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View Full Version : Let's talk about heat sinking...



Eandori
11-12-2007, 01:35 AM
Hey Guys,

I wanted to make a separate post to talk about this. I've seen lots of saber LED mounts that are trying to maximize heat sinking, but I believe their are some misconcepts floating around about heat transfer.

Heat Channel:
Just like electricity needs a fat wire for high currents, heat needs a thick heat channel to conduct a proper amount of heat. If you have a wire that's as thick as a pencil on both sides, but with a middle section as narrow as a toothpick, how much current can you get through it? As much as that toothpick will allow to flow. Same goes for heat. If you have a constricted section of your heat flow channel then you won't get much heat to flow. Put simply make sure that from the back of your Luxeon Star to the cooler metal part of your saber has a very thick metal channel for heat to flow.

Heatsink Fins:
I see lots of heatsinks that are intended to be mounted INSIDE a saber that have fins/blades/pins for heat dissipation. Similar to heat sinks inside a computer on the CPU. One difference here, you MUST HAVE AIR FLOW for that kind of heat sink to work. The idea behind fins/blades/pins on a heatsink is that it maximizes the surface area between the hot metal and the cooler air around it. Air is a great insulator, if air is not flowing it's probably keeping the heat inside your saber. You would be better off with a thicker chunk of metal to have more heat storage capacity. Speaking of heat energy storage...

Heat Resevoir:
Which do you think would keep your LED cooler? A quarter sized Iron chunk on the back of your LED, or a 1 cubic foot chunk of iron? Of course the chunk of Iron. Not only because it has more surface area, but it also has more space for that heat to flow. Heat is just like electricity where it moves UNTIL it's uniform in density. If you have a metal chunk with 5v applied to it and no current flowing through, then the electron density in it is UNIFORM across the metal chunk. Same with heat. If that same metal chunk is 30 degree's centigrade then no heat is flowing and the heat energy is uniform across the chunk. Now... if one side of that metal chunk was 20 degrees and a 50 degree Lux Star is placed on the other side, then you have a heat difference and heat will start to flow. But it will only flow OUT of the Lux star until the entire unit is uniform heat. So the bigger your heat resevoir is, the more heat energy it takes to make it uniform. Once your heat resevoir is large enough with enough surface area, then the LED cannot put out heat fast enough to raise the temperature past a certain point and now... you have a proper heat sink.

Heatsink Material:
Some metals transfer heat better the others. Just like some metals conduct electricity better then others. Copper is a fantastic and not super expensive heat conductor. Making your heatsink out of the right kind of metal could have big benefits.

Contact Pressure for heat transfer:
Two apparently flat metal surfaces usually don't make as good a contact as you might think. That's why pressure is needed. More pressure on a contact area forces more of that area to BE in contact. Computer CPU's and many other devices use a thermal "grease" as well. This simply fills in those small gaps so the resultant surface area between two items is increased. When you think about it, this is really going back to my first point... increasing the size of the heat channel.

Most lightsabers have...
-limited space for heat sinking
-zero air flow inside the saber tube
-metal hilts usually made of some kind of metal tubing.
-Some difficulty in mounting the Luxeon LED inside the tube.

So how can I sum this up? Here's what I'm saying would be the BEST SINK for the inside of an average lightsaber.

A copper, thick plug (shaped like a canister of Carmex lip balm), with mounting screws that can apply large pressure to the Luxeon/Heatsink contact, AND the heatsink/sabertube contact. The Luxeon now has a thick heat channel for heat to flow out the back of the luxeon star to the body of your saber. Air flows by the outside of your saber (especially when doing spins) already, but you need to make sure you are getting the heat piped form your LED to that saber body.
http://home.comcast.net/~eandori/LEDheatflow.JPG
Note the 3 mounting screws on one side, that is so that one side will have plenty of pressure between the heat sink and the saber body. The one screw on the other side is just for stability, you would not want to tighten it too much. Also note the 4 nylon screws holding down the LED. More pressure=more contact area=wider heat channel=cooler luxeon star.

I'm not just shooting from the hip, I have actually studied thermodynamics and applied it in projects and in my career. So what I wrote is not just opinion :) I drew some images of what I am talking about and sent them to Novastar awhile ago. I'll post them here probably tomorrow. Any/All discussion is welcome.

Cheers,

Angelus Lupus
11-12-2007, 07:42 AM
Very well writen and informative. I'm sure this will be usefull to a lot of people. How about making this thread sticky?

Vazan Maceu
11-12-2007, 12:52 PM
I second that. Clears up tons of doubts about heatsinking for our purposes. A great post, Eandori.

neophyl
11-12-2007, 02:26 PM
Funnily enough Ive always done my heatsinks that way. I could never see the point of finned heatsinks in a sealed tube.

Tekka
11-12-2007, 02:46 PM
Same here I always thought finned heatsinks were a bit silly without some kind of air flow. I was wondering if i could use some thermal foil or Artic Silver (thermal compound brand for a CPU) in between the heatsink and LED base to have better contact between the 2 metals. 4 nylon screws is a bit hard to do since the led holder would have to be modified a bit to fit wouldnt it?

