LED Heatsink thread: Where to find them, what to look for....save cash! - The Planted Tank Forum
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post #1 of 112 (permalink) Old 07-28-2011, 01:47 AM Thread Starter
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LED Heatsink thread: Where to find them, what to look for....save cash!

I'm starting this thread so that we can put together a group effort on making this sometimes frustrating part of DIY LED work much easier.

Please share your experiences/sources/DIY methods for affordable heatsinking. Feel free to ask any question about selecting a heatsink.

I'll admit I'm a firm believer in overkill with heatsinks-- it's good insurance in case I ever decide to crank up the current, but it's not always affordable. Lots of people use aluminum C-channel and similar flat stock, I personally advise you to use stuff that's a minimum of 1/4" thick and 1.5" wide, but if you run the LEDs at low currents, then you can possibly get away with thinner.

For info on thermal adhesives and epoxies, etc.... look at post #3.

So here are a couple resources for legitimate manufactured heatsinks that do a very good job.
For LARGE, individual LEDs (10 watts and higher)

It's hard to beat star-shaped heatsinks like these, made by Wakefield, at a very reasonable price:

http://www.newark.com/jsp/search/bro...questid=503476

(Newark also sells the wonderful HUGE and powerful Bridgelux LEDs so you can order both from the same place).


There are also some nice heatsinks and lower-cost "import/generic" type LEDs available at Satistronics.com

http://www.satistronics.com/Wholesal...-for-led_c1027

I'm partial to this one, it comes drilled, tapped, with screws included that fit their larger LEDs.
http://www.satistronics.com/high-pow...30m_p2162.html



For larger arrays using many LEDs, the beefiest and most affordable heatsinks I'm aware of-- and the ones I use on most of my stuff--- is the custom-cut offerings from:

www.heatsinkusa.com (see posts BELOW on selecting a heatsink size for your tank, don't spend too much for an oversized heatsink)


Finally, if you are lighting a small tank(5.5g or smaller, or something that's under 15" long) you can also just use leftover computer CPU heatsinks, and possibly even the fans if you need it.

There is no real reason you couldn't use multiple CPU heatsinks over a large tank as long as you don't overwork them by using too many LEDs and high drive currents.


Now please, everyone share your sources, or your DIY work.


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post #2 of 112 (permalink) Old 07-28-2011, 01:55 AM Thread Starter
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On selecting the size of the heatsink if you are going with a custom cut size from a site like HeatsinkUSA....or if you are replicating this by using aluminum C channel.

There is no magic formula, and there are several factors that interfere with making a cookie-cutter formula. The angle (or absence) of optic reflectors, the height you hang the array at, the number of LEDs, and the intended drive current all effect the size of the heatsink you'll likely need.

BUT!

I think the following criteria is helpful. If you are building a typical LED array, that uses 60 degree (or bigger) optics, and are using a larger number of 3-5w LEDs (like Cree XRE/XPG/XML types), you'll basically want two rows of LEDs, 3" apart, for most tanks that are 10-15" wide. So two rows, centered, with 3-4" in between them.


It needs to be about 1/3 the width (not length!) of your tank. In other words, for a 55g (13" wide), you would want a heatsink that's about 4" wide.



For length, this is much easier. Just knock a few inches off of the length of your tank. So a 48" long tank would need a heatsink that's 42-47" long.


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post #3 of 112 (permalink) Old 07-28-2011, 02:14 AM Thread Starter
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Regarding thermal adhesives. You have a few good options.

Most of us, who don't work the death out of LEDs can just use whatever cheap thermal adhesive you can get at any computer place. Make sure it's a grease that never evaporates.


Option #1, the best option:
Arctic Silver Thermal Compound and similar products. This IS NOT A GLUE and won't hold the LED in place for long. You MUST drill/tap your heatsink and screw the LEDs down... or some other way of attaching the LED. The screw and thermal grease method is probably the most effective, but most SWEATY and labor-intensive method. Fortunately some places like RapidLED.com sell pre-drilled heatsinks. Well worth it.

http://www.arcticsilver.com/as5.htm


Option #2 (not best, but very good): Thermal Epoxy/Adhesive.

