprocess

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I believe that Total Power Dissipation ratings for CPU heatsinks are based on the far more robust thermal margins of CPU's along with the already-stated assumption of forced-air cooling.

I know that if you spend more than the minimum on a heatsink/fan combo, you tend to get a fan that will run for many years continuously without trouble ... dust accumulation and blockage will be your main problems.
 

Orum

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I think at all costs you want to try and cool passively, I for one don't want to listen to computer fans in my living room, it's bad enough in the office.
The room these will be going in already has a PC in it, and if I'm in the room, chances are it'll be on. If you undervolt the fans they can be quite quiet.
The 95W rating of those coolers is the absolute mxaimum. Normally when a cpu is idling (most of the time) is produces muuuch less heat. At 95% the fan will be blowing full power (another 6W). You can calculate though how much heat you can produce without using fans with this heatsink. The sorface area of the fins is very important for this.
This is true, but the other half of it is they actually produce more than the TDP under constant load. This is due to how Intel (and AMD as well in recent times) defines TDP--it's not an absolute maximum, just what they expect to see when running "real" applications (Intel's words, not mine!).
Regarding the mounting options: ...A more realistic method is using emitters on stars and screwing those done (with set screws or better even torx screws) and arctic silver in between. For optimum efficiency you could use 3 or even 7 XM-Ls. You could also use one of the big bridgelux leds, which are made for this kind of thing. If you want "quality" light use an led with a high cri rating (90 or more) and no less than 3000K. These leds wont be nearly as efficient as cool white ones though.
Well, I don't need really high CRI, but I definitely don't like cool lights. I put up with cool LEDs in my flashlights as there efficiency is paramount, but for indoor lighting I'm willing to sacrifice some efficiency for a more ideal color temperature. Good idea on the mounting!
I use standard Epoxy to mount LEDs. Bolting the led to the heat sink is the most efficient way, but I don't have a machine shop. It's the width of the gap that matters most, and in this respect fancy thermal adhesives are rip off.
I think I'll stick with the paste that's already on it, and just bolt it down well. I'd rather avoid epoxy as I'd like something easily removable.
Inventronics drivers have the easiest built in dimming, but are more expensive than Mean Wells. Dimmable bucks are the easiest to use, but require a fixed voltage supply. Many easy ways to do dimming.
Ah, thanks. I was considering building my own, but my knowledge of AC to DC conversion is lacking (most of the stuff I do is just DC->DC LDO, etc.). If I can buy a good supply, and just slap a pot on it for dimming, that will more than suffice.
 

Illum

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Given the nature of fixed lighting, passively cooled will see neglect in cleaning over time and become a "sediment tank" for the dust that floats around in the air in the house. So forced cooling is a good thing, but reliability is drastically reduced compared to that of passive cooling. If the fan fails the heatsink is no different than a block of aluminum with little or no air circulation in between. A heatsink with large spacing between fins coupled with a low rpm 120mm box fan I think noise will not be a significant issue.
 

Fird

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As a computer repair tech I've seen some of the newer radial heatsinks are definitely under-sized but with the fan having an open frame and actually an airfoil design (on the latest Intel's at least) they would be rather ideal for cooling. I wouldn't run an LED at the 65 or 90w TDP spec, but 15-30w of LED's with a 6-10v powered fan turning slowly would last years and probably throw out a ton of light. If you wanted to get really creative, the fans now have PWM drive pin, one could create a PWM signal for dimming the led's and feed an inverse signal (because no PWM signal = fan runs wide open) simultaneously to the fan, more light = more fan.
 

deadrx7conv

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Passive CPU coolers aren't really passive. Many rely on case airflow from other means. The computer power supply and computer case fans usually draw air through the computers case, and there is some airflow turbulence from graphics cards too. There is no point in spending $100 on a fancy passive CPU cooler when all you need to do is find the biggest free-$10 cpu cooler and remove the fan. Surface fin area and thermal mass are what you want.

Other so-called passively cooled LED lights are used by the ATV, bicycle, bike, snowmobile, boating....crowd. Many of these small and high powered 12v LED lights have minimal thermal mass and fin area, but do work fine as long as there is some 'external windchill'. They also heat-sink to whatever they attach to.

