How to adhere 3 emitters to a heatsink??

Wurkkos

xbrite

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Can anybody recommend a reliable way of adhering 3 series connetced emitters to a heatsink??

I am going to use a boost converter and wiring the 3 emitters in series but I know the slug of the emitters is to be insulated. For a single emitter, I used Arctic silver adhesive but I don't think I can use this adhesive for 3 emitters in series.. I know it will be okay with 3 stars..

Thanks..
 

markus_i

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Ulm, Germany
Isolate them /ubbthreads/images/graemlins/grin.gif

Seriously:
- for a start, it isn't ok for (now) most Stars - neither the 5 nor the 3 W Stars are isolated against the emitter
- everything else depends on your heat sink:
for an aluminium HS with an anodized finish, just use AS and make sure the emitters don't touch. The anodization is a good isolation, at least in this voltage range. Just make sure that the holes you drilled under the LEDs don't have _any_ edges/filings protruding from the drilling /ubbthreads/images/graemlins/blush.gif
For a blank Al/Cu HS, you'll have to use an electrically isolating thermal adhesive. Their thermal properties are usually worse than AS, so you might have to compensate for that.

HTH
Markus
 

andrewwynn

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arctic alumina or arctic silver adhesive should either do the trick... how they make something 80% silver non conductive, i'm not sure... read the specs... it works perfectly
 

xbrite

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Dear Darell,

What do you mean by two thin layers of AS?? Do you mean that you apply a thin layer of Arctic Silver, et it dry and then reapply AS?? I thought AS is conductive while AA is non conductive since AS uses oxidized aluminum..

Thanks..
 

markus_i

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I'm not darrel, but generally:

AA is supposed to be completely non-conductive - unless you do have some point where the metal parts actually touch (instead of being seperated by AA or, worst case, an air bubble)
AS should be non-conductive unless by chance (or applying too much pressure) you get a conducting path, since every particle should be surrounded by a film of epoxy. A lot of 'should', so sometimes things go wrong. Using two layers seems like a good idea to me.
The stuff I use (electrolube thermal epoxy) contains tiny spheres (microballoons?), which ensure a defined spacing between the two parts - and uses a non-electrically conductive epoxy/filling.

Bye
Markus
 

andrewwynn

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I bought and used arctic silver... the price wasn't big enough of a difference to give me a reason to skimp... worked perfectly.. for mounding.. i put the LEDs flat on the heat sink and put a piece of cardboard across the three emitters and about 4oz weight on them.
 
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