Is it worth adding miscellaneous heatsinks to lights that 'don't need a heatsink'

I might be getting my explanation a bit mixed up as its based on practice, i suggest anyone try to see what happens if you put this in practice.

Let me put it too you this way: 2 heat sinks with same surface area. One has twice the weight due to base being 5mm thick instead of 1mm, this one just having a bit extra fins. Which one do you prefer running higher power?

Thermal dynamics are much trickier than just surface area. Also note how thermal resistance is not really a constant, its a curve in relation how much energy you push thru the sink.

The mass of the sink relates to how much power you need to heat it up. The difference in temperature between sink and air, together with surface area determines how fast the sink sheds that energy to the air. The maths get complicated fast. But mass is defo part of it.

If youre running naked boards, what heats up more? A 1mm board or a 3mm board, difference in surface area is negligible? Isnt it fair to say 1mm hotter?

Rocket Soul said:

If youre running naked boards, what heats up more? A 1mm board or a 3mm board, difference in surface area is negligible? Isnt it fair to say 1mm hotter?

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Now you are comparing different materials. That's not a fair comparison.

If you compare a 1mm strip to a 3mm strip as heatsink, they will run pretty much the same temperature since the surface area is almost the same. For dissipation of heat only the surface area is relevant. Adding 2mm of thickness will increase surface area only a tiny bit.

Only for distribution of heat through the system the thickness is relevant. It takes only a few minutes for the 3mm board to heat up, but that's not significant enough to matter.

Putting another 1mm strip at 90degrees on top of the original strip 9ie create a T-profile) would double the dissipation. Adding 1mm of thickness to the strip does pretty much nothing for dissipation.

wietefras said:

Now you are comparing different materials. That's not a fair comparison.

If you compare a 1mm strip to a 3mm strip as heatsink, they will run pretty much the same temperature since the surface area is almost the same. For dissipation of heat only the surface area is relevant. Adding 2mm of thickness will increase surface area only a tiny bit.

Only for distribution of heat through the system the thickness is relevant. It takes only a few minutes for the 3mm board to heat up, but that's not significant enough to matter.

Putting another 1mm strip at 90degrees on top of the original strip 9ie create a T-profile) would double the dissipation. Adding 1mm of thickness to the strip does pretty much nothing for dissipation.

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Im not sure if im getting my point across, all i saying is that mass plays a role in how much a sink will heat up. That there is a difference between 1mm and 4mm backing (as in different heatsink temps at same wattage) and it doesnt depend on those extra 3mm of surface area, it depends on the mass. It might not seem that way from a theoretical standpoint, i urge you to try in practice and will happily eat my hat if it turns out that im wrong.

Mass can be just as important as area. The more energy you are trying to firstly-sink. And then secondly- dissipate, have to be factored in. Supra had another long thread covering heatsinks, from back when everyone was getting into cobs.

Things get more critical the harder the diodes are driven and the greater the density of diodes, leading to greater consideration for thermal mass.. Heatsinking a QB96 is entirely another matter, compared to running QB120 or strips at nominal.

I saw a simulation of an example somewhere that showed a heatsink with a multitude of thin sinks actually trapped heat and stymied the transfer of heat to the ambient.

Companies such as Osram and the like, put out application notes spelling out basics for calculating heatsinking. I find the maths quite involved and exhausting.

With the prices of slightly lower performing diodes dropping, it begins to make more and more sense to run loads of them at/or below nominal. Park them right above the canopy and still expend similar amounts of energy, as some overengineered compact lamp that has to be hung 18-24 inches above. In which case, those spread out diodes running at/or below nominal current have less critical heatsinking requirements. Then the worry becomes how to make the fixture rigid.

@Rocket Soul
"all i saying is that mass plays a role in how much a sink will heat up"
sorry, but its really more a matter how long it takes to heat up with more mass and same surface area, how much will be the same.

@end_of_the_tunnel
"The more energy you are trying to firstly-sink. " thats the point, its not a whole lot on midpower leds, COBs are adiff. story, true.
we all refer to mid power strips here i guess.

"a heatsink with a multitude of thin sinks actually trapped heat" that was for sure a heatsink ment to be actively cooled and not missused as passive hatsink.

agree complete on simply buying more diodes and drive them low, its quite simple to reach a point where thermals dont really matter anymore.

cobshopgrow said:

@Rocket Soul
"all i saying is that mass plays a role in how much a sink will heat up"
sorry, but its really more a matter how long it takes to heat up with more mass and same surface area, how much will be the same.

@end_of_the_tunnel
"The more energy you are trying to firstly-sink. " thats the point, its not a whole lot on midpower leds, COBs are adiff. story, true.
we all refer to mid power strips here i guess.

"a heatsink with a multitude of thin sinks actually trapped heat" that was for sure a heatsink ment to be actively cooled and not missused as passive hatsink.

agree complete on simply buying more diodes and drive them low, its quite simple to reach a point where thermals dont really matter anymore.

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It runs sort counterintuitive to what ive seen but youve been right with me before so i may have to read up a bit a sharpen up before i get back into this.

dont get me wrong, knowing your builds a bit i know where youre come from and can understand your thinking well.

cobshopgrow said:

dont get me wrong, knowing your builds a bit i know where youre come from and can understand your thinking well.

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What gets me here is that why would a 550 use a 4mm plate and not 3 or 2 if its all the same? And also seems like (but id have to do numbers) 4 single sinks would be much better than a 550 plate due to higher surface area?