Eandori
11-12-2007, 06:08 PM
Thanks for the replies guys, gotta keep moving the Saber community forward :)

The first heatsink I showed above would be for mounting just inside a tube. If you were using the TCSS Modular Hilt System (MHS) I would say this type of heatsink would yeild better results.
http://home.comcast.net/~eandori/TCSS_heatsink_adapter.JPG

To be more specific, I could even see running a Lux V at 1 amp continuously with that type of heat sinking. In the current TCSS MHS setup I do think the LED gets gradually hotter as time goes on since heat is not currently being transferred to the saber body fast enough. I have some glue (from a glue-gun) holding my lens mount to the LED mount, and after having my Proto2 saber on for like 20 min that glue begins to melt a bit yet the outside of the saber is just "warm".

I want to be clear, I'm not knocking TCSS products. I'm REALLY glad this buisiness exists and I'm a customer of theirs. I just want to see the heat sinks improved a bit :)

Novastar
11-12-2007, 08:00 PM
Agreed with Eandori on this one... I was speaking to him about this some time ago and... when he started saying that (essentially) a thick slug of aluminum/copper/etc. would be better, at first I was thinking: "Well... what about fins?" But... duh, then he says--"well, what good are fins without air flow"?

So I paused and then... .... (!!!!) D'OH! What was I THINKING?

Totally right: without a cooling fan or SOME kind of airflow--heat fins become essentially irrelevant to helping cool things down. Because if the air AROUND the fins is still about the same temperature AS the fins... then you might as well have more real estate. AKA: more copper/aluminum. Now if I had just stopped and thought about it it would have made sense, but... NO. I had to just... like... go too fast. So... discussing it was a good way to get totally "locked in" clear on things.

I mean... you wouldn't buy a Dual Core Pentium, give each CPU a heatsink... and then SKIP the fans... would you? Because... what's one of the most important things about a CPU...?

well... BEING ABLE TO FLIPPIN' USE IT!

Without it burninating. :)

Strydur
11-12-2007, 08:55 PM
Well if you wanted to lobby for a new design you are about a month to late considering I have about 1400 of the current design to sell now. But 1000 of them will be c11000 copper which has 2.3 times more thermal conductivity than 6061 aluminum.

That said, me and Ultra we have been putting lux V in sabers using these same heatsinks for well over a year now with virtually no problems so I really dont think its that much of a concern. For one I think it is pretty rare that people run them for more than 10 minutes or so at a time.

It would also be damn near impossible to get the heatsink made like you showed in order for them to make good enough contact with the sides of the MHS to make a difference. I agree a larger massed heatsink would probably work better but trying to lock it to a tube with 3 screws or making it friction fit is not necessary. Now if you where trying to make a heatsink for 10w or 20w LED's then every little bit would make a difference and the LED/Heatsink etc should be lapped to be perfectly smooth and as large as possible etc..

This thread does share good information. The only problem I have with it is that it sounds like you are saying the current setup does not work when it obviously does. I just dont want customers to read this and then be concerned that they are going to have heat issues.

Could the heatsink be better designed for our application? Probably
Does it need to be better designed for our current application? Probably not

Lord Maul
11-12-2007, 08:57 PM
I agree with Strydur. I had my MHS 5 watter on for 2 HOURS non stop for Halloween, and nothing bad happened. James also ran a 5 watter until the batteries ran out with the MHS stuff, with no ill effects.

Ghostbat
11-12-2007, 11:19 PM
I saw a few MHS sabers in operation at burning man for a very extended fight, I would say I was out there jumping around with a maniac and destroying my force fx blade for several hours and theirs were fine. Talk about a stress test!

'Ideal' and 'Works fine' can sometimes be pretty different things :)

Novastar
11-13-2007, 01:28 AM
I will chime in again to simply say... innovation is where it is at, with the CAVEAT that: no, most small businesses that make products cannot afford to take every single solitary "upgrade" or "tweak" or improvement... and apply it to every single product.

It is true what Eandori is saying regarding the heatsink being able to disperse/absorb heat better. Is it CRUCIAL to 98% of those building LED sabers? Absolutely not.

But I say this doesn't mean let's get on the "should Tim make 1000s of these or not" bandwagon. No. We should get on the thinking that--yes, certain heatsinking styles are better for certain projects... in this case--since Eandori is always trying to maximize his sabers (for sound... LED power... even brightness... comparison to other LED array styles... better driving via CF, etc.)... well it's no surprise that heatsinking is becoming key for him seeing as he's trying the Lux V over-driven @ 1A.

Finally, for more perspective: could saber TIPS be improved? Yes. For reasonable costs? Doesn't seem like it. So... to re-iterate (and Eandori said it too)... no one is attacking Tim's parts. We DIG the parts...

...but kudos and three cheers for innovation as well, s'il te plait!

