D4 Titanium!!!

waiting’ for king Richard to announce they are in stock!

It is a common misconception that higher thermal capacity is bad because the item will need more time to cool down.
Higher thermal capacity mean that the item will take longer both to heat up and to cool down. If TC is increased and other variables unchanged, a light with higher TC will always have strictly lower average temperature.

A flashlight uses 3 cooling mechanisms:

  • radiation to air
  • conduction to user hand
  • wind (with fallback to convection when wind is unavailable)

I have no idea how important is each of them. Would love to know.

Efficiency of each of them depends strongly on surface temperature.
But when temperature is software-limited, a limit on temperature becomes a limit on power.
The limit is not the same for different materials because:

  • they have different emissivity
  • they have different conductivity and thus surface temperatures are less even

Emissivity of oxidized copper is about the same as anodized alu. Polished Cu is worse, polished Ti even more so. I failed to find numbers for oxidized Ti.

In a pure copper light surface temps would be more even than in alu one.
In Cu-Ti the head will be much hotter than the rest.
With properly tuned heat regulation, peak head temperature would be the same as in alu light. Sustained output would be lower. But it’s possible that Hank didn’t re-tweak the thermal algorithm to fit the new host better.

BTW one interesting development would be to increase cooling by upping surface temperature significantly above what user can touch painlessly….in areas that user can’t touch. Like bottoms of deep fins. I guess it wouldn’t make a big difference, but maybe I’m wrong. :wink:

Convection (to air) is most significant for a flashlight in normal use. Radiation and conduction to hand are negligible in comparison.

Wind and convection are same thing….wind just allows for more convection than static air.

For the durability of titanium, especially the threads it’s worth a bit of a draw back in heat. Its going to be in my hand anyway, my hands will absorb heat slower that titanium can move it.
Just like my hands absorb heat slower than aluminium can move it.
But aluminium is softer than titanium, and will wear faster i imagine.

Do you think Swarovski-crystal encrusted platinum would retain heat in this light?

So copper conducts heat better but overall for a flashlight it’s worse? I’m having a hard time following XD

In addition to thermal conductivity issues, titanium has the clear disadvantage of undermining the tailcap lockout feature—an important one on this light.

If I’m not mistaken, there should be tailcap lockout. Current is interrupted at the tailcap PCB, and current does not travel via tailcap itself.

Do any of you guys realize what titanium and machining titanium costs? This is cheap for the size of the piece plus electronics, wages, and other costs.

As for appeal, why do people buy expensive cars, jewelry, sports memorabilia, etc…

You can gain a rudimentary understanding of how natural convection and radiation contribute to overall heat transfer by looking at the well-understood model for a horizontal cylinder suspended in a fluid. This doesn’t account for the addition of conduction into the hand and the lost surface area for convection, nor for any type of forced convection (e.g. wind) but it’s a reasonable starting point.

Here is a calculator that will determine the total heat transfer, split between natural convection and radiation, for such a case: Maya HTT - Thermal Wizard

I entered the approximate dimensions of the D4 in meters (.094 L x .024 D) and the approximate emissivity for anodized aluminum (0.8 - quite good!). At an ambient temperature of 20°C and cylinder surface temperature of 50°C (about as hot as you can hold continuously), the D4 can only get rid of about 2.5W. That’s 1.4W by convection and 1.1W by radiation.

At an emissivity of 0.2, which seems to be closer to the value for machined titanium, the total heat transfer drops to only 1.7W, with the same 1.4W from convection and only 0.3W from radiation.

It’s worth pointing out that these rates of heat transfer are at steady-state when the heat generation is equal to the heat dissipation and temperatures are constant throughout the system. It’s obvious that the D4, even with the good emissivity of anodized aluminum, just does not have the surface area to dissipate anywhere near the amount of heat it generates at full power. In theory, thermal regulation should settle on a power level that results in 2.5W of heat generation in the aluminum D4 and 1.4W in the titanium.

More practical questions like how long a light can run before stepping down require more complicated models that look at how temperatures change over time on their way to steady-state, and do factor in the thermal conductivity of the material (notice how that doesn’t matter in a steady-state analysis).

I just took a closer look and you appear to be correct - as long as the PCB’s copper layer does not contact the tailcap body. It comes pretty close to the edge.

I can’t check any of my aluminum tailcaps for continuity to the PCB because, well, they’re anodized.

So, as far as I can understand, buying titanium or copper flashlights is more a matter or durability and aesthetic than performance? Since copper will oxidize anyway, performance-wise it will end up being close to aluminium?

Not quite, copper will allow a much more heat to be absorbed before it gets as hot as an equal volume of aluminum. I’d compare it to high capacity vs low capacity batteries. Longer to charge at a given rate.

Is it more difficult than machining stainless steel?

Because they have money to spare…

I think the copper ‘engine’ is a good idea for the D4, but they should have chosen to rose gold plate it (to avoid the patina, keep it shiny) and stick with the Aluminium parts for heat management.

Copper and aluminum sounds good to me.

disagree
Copper is 69% MORE heat conductive than Aluminum.
see here

Titanium is 95% LESS heat conductive than Copper

Holding a flashlight in your hand moves MORE heat away from the body of the light, than freestanding the light in still air.

So when using a Titanium/Copper D4, the BEST way to keep it cool is to hold the Copper part in your hand. Holding the Titanium part won’t do much.

and btw, the reverse polarity protection of the D4 does not work. IF you put a battery in backwards it WILL heat up AND overdischarge (to prevent that, be sure to test turning on the light when you insert a battery)
video courtesy of RobertB

Conductivity is the travel of heat in the material itself and is not a bottleneck with CU and AL in flashlights, what interest us is the heat transfer coeficient through convection, it’s better with AL than CU, anodized AL is better than non anodized AL (17% advantage at 0 air speed, so only convection moves air), oxidized CU is better than non oxidized CU among other factors because the oxidized one has a larger surface area than polished one.

Edit: oh i see you edited your post.

I dont quite understand your post
are you agreeing that copper is more heat conductive than aluminum?

you seem to be focused on convection, if by that you mean heat transfer to AIR, that is not the primary cooling mode for a flashlight. Holding it in the Hand moves heat away by conduction, much more than still (no fan) air convection. Or maybe I misunderstand your terminology.

In any case, yes, the copper head will get a lot hotter than the Ti body.

There is heat transfer:

1) from led (primary heat source) to surface of flashlight ==> thermal conductivity of materials

2) Dissipation of heat from surface of flashlight to surrounding, whether it is air, or physical contact (hand). ==> radiation, convection and conduction.