Are You On Pot????? (potting and heatsinking with epoxy and silicon carbide)

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18sixfifty
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texas shooter wrote:
Great idea thanks for sharing. I’ve got two drivers I’ve held back on. This also looks like a solution to a too thin LED shelf. Straws to protect the shelf holes then pot the under side to a more desirable thickness. Maybe cap off the underside with an Aluminum or Copper plate.

You’re welcome and I bet it would work.

I’m a junky, I mod lights so I can sell lights so I can buy more light to mod so I can sell lights to buy more lights to mod.

comfychair
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18sixfifty wrote:
How do I know it works? Well the light gets hot very fast, the heat transfer to the outside of the light is almost instant. Also the lumens stay high instead of dropping off like they would without all the extra heatsinking and potting.

So, does it not do that if you use only the JB Weld and leave out the powder?

What about potting drivers that don't generate any significant waste heat? Does it make those better, too?

I fully understand that this powder had good thermal properties, but what happens to those thermal properties when it's broken down into fine particles, and then mixed into an epoxy? Where the particles are no longer in direct contact with each other, but all have gaps inbetween filled with the epoxy? Why would the thermal properties be better than just the epoxy alone, since the heat has to jump the epoxy gaps between the silicon carbide particles to get where it needs to go?

fellfromtree
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Yeah not sold on potting dough so much as using strait copper, which does have a very high heat transfer. Like create a copper sheet to contact areas of the driver that need cooling like the fet, it should be enough. I’d be scared this would trap heat. But fifty is using copper in the potting, that may be why it draws heat and works instead of insulating it.

It’s interesting that’s for sure Smile I’m going to stick with copper and aluminum, know what works. Coolabs works great too just not good on strait aluminum. You have to solder a thin copper sheet to the aluminum pill then use the coolabs on the mcpcb and copper sheet to get the best heat transfer (imo). Then you could still replace the emitter and not worry about the tim breaking down over time.

I can’t wait for my stuff to get in really.

18sixfifty
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comfychair wrote:

18sixfifty wrote:
How do I know it works? Well the light gets hot very fast, the heat transfer to the outside of the light is almost instant. Also the lumens stay high instead of dropping off like they would without all the extra heatsinking and potting.

So, does it not do that if you use only the JB Weld and leave out the powder?

What about potting drivers that don’t generate any significant waste heat? Does it make those better, too?

I fully understand that this powder had good thermal properties, but what happens to those thermal properties when it’s broken down into fine particles, and then mixed into an epoxy? Where the particles are no longer in direct contact with each other, but all have gaps inbetween filled with the epoxy? Why would the thermal properties be better than just the epoxy alone, since the heat has to jump the epoxy gaps between the silicon carbide particles to get where it needs to go?

I don’t really know, all I know is that it works great. You could maybe ask why the guys that make arctic thermal how it works. They use it in their AS5 and alumina in Arctic alumina which has good thermal properties but not as good of thermal properties as silicon. Also Arctic alumina has been tested side by side with AS5 and it isn’t as good.

Also it is easier to work with than simple JB weld because if you add enough it becomes a putty form.

I’m a junky, I mod lights so I can sell lights so I can buy more light to mod so I can sell lights to buy more lights to mod.

18sixfifty
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fellfromtree wrote:
Yeah not sold on potting dough so much as using strait copper, which does have a very high heat transfer. Like create a copper sheet to contact areas of the driver that need cooling like the fet, it should be enough. I’d be scared this would trap heat. But fifty is using copper in the potting, that may be why it draws heat and works instead of insulating it.

It’s interesting that’s for sure Smile I’m going to stick with copper and aluminum, know what works. Coolabs works great too just not good on strait aluminum. You have to solder a thin copper sheet to the aluminum pill then use the coolabs on the mcpcb and copper sheet to get the best heat transfer (imo). Then you could still replace the emitter and not worry about the tim breaking down over time.

I can’t wait for my stuff to get in really.

When possible I do use copper but if you have an air gap you need to fill that in with something or it acts as insulation. Also you can’t use copper in places where it can cause an electrical short. There are other advantages as well. This includes making the driver shock resistant and corrosive free. Copper is great but if it’s not making contact then it’s not going to transfer heat. Also on a driver the chips are surrounded by air and that air works as insulation, potting with anything will at least get rid of that insulation. Think about putting down a sinkpad. Direct copper but unless you remove the air between it and the pill it’s going to be trouble.

I’m a junky, I mod lights so I can sell lights so I can buy more light to mod so I can sell lights to buy more lights to mod.

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For those doubting the effect of these compounds.

It is nothing new. The electronics industry has been using similar or exactly the same compounds since it became an industry.

They work. And better than just straight epoxy.

A quick google search would set you up with more litterature of lab tests from many different compunds than you probably care to read. 

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texas shooter
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It probable works. Vinz used diamond dust with his potting material and claimed great thermal transfer. A modified style might evolve where copper is bonded to the hot components. Then potted with JB Weld and Silicon Carbide.

fellfromtree
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18sixfifty wrote:
fellfromtree wrote:
Yeah not sold on potting dough so much as using strait copper, which does have a very high heat transfer. Like create a copper sheet to contact areas of the driver that need cooling like the fet, it should be enough. I’d be scared this would trap heat. But fifty is using copper in the potting, that may be why it draws heat and works instead of insulating it.