Arctic Alumina Thermal Adhesive (and the similar Arctic Silver Thermal Adhesive) is a VERY STRONG two-part, mix-yourself epoxy. A very little goes a very long way. This is a permanent glue joint that you may never be able to undo once you glue it, so make sure you have that LED where you want it! This is mildly less effective than the thermal grease above, but quite effective anyway. Benefit--- you only need to secure the LEDs while it's curing, which is only a few minutes.

http://www.arcticsilver.com/arctic_a...l_adhesive.htm


Option #3 (quick, easy, and effective, but #3 in terms of efficiency):

Thermal Tape/pads.

Bergquist Bond-Ply is a very good product, and for our purposes, is VERY effective and by far the quickest, cleanest way to do this. This is mainly what I use.

Here is a 6" square sheet for $22, but keep in mind that this is enough to do at least 40 LEDs (3/4" squares). If you are good with the razor knife, or use a paper-slicer, you can actually get 48 out of it. Newark also sells nice Wakefield heatsinks for individual, LARGE LEDs and also the lovely Bridgelux higher-power LEDs, all at very good prices.

http://www.newark.com/bergquist/bp10...eet/dp/47T1948


Here are the pre-cut ones you can get from aquarium-spec shops.
http://www.nanotuners.com/product_in...roducts_id=627
http://www.rapidled.com/servlet/the-...dual%29/Detail


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post #4 of 112 (permalink) Old 07-28-2011, 04:53 AM
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I noticed a lot of people get their c-channel from Home Depot. IME Home Depot isn't the cheapest source for this kind of material. I called around and found a metal wholesaler and got exactly what I want, cut custom. They also have scrap bins you can pull from. It's easy to cut a deal with that stuff because they consider it waste.

Another thing I noticed is that most people are still putting their fixtures right above the tank. LEDs are nice and powerful so if you have a rimless or open top tank, why not hang that light up nice and high? Optics are cheap cheap and if you slap 40 degree optics, you can raise your fixture up a couple feet and their are lots of advantages. The spread can be the same, or adjusted for less spill, more power from your LEDs, easy access to the tank and best of all, more consistent par levels throughout the tank. As you get further from a light source the difference in par becomes less. Close to the light is drops off very quickly, but get the fixture up there a bit and the par levels at the surface and substrate will be much closer together than if the fixture is on the rim.

Also, almost everyone goes waaaaay overkill on their number of LEDs. Take a look at all the other builds and notice how everyone ends up dimming their fixtures down. Also consider that in 5 years, XPG will be history. So don't be afraid to run a decent current through them. They are good for 1500mA, so you don't need to limit your current to 700mA for fear of burning them out early. You probably wont be using the same LEDs in 15 years. Think about utilizing the power they have.

Just some food for thought.


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post #5 of 112 (permalink) Old 07-28-2011, 01:23 PM
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My testing has shown that it takes approx. 40 square inches of surface area to maintain touch-safe temps for a 5 watt led driven to it's limits.

This requirement falls off FAST as the drive current is reduced. The above test was pushing the diode at 1.5 amp and resulted in heatsink temps of approx. 130F. Dropping the drive current to 1.2 brings the heatsink down to about 100F. (room temp was 72F)

This is passive cooling and a finned aluminum heatsink. Adding a small fan drops the temp down to near ambient.
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post #6 of 112 (permalink) Old 07-28-2011, 02:03 PM
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Very good thread. I think the more information we can collect in one place the easier DIY LED builds will be for others in the future.