The issue with indoor lighting is that the bulb needs to be pretty and/or enclosed. You can't suffocate the heat sink. If you do, it'll overheat. You might be forced to use an under driven fan. Another option is the hidden heat sink... like a 3-4ft aluminum bar-stock tucked into the rafters or wall with a thermal connection/pipe to your LED's heat sink.

You'll need to drill/tap the heat sink so that you can mount LED star board to it. A little thermal paste should be used.
Another option is to use a thermal adhesive.

Smaller LEDs are mounted on star boards. LED output is great. But, sometimes it is difficult to put the light where you want it. You'll need lens, reflectors, diffusers,..... to move that LED light around some. The lens and LED will determine if you'll get a flashlight-like spotlight on the wall, or if you'll get a good 360 degree flood.

I've used CPU coolers. Simple divide by 10 will give you a good starting point for a passive LED light cooler. A 100w sized CPU cooler should give you excellent passive cooling for a 10w LED. Invest in an IR temperature gun for timed temperature measurements.

A 10w LED, the the CREE XM-L could give you the 1000 lumen. You'll take a 10-20% hit when you toss in the lens/diffusers...depending on the beam that you're looking for.
Plenty of LEDs to choose from depending on the light type, budget, skill ability, driver chosen..... If its interior lighting, I'd even skip some of the higher output LEDs for something with a tad less efficacy/efficiency in order to improve CRI. Bridgelux is another good choice.

It would also be good to read into this forum for several pages. Many have experimented and have built lights.
http://www.candlepowerforums.com/vb/showthread.php?149183-LED-Fixed-Lighting-Threads
 

blasterman

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I have a better idea on this theme if you want to go passive. Google older coolers designed for Pentium 3's and 4's. For instance, some of the passive heats-sinks Dell used for their P3 and P4 towers were stupidly huge, and if you were to buy the equivelant performing heatsink from Mouser or Newark today you'd pay $30-40. Some of the older Dell sinks also had thick, pin type radiators -vs- the thin metal fins we see on today's coolers. The former are far superior for passive cooling.

At one job I was at the older PC tech I was working with was saving all heat sinks from junk PC and had a large box filled with these passive coolers, and they were all the legacy bigger ones. His theory being the aluminum at some point would be worth a lot of money.
 

Lon

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I used blastermans advice on the recycled PC sinks. I went to all the local PC repair shops, most had a box full of various sinks. 5-10 bucks usually, I found 4 all copper, heavy slug sinks. Cant use them passive, but Im runnin about 125 watts to a bridgelux with active cooling. Im a total novice in the electronics compared to most of yo guys, but this DIY lighting is addictive.



Your image is too large and has been replaced with a link.
See Rule #3 If you post an image in your post, please downsize the image to no larger than 800 x 800 pixels. - Thanks Norm
 
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eebowler

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DUDE I WANT BEAMSHOTS!! Wrt passive vs active cooling, the fan has three wires, I'm not good with electronics but doesn't this mean that a simple +ve and -ve connection wouldn't work?
 

Lon

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I call that pic "say Ello ta ma little freindS".
I have 4 of those mounted to my boat for fishin. 2 front, in pic, and 1 on each side. These are designed to flood light wide and down at the water. Im not sure what your asking about the fan anf the + - VE.


Your images are too large and have been replaced with links
See Rule #3 If you post an image in your post, please downsize the image to no larger than 800 x 800 pixels. - Thanks Norm
 
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Lon

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Thanks man.
As a reread, Id say blasters right from my experience, the CPU sinks are good for 10w, maybe 20w with one of the warm white 3000ish K arrays. Bridgelux has a nice selection of CCT in their lineups, I also found these mounting brackets(term?) from Molex for the RS series Bridgelux, nice little spring contacts fit right over the chip, and give you quick stab wire connection, very easy to use. I kinda rednecked mine and just used screws screwed into the fins, frame, or whereever I could predrill a hole. Mine need to be bulletproof for the beating they take trailering the boat and in rough waters.
 
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blasterman

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Ya know, I hear all the time from the flashlight freaks that you can't use Bridgelux in portable lighting because they 'have no throw'.

Eh, what's that again :)
 
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