Titanium

[JMP]

Yea, I think SM-100 might be a little excessive for a flashlight. As a blade? Im in the market for one. Theres only a few knifemakers using it at the moment. Its very expensive stuff!

 

[cyclesport]

Saw some interesting discussion of "SM-100" (or nickel-titanium alloy NiTiNOL 60) ... might be amazing stuff for a flashlight host ???

Probably super-expensive though

Another fan of Everyday Commentary I'm guessing?

 

[merc240d]

Would like to try a Titanium light for offshore sailing. Sounds like an incredible material for the case. Where would I look for a red, night vision, version?

 

[nbp]

I think Don has some red LEDs, I'd contact him. I think a member got a red emitter Haiku not long ago.

 

[BenChiew]

Would like to try a Titanium light for offshore sailing. Sounds like an incredible material for the case. Where would I look for a red, night vision, version?

Here you go. Don's Sundrop in Red Dragon. Disregard the center spot. It is not there. Just my IPhone 3GS picture.

 

[rlichter]

Thank you so much for the highly informative and interesting post. It makes it easy to share your excitement for this amazing metal!

 

[thedoc007]

Post deleted, no longer relevant.

 

[nbp]

Maybe aluminum and copper are too conductive and titanium is in fact just right. haha

Personally, having had at least a dozen titanium flashlights, I think some people overstate the severity of this disadvantage of heat and electrical conductivity. I have never had a functional problem with a flashlight where the fact that it was titanium was the culprit and an equivalent aluminum light would have been just fine. I think parading around these "disadvantages" (it happens in any discussion about Ti lights) is simply a way for people to convince themselves that they have found superior lights at a lower price by buying aluminum and people who like Ti lights are just elitists who want blingy lights even though they are functionally inferior.

Ti lights handle LEs putting out a couple hundred lumens just fine, and that's all I need. If I get a light that makes 1500 lumens it's going to overheat no matter what it's made out of and probably has auto stepdowns built in anyways. So, I fail to see the "problem".

 

[RetroTechie]

Super informative thread this! :thumbsup: I think I've gained an IQ point or two by going through a number of linked articles.

Aluminum is 205 W/(m.K). Titanium is a mere 22 W/(m.K). In fact, aluminum is almost ten times as thermally conductive as titanium. And copper is close to twenty times more thermally conductive. Among metals, titanium is decidedly BELOW average in thermal conductivity.

Use of pure metals is rare. Usually we're talking about a few out of a gazillion different metal alloys. So when talking about the properties of such materials, one should also mention which alloy(s) we're talking about, since its properties could be very different depending on which & how much other metals were mixed in. And no, often properties are NOT a sliding scale that goes smoothly from "number for metal A" to "number for metal B" when talking about an A/B alloy. Then there's A/B/C alloys, A/B/C/D alloys etc, all in varying percentages. Not to mention temperature treatments etc.

So that aluminium alloy used for your average flashlight might be a much worse thermal conductor than pure alu. Likewise, that Ti alloy used might be a much better heat conductor than pure Ti.

There is no way you can say that titanium "conducts well" when you look at the numbers.

One is always comparing to other materials. Compared to pure alu, pure Ti might conduct heat poorly. But compared to ABS plastic, it conducts heat extremely well. And in most cases, more than enough for use in a flashlight. This also depends on how hard a LED is driven, how good the thermal contact between LED die and flashlight body is, what temperatures a particular LED can safely handle, etc.

Low electrical conductivity means you waste more power if you use a titanium body as part of the circuit, as many lights do.

Ehm... NO. I don't have a math example ready, but I'm sure if done, electrical conductivity of the flashlight body (as long as it's metal) is way, way, way, waaayyyy down on the list of electrical losses. Contact areas (threads for one) maybe not so. But the body metal itself = a don't care in electrical terms. For starters, most LED lights I've seen have a linear driver, where current is fixed and excess battery voltage is wasted in the driver. If the body has a slighty higher resistance, then a slightly higher voltage drop will occur over the flashlight body, vs. being wasted in the driver. Oh wait, that would actually be beneficial... :huh: :laughing:

And arguably even more important, you have to substantially reduce drive levels if you build a light body out of titanium, or it will overheat. It just isn't capable of spreading the thermal load like aluminum or copper.

Yes. So if the drive level is appropriate, there is no problem. And that appropriate drive level might be more than enough, if other factors are limiting (battery capacity, practical output levels for a close-range, EDC light, etc).

