Mag Thermal Profile

It's not a flashlight but have everything to do with almost everyone of us.

I promised some people a while back some thermal modeling of our beloved Mag mods, well here it is.


Case #1 - PSS (Modded Hotlips/Osink) - Single Luxeon III
Nothing special here


Case #2 - PSS (Modded Hotlips/Osink) - Hi-Output Single Luxeon V
Worst case scenario for a single Luxeon, LuxV @ 1.2A (~8.5W) ... well for normal people. I don't count unnerve's LuxIII @ 3A the typical case now.



Case #3 - PTS-D - 3x LuxIII @ 1.0A each (~10W Total)
This could handle the 10W power source but it's pretty much at its limit.
The same would apply to any "disk" profile heatsink. It's just not enough height to effectively transfer the heat out radially.


Case #4 - PTS2-D - 3x LuxIII @ 1.0A each (~10W Total)
10W it's not much of a problem. One of the key feature, E-Can, actually have a major negative effect on the heat transfer. If the E-Can is not present the thermal transition will be much smoother and w/o a localize hot spot in the rear.


Case #5 - PTS2-D - 3x LuxIII @ 1.0A each (~10W Total) with standard Mag head
Notice how all the heat is rushing to the rear.


Case #6 - PTS2-D - 3x LuxIII @ 1.0A each (~10W Total) with grooved Mag head
Surprise! So am I, let me attempt to explain. This model deals with stagnant air where the heat transfer coefficient for natural convection is only 1-50 W/(m^2K), in our case 5 W/(m^2K) While force convection will be dozens of times higher. When conduction (hand) is greater than convection (air) adding fins is a waste. It only create localize hot spot. However, if there is some air flow thru these fins it greatly help with the cooling.


Case #7 - PTS2-D - 3x LuxV @ 1.0A each (~21W Total) with grooved Mag head
Insane case for those who wish to drive 3x LuxV @ 1.0A (~21W). You better put a dimming control circuit in that thing.
I'm not even gonna attempt the 4xLuxV scenario.


Case #8 - PTS2-D - 3x LuxIII @ 10A each (simulating ~100W hotwire mod) with grooved Mag head
Since most sources indicates that 90% of halogen/incandescent light are infrared so only 90W of power is applied to the model. Forget about burnt marshmallow; watch your roast skins instead.


* Pay attention to the temperature scale; don't just look at the beautiful colors now.
* Model values are 10-20F less than the actual values that I've seen in real time test w/o hand contact as a sink.
* Case 1-4 does not utilize hand contact as a sink temp, where case 5-8 does.


=== Assumptions ===
- Maximum hand contact surface temp = 110F / 43.4C
Biggest assumption! No matter what's the light source, you 97.8F hands will attempt to maintain 110F.
- Edge Stablelization temp = 120F / 48.9C
2nd biggest assumption. This is valid for 7-9W w/o hand contact. You actually have to perform a runtime test to get this number FOR EACH TEST CASE.
- Ambient stale air temp = 70F / 21.1C
- Natural Air convection coefficient = 5 W/(m^2K)
- All mating surface are flushed/merged
- Does not account for radiation or convection in pockets
- Ignored all heat generated by the batteries system

* If there is any major flaws in these assumptions please let me know and I'll update the model.


=== Conclusion ===
It's amazing the affect of liquid cooling (your burnt hands) on the system. It's much more effective of a cooling mechanism than the air cooling.

Realistically you can put a 500W power plant in a Maglite but as long as it's for "short" duration then it's relatively safe. Great examples of these are bwaites' USL & cmac's "the Torch". This is because it takes some time for the heat to saturate all the components (reflector, batteries, switch, etc).

It's when modders pushing the limit to increase the overall output AND runtime that's when it's a problem. Practicality and safety are sometime placed in the back seat.

I hope this information can help future generations of Mag modders.


=== Side Note ===
It's amazing how much PC have progressed over the years. Back in the days @ RPI, it took our IBM RISC station (latest & greatest @ the time) over 40 minutes to generate the results with coarse meshing on ProE (or was it UniGraphics :thinking. Nowadays, my 16m old PC can do ultra fine mesh within 10 minutes

But the 100W incan doesn't to sink anywhere near 90W of heat. Most of the infrared actually exits via the front of the flashlight, right?

Good point paul.

The amount of heat sink should be only the sum of the following
a) 17.2% (90% infrared * (1 - 92% reflectance)) for the reflecting surface
b) 90% of the bulb ream radiation.

This will make it significantly less.
Interesting question then becomes how many watt of heat (infrared radiation) can the stock plastic lens take.

I'll try to update this result the next time I run the model.

