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ArcticMyst Security by Avery

Warm to the touch

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May 3, 2014
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I am fairly new here and certainly haven't read every post on the forum (so might have missed some discussion of this), but I have seen several threads, particularly reviews, that seem like they might be missing a basic concept. I have seen many people gushing about "really great thermal capabilities" of a particular heat sink, host, or the combination thereof using statements like "It barely get's warm to the touch after being on almost a full minute" I just wanted to point out that if the host doesn't get warm to the touch it could be due to very poor thermal behavior. If you had a 100 deg.C diode surrounded by wood/plastic/fiberglass, you might easily say that it doesn't get warm to the touch. It seems that the best performance would come from a build that does get warm, as this means it is effectively absorbing heat from the diode, and will also be able to give that heat up to the air/your hand so it can be turned on again without too much wait. Admittedly, if it's a very large heatsink with the purpose of allowing a long transient "on" time before it must first be turned off, then it would also be cool to the touch for some time after a "cold start".

Does anyone have a sink/host they would describe as a great thermal performer, that they would also describe as getting warm quickly?
 





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You are entirely right. I have a solid silver host, known to have great thermal capabilities, and it clearly gets "warm to the touch" after a short 20 seconds or so.

However, sometimes, if the heatsink is properly designed and made out of a clearly effective thermal conductor (like copper or aluminum), the heatsink will have a large enough surface area to radiate the heat it takes on quickly. This means that the equilibrium temperature is significantly lower than that of a cylindrical heatsink, and therefore it takes a longer time to reach the same temperature as a cylindrical heatsink would. Sometimes, this is what some people refer to. Other times, however, people just don't realize that diodes don't actually put out a lot of energy, so they think their heatsink is performing well when actually the diode just isn't outputting a lot of heat in the first place.
 
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you are correct. I have a solid sterling silver hose that houses an aixiz module, and I use silver foil to make a tight fit. it gets pretty warm in about 30 seconds.

btw, where did you get that 100 degree C from. that is actually the optimal temp for the Oclaro 445s. =)
 
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Still, some of the heat sinks people use are made of copper, which has a pretty high thermal mass despite its great conduction. Those heatsinks really aren't meant to be used to quickly move heat to the air, but rather just sink the heat directly, which is probably fine given peoples' usage patterns. Ideally, for infinite duty cycles, the host/module would have enough surface area to dissipate the heat into the air, for no net gain in temperature after a while.
 

Benm

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You are correct. I've attempted to do a bit of a writeup on the subject in the past: Merghart.com - Heatsinking laser reference

And yes, a powerful laser (something like 1 watt) should probably get warm to the touch unless it is fitted in an enormous heatsink/host.
 

upaa27

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You are so right. I know this wasn't ment to be funny but couldn't help but chuckling(memories).

Have a good one XD
 
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By "thermal capabilities" do you mean thermal conductivity or specific heat capacity? or both?
 
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I suppose the thermal capabilities of some module/HS/host combination would be best quantified by the ability to keep the diode below some target limiting temperature for a specified time given some ambient condition. This effect is a function of the conductivity,heat capacity, emissivity, and geometry. I seem to remember a thread devoted to touting/arguing the benefits of heat capacity over conductivity, which included some discussion of "aluminum dissipates better even though copper conducts better" nonsense, but I don't think the thread ever came to a productive/practical conclusion. All of the thermal material properties of a heatsink, combined with the size and geometry affect the performance, and one particular attribute cannot necessarily be prioritized above the others. A decent thermal model (even a simple 1-D model) could go pretty far in allowing fast comparisons of two materials for a given geometry (I found it somewhat amusing in reading the above mentioned thread that nobody actually used a mathematical thermal model and plugged in some numbers to "back up" their position on the subject). In this thread I simply wanted to point out my observation that some people may be drawing the opposite conclusion about the thermal performance of a build when using the "to the touch" measuring technique. I think the measurement itself, while not objective and repeatable, may still be valid to some extent. The interpretation of the results is, however, often flawed in my opinion. If "thermal performance" is not in fact related to keeping the diode cool, but keeping the hand of the laser wielder cool, then my opinion would change.
 
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good observation, I had thought the same thing but never voiced it. it's aways good to not assume things, or make baseless claims.

yes the point is to draw the heat away quickly, so you could argue the faster the host feels warm, the better the heat sinking is working. (or smaller your heatsink is)

I want a silver host, lately it's dropped below $18.75 per oz, so maybe I will.
 
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Zar

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this is very true OP, which is why I love iPhone design, it gets hot when I do intense internet activity over LTE, but then cools down within a minute once I stop, and my old Galaxy S3 would take long time to heat up but then stay hot for very long time
 




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