But I don't think we should pretend it is a miracle metal...like all others, it has advantages and disadvantages.

Indeed.

And frankly, in my opinion, for flashlights, the advantages of copper or aluminum are more suited.

Again, that depends on which copper, alu or Ti alloy, and which type(s) of flashlight one is building.

 

[KITROBASKIN]

You all are much more informed than me but I can tell you that a Commercial Pure, Type 2 titanium sheet that I use for baking pizza and cookies does resist heat better than a steel cookie sheet. (I like softer pizza crust and thin cookies without brown on the bottom)

The MBI HF Ti that I have does conduct heat from the Nichia LED. Presumably the titanium is an alloy but I don't feel like that flashlight is hindered significantly because it is Titanium.

 

[calflash]

Isn't he REAL thermal bottleneck in a well designed, bare metal flashlight, from the surface of the light to the air or to the hand? I may need corrected on this but isn't the term emissivity? Where is Ti on that scale?

I care less about the LED's temperature than my hand's temperature. One reason I like titanium is because the heat doesn't migrate from the LE to the handle as fast as a material like copper. I once measured the temps of two identical lights, one in copper and one in Ti. The handle on the copper light reached uncomfortable temps in half the time of the Ti light. Once they reach that level you have to do something because the light is useless if you can't hold it, no matter what metal it is. So I am of the mind to conclude that titanium is more than acceptable for a flashlight thermally, since it transfers the heat away from the LED faster than it expels the heat from the body of the light.

 

[McGizmo]

I do appreciate you taking the time to make this thread, and you do have some good information. However, there one point you make that is just plain wrong.



This is the biggest issue I have with your info. Titanium is in fact a lousy conductor. You acknowledged that copper is a superior conductor, but without numbers people might not understand the ENORMOUS difference. Taken from http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html. Copper has a thermal conductivity of 401 W/(m.K). Aluminum is 205 W/(m.K). Titanium is a mere 22 W/(m.K). In fact, aluminum is almost ten times as thermally conductive as titanium. And copper is close to twenty times more thermally conductive. Among metals, titanium is decidedly BELOW average in thermal conductivity.

And from this same table of conductivity, what is the thermal conductivity of air or water or whatever else there is available to dissipate the heat from the flashlight once it has made it to the surface? I don't disagree that titanium is a poor conductor of heat relative to other metals that can be used for flashlights and it would be despite this shortcoming should one decide to build a light using titanium as I have. I held off using titanium for a flashlight for a few years until I felt the efficiency of the LED's had reached a point that the wast energy in heat could be managed with a titanium design. The important consideration is the temperature of the LED and components in the driver circuit. If they are at acceptable levels then cool and if not, then not cool. The thermal mass and surface area of the light body are every bit as significant as the materials used if you want to look at the complete thermal picture and consider the various temperatures at steady state and whether these temperatures present a risk or concern for the user as well as the well being of the light and its components. A copper flashlight could fail due to thermal problems whereas a flashlight made with a ham and swiss cheese body might do fine, thermally.

The difference in electrical conductivity is similar. Aluminum is fifteen times as electrically conductive, and copper over 30 times as electrically conductive, compared to titanium.

There is no way you can say that titanium "conducts well" when you look at the numbers. This also happens to be among the most important properties in flashlights. Low electrical conductivity means you waste more power if you use a titanium body as part of the circuit, as many lights do. And arguably even more important, you have to substantially reduce drive levels if you build a light body out of titanium, or it will overheat. It just isn't capable of spreading the thermal load like aluminum or copper.

I am in fact a huge fan of titanium...ever since I learned about the SR-71 Blackbird. A design like that would not have been possible without titanium. But I don't think we should pretend it is a miracle metal...like all others, it has advantages and disadvantages. And frankly, in my opinion, for flashlights, the advantages of copper or aluminum are more suited.

What is the electrical conductivity of aluminum oxide compared to titanium oxide? I agree with you that aluminum and copper are superior metals for thermal conductivity compares to titanium and I agree that copper is superior in terms of lower electrical resistance as is aluminum provided it does not have an oxidized surface in the electrical path (not always the case in some designs).

I believe your opinion of the superiority of copper and aluminum is based on sound reasoning but also on a set of parameters or priorities which may or may not be held in the same values by others of us; me for one. :nana:

You state that js's statement is just plain wrong but he qualifies titanium as serving "well enough" and I agree with him. He says you wouldn't use Ti for house wiring and if you are old enough you might remember when a serious mistake was made when aluminum was used for house and commercial wiring! :green: If you aren't old enough to remember this, the problem was not in the electron flow through the aluminum wire, it was at the junction points and terminals where it often had difficulty getting in or out of the wire. If you are going to base the choice of metal in a light on both thermal and electrical conductivity then copper is king but you need to qualify aluminum on the electrical conductivity to some extent.

