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Old 07-05-2012, 05:43 AM   #9
theblondskeleton
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Default Heatsinks

9. Heatsinks

What is a heatsink?
Common usage sets the standard, but a “heat sink” when referring to LEDs is actually a heat conductor that absorbs the heat from the functioning emitter, and transmits it to the air over a large surface area (hence the fins) relatively quickly. However, the term “heat sink” has become the popular nomenclature, and thus, we are stuck with it.
What can I use as a heat sink?
The heat sink is the foundation upon which you will build your LED fixture. It is more than just a mode of conducting heat away from the LED to prolong its life and preserve your investment; it is the structure that carries your emitters, wiring, active cooling system, and any aesthetic or practical touches like housing or splashguards. It is also a place where you have one of the widest margins of cost difference. Aluminum does a fabulous and inexpensive job of this.
How much does a good heat sink cost?
For a 4-foot tank, you can go cheap and marginally functional at around $20 (1/8” flat aluminum bar stock no fins). This material can be found at any big-box home improvement store, or hardware store. It has been posited that running high current emitters at a lower current reduces the amount of heat that needs to be conducted, and a simple aluminum bar can do the job sufficiently. It has also been posited that fins or active cooling are necessary to keep operating temps within optimal specs for longest emitter life. An engineer would need to chime in here to help settle this one - let the games begin!

Conversely, you can go “pro” with a fancy designer heat sink to the tune of a couple hundred dollars – no joke. These are available through MakersLED and they are pretty amazing but carry an equally amazing price for the larger pieces. They come equipped with cooling fans for every 12" of length and are available in multiple lengths.

The mid-grade choice is a wide selection of finned heat sinks in many sizes and shapes that are reasonably priced for what they provide: a great foundation for a good-looking fixture that functions very well. Heat sinks are available anodized or bare aluminum, pre-drilled and tapped or raw. They are available through some of the all-in-one vendors like RapidLED, LEDgroupbuy, and Aquastyleonline or individually through sites like Heatsinkusa.com.
How do I attach the emitters to the heat sink?
There area few different ways to attach emitters to the aluminum heat sink of your choosing. Some are considered to be better than others, but all are effective to some degree or another.

Drill-and-Tap/Thermal Grease

For this technique, you would plot your layout pattern on your heat sink, and then drill holes in the heat sink, which would be tapped to receive screws or bolts. For this to work without risking creating a short from your wires to the heat sink itself via the screws, you need to use insulating washers. To improve heat conduction between the emitter and the heat sink, it is highly recommended to apply a non-adhesive Thermal Grease to the back of the emitters to fill the microscopic gaps between the emitter and the heat sink.

This is by far the most labor-intensive method of emitter application as drilling and tapping the holes could be an hours-long process, and requires a certain amount of skill/technique to do correctly. One could also hire a machine shop to perform this task as well. Risks include but are not limited to: misaligned holes, broken taps, stripped threads from overtightened fasteners, and shorting of electrical connections to the heatsink. Benefits are the ability to swap out emitters in the event of a burnout, excellent heat conduction, no permanent goop, the ability to swap colors if you are displeased with the rendering, and the pleasure of hard labor.

Thermal Adhesives

This is one of the more convenient methods of application. Thermal adhesive typically comes in a 2-part epoxy that is applied in a small amount to the back of the emitter "stars", and it is then permanently affixed to the heat sink. Thermal Epoxy is formulated to provide a good amount of heat transfer between the emitter and the heat sink. The benefits include relatively fast application, good heat transfer, and permanent attachment when the epoxy sets. The risks include but are not limited to messy application and permanent attachment.

*Hoppy reports that with aluminum oxide based adhesive, he was able to pop off the stars using the blade of a knife and a little prying.

Thermal Self-adhesive Pads

This is essentially double-sided tape that is designed to conduct heat away from the emitter and into the heat sink. These are available pre-cut and ready to apply through several vendors, and are by far the simplest way to attach the emitters to the heat sink. Just peel the covers off, and stick it down. The reality is that as with any other application method, it takes a steady and sure hand to apply these consistently. It has been said that the heat conduction they provide is poor by comparison to other methods. The risks include semi-permanent application, poor heat conductivity, and higher price. The benefits include relatively fast and simple application, no mess.

Pre-drilled/Flexible Application Heatsinks

This is a relatively new class of heat sink that includes the MakersLED "designer" heat sink available through LEDGroupbuy.com and some other options available through other vendors. This particular model includes several "t" slot channels that receive bolts and nuts which when paired with the included insulating washers make applying the emitters relatively easy, flexible and semi-permanent. This virtually eliminates the drawbacks to the drill-and-tap method while maintaining the benefits. They are designed to receive most, if not all, brands of emitters. The benefits are the same as the drill and tap method, and the risks include a higher price.


Last edited by theblondskeleton; 09-14-2012 at 04:38 AM..
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