diy led problem / help

jason83(Zone 8b/9a (North Florida))December 1, 2012

Hello everyone! I'm making an LED light for a 2x4 area of mounted orchids, consisting of 3w LED's: 4 cool white, 4 neutral white, 10 warm white, 4 deep red (660nm), 1 royal blue and 1 actinic 420nm. They are on a 10x14" heat sink.

I'm having a huge problem. I used the Arctic Silver thermal paste and it's been almost two weeks, and the LED's are still not adhering to my heat sink. Was I wrong to assume this stuff would act as adhesive? I've attached a picture of the whole setup, and I'm eager to get soldering.. my questions are,

Can I just lift the LED's up a little and dab some super glue in there or something? Do I need to wait longer for this stuff to dry? Perhaps if I used a fan to blow on it or something?

Please help! :)

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grizzman

Generally, thermal paste is not an adhesive. with some heat, it oftens gets hard like that, but that is not how it is designed.
Regarding lifting and glueing; the super glue will likely create seperation between the sink and light. Why not just leave them in place and glue around the edges? of course, I'm not sure superglue will adhere them either.

    Bookmark   December 1, 2012 at 8:55AM
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jason83(Zone 8b/9a (North Florida))

How about an epoxy? What's the general idea as far as affixing them to heat sinks? Screws? I'd prefer not to do the drill & tap...

    Bookmark   December 1, 2012 at 11:57AM
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on-call

thermal paste will transfer heat from the LED away to the heatsink but is not a adhesive. the cheaper brands will dry and harden with glue like properties after exposed to CPU heat however a good brand like Artic Silver will stay paste like and not harden.
I attached a crude MS paint diagram of a paperclip straightened with loops on each end for self tapping sheet metal screws 2 over each LED would work to hold lights in place.

This post was edited by on-call on Sun, Dec 2, 12 at 9:58

    Bookmark   December 2, 2012 at 9:55AM
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on-call

better yet you can buy these from any hardware store, strip off the insulation, cut to size and loop the other end with needle nose pliers

    Bookmark   December 2, 2012 at 10:04AM
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HayBerry

How about another layer of heat sink material (with holes) on the emitting side of the LEDs? The LED edges will be sandwiched between the two heat sink layers, which can be screwed or epoxied together.

    Bookmark   December 3, 2012 at 6:17AM
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jason83(Zone 8b/9a (North Florida))

Thank you very much on-call and HayBerry for your help. I'm a bit lost on some of the ideas lol... but I will re-read then later today and hopefully get something out of it and have a fab LED light :)

    Bookmark   December 3, 2012 at 7:03AM
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grizzman

I would probably either:
use a self tapping screw
find a conductive adhesive
or just use an plain epoxy.
the bulbs do get hot, but not so hot that you really need conductive paste between them and the heat sink.

    Bookmark   December 3, 2012 at 6:51PM
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grizzman

a thought just occurred to me; are you planning to run all your connecting wires on the same side as the lights or are you going to drill holes to run them on the backside? If you're planning to drill holes, the stiffness of the wires is probably adequate to hold the bulbs in place if using thermal paste.

    Bookmark   December 4, 2012 at 8:08AM
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jason83(Zone 8b/9a (North Florida))

Thank you grizzman! I've had to put this LED project on the back burner for the last few days so will take a crack at it this weekend. I think I'm going to try to keep it simple and go for the epoxy...I'd hate to have to drill holes because where the LED's are situated on the heat sink, the fins on the back of it don't line up properly with any holes I could drill on them.

    Bookmark   December 6, 2012 at 4:39PM
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