You say you have to substantially reduce drive levels if you want to use titanium. With efficacy now above 100 lumens/watt I don't consider this a sacrifice at all but what you say is true. If the goal is maximum power to the LED then titanium is indeed a poor choice compared to other metals. It is superior to ham and cheese though.

 

[thedoc007]

I believe your opinion of the superiority of copper and aluminum is based on sound reasoning but also on a set of parameters or priorities which may or may not be held in the same values by others of us; me for one. :nana:

My opinion of titanium is that is an a pretty awesome metal. I did explain what parameters I was looking for, and do acknowledge that other people have different priorities. My response was geared toward those who honestly believe (or pretend) that titanium is good at everything. The FACTS do not support that.

You state that js's statement is just plain wrong but he qualifies titanium as serving "well enough" and I agree with him.
You say you have to substantially reduce drive levels if you want to use titanium. With efficacy now above 100 lumens/watt I don't consider this a sacrifice at all but what you say is true. If the goal is maximum power to the LED then titanium is indeed a poor choice compared to other metals. It is superior to ham and cheese though.

You are right, we simply have different needs. I do want to have the option of crazy brightness...even if I rarely use it. And titanium tends to limit your options there, where conductivity is somewhat more important. If you notice, my comment about conductivity arose from his statement that titanium "conducts well". I think in comparison to other common materials, this is misleading. Among metals, it is below average, and saying it conducts well is misleading. If he had only said that it serves "well enough", I never would have bothered.

All that aside, your lights are amazing. And the "Trial by Fire" thread clearly shows one of the unique advantages of titanium. If I had more money to spend, I'd definitely be looking to buy one of your lights, despite the conductivity drawback. Again, all I was trying to do is provide some perspective...it isn't a miracle metal, and it has strengths and weaknesses like every other metal.

 

[McGizmo]

thedoc007,

Thanks for your response and I appreciate your comments. I think you hit one of of titanium's most significant short comings in your last post and it is one that you didn't mention initially. That would be the prohibitive cost of titanium. The cost is not just in raw material but the time and tool wear in machining it. I have read some exciting news regarding new technologies and the potential of producing titanium powder at a much lower cost as well as the creation of parts from this powder at significant cost savings compared to current methods. I consider this great news for the most part but it could well be the end of my little niche. I switched from designing and building aluminum flashlights as the real manufacturers came up to speed with the new LED's and converters and recognized a growing market that was viable in supporting their business. I could never compete with them and frankly didn't want to because based on my personal set of priorities, titanium, despite its cost, was the material of preference and its thermal shortcoming as you have mentioned was no longer of a critical nature; at least in the design parameters I was working with. I don't venture out past the McGizmo forum but I am aware that there are others offering titanium lights and my days may be numbered anyway. I have seen pics of lights that people have mistaken as part of my offerings based on design elements and appearance. It's a real bummer to me but that's my problem and I understand this.

As long as I can build and offer lights based on my parameters and compromises I feel justified and there are those who want my lights I'll continue to build and offer. :bow:

 

[js]

I do appreciate you taking the time to make this thread, and you do have some good information. However, there one point you make that is just plain wrong.



This is the biggest issue I have with your info. Titanium is in fact a lousy conductor. You acknowledged that copper is a superior conductor, but without numbers people might not understand the ENORMOUS difference. Taken from http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html. Copper has a thermal conductivity of 401 W/(m.K). Aluminum is 205 W/(m.K). Titanium is a mere 22 W/(m.K). In fact, aluminum is almost ten times as thermally conductive as titanium. And copper is close to twenty times more thermally conductive. Among metals, titanium is decidedly BELOW average in thermal conductivity.

The difference in electrical conductivity is similar. Aluminum is fifteen times as electrically conductive, and copper over 30 times as electrically conductive, compared to titanium.

There is no way you can say that titanium "conducts well" when you look at the numbers. This also happens to be among the most important properties in flashlights. Low electrical conductivity means you waste more power if you use a titanium body as part of the circuit, as many lights do. And arguably even more important, you have to substantially reduce drive levels if you build a light body out of titanium, or it will overheat. It just isn't capable of spreading the thermal load like aluminum or copper.