Im allways a bit suspect of simple rules and truths on thermodynamics, its one of the hardest areas in physics when you start scratching thru the surface.

i think 2mm as a base for a 550 quad lboard light is mechanically not strong enough, 3mm may do it, 4 is a safe bet.
just guessing of course.

a cpu cooler have a massive base too, for mechancial reasons and of course there the thermal "buffer" works better as often the CPU are just working hard for a few min.
the thick baseplate take the heat for a time when the cpu is working cooler afterwards the heat can be given to the air by the fins form the baseplate.

I always put a couple of 12v pc case fans on the top of my QB heatsinks.
Lowers the temperature a lot.

SomeOldHippieDude said:

You should be able to clearly cite your point in literature.

Or you could also clearly show the test and results you are telling others "trust you" and do themselves. Just present the data.

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Fair enough, thats what im looking into right now. And ill happily admit if im wrong.

Rocket Soul said:

Im not sure if im getting my point across, all i saying is that mass plays a role in how much a sink will heat up.

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The only thing I can imagine that thickness has an effect is for heat distribution through the heat sink.

For instance a very hot COB will benefit from a thicker base of the heat sink to make sure the heat can actually be transported away from the COB. It needs to spread out over the heat sink to be able to dissipate the heat over it's surface. If the heat can't go anywhere then it won't dissipate either.

With led strips you don't really have this issue. If you make the heat sink extremely thin then the heat wouldn't even be able to get away from even the small leds on a led strip, but then the frame would be to weak to carry the strips too.

Either way, it's not so much the mass absorbing heat as a whole that will cool things. Unless you use so much mass that it would take 12 hours to warm it all up. If you would use 1000kg of aluminium you'd probably be busy for quite a while to heat it all up.
.

Rocket Soul said:

Thermal dynamics are much trickier than just surface area.

If youre running naked boards, what heats up more? A 1mm board or a 3mm board, difference in surface area is negligible? Isnt it fair to say 1mm hotter?

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I have to agree that thermal dynamics is far more complicated than just surface area! It's why they use computer modeling.

With less thermal resistance, wouldn't the thin board transfer more heat from diode to board surface, resulting in cooler diodes and hotter board surface?

1212ham said:

With less thermal resistance, wouldn't the thin board transfer more heat from diode to board surface, resulting in cooler diodes and hotter board surface?

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That would be the case if the thin board is really that thin that it doesn't conduct heat properly. Which can't really be the case for boards that are already conductive enough to work without a heat sink (ie the topic subject). Let alone after adding a layer of aluminium on top of that as an extra heat sink.

Some keywords for anyone who wishes to delve futher into this. Thermal diffusivity. Thermal conductivity.

Returning to the OP's first post.

drcucumber said:

I have one of the basic LEDs that are supposed to be fine with no heatsink, but I would just prefer if it were cooler. Is it worth adding for example various heatsinks from computer parts to the top of it.

Obviously the heatsinks designed for such boards is an option but then you are defeating the object of getting a cheaper ' no heatsink required' board

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Is there an optional heatsink recommended for your board? What drive currents are you intending to run your board at? Is this a china or USA product?
Have you done a finger test on the surface of the board whilst it is running?

wietefras said:

That would be the case if the thin board is really that thin that it doesn't conduct heat properly. Which can't really be the case for boards that are already conductive enough to work without a heat sink (ie the topic subject).

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Care to explain why?

1212ham said:

Care to explain why?

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Explain what? That a heat conductive material transfers heat?

Ill see if can get back to this after doing actual tests, thermodynamics (what heats more 600w of leds or hps?? The devil subject of flame wars ) is complicated, probably more so than just getting this tested. It might be some time though and im not sure if my alu people will make a custom bit of 2mm thick plate, i think they only do 3mm and up. References in wiki gives right to cobshopgrows on this though and im used to be schooled by him so i wouldnt be surprised if i was wrong.

In any case, for op, a small fan is much better but better not depend on it, all thingss break

1212ham said:

I have to agree that thermal dynamics is far more complicated than just surface area! It's why they use computer modeling.

With less thermal resistance, wouldn't the thin board transfer more heat from diode to board surface, resulting in cooler diodes and hotter board surface?

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i just know that for FR4 material its desired to have a thin board for better heat transfer.
mainly due to the reason FR4 isnt that good in conducting heat, the thinner the less resistance.
heat transfer there mainly relys on thermal vias and the copper areas, top bottom, inside.
shorter thermal vias used on thinner boards are better conductors (by quite some percent).

for the heat cpacity and surface area discussion.
i ran a diy water cooled pc more then a decade back, i ve tested a lot of stuff there.
the more water you have in the system the longer it takes to heat up but you cant get away without adding surface, area if you want lower temps.
pratically i added some copper tubes outside of the PC, the water volume increased therefore and it took much longer till i reached the wroking temparature.
while the tubes surface wasnt much compared to a propper radiator and it wasnt able to lower the temp drastically, but the added water volume in the tubes delayed the rise of the temp.
its good for running a overclocked benchmark for example, for a few minutes, it wont help much if you let your pc cruch prime number for weeks.
some crazy guys at that time simply used big water reservoirs, lots thermal mass, but they let that cool down from time time, knowing their heat exchange is limited...... or simply burried their big water reservoir in the garden which gave enough cooling.