# 100w LED array heat sink?



## Lon (Jul 8, 2011)

I got this old cast Aluminum halogen fixture. Its 14" by 10" approx. 
Any ideas if this would work as a heat sink if I machined a flat surface to attach my array directly to it with a thermal paste between?
thanks


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## Curt R (Jul 8, 2011)

Ideal surface area requirement is 10 square inches per watt of led drive power.
You can get by with 5 sq inches with some air circulation. 

Curt


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## deadrx7conv (Jul 8, 2011)

Looks like a good housing to weld a large heatsink inside. Other option is a waterproof fan and drilling a couple vent holes.


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## Lon (Jul 8, 2011)

So best I can figure the housing has about 400 sq inches exterior surface area.
Deadrx what kind of heat sink would you weld to it? So you dont think the housing is enough?? I have a round finned 1.5" deep heat sink and a fan that runs it now, it doesnt seem to have near the 5 sq inch per watt surface area.
Sorry for so many questions, I just dont want to burn up my array.


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## Lon (Jul 8, 2011)

whoops double post


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## deadrx7conv (Jul 9, 2011)

The above is the dimensions for a China-sourced typical 70w-100w outdoor LED flood light. The bottom 112mm is the driver. Notice that your recycled housing is lacking fin count surface area. 

I'd carve up ANY large CPU heatsink that would fit there. If you can drill/tap, then you can hard mount your heatsink/fan combo and see how it goes. You want to make sure there is some type of thermal connection between the heat-sink and that housing. Otherwise, the housing turns into an enclosed convection fan-oven. Welding is probably the best way to make that connection. But, we here tend to use thermal epoxies as another option. 

The other option is to do some backyard 'aluminum pouring'. Fill the housing and mount your LED directly to the aluminum fill. 

If you're driver is variable, start with a lower 30-50w(if the LED lights) and move up from there. Monitor the temps will determine how good your heat sink method is. 

Something like this cut to fit and mounted inside? 
http://www.heatsinkusa.com/categories/10.000"
http://cgi.ebay.com/370491621077
http://cgi.ebay.com/300571764120

Other good sources of heatsinks are burnt out car stereo amps or home stereo receivers.


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## Lon (Jul 9, 2011)

Awesome, thank you so much. I found some 40mm x 10 mm fans, thought maybe a AL fill and a fan in the side with vent holes to cool the Housing might work. Great ideas are welcome and appreciated.


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## Lon (Jul 18, 2011)

What about some 1 1/4" copper pipe connected (4'-5' of pipe between lights) between with a fresh cool water supply circulating to the endcaps with the arrays thermally welded to end caps?
Or maybe just the copper pipe alone at length?


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## deadrx7conv (Jul 18, 2011)

It should work. Water filled copper pipe is an excellent way to move heat from the inside of the housing to the outside, and affordable too. 

But, like anything, you should test the LED at different wattage levels monitoring temperature.


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## Lon (Jul 18, 2011)

I guess I need to bite the bullet and get something to monitor temp. Any inexpensive ones out there?


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## Lon (Jul 18, 2011)

Ok heres another idea I was working on, this will qualify as the ugliest light ever, but I just care about function.
How about lots of copper wire thermally welded into the copper pipe sticking out the back of that housing.


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## Lon (Jul 18, 2011)

whatcha think, just a mock up so far.


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## deadrx7conv (Jul 18, 2011)

Very creative and original design!

Make sure you use a pipe plug to mount the LED to. The pipe cap might need a little filing to flatten it. 





I just don't see enough surface area for 100w yet, even with the mop of copper wire. 

You could try to use 'baseboard heating' which is finned pipe and might give you the surface area you need, or try the slip over pipe fins. Check with your local hardware store, plumbing and heating supply, or plumber/HVAC guy for scrap pieces. 










Baseboard heating pipes can be 'manifolded' together either vertically or horizontal across the back of that recycle light housing. 

I still think that the best mount for your LED is a recycled heatsink, from a Pentium4 or equivalent. You can drill though the back half of the CPU heatsink to push that "pipe idea" and the pipe should be 'press fit' into the CPU heatsink along with being pressed into the light housing's hole. Braze/weld it all together once you set the LED height in the housing. Don't forget that the 'metal reflector' is also 'heat sink area' too. So, you want to drill several small holes around the CPU heatsink and attach the reflector to the heatsink.