I am in fact a huge fan of titanium...ever since I learned about the SR-71 Blackbird. A design like that would not have been possible without titanium. But I don't think we should pretend it is a miracle metal...like all others, it has advantages and disadvantages. And frankly, in my opinion, for flashlights, the advantages of copper or aluminum are more suited.

thedoc007,

Titanium is a good conductor of electricity compared to a great many materials. It is a metal; it's kind of in the job description. Yes, relative to other metals, titanium is relatively poor at conducting electricity. But total resistance is determined by resistivity and the geometry (i.e. the volume involved). You can achieve the same total circuit resistance by less of a very good conductor (such as copper) or more of a less good conductor (such as titanium). But in the case of a flashlight BODY, there is a LOT of material! If I tell you that the total resistance is, say, 0.01 ohms total for a titanium flashlight body, and .0001 ohms for copper, you could say that the resistance of titanium is a hundred times higher! OMG! But I could say--with equal truth, and more relevance--that the resistance of both of them is very low relative to other resistances in the circuit. And that is in fact the case here. And more importantly, the contact resistances and resistances of the oxides are more significant, and here titanium has a decided advantage.

As for the thermal situation, you are mistaken. Here is a detailed analysis of the thermal situation in the LunaSol 20 from my thread on the light. The situation is quite similar with the Haiku. Titanium has plenty of thermal conductivity to handle the heat dissipation loads involved in LED flashlights:

*****

TITANIUM

I have to confess that when I first saw the various custom made titanium lights on CPF I had exactly the same reaction that most people have. I was like "Titanium? Doesn't it have a higher resistance than aluminum? And doesn't aluminum conduct heat better than Titanium? Why would you pay so much more for a Titanium light? I don't get it!"

Now, some people like to "answer" these questions by saying that titanium is just "bling", just "man jewelry"; that it's a status symbol kind of thing, like a Rolex watch; that if you were just thinking practically and rationally, you'd use aluminum. However, this sort of psychological write-off really isn't true, as I've come to find out both from my experience owning titanium lights, and my scientific research into the question of titanium. So, let's look a bit more deeply and more thoughtfully into the question of titanium flashlights.

Electrical Resistance

Right off the bat, let's knock the electrical resistance thing on the head! Yes, titanium does indeed have 26 times higher resistivity than aluminum, but that's still pretty good. Nickel has almost 3 times greater resistivity than aluminum, and yet it is used for 1/4 inch wide .005 inch thick ribbon strap connections between cells in a welded battery pack. And those straps are often asked to conduct four or five amps or even more. Metals—all metals—are good conductors of electricity. It's sort of in the job description. Further, the amount of material involved in a flashlight body's conduction pathway is enormous. There's a lot of titanium there—many orders of magnitude greater an amount than that involved in a battery packs' nickel ribbons; more even that that in a 12 gauge wire—and thus the total circuit path resistance involved in both the aluminum and the titanium flashlight is so low as to be insignificant.

Most of the time, that is . . . because the story of electrical resistance doesn't end there. The thing is that both aluminum and titanium (and most metals) oxidize in air, and a surface layer forms, which may or may not be conductive. Aluminum's surface oxide layer is most emphatically NOT very conductive. This is why aluminum lights are Chemkoted so that they have a different surface layer that is electrically conductive, and which is environmentally stable and corrosion resistant. Otherwise, any bare aluminum to aluminum joints in the conduction pathway will eventually develop significant resistance, totally negating the low resistivity of pure aluminum. Titanium's surface oxide layer, in sharp contrast, conducts electricity just fine and bare titanium to bare titanium is a totally viable and environmentally stable corrosion resistant joint just as it is with no special treatment. So, if we were to reckon up titanium's advantages, ironically "electrical conductivity" might actually be one of them, considering it's surface oxide, but you could argue against this view if you have complete trust in the Chemkote surface layer on the aluminum light.

Heat Conductivity – The Long Version

Heat conductivity is a much more complicated consideration, unfortunately. I will show below that regardless of any theoretical calculations and discussions that may follow, the LunaSol 20 manages heat very well even in worst case scenarios (as does the Ti-PD-S), and honestly, I don't know why that should surprise anyone as many plastic LED lights exist that also perform just fine, if it comes to that, and I can guarantee you that titanium has better heat conductivity than any plastic. However, let's take a look at the heat transfer problem from the theoretical perspective, just for fun. And don't blame me if it starts to get a little tedious! Feel free to skip the rest of this section at any point and jump to "Heat Conductivity – The Short Version" below.

