So with an upcoming mod, I intend on running an mtg-2 pretty hard in my 4D table and need a beefy heatsink.
I planned on using a decently thick aluminum round at about 6” in diameter. Possibly 1/4in the 3/8in thick which leads me to my question, would a thinner heatsink allow the heat to migrate farther from the emitter star, or would the added mass help soak up the heat more effectively?
I would like to have alot of mass to have a longer runtime before the thing overheats, fins arent practical in my case as it would leave shadow in the frosted shade. It would also be enclosed in a plastic shade with stale air so I am assuming more mass MORE BETTER?!
I am not familiar with thermal characteristics.Hopefully some awesome person here is
Copper conducts heat away from the LED better then aluminum
Anodizing has far, far more emissivity compared to metals
You want the heat to get to the anodization as quickly as possible because the bigger the temperature difference, the faster the heat can be removed to the environment
more metal usually gives more surface area, allowing more conduction and radiative emission of heat
So, how exactly would a heatsink be better or worse with the same material? I understand that more fins multiplies surface area for heat being radiated, but how would material mass effect that being just planar?
I was assuming:
1.LED creates heat.
2.LED thermal pad transfers heat to sink (via star or direct solder:not in my case)
3.Heatsink temperature under thermal pad rises after ambient temperature is overcome
4.Surrounding material of ambient temperature disperses that created heat at a given rate(material dependent)
5.Temperature rises around the heatsink until LED heat is dispersed through surface area.
6. Temperature rises until a plateau of heat is had or thermal runaway kills components, thus killing the heatsource
What am I missing? Would the mass be counterproductive only allowing a certain amount of radiation but still allowing thermal runaway?
I’m not sure i am understanding how your thinking, radiation depends upon the emissivity (radiative ability) of the surface, be it metal or anodizing (for flashlight purposes), metals have poor emissivity, anodization has excellent emissivity
heat is lost through conduction, convection and radiation, so for example paper has excellent emissivity, but would act as an insulator opposing conductive heat transfer
i remember reading somewhere that anodization has an emissivity of about 0.9
i did a post in a thread about this chain of events recently (led on to lumen stabilization), but i couldn’t find it in a quick search of my posts
If you know your host cant handle the power, you want to have as much mass as possible. That will give you more time on maximum output before the light gets too hot to hold.
My two bobs worth. Look at an air cooled engine. Does it have a solid block off metal around the barrel? No. It has enough metal around the barrel to not distort under heat and load which has cooling fins attached. The hottest part off a two stroke was the head where radial finned heads evolved before water cooling came into fashion. PC cpu’s heatsinks have also evolved with heat copper tubes running across the cpu through fins to cool the air inside the tubes to keep the cpu cool. All this needs air flowing across the fins to keep cool.
My take on all this is that you need a good material, copper to take the heat away from the led and as quickly as possible spread the heat out into the fins and allow as much moving air as possible to cool it.
All arguments are welcome.
My personal opinion is to have a direct thermal copper board for removing heat efficiently from the emitter to the aluminum heatsink/fins on your flashlight. For most flashlights the bottleneck point for heat transfer is from the back of the emitter to the heatsinks/fins on the flashlight body. You have an interesting situation where you want to have the "longest" runtime available before the heatsinks are overwhelmed but you are enclosing the entire thing to stale air? In which case it will take longer for aluminum to heat up as it has a higher specific heat than copper but also causes it to dissipate heat more slowly than copper. Also Aluminum is also ~3x cheaper and lighter than copper. Feel free to correct me if I'm wrong.
copper to get heat from the emitter to aluminum heatsink is very nice, but is rather rare, most LED “pills” are made from aluminum which does fine, but not as good as copper would of course
By stale air I mean to say that it is fully encapsulated in plastic. I will drill some holes in the underside under the heatsink but would like to minimize dirt/water entry as it will be used for camping.
So while not being IDEAL, a 1/4in 6” round heatsink would keep an MTG-2 safe for HOURS right?
without any airflow or even access to the outside air, you’re going to be somewhat limited by how hard you can drive it. One approach would be to work out the maximum runtime on what ever batteries you’ll be using, then figure out how big a chunk of metal you’ll need to keep the LED under 85C for that time.
how much light do you need though? Both the camping lanterns I’ve made run at 3W or under, which is more than adequate for our needs and doesn’t annoy the neighbours too much either
Matt, good point on the reverse engineering part. Do you know how i would calculate the heatsink based on that? I seem to have left out some info as well.
A major point to note would be that I just want full brightness when i need it ( setting up a tent late) or on a trail where others need a spread of light as well. I want modes or a potentiometer to dil it back into reality but if I need LIGHT for a while I want the capability.
Fins are more to sustain safe temps, and the center mass of a heatsink soaks up the heat in reserve for the fins to.radiate?