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## Lon (Jul 18, 2011)

Well I guess thats good, that mop of wire is hideous. Off to try to locate old CPU heat sinks. This is fun in masochistic sort of way.


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## IMSabbel (Jul 19, 2011)

That mop of wire is not even be sufficient for 20W, not to speak of 100. Tiny surface area.

There is no cheaper way to cool such a fixture than a heatpipe cpu heatsink. You can get nice big ones for $20, which are good enough to cool away 100W without getting too loud.

And Lon, 40x10mm fans are great as noisemakers, but you will be much more happy with any fan >80mm.


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## Lon (Jul 19, 2011)

Right on, this is the stuff I need to know, I found a couple computer repair shops with drawers full of heat sinks, so I need to go pick out a big un.
Will I need a fan with the CPU heat sink and copper cap/pipe (no mop)?


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## blasterman (Jul 19, 2011)

Cap mounting LED arrays this way only works up to 5watts or so. I've tried it - doesn't work. Conceptually the copper cap the LED is mounted to works as a flat piece of metal, and even at 1/8" of an inch thick it can't radiate thermal from the big emitters fast enough. Then the junction between the cap and the copper pipe comes into play. So, drop the pipe idea unless you want to point it at things to set them on fire  You won't need a thermal probe because the solder joints on the array will catch fire in a few minutes and melt anyways.

Even if the pipe were a solid core of copper it would need an extensive array of thick cooling fins with 1/4" junctions directly to the 'solid' rod. Even then, running the modeling in my head my intuition is there would still be issues. You have no idea how much thermal these big arrays generate. 20watters are bad enough.



> So best I can figure the housing has about 400 sq inches exterior surface area.


 
No....looks about half that. The inside is sealed so it doesn't count after it warms up and the fins aren't long enough. 

Still, if the wall of the fixture is more than 1/4 thick your original idea of machining it and mounting the emitter on it might be the best. 

Otherwise, the only way to practically cool these fat, inefficient chiense arrays is via active cooling. The older Pentium style passive sinks typically used on Dells work better than modern ones with thinner bases and thinner fins. Then stick a super high RPM 80mm on it.

Insert my scripted lecture that you can usually get more Bridgelux lumens per dollar than these Ebay arrays at about 40% less energy consumption.


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## Lon (Jul 19, 2011)

Thanks Blasterman, very good info, I will search out your lecture. I started with this ebay array cause the guy sold it, a finned heat sink, fan and some lenses for 55 bucks, I have some bridgelux coming, and spoke to a tech there, i know they are better, just wanted to experiment on the cheapy as I will likely destroy it as Im learning. 
The fixture is right at 1/4" thick. I am going to a Comp. shop to get some old sinks, will rework and post up, thanks ALL for the advice, its likely saving me big time.


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## Lon (Jul 19, 2011)

OK, quite a bit cleaner look now.


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## deadrx7conv (Jul 19, 2011)

You seem to be right on track now. Add a waterproof fan or two and see how it runs. Gelid, Nanoxia, and ADDA have waterproof fans if its for outdoor usage. 

Google heat-sink lapping to smooth out the LED and heatsink mating surfaces. Don't forget to use artic-silver or equivalent thermal paste on the LED/Heatsink surface. You should also use the thermal paste along the heatsink/housing mounting area(or just braze/weld the heatsink to that housing). 

Is this for indoor or outdoor usage? what type of power supply or driver do you plan on using?


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## Lon (Jul 19, 2011)

It is going on a boat for night fishing, so it needs to be somewhat water resistant, but its not going to get really wet. Should be good airflow around them. But I will look into waterproof fans, I have some artic silver already and will google the lapping. Thanks
I have one of those dc to dc converters you linked from ebay, and the 120v to 30vdc driver that I got in a package deal with the china array, the drivers will be mounted in a remote bow to protect that circuitry and will keep them ventilated as well. its coming together thanks to your guys help, much appreciated and any other ideas are as well.:twothumbs


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## IMSabbel (Jul 21, 2011)

Lon said:


> It is going on a boat for night fishing, so it needs to be somewhat water resistant, but its not going to get really wet. Should be good airflow around them. But I will look into waterproof fans, I have some artic silver already and will google the lapping. Thanks
> I have one of those dc to dc converters you linked from ebay, and the 120v to 30vdc driver that I got in a package deal with the china array, the drivers will be mounted in a remote bow to protect that circuitry and will keep them ventilated as well. its coming together thanks to your guys help, much appreciated and any other ideas are as well.:twothumbs



Yeah, with the fan there should be no worry about 100W.

