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Topic: Suitable heatsink for high-power LEDs (Read 2 times) previous topic - next topic

zenwebb

I'm looking to produce a small run (5-10) of high-power RGB LED lamps, and am curious about what kind heatsinks I can get away with. These LEDs are 3W RGB LEDs (1W per channel), as seen here: http://cgi.ebay.com/3W-High-Power-RGB-Led-6-Pins-10-pcs-/380342493606?pt=LH_DefaultDomain_0&hash=item588e2de1a6#ht_1893wt_1086

These lamps could potentially be run for many hours at a time, so the LEDs need to be properly cooled. Can I simple flat pieces of aluminum, or should I spring for some professional heatsinks? If aluminum, approximately what thickness and size should I make?

Here is a heatsink I've found on eBay, but its international, so it'd take a while to ship and is a bit of a gamble: http://cgi.ebay.com/5-x-3W-Aluminium-Heatsink-High-Power-LED-Bulb-/170613491066?pt=LH_DefaultDomain_0&hash=item27b95b457a#ht_632wt_698

If I can make my own that'd be great, just curious about other people's experiences.
Grad student, creative technologist, OSHW engineer
http://jason-webb.info

Grumpy_Mike

You can make your own heatsink quite easily. The thickness does not matter what is important is the surface area. So lots of thin sheets clamped together at angles would be best.

jluciani

You can also buy a length of extruded heatsink and cut it yourself
or have it cut. I bought a length of heatsink on ebay and the fellow
that sold it cut 6 2" strips from the length at no charge. IIRC
the strips and remaining 12 or so inches was around $30 or so.

I drilled and tapped holes for the LEDs. A picture of the prototype
is at http://wiblocks.luciani.org/not-quite-ready/ZB1-ISINK-index.html
Unfortunately the heatsink is hard to see :(

(* jcl *)
www: http://www.wiblocks.com
twitter: http://twitter.com/wiblocks

zenwebb

I know I can pick up scrap pieces of aluminum sheet pretty cheap at my local hardware store (~$10 USD),so that'd be a great option. The sheets I am thinking of, IIRC are about 1/16" thick.

Would a 3x3" piece be too small / large? Should I make two layers, and attach them with something like silicone adhesive?

The heatsink is likely to be installed in a ~7x7" MDF box - would it be better to have an air gap between the bottom of the heatsink and the floor of the box, or rest it right on it?
Grad student, creative technologist, OSHW engineer
http://jason-webb.info

Grumpy_Mike

Quote
Would a 3x3" piece be too small / large?

It depends on the amount of heat you want to dissipate. Heat sinks are defined by their thermal resistance, in degrees per watt. This means that for a heatsink with a thermal resistance of say 10oC/W for every watt you dissipate you get a 10oC rise in temperature.
See this link:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html

Also they are defined in 'free air' the effectiveness goes up with forced air and down if it is restricted. You want as much natural air circulation as you can get.

In order to see what thermal resistance you need and hence what size it has to be then you need to know what power you will dissipate and how hot you want to let it go.

Quote
Should I make two layers

No there is no point, as I said it is down to area not thickness.

Quote
and attach them with something like silicone adhesive

If you make a multi piece heat sink to get more area then bolt the pieces together and use heat sink compound between the pieces. Aslo use this compound between the piece and the component.

zenwebb

Interesting. I've dug up some more info that could help narrow down the heatsink options:

Maximum power to dissipate: 3W
Maximum temperature: 80 degrees C

Seems to me that the heatsink may not need to be too substantial - 80 C is quite warm!

Does a single piece of 3x3x~1/16" aluminum sound like a good idea now, or should I go bigger?

Again, to increase natural air flow, perhaps I should mount a couple of stand-offs to this thing, to allow for air to travel below the heatsink as well...but if that doesn't help, it saves me the labor.
Grad student, creative technologist, OSHW engineer
http://jason-webb.info

johnwasser

Episode 105 of the EEVBlog podcast shows the calculations needed to properly size a heatsink.  It's just over 30 minutes of video.

http://www.eevblog.com/2010/08/15/eevblog-105-electronics-thermal-heatsink-design-tutorial/
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