Heat transfer can happen via conduction, convection, or radiation, and a general heat transfer scenario is painfully difficult to calculate theoretically. Conductive heat transfer, or transfer scenarios dominated by conduction, or which can be reduced to an equivalent conductive (and thus simpler) problem, are much easier to deal with, and can be thought of just like an electrical resistance problem with wires and current and voltage and a number of resistors. The current is the heat flow and the resistors are the junctions or conductive elements. An LED, like a transistor or MOSFET, has a degrees C/W rating, which predicts what the temperature drop across the junction will be when a certain number of watts are dissipated through the device. This is analogous to a resistor's voltage drop when a known current flows through it. The equation is very simple:

dQ/dT = deltaT / R

q = deltaT / R

where dQ/dt is the rate of heat flow in watts, deltaT is the temperature difference, and R is the resistance of the junction (or in general, of the material conducting the heat flow). For simplicity, I will let small q = dQ/dt. Some may recognize this as Newton's Law of Cooling, by the way. So, for example, a 10 C/W junction dissipating 2 watts, will have a 20 degrees C temperature differential across it. This, however, doesn't tell you the die temperature unless you know the temperature of the other side of the junction—usually a heat sink. The heat sink, in turn, has a temperature drop across it. This can be calculated by expanding the "R" term above. For a simple rectangular block of material:

R = L / (k * A)

where L is the length over which the heat must flow, k is the thermal conductivity, and A is the area through which the heat must flow. Notice that R increases with L, but decreases with both k and A. Notice also the k must have units of watts / ( meters * degrees C), although usually it appears as degrees Kelvin, actually, but 1 degree C = 1 degree K for differences, as Kelvin is just Celsius with a different zero. This makes R have units of (degrees C / watts), which you can work out for yourself if you wish.

Sadly, the MCPCB heat sink in the LunaSol 20 isn't rectangular, with the area constant across the length of heat flow. The Golden Dragon LED is at the center of a disc of aluminum, and thus heat flows out from the center to the edges, and also out of the top and bottom. Since I want to calculate a worst case scenario, and because the top and bottom are much more complicated heat transfer situations, I will pretend that no heat escapes from the top or bottom of the .75 inch diameter, 2 mm thick heat sink. Now, if we think of a very thin cylinder where heat flows from the inside to the outside, it should be clear that the rectangular equation above easily applies because the cylinder can be unfolded, without any significant distortion, to a rectangle of 2*pi*radius width, h height, and t thickness, where t is small. If t were large, then we couldn't unfold it without distortion. But, with that in mind, we can think of the MCPCB heat sink as a big collection of nesting cylinders, all which have a small thickness, and then we can just add them up. Such is the power of integral calculus! LOL! So, thickness becomes dr, width is 2*pi*r, and height is still h. Rearranging terms above we get:

deltaT = q / k * integral (dr / (2*pi*r*h)) from r=inside to r=outside

We can pull 2, pi, and h from inside the integral as they are constants:

deltaT = q / (2*pi*k*h) * integral (dr/r) from r=inside to r=outside

But the integral of dr/r is just ln(r), so,

deltaT = q / (2*3.14159*237W*m^-1*K^-1 * .002m) * (ln(.375inch) – ln(.125inch))

deltaT = q / (2*3.14159*237W*m^-1*K^-1 * .002m) * (ln(.375/.125))

To determine q, we can put an upper limit on the heat dissipated by just making it equal to the power of the light. (The actual heat dissipated would be less than this, as some of the power goes into the production of light energy.) Back of the envelope calculation of that is simple: take the Wh of a CR123A cell and divide by the runtime in hours. The Wh of a good CR123A cell at a .5 amp draw rate (the current to the Golden Dragon is 425 mA) is right around 3.7Wh. This makes for 1.85 Watts due to the 2 hour runtime of the LunaSol 20 on high. So q = 1.85W, and to clean up some more, .375/.125 = 3, and ln3 = 1.0986. Here's what we have now:

deltaT = 1.85 / (6.28318*.002*237)*1.0986 K

where I canceled some units and moved K^-1 at the bottom to K at the top. Work this out and we get the result:

deltaT(heatsink) = 0.68 degrees C

This is the drop across the heat sink. And we can also add to that the drop across the LED to MCPCB solder joint. From the spec sheet the Golden Dragon has an 11 C/W thermal resistance. So, q*R will give us a result of