Vazan Maceu
11-13-2007, 05:24 AM
I think that, IMHO, this thread is aimed to some extent to those who like to tinker and build their own parts. I donīt think that Eandori is stating that the current MHS heatsinks are not good, and heīs simply offering another way to do the same, based on his own experience. The quality of the MHS system is proven via the feedback in this forum, and I will check it myself whenever my order arrives (wouldnīt have bought anything from here if had a doubt, you know :wink:).

Just my peronal view on this :)

Strydur
11-13-2007, 09:40 AM
Like I said.. I am not trying to arque about any of what Eandori wrote.

From my standpoint "most" people will look at a solid lug heatsink and a finned heatsink and "think" that a finned would be better. I could probably cut the fins off our heatsinks and 99% of customers still would not notice any heat issues. From a cost perspective it would be a ton cheaper to have them made with no fins. So in the future I will definately take this all into consideration when its time to order more heatsinks.

Eandori
11-13-2007, 03:41 PM
Right, I should have been more clear. Sorry about that.

I'm have been running a Lux V in a MHS setup at 1 amp for awhile now and it DOES indeed work fine, even at the 7 watts that setup is putting out.

However, I didn't run it longer then 15 min at a time because I observed the LED was getting hot enough to melt glue from a glue gun, while the outside of the saber was just "warm." That tells me that heat was not being piped out fast enough and heat energy was definitely building up on the Luxeon LED. I have not looked up melting points for crafters glue and plastic (LED lens and holder...) but I know I don't want either of them getting that hot if I can avoid it.

So I'm 100% in agreement that the current MHS setup is more then good enough for nearly everybody at this point. Lux III, K2, no prob. From my personal experience I think Lux V at 1 amp is about the limit though. I could be wrong.

My point for making this post (and everybody seemed to pick up on it) was to get the information out there on what makes a good heat sink. I just have experience in that area and I was sharing to the community.

To the point Novastar was making, yeah I'm always pushing the limits. That's what I do and it's very fun for me. :) In my mind, the next steps for us saber builders will be mounting 3+ rebels inside a saber. Or perhaps Phillips will release a Luxeon X that roughly baselines at 10 watts and can be overdriven around 13? Who knows what the future holds.

I personally have the goal of buying a tri-rebel star and working on some optics to jam it into a saber. With that kind of LED array you are looking at 540 lumens of light output with about 10 watts of base power being used. Meaning I might be able to safely overdrive up to 12-13 watts. That's nearly twice the power output of a Lux V and I do believe some more serious heat sinking will be required.
540 Lumen, 10 watt, Tri-Rebel Star: http://www.luxeonstar.com/item.php?id=5537&link_str=1430&partno=7007-PWC-10-3

But now that this thread exists, the information on heat transfer and heat sinking is easily available to saber smiths. So we can all prepare for the next steps. After all, isn't it always more fun to make it better?

Cheers,

Novastar
11-13-2007, 03:48 PM
Awesome, Tim! That's actually a pretty cool "side effect" of having the heatsinks be more of a "slug"... I never thought about that concept, that it might actually be less expensive for you to design/create!

So, hey--there ya go... in a way--looks like (all in good time), the innovation and "tweaks" can be there... AND it can be EASIER for Tim!

I say this thread was a bloody winner for ALL. :)

But I do agree with Tim in that... a 10% or 20% or whatever percentage increase/improvement in heatsinking... won't help the MAJORITY of saber-makers for the moment... in fact, most are using Lux III. A few go to K2s but... not much heat differences there--not significant ones.

The smallest percentage (at present) of folks use Lux V, and even they do not EXCLUSIVELY use them--for many obvious reasons (sound debacles, only "lightside" colors, voltage req's).

Still... as LED tech improves, if Tim eventually converts over to the "easier-to-make" heatsink... he'll not only save money on design costs, but I could see the things standing up to the test of time as... let's say for EXAMPLE... someday in like 2010 or whatever... 10w LEDs for sabers become "mainstream" or whatever.

Wow... this was probably one of the coolest threads I've read lately. Sorry for the pun.

Strydur
01-25-2008, 12:00 PM
http://www.thecustomsabershop.com/Copper-MHS-LED-MountHeatsink-P234.aspx

Eandori
01-25-2008, 12:19 PM
Tim... you rock. How else can I say it.

I just placed a huge order at TCSS very recently and he's adding these into my order. I'm very sure that this setup will be more then enough to handle a Luxeon V at 1 amp (a 7 watt setup). I'll do tests with this when I get it and post how awesome it is online.

But you have really covered the bases here. You have a more thermally conductive material, it's thicker to support a wider heat channel, and since there is more metal there is a larger heat resevoir. Now just tighten down those nylon screws pretty good to really fasten the LED to the heat sink and BAM. Awesome setup.

DACOTA
01-25-2008, 12:32 PM
Man those new copper heatsinks are sweet, and they should remove the heat even better.
Thanks Strydur!

[EDIT] Yeah, 800 posts!

Novastar
01-25-2008, 06:48 PM
Ah, beautiful!

Probably easier to have machined, too... :) Great work Tim.