I bought a stick of alum fast stick epoxy putty and was curious as to how much heat sinking and heat transferring ability it possesses. As a quick test I kneaded a decent gob of it until uniform, pressed it onto a chunk of aluminum rod and in turn pressed a 16mm noctigon on to the top of the gob. The emitter is an XM-L2 U2 in a disposable CW tint. I balanced an S2 reflector so I could check for tint shift without burning my retinas.
Bottom line is that I could run the emitter from where the cell gave up 3 amps to when it sagged to under 2.7 amps (~1/2 hour) with no ill effects. There was some initial increase in current draw by a tenth of an amp or so as forward voltage dropped with the heat increase but it quickly stabilized. The epoxy and the aluminum rod were both too hot to touch by the end of the run. I am not set up to test light output so thermal sag wasn’t measured.
A test of a 4.5 amp draw with a Sony VCT5 quickly resulted in a melted plastic centering gasket and a de-soldered positive lead. The epoxy and aluminum rod were room temperature during this test. The emitter survived but the system obviously isn’t stable at that heat level.
Great information, thanks KYfishguy. Looks to be good in some applications and obviously this thick blob is a worse case scenario!
I have been keeping an eye out for this stuff locally, not seen it anywhere I have been normally. Would you have a link or a common store that you found it in?
Is it just me, or do some things sound cooler in Spanish? “El Adhesivo Rapido” just rolls off the tongue…. Way easier than “The Fast Adhesive”….
Stands to reason, that much epoxy with a lower thermal conductivity will transfer well enough at reasonable output to simply saturate but at higher output cannot keep up with the extra heat input and the star temp rises until the solder melts. The shorter the distance between the star and the aluminum the closer you will get to the performance demonstrated in Djozz’ tests. Might be a different way to desolder emitters if the current is cut just prior to removal(avoids short under led) but reflow can’t be done since current won’t flow until the connection through the led is established. I think maybe this is why cree establishes such low max perameters for their LEDs so that they can ensure adequate performance under less than ideal conditions.