deltaT(junction) = 20.35 degrees C

Having fun yet? Let's move on to the temperature drop across the titanium body. Using the entire body for the calculations would be too optimistic, because the heat has to flow from the heat sink to head mating surface, and then all the way down the body before it gets to the tail, and this doesn't happen without a temperature drop. The tail section does indeed draw away a significant amount of heat, but since that is hard to calculate, and since I'm interested in a worst case scenario, I will pretend that the titanium body only consists of the head (with maybe a bit extra length to partially compensate). So, I will use a .125 inch thick, 1.5 inch high, 1 inch outer diameter cylinder. It is interesting to compare the simple rectangular equation's results with our more accurate one in this case, since the thickness (.125 inches) is not exactly large with respect to the diameter (1 inch), but I will leave that as homework. (Yes, I'm having fun with this. *cough* Sorry. *sheepish grin*) OK. So, let's use the same formula, but this time we use titanium's heat conductivity of 21.9W*m^-1*K^-1, an h of .0381m, an inner radius of .375inches, an outer radius of .5inches. The result is,

deltaT(titanium case) = .10 degrees C.

MY GOD! That's crazy! Clearly we needed aluminum there, didn't we? After all, if we had used aluminum, the result would have been,

deltaT(aluminum case) = .009 degrees C,

and isn't that a whole order of magnitude better, after all?

Now, I've left two important pieces out so far, and those are the case to air junction and the heat sink to case, and MCPCB solder joint to heat sink contact resistances. If you take any two blocks of materials, A and B, and push them together, and cause heat to flow, there will be a discontinuity of the temperature from the left end of A, to the right end of B, where they meet. This is called the thermal contact resistance, and it is notoriously difficult to calculate. I don't know much about it, but I did do enough research to know two things: a value of .5 C*in^2*W^-1 for our situation is conservative, and that contact pressure is the most important parameter for smooth mating surfaces with little to no air gap (hence the need for heat sink grease in such cases, by the way). Why do I mention the pressure thing? Well, when aluminum heats up, it expands at a greater rate than titanium which greatly increases the contact pressure on that mating surface, ensuring a nice thermal joint there. It's a nice side benefit to using a titanium body in your flashlight. Anyway, moving on, the delta T across that junction will just be q * (Rc / A) where A is the area, which we calculate from a .75inch diameter and a 2mm height. Thus,

deltaT(heatsink to case junction) = 1.85 W * .5 C * inch^2* W^-1 / (pi*d*h)

deltaT(heatsink to case junction) = 1.85 * (.5 / (3.14159*.750*.07874) C

deltaT(heatsink to case junction) = 4.99 degrees C

For the solder joint to heat sink junction, we need to use an area of .45 in by .4 in (from the golden dragon spec sheet), which yields

deltaT(solder pad to heatsink junction) = 5.14 degrees C

Now, all that's left is the case to air junction. Oh, that's all, is it? Good grief! Calculating that from theoretical considerations would not be trivial. What I can tell you about it is that the greater conductivity of aluminum wouldn't play much of a role. Here, emissivity is more important, and titanium has a pretty good emissivity, although hard anodized aluminum is also good. I'm not going to get into any numbers or make any arguments. This part of the thread is already way too long. All I am going to do is to steal some of Don's measurements. And thank God for those. Nothing like predicting reality from reality. OK. So, Don set up an FLIR measurement and measured 47.7 C at the hottest part of the head, and this was a worst case scenario, being constant on just sitting in open air. See for yourself, as the setup is kind of neat, and I already uploaded those pics to my server space:

Note that the ambient temperature was over 28 C! Which means that the temperature delta from head to air was 19.2 C, yielding an R value of 10.4—very close to the R of the Golden Dragon LED itself, interestingly enough. More importantly, though, consider that if the air had been at 20 C, then the head would have been just below 40 C instead of 47.7 C. But, again, since we are interested in the worse case scenario, let's use the 47.7 C value.

So, let's add it all up

47.7C + 0.10C + 4.99C + 5.14C + 0.68C + 20.35C

die temperature of LED = 78.96 C,

and the maximum junction temperature of the Golden Dragon LED is 125 C.

So, note a number of things here. First, that even in a worst case scenario and making an upper bound sort of estimate, the die temp is well within limits. Second, notice that the largest contributions to the die temperature do not come from the heat conductances of the aluminum or titanium parts, but rather come from the body to air junction and the LED junction. They dominate the calculation. And the next largest component comes from the contact resistances. So . . . maybe we could all please agree that titanium's thermal and electrical "disadvantages" are non-issues for most flashlight use situations?