Note that this type of CPU sink is not that well suited for passive operation (it is optimized for fans): The fins are pretty close to each other, which increases surface area, but reduces natural convection airflow.


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## bshanahan14rulz (Jul 22, 2011)

I've got that same heatsink, more or less, for use with a 125W processor. Should have come with a fan. Those fans are cheap, standard sized, and easy to replace. Check on prices of, say, 5-packs of those fans or something. It might even be worth just buying spares and not worrying about the fan as much.


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## Curt R (Jul 22, 2011)

If the driver is remotely placed as to the LED assembly the connecting
wires could act as an inductor and destabilize the driver output. More 
output capacitance may be needed. It would be better if the driver is
mounted in a water proof housing close to the LED, but insulated from 
the heat.

Curt


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## Lon (Jul 22, 2011)

Thanks guys, good stuff, is 5 feet away a problem you think Curt? I do have a couple fans, thermo tester enroute, will to some testing. Thanks again for all the help, you guys are awesome.


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## Curt R (Jul 22, 2011)

Hard to say if 5 feet is too far, depends on the circuit. We keep our circuits
to the LED within four inches. A change in output inductance could change
several parameters and upset the analog side of the circuit causing it to do
strange things. A DC-DC integrated circuit is designed to have an analog side
that controls the function of the IC with a compensation circuit for stability.
The other side of the circuit is the power side where the input and output
capacitors, inductor, diode and transistor are located. This is a physical layout.
We try to keep these two separate from each other so that the frequency
generated on the power side does not overload the analog side. There is a
narrow window of matching the inductor value and output capacitance as a 
team for stability of the circuit. Any length of wire can act as an inductor.
By adding a long length of wire to the output, you change the balance of the
team that could cause the circuit to not function properly.

Bottom line is that during your testing and everything works well, and when
installed you have problems, you now have somewhere to look to solve the
problem. Good luck. 

Curt


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## Lon (Jul 26, 2011)

Well I tested it out with 14 foot 16 gauge wire for input to the driver and 14 foot 16 gauge to the array from the driver, seems to work OK...hope it lasts, going to do a 6 hr continuous tonight.
Ran it for 20 minutes with a fan blowing on the sink, it didnt even get remotely warm to the touch(sink), not sure if thats any kind of indicator, maybe it will work as a passive sink???
Any recommendation on an inexpensive thermometer for testing LED temp?
Thanks


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## qwertyydude (Jul 26, 2011)

Least expensive thermometer option is a cheap infrared non contact thermometer. Search for a Cen-Tech Non-Contact Thermometer. They're usually about $15 bucks but shipping can cost some. If you have a Harbor Freight near you they often go on sale for $12.

All you have to do is turn off the light before you point it at the star, get up close for more accuracy.


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## Lon (Jul 26, 2011)

Thanks qwerty, Lowes wanted 50 bucks for one of those, Ill swing by harbor freight. I was wondering how/where to point the infared.
Well I just ran it for a half hour without the fan and it definitely got the sink warm.


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## IMSabbel (Jul 27, 2011)

Lon said:


> Well I tested it out with 14 foot 16 gauge wire for input to the driver and 14 foot 16 gauge to the array from the driver, seems to work OK...hope it lasts, going to do a 6 hr continuous tonight.
> Ran it for 20 minutes with a fan blowing on the sink, it didnt even get remotely warm to the touch(sink), not sure if thats any kind of indicator, maybe it will work as a passive sink???
> Any recommendation on an inexpensive thermometer for testing LED temp?
> Thanks


 
If the fins are cool, its not an indicator
Take a look at the design of the heatsink: If you touch it at the outer part, you are well away from the heatpipes that actually represent the real temperature. Those thin fins dont conduct heat very well, so there will be a huge temperature drop along the fins under forced air cooling.

So just switching off cooling could cause overheating before it gets really hot at the end of the fins.
If you want to try it, touch the base of the HS (where the heatpipes are mounted) without the fan on. If it gets too hot to touch (even for a moment), you need the fan.


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