Finding an appropriate heatsink for 5V 3W LED?

Hello, I have bought some 3W 5V leds, and now I have to dissipate the heat they produce. I am thinking of using an xbox 360 GPU heatsink i have laying around (

), cut in apprpriate size. Then I would glue the led with thermal epoxy to it. 

Can somebody suggest an adequate size for the heatsink? I can't find any info around. I have other heatsinks as well, I would rather not buying a LED heatsink if that's not mandatory.

Thanks in advance :)

Picture of the leds attached, they have no board to screw them with.

Picture of Finding an appropriate heatsink for 5V 3W LED?
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I'd not glue them on, I'd use screws and heatsink compound. The cooler you keep the LEDs the longer they'll live.

en_rov (author)  steveastrouk3 years ago

Do you think thermal compound is not enough to ensure a good heat transfer? I can' use screws, the leds are without board.$_12.JPG

I've had good success with these things mounting them on 30x 30mm PCB squares, with a little thermal compound under them

en_rov (author)  steveastrouk3 years ago

What kind of PCB did you use? The star-like most high-end Cree leds use?

The crees are using aluminium substrate material, which isn't easy to get as an amateur. I just used plain FR4 for these little LEDs. If you're making real boards, then you can put a load of vias through around the LED into the layer on the back, and get improved cooling performance.

en_rov (author)  steveastrouk3 years ago

All right, ordinary boards seem just the right way to go. So I can just use a spare circuit board with some thermal paste under the LED, right? Thank you for all the help!

en_rov (author)  steveastrouk3 years ago

Do you think that just the PCB is enough to keep it cool? I don't think so but I assume I would able to screw the pcb on the heatsink then.