Heat Conductivity – The Short Version

There was actually a much easier way to demonstrate that the LunaSol 20's die temperature is well below the limit, and that is to look at the runtime / output plot which appears below.

Note that the output does not diminish with runtime. If the thermal situation was pushing the edge, then the output would start at a maximum then ramp down to a lower level due to rising die temperature, which causes loss of efficiency and output over a low temperature die running the same current. This is something I have seen before in multi-level flashlights. It happened with the Arc4 and appeared in this_is_nascar's output graphs of the Arc4 at various levels. The highest level graph showed this ramp down, and TIN complained about it, and Peter Gransee told him it was thermal and that if he just held onto the light the whole time it wouldn't happen. TIN did that, and lo and behold, the output stayed at the high starting level for the whole run due to the lower surface temperature of the body of the light (and thus also of the die) when held by TIN's hand.

 

[thedoc007]

Frankly, that is far more information than I want. Don't want to spend that much time parsing your post. Seriously, my point was simple. Compared to other commonly used metals, like aluminum and copper, titanium is markedly inferior at conduction, both thermal and electrical. I never said it didn't have its uses, I never said it was a problem for any given light - I just wanted to correct the "titanium conducts well" statement that I quoted. Sure, compared to Styrofoam, it conducts well. But that isn't really relevant to my point.

I bow down to your much greater technical expertise...but I stand by my original statement. Titanium is awesome, but it does have drawbacks. All I want to say.

Thanks for the write-up, though! I learned several new things about titanium.

 

[js]

Well, this isn't the first time that I've gotten TL;DR in response to one of my posts. So let me shorten things. But first let me clarify something.

This is what I said about titanium being conductive (emphasis added):

Titanium conducts both heat and electricity well. Not as well as copper, certainly, but quite well enough to serve as a conductor of either heat or electricity if needed. Obviously, you wouldn't use titanium for house wiring, nor for the fins of a baseboard heating unit, but where other factors dictate its use, such as in heat-exchangers in a nuclear power plant, or in a flashlight body, the metal will acquit itself well enough indeed in terms of both heat and charge conduction.

So, I never said that titanium was awesome at everything. Moreover, in the section on machining, I specifically quoted that one of the big drawbacks of working it is that it does not conduct heat well:

Heat Conduction. Titanium is a poor conductor of heat. Heat, generated by the cutting action, does not dissipate quickly. Therefore, most of the heat is concentrated on the cutting edge and the tool face. Tool life is adversely affected.

There it is in black and white. So you really needn't have posted that I was "wrong" about calling titanium "conductive". Everything has a context. I called it conductive within a context (for flashlights, and even for heat exchangers in corrosive or radioactive environments--where it is in fact used--to conduct heat). And yet within another context (machining) I called it a poor conductor--or the source I quoted did. But the amount of heat generated during a machining operations is a lot larger, over a a lot shorter times span, and over smaller areas. So in these cases, the difference in heat conductivities between aluminum and titanium are very significant.

The short version of what I wrote in my LS20 thread is this:

1. The largest contributions to the die temperature don't come from the conductivity of the flashlight body.

2. In point of fact, for Don's titanium lights, the die temperature is well within limits, and wouldn't be significantly lower even if he did use aluminum.

3. And the lumens vs. runtime graphs will tell you this because they are flat until the battery gives out. If thermal overload is an issue, then output decreases as die temp increases (especially as it heads towards the limit).

4. But, really, is it any surprise that titanium conducts well enough? After all, there are plastic LED flashlights in production, and titanium is a lot better conductor of heat than plastic.

 

[thedoc007]

If I was talking about Antarctica, and said it wasn't as hot as Saudi Arabia, that would undoubtedly be true. But it would also be extremely misleading, because that doesn't tell the story. It isn't just not as hot, it is FREEZING! That's how I read your original comment about titanium conducting well. Yes, you said it wasn't as good as copper, but "not as good" is inadequate to describe it when the difference in conductivity is that large. For those particular properties, copper and aluminum are VASTLY superior. So I commented, and as sometimes happens, I took it too far the other way, and called it a lousy conductor. Mea culpa. But I'm glad I did...now, there is more than enough information in the thread for any individual to develop their own opinion, and someone else even did most of the work! That sounds like a win to me...