Modamag - what thermal program did you use? I notice that you mentioned ProE, I use ProE everyday just not for thermal and only for the occasional stress analysis. Anyway, what's the chance of doing a comparison of a head with and w/o fins using the same light source and output, say 35W?

Thanks

Hey Modamag, good of you to spend the time to do these. :thumbsup:

Outstanding :rock:

Thanks much for the trouble to get these done and sharing them with us

Will

Great Stuff!

Just one quick question, how long were the lights run for them to reach these temperatures?

Nice Graphics, Just wondering if these are built using Photoshop or a result of Infrared Heat sensitive cameras?

because, if using commen sense... for
Case #3 - PTS-D - 3x LuxIII @ 1.0A each (~10W Total) and
Case #4 - PTS2-D - 3x LuxIII @ 1.0A each (~10W Total)

since the luxeons are distributed, how come the heat is being max at the center of the slug? the high temprature zones should logically be at the periferi... not the center....

If these graphics are a result of some sort of 'simulation' from a model, perhaps you should relook at the case 3 and case 4.... may be you have assumed all the three emitters located in center?

NewBie & some others have modified simple Digital camera's (by removing IR filters) to generate simple IR Sensitive Cam, they really show the heat generation to a great extent.... in seconds...

more accurate way would be run the luxeons at the said currents and then take a 'picture' ....

So for us laypeople do your findings mean that grooved heads actually do less to cool than more?

Grooving a mag head is then more of a asthectic mod then practical unless there is air moving across the fins?

jwl: The program I currently use is SolidWorks 2006 SP2. If you use ProE you can get the thermal analysis with the Pro/MECHANICA package. Here's a nice tutorial from Carnegie Melon. I'm not too familiar with it. I used ProE & Unigraphics way back in the college & internship days.

As for a 35W comparison fins vs w/o fins, no problem. What light, Mag? I assume 35W sink ... or do I have to calculate/estimate the % of heat sink based on reflector size/coating/etc.

If you're just interested in a Mag head then here it is.



If not then send me your drawings and I'll try to perform the analysis based on some (my) common sense boundary conditions.
This offer is valid for any CPFers given that I have the time.

hotbeam: Nice to see you back my friend.

flash: This is steady state analysis. Basically it means you have to leave the light on for a long time for everything to reach equilibrium.

ViReN: It's solid modelling (simulation), no graphics or picture. The result however is pretty close to my own temperature sampling (see PTS original test). To get more accurate modeling, "we" would need to perform the test manually with multiple probes then rerun the simulation. I'm interested but I don't know if others are or willing to participate.

The thermal source (3W/5W/etc) is applied uniformly accross the surface. This is where the Luxeon emitter/star makes contact with the heatsink. The hotspot is centered because at the center the heat can't get out as quickly as the edge. Remember this is steady state analysis. Transient cost too much computing time.

I'll leave it up to NewBie and other to provide the actual photographic data if they choose. :nana:

Mirage_Man: Grooving is great for:
1. aesthetics
2. lights that are not stationary.
3. great for cooling IF the fins are in a vertical position to allow more free convection surface.

They are not good for cooling of our maglite if you put them in a stationary location sitting on it's tailcap or worse sitting face (head) down :heheh:

Hi modamag, I am not an engineer -- just a lowly physicist by training . I am quite interested in your simulations. Are these solutions to the heat diffusion equation? If so, what are the boundary conditions? Do you assume a certain loss of heat at the edges due to convective losses? How do you estimate this?

Hi Sawtooth,

You're too humble :blush:. It's the physicist that gave us all the theories for our engineering applications.

The boundary conditions are as follows.
1. Free convection at all surfaces with different air temperature depending on which region. 70* outside, 90* between the heatsink & the reflectors, 100* between the switch assembly & the heatsink.
2. Constant & uniform power source where the Luxeon makes contact with the heatsink.
3. The lowest point of the MagD head is at a constant 110F due to the fluid conduction cooling of your hand.

To get the actual thermal coefficient you have to take into account too many things, air condition, breeze, moisture ... too many variables. I just simplified it to 5 W/(m^2K) for sanity sake.

There are definitely alot of assumptions in the model so take this results with a grain of salt. Don't based your 1 million $ design off this.

=== Assumptions ===
- Maximum hand contact surface temp = 110F / 43.4C
Biggest assumption! No matter what's the light source, you 97.8F hands will attempt to maintain 110F.
- Edge Stablelization temp = 120F / 48.9C
2nd biggest assumption. This is valid for 7-9W w/o hand contact. You actually have to perform a runtime test to get this number FOR EACH TEST CASE.
- Ambient stale air temp = 70F / 21.1C
- Natural Air convection coefficient = 5 W/(m^2K)
- All mating surface are flushed/merged
- Does not account for radiation or convection in pockets
- Ignored all heat generated by the batteries system

Modamag - We have ProE & Pro/Mechanica (Stress & Motion but not Thermal) and I doubt I could convince them to purchase it. Below are the spec's of the light I have. I'm trying to decide if it is really worth the expense to fin the head or just do it for the cool / custom look (harder to justify).

