Hi. From some days I have new thermal phone imager and its great. I also make some test of my light and main issues of all kind of lights which are made from 3 pieces and not made from one body piece there is large thermal bridge from flashlight head to battery tube. That prevent for quick and efficient spread of heat over large surface which is like a heatsink. I have question how we can improve thermal resistance between battery tube and head. There is about 10 degrees difference between them when flashlight is cold and turn on turbo. Any Ideas?
Here are some quick examples of my bike lights Fenix BC30 and AStrolux BL03 vs Wildtrail WT3M. In WT3M you can see big difference between body and head temperatures.
I think of this as a feature sometimes. Keeping the handle cooler and protecting the battery from some amount of heat.
Short of a billet/cast unibody design, thread fit is going to be the most important factor. Thermal paste or grease of any kind for that matter can help, but in practicality just makes a mess for minimal gains.
I thought about to try that. But thermal paste will be little mess if I want to clean it after that. Also I cant try to add copper foil for better heat transfer between threads.
Heat rises. By tail standing ,as heat is being generated at the head and rising it’s drawing air currents from below to keep the handle cooler. You might get slightly different results if the flashlight was horizontal. You will get slightly different results if you hang that flashlight pointed towards the ground. All this is assuming testing is indoors with near zero air flow. Will it be enough of a difference to really matter?Maybe not. I just tested two separate identical flashlights, one tail standing and one hanging head down both running at the same time and after a minute I can measure a difference at handle temperature. After 2 minutes I had 10° F difference in handle temperatures.
Interesting that you measured the thermal performance of the Astrolux BL03. I did the same a couple of weeks ago for the BL03 and its companion model the BL02 (but since these are bike lights, posted it in a bike-specific forum).
The results for the BL02 and BL03 were quite different (temperatures in deg. F):
While the BL03 has a smooth thermal gradient over the body (as seen by icpart as well), there is a sharp temperature jump at the lighthead/body junction in the BL02.
I was able to reduce these thermal gradients by thermally contacting the body and head of the light to a single large Aluminum heatsink using thermally conductive tape. That was effective for my purpose of keeping these gradients (and overall temperatures) down while doing runtime tests with an integrating sphere, but admittedly not of much practical use for the light on a bike or in hand.
Playing around with thermal compound inside the light would be the next step, but this was around where I stopped since I didn’t want to try to open these lights up.
Malkoffs are purposefully utilitarian in design & function. Heat is not an issue because he (Gene Malkoff) doesn't overdrive any of his products. His focus is primarily with providing the military & law enforcement markets with the best available products through reliability, indestructability, efficiency and high quality illumination (pure tints & high CRI), not with wowing the "enthusiast" market. Every one of my Malkoff lights and P60 modules can be run on high until the batteries are depleted. That, along with a bit higher cost, and the fact that his light engines & electronics are fully potted are why Malkoff doesn't garner much interest here on BLF.
Agree. Except for extremely cold weather there is probably never a good reason to transfer heat to the battery/compartment. That would apply to flashlights or vehicles or any batteries. And testing bike lights indoors with no air flow is not realistic.
This is a long-known fact that unfortunately most light makers still ignore.
If you want the lowest thermal resistance, unibody is the thing. If you want just right thermal resistance to have good thermal transfer yet avoid burning you fingers - add thermal bottlenecks where it makes sense. Having ultra-short thermal path to the switch and a thermal block on battery tube is a poor choice…
As to putting thermal compound on the threads - This has been discussed before as well but I think I haven’t seen anyone doing this yet.
The reason is that these compounds are abrasive and will quickly eat your threads. So you should be careful to always unscrew from the tail and don’t even move the other thread unless for occasional maintenance. Is it worth it? Maybe.
(usually, depending on host design) beefier thermal paths, so lower thermal resistance
Specific heat capacity is a thermal buffer. The more you have it, the slower temperature rise at any given heat production. But this only helps make Turbo last longer. Over a long time, even a slow rise will end up at the same maximum temperature.
Lower thermal resistance, if present has a couple of effects:
it may make the surface temperature more uniform; cooling is very roughly linear with host temperature. Average temperature, not maximum. If you have a fixed power output, a host with more uniform surface temperature will have a lower temperature of its hottest point. In other words - will be cooler.
this is a marginal effect but lower thermal resistance means that LED runs cooler. And cooler LEDs are more efficient, so at the same output level they produce less heat (I’m not sure but I think that at the same current level a cooler LED produces more light AND more heat).
And, BTW, weight matters only if you compare 2 hosts made from the same material. There are huge differences not only f.e. between alu and copper but even between aluminium alloys.
We use to cut fins in 2D maglites to help improve the heat dissipation. Aussie-Yank Flashlights Inc. Or how to span the oceans with crazy mods and good BLF friends. All Done
We were loosing mass but creating fins, which increases surface area to shed heat. Most all plain aluminum heat sinks use the same thing. I have always read that copper absorbs heat better and aluminum sheds the heat better. CPU heatsink designers used both materials in several high performance CPU heatsinks. Since they spend lots of money and R&D to try to win the lowest running heatsink award. I assumed, They have done the reserch and know what works.
That’s not true. Copper has much better thermal conductivity and higher volumetric heat capacity, so if you compare the same part made in both materials, copper wins on both counts. If you make the part larger, so it has higher volume and the same weight, it will be the opposite though. For CPU heatsinks, I guess that weight is a limitation, so they use copper close to the CPU where it matters the most and alu elsewhere.
ADDED:
Some old data that I had available easily:
Regular alu 6061 has thermal conductivity of 150 K/W and heat storage of 2.42 J/mm³K. 6063 has 200 K/W and nearly the same 2.43 J/mm³K. Copper has 400 K/W with 3.44 J/mm³K. 7068 which I think is the overall best flashlight alu for being much tougher than 7075 with great thermals – has 190 K/W with 3 J/mm³K.
ADDED2:
Well, the “copper wins on both counts” is not so simple. What are we counting for capacity? Comparing pure numbers - it’s what I wrote above. But what really matters in our context is time before the surface temperature reaches 60 °C. Which is different.
I don’t understand the physics of heating-up too well but what I understand is that there will be temperature gradient - the closer to the LED, the higher temperature. The gradient will be steeper with alu because of its lower conductivity. The LED will be hotter and the material close to the LED will be hotter as well. If we had 2 materials with the same volumetric heat capacity and different heat conductivity - the one with lower conductivity would overheat slower because the hotter material would absorb more heat. But here alu has both lower conductivity and volumetric heat capacity. So which one would overheat faster? I don’t know.