Your points about the practical application are also well taken. If you read my other posts, you'll note that I argued that for me, the thermal conductivity is an issue. I prefer bright lights, that push the boundaries of what can be done in a given form factor. Thermal conductivity does become more important as you drive a light harder. I never said that a McGizmo would be better if he would just make it out of aluminum. For some people, and some lights, it is indeed irrelevant - it can perform WELL ENOUGH in many circumstances.

When you called it "the metal of the gods", you triggered my fan-boy alert. Some people refuse to admit that something they like has drawbacks, despite abundant evidence to the contrary. Clearly, after your later posts, you are not one of them, and I do appreciate you taking the time to educate the readers of this thread. Hopefully my point is clear, and certainly I understand more about it than I did before we engaged in this debate!

 

[js]

thedoc007,

Point taken. I certainly could have been more clear on the context and elaborated more. And I'm thinking I will edit the initial post in this thread to clarify. So thank you for that! Like you say, the end result of discussions like this can (and should be) improved knowledge for all of us.

But--and I don't mean to beat a dead horse or seem overly argumentative (although I perhaps am, at times)--the thing is that for almost any flashlight application, titanium is indeed a good choice, thermally. I did a very careful and thorough, and worst case scenario in my LunaSol 20 thread of the die temperature, and I would urge you to take the time to read and understand it. It's not that long and it's not that hard to understand.

See, the thing is that the two largest contributions to the die temperature of the LED are it's C/W junction rating--which is beyond our control--and the body to air junction rating, which is actually NOT a function of heat conduction through the metal body, but of heat transport from the surface due to convection of the air around it, and black body (or rather grey body) radiative cooling via the Stefan-Boltzman Law, and that is a function of a materials emissivity. A true black body has an emissivity of 1.

The conduction of the heat through the flashlight body is negligible for both titanium and aluminum. If you look through my calculations, you will see that having a titanium case means a heat drop of 0.1 C, whereas an aluminum case--which is more than ten times better--means a heat drop of 0.09 C. It's similar with the heat sink on which the LED is sitting. It's 0.68 C for aluminum. I didn't calculate what it would be for titanium, but off the top of my head, I'd say it's just 10 times worse, or 6.8 C. But no one is suggesting we make the MCPCB out of titanium. But even if you did, it would only mean a 6 degree C rise in the die temp. But the BODY? Insignificant.

So, the question is, what would we find for the case to air junction of aluminum vs. titanium? Well, I can tell you that the emissivity of polished or machined titanium is about 0.2, whereas for polished aluminum it is about 0.05. However, black anodize that bad boy and you get an emissivity of 0.77 or higher, depending on which source you reference. This is why electrical heat sinks are ALWAYS black anodized aluminum. It kicks *** at radiative cooling. But black anodize (or paint) titanium and it would also be similarly bad ***. But not as purdy.

Now, how much of the body to air junction is radiative, I honestly don't know. I'll look into it. But I can tell you that my intuition is that the convective component is at least equal to the radiative component--hence the reason why heat sinks have all those freaking fins! The air FLOW through the heat sink is way more important than anything else. I know this from painful experience! LOL! Plus, while I haven't run the numbers yet, I'm pretty sure that blackbody radiation isn't that significant at these temperatures. Add 100 C and the story changes dramatically. It's why you can FEEL a woodstove with your eyes shut. It radiates heat. So does an incan of any power because the tungsten filament is ridiculously hot. But, try as I might, I don't feel much of any radiative heat component from the head or body of any of my LED lights.

Plus, I've seen these sorts of constant on max temp in air tests before with anodized aluminum lights, and their case temperatures were comparable, I think. Maybe Don or others can help me out here.

In any case, calculating the radiative heat component from the emissivity and temperature and geometry isn't hard at all. I'll look into it and post back.

Still, I can tell you that anodized aluminum would certainly be BETTER. But probably not significantly better. I would guess something under 5 C.

So titanium isn't just good for lower powered McGizmo lights. It'd also be fine for higher powered lights. Except it'd be expensive and harder to machine, of course! LOL!

 

[fyrstormer]

I continue to be puzzled by people who seem to make it their mission to make sure the world knows that titanium is a crappy metal for flashlights. Thousands of users are not wrong. They may have different priorities, and are willing to make different compromises, but they are not wrong. Not everyone gives a damn about extra electrical conductivity that would only matter if their flashlight used 10x more power than it actually does, and not everyone gives a damn about extra thermal conductivity that would only matter if their flashlight had 10x the runtime it actually does. I, for one, care about having a flashlight that can survive absolutely anything I can subject it to without suffering so much as a scratch -- because that is a scenario that I know will actually happen.