Maglite 6D
UCL lense
FM2 LS Cammed aluminum reflector
Pelican #3854 24W Incandescent bulb driven to ~31W
Stock switch & post

I'm guessing that you have to input some time variable to get the results, if so what time did you use? If you don't have a model of a reflector (though I imagine you do) I could model one. Sorry I can't be or any assistance on calculating / guessing the % of heat sink, I would if I could.

Thanks in advance.

The model is for steady state. So timing is infinite. If I was to guess the time it would take a 35W to reach within 90% of this model I would say somewhere around 20-25 minutes.

I don't have any of fivemega's reflector that were produce within the last 12 months. I can ask one of the members around here and recreate if really necessary.

I can get a close enough estimation. Just need the kids to sleep well for couple hours and to sit down with a math book

Just another newbie question, for each of the diagrams, the hottest parts on in the diagrams vary from 114 degrees to 133 degrees. I'm guessing that the actualy LED operating junction temperatures would be higher. But is there any means of determining exactly how hot the LED's themselves will run? Because at the end of the day, it's all about maintaining the life of the the LEDs.

Very nice!

At what rate of air flow would the fins start kicking in to cool the light? Apparently these are good for bike lights, but is walking in still air perhaps enough? I know this also depends on the ambient temperatures, but given your assumptions. So it appears the heat is blocked from conducting to the rear of the head by the air spaces in the grooves? So basically it's a double whammy, since the fins are removing thermal mass as well?

Thanks

modamag said:

<Snip>
ViReN: It's solid modelling (simulation), no graphics or picture. The result however is pretty close to my own temperature sampling (see PTS original test). To get more accurate modeling, "we" would need to perform the test manually with multiple probes then rerun the simulation. I'm interested but I don't know if others are or willing to participate.

The thermal source (3W/5W/etc) is applied uniformly accross the surface. This is where the Luxeon emitter/star makes contact with the heatsink. The hotspot is centered because at the center the heat can't get out as quickly as the edge. Remember this is steady state analysis. Transient cost too much computing time.

I'll leave it up to NewBie and other to provide the actual photographic data if they choose. :nana:

<snip>

Click to expand...

modamag said:

The model is for steady state. So timing is infinite. If I was to guess the time it would take a 35W to reach within 90% of this model I would say somewhere around 20-25 minutes.

I don't have any of fivemega's reflector that were produce within the last 12 months. I can ask one of the members around here and recreate if really necessary.

I can get a close enough estimation. Just need the kids to sleep well for couple hours and to sit down with a math book

Click to expand...

I still Have one query... I may be wrong.. but please explain....
In Stable State, (do you mean Luxeon's not reciving any current?)
if in stable state, luxeons recievingcontinious current... i.e. generating heat continiously... that means.. there have to have 3 hotspots(similar to 1 and 2 case) apart from the center hotspot as shown.

how can temprature right next to heat generator be low as compared to center of core?

i still believe that the steady state shown is for luxeon's not generating heat...

by saying thermal source applied uniformly.... does it mean that you are superimposing 3+3+3 = 9 Watts of heat generated applied across whole surface of heat sink(not actual)? or there are 3 equal heat generating sources at 3 symmetrically placed locations on the heat sink(actual condition)?

please reconsider the fact that temprature cannot be low as shown if Luxeon's are ON and generating heat .... especially as compared to the center... there will be 3 hotspots apart from the center hotspot (in the section may be only 1 through and 2 partialy may be seen)....

flash: I believe evan have some way of calculating the LED junction temperature. LEDs will produce basically the same amount of heat base on the Vf & drive current. The problem is how to quickly remove that heat so there is no buildup.

Bogus1: One of these days I'll do a complete transient analysis with fluid condition and find out.

ViReN: You are absolute correct with your observation. In reality there should be three hotspot where the Luxeon emitter are located. But if the star HS is doing it's job properly that HS will not be very prominent.

In the 3x3W model I "simplified" the problem by applying 10W of uniform heat accross the entire surface where the stars meet the HS. A more accurate way would be to get a thermal profile of the star base (not the LED base) and apply that to the HS.

At work we do have some SensArray probes [/b] for wafer temperature. I'll check to see if it's possible to integrate it between the stars and HS to get some additional data.

Modamag, this is the first time I have seen this thread as I have mostly been away from CPF for the past year or so. My hat is off to you, my friend, Great work.

Welcome back Doug. We missed you.