For my own build, I used 12 XP-G's, separated into two rows of 6. Each row was placed in 2"Wx1H" 1/8" thick aluminum channel, 28" long. Running at 1 A, I have no heat whatsoever, the channel is maybe 5-10 degrees above ambient (78). This was using Arctic Alumina thermal adhesive.
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post #7 of 112 (permalink) Old 07-28-2011, 03:12 PM
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Originally Posted by h2oaggie View Post
Each row [of 6 XP-Gs] was placed in 2"Wx1H" 1/8" thick aluminum channel, 28" long. Running at 1 A, I have no heat whatsoever, the channel is maybe 5-10 degrees above ambient (78). This was using Arctic Alumina thermal adhesive.
I show that channel as having approx. 218 square inches of surface area, or a bit over 36in^2 per LED. That jives with what I got.
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post #8 of 112 (permalink) Old 07-28-2011, 04:06 PM
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Here's an other overlooked source for heat sinks- Car Audio shops Broken car amplifiers can be used for their heat sink and often times purchased very cheaply or had for free.I used 3 of them in my very first build. 30 Cree XR-Es consuming 5 amps total, and barely warm to the touch. Here's a photo of one-

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post #9 of 112 (permalink) Old 07-28-2011, 04:35 PM Thread Starter
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Originally Posted by cggorman View Post
My testing has shown that it takes approx. 40 square inches of surface area to maintain touch-safe temps for a 5 watt led driven to it's limits.
Using what thickness heatsink, with what fin type/size/number?

The heatsinks from Heatsinkusa, and those big star heatsinks from Satistronics can handle quite a bit more wattage than 5w at 40 sq inches.

The star heatsink I used on a 10 watt emitter (at 1000mA) was about 4" diameter, with a center solid aluminum cylinder about 1"X1", the rest was fins.


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post #10 of 112 (permalink) Old 07-28-2011, 04:35 PM Thread Starter
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Here's an other overlooked source for heat sinks- Car Audio shops Broken car amplifiers can be used for their heat sink and often times purchased very cheaply or had for free.
And AWESOME point. Thanks!


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post #11 of 112 (permalink) Old 07-28-2011, 05:33 PM
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Using what thickness heatsink, with what fin type/size/number?

The heatsinks from Heatsinkusa, and those big star heatsinks from Satistronics can handle quite a bit more wattage than 5w at 40 sq inches.

The star heatsink I used on a 10 watt emitter (at 1000mA) was about 4" diameter, with a center solid aluminum cylinder about 1"X1", the rest was fins.

Right. More fins in a given volume means more surface area.

The sinks I was testing were cannibalized computers heatsinks. One was a large northbrige heatsink around 20 in^2 with pins (not fins) and the other was a CPU heatsink that I cut into 4 equal pieces about 1.5x1.5 I also did another CPU sink with 4 diodes mounted to it.

Of course, there is also the large tubular air manifold I built for my corner tank setup. It is approx. 925 square inches of surface and holds thirty 5 watt diodes. That's about 30 square inches each and it gets quite warm when all the diodes are driven to 1.5 amp. I didn't put a probe on it, but I would guess 130F. I measured it last night and got 104F with the diodes running at 1.2 amp. (room temp was 77F). This is an ACTIVE cooling setup. Fans push air thru the inside of the tube at a theoretical speed of about 750 linear feet per minute. (I don't know what kind of loss I'm seeing from friction in the tube. I could borrow an anemometer from work to measure it, but don't care that much )
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post #12 of 112 (permalink) Old 07-28-2011, 09:06 PM
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Quote:
Originally Posted by O2surplus View Post
Here's an other overlooked source for heat sinks- Car Audio shops Broken car amplifiers can be used for their heat sink and often times purchased very cheaply or had for free.I used 3 of them in my very first build. 30 Cree XR-Es consuming 5 amps total, and barely warm to the touch. Here's a photo of one-

What are the dimensions of these? If I ever make another LED light this would be something I will consider.

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post #13 of 112 (permalink) Old 07-28-2011, 09:36 PM Thread Starter
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Hoppy, they all vary in size but I think common sizes (depending on what you ripped them from ) will be 4X8, 8X10, etc..

You can get them off of used audio amps and also off of used AC/DC automotive converters.


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post #14 of 112 (permalink) Old 08-02-2011, 12:07 AM
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Why is thickness even in the equation?

I keep hearing "thickness" thrown around...but I have no idea why...

