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,
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,