I suppose thickness would be important if you were trying to optimize thermal conductivity between source and a large surface area...but not that big of a deal considering the junction between the diode and the heatsink will be your largest bottleneck. The main concern should be the surface area of the heatsink(to a point).

Here is my point. Would it be better to buy 1" L stock(1" x 1") at 1/8" or 1" flat at 1/4"? I would double my surface area with the L and use the same amount of material(roughly the same cost).

Finally, unless you have some reason for "super-cooling" your LED rig I dont know why people get so worried about getting it "cool to the touch". These LEDs will run easily up to 90 degrees C.(you could estimate a thermal drop of about 30 degrees between LED and sink). All 90 degree C does to life is cut it by about 50%. That means that with a worst case temp drop from junction to heatsink of 30C(which is pretty lousy) and getting your heatsink up to 140F...you would have to change your lights out in 6 years when the cost of the original LEDs will probably be close to $1 a piece. So...if you have 24 XP-Gs and you buy a $60 heatsink instead of 2x$5 pieces of stock aluminum all you are doing is spending more money and losing out on the possibility of upgrading in 6 years.
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post #15 of 112 (permalink) Old 08-03-2011, 04:33 PM Thread Starter
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I keep hearing "thickness" thrown around...but I have no idea why...
I assume you are referring to as "throwing around" thickness. The reason I suggest thicker heatsinks is because I see so many people wanting to use cheap/easy to find 1/16th thick aluminum, which is (IMO) quite inadequate. They might get away using 1/16th stuff if they only run the LEDs at 350mA or less, but not all of us do that.


Safer is better than sorry.



Two materials of the same square footage, but of different thicknesses, will have different abilities of heat sinking. But you know that already. LED's will create a hot spot directly behind the star, in the spot you mentioned which is the real weak link (the spot between the LED star and the heatsink). That hot spot is greatly cooled by more mass in the immediate area of the LED. Thickness is a very effective, simple way to do this.



Quote:
The main concern should be the surface area of the heatsink(to a point).
It is, and nobody is arguing against that, but the use of even thermal two-sided tape seems to be perfectly sufficient. This might be the most important part, but it's actually one of the easiest to accomplish to a sufficient degree.

Quote:
Here is my point. Would it be better to buy 1" L stock(1" x 1") at 1/8" or 1" flat at 1/4"? I would double my surface area with the L and use the same amount of material(roughly the same cost).
The extra surface area would definitely give you more passive cooling, but is there enough mass right near the LED to wick away the heat? At 1/8" thick, maybe up to around 500mA, I don't know for sure.

I'll test it soon, I have some 1/8" thick flat stock I'll use over a shrimp tank, as soon as my drivers make the ever-so-slow transit in from DX.

Quote:
Finally, unless you have some reason for "super-cooling" your LED rig I dont know why people get so worried about getting it "cool to the touch". These LEDs will run easily up to 90 degrees C.(you could estimate a thermal drop of about 30 degrees between LED and sink). All 90 degree C does to life is cut it by about 50%. That means that with a worst case temp drop from junction to heatsink of 30C(which is pretty lousy) and getting your heatsink up to 140F...you would have to change your lights out in 6 years when the cost of the original LEDs will probably be close to $1 a piece. So...if you have 24 XP-Gs and you buy a $60 heatsink instead of 2x$5 pieces of stock aluminum all you are doing is spending more money and losing out on the possibility of upgrading in 6 years.

Reasonably good point, especially if using import low-cost LEDs. But buying more expensive heatsinks isn't costing you the opportunity to upgrade in 6 years by using a larger heatsink. You're actually postponing the need to upgrade in 6 years. You may get 10-15 years.

Using a smaller, less effective heatsink is potentially forcing you to upgrade quicker, or forcing you to swap out a blown LED when one fails, which can happen.

We don't know just how much the LED scene will improve over the next few years. It may be leaps and bounds, maybe not. I think spending the extra cash on a larger heatsink is well worth it, but then again, that's the whole point of this thread---- how to save money and still have "definitely sufficient" heatsink. Not "somewhat sufficient".


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