It’s interesting that’s for sure Smile I’m going to stick with copper and aluminum, know what works. Coolabs works great too just not good on strait aluminum. You have to solder a thin copper sheet to the aluminum pill then use the coolabs on the mcpcb and copper sheet to get the best heat transfer (imo). Then you could still replace the emitter and not worry about the tim breaking down over time.

I can’t wait for my stuff to get in really.

When possible I do use copper but if you have an air gap you need to fill that in with something or it acts as insulation. Also you can’t use copper in places where it can cause an electrical short. There are other advantages as well. This includes making the driver shock resistant and corrosive free. Copper is great but if it’s not making contact then it’s not going to transfer heat. Also on a driver the chips are surrounded by air and that air works as insulation, potting with anything will at least get rid of that insulation. Think about putting down a sinkpad. Direct copper but unless you remove the air between it and the pill it’s going to be trouble.

That makes sense. Can give it a try.

eas
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comfychair wrote:

18sixfifty wrote:
How do I know it works? Well the light gets hot very fast, the heat transfer to the outside of the light is almost instant. Also the lumens stay high instead of dropping off like they would without all the extra heatsinking and potting.

So, does it not do that if you use only the JB Weld and leave out the powder?

What about potting drivers that don’t generate any significant waste heat? Does it make those better, too?

I fully understand that this powder had good thermal properties, but what happens to those thermal properties when it’s broken down into fine particles, and then mixed into an epoxy? Where the particles are no longer in direct contact with each other, but all have gaps inbetween filled with the epoxy? Why would the thermal properties be better than just the epoxy alone, since the heat has to jump the epoxy gaps between the silicon carbide particles to get where it needs to go?

For the same basic reason its faster to drive your car to work 20 miles away, than it is to walk, even though you have to walk from your front door to your car, and from where you parked the car to the front door of the office. For that matter, its why having more metal in the heat conduction path is good for heat dissipation, even though the heat still ends up being transferred to the air.

I’m thinking of trying this with some sort of silicone as the binder so I can remove it. I think a mix of grits is optimal, though I don’t know the optimal mix. If it is all fines, then there will be a lot of binder between all the fines to hold them together. If it is all coarse, then there will be big gaps filled with binder. With the right mix the coarse stuff should be packed as tightly as possible, with finer grit filling the gaps, and then even finer grit filling the remaining gaps, etc, and just enough binder to keep it together nicely.

I guess the way to do it is start with a known volume of coarse, then add a finer grit until the total volume starts expanding, which means the gaps are filled. Then add an even finer grit until the volume just starts expanding again, etc.

BTW, According to its MSDS, JBWeld is 5-10% powdered iron. They claim it doesn’t conduct electricity, but it sounds like it might conduct, slowly, under some conditions, or at least some people on the Google think it may have added slow short to some of their circuits.

scottyhazzard
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Here you go, Lapidary Diamond a couple of large and small grit sizes to help fill in the space. I have lost the link to the research document but lapidary diamond is synthetic and because of the structure of its crystal being a tad bit different from real diamond, it conducts heat better than real diamond. (At least the synthetic diamond used for the engineering paper) I was going to try but did not have a good recipe for the epoxy, until now…

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DavidEF
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scottyhazzard wrote:
Here you go, Lapidary Diamond a couple of large and small grit sizes to help fill in the space. I have lost the link to the research document but lapidary diamond is synthetic and because of the structure of its crystal being a tad bit different from real diamond, it conducts heat better than real diamond. (At least the synthetic diamond used for the engineering paper) I was going to try but did not have a good recipe for the epoxy, until now…

Have you gotten a chance to try it yet? I was looking at some materials’ thermal conductivity properties here and it seems to me that maybe a high concentration of diamond in epoxy might be a better heat conductor overall than pure copper! Do you think that’s possible? Especially, if it’s true that the lapidary diamond is an even better conductor than real diamond, it should do quite well if you can get enough diamond mixed into the epoxy. What do you think?

Edit: For example, if diamond has a thermal conductivity of 1000, and epoxy is negligible (0.35 though, if ya want to know) then a 40% mix would have a thermal conductivity of 400, right? Or am I doing the math wrong?

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comfychair
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How much more light comes out the front, comparing a hot driver (one that truly needs cooling) potted with plain JB Weld vs. same driver potted with JB Weld + diamond/silicon carbide?

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Who's got the time and resources to answer another innocent comfy Q? Smile Sure is a simple question... Wink

I'm assuming this JB Weld and fine grit silicone carbide harden as much as JB Weld itself?

comfychair
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If it hasn't been tested there's no way to know if it helps or not. I'm not a fan of doing extra stuff that has no benefit, sorry but that's getting too close to superstition for my taste. :shrug:

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I'd like to know a whole bunch of things of aluminum vs. copper, AS5 vs. toothepaste, but the comparative tests at the detailed and controlled level for our very specific applications would be a huge under taking, so, we have to fallback to theoretical premises.

I'd love to see some tests done on the Convoy S2 modded with triples and actually see what, if any, the RMM aluminum vs. copper spacer, but the tests would be insane - can't just do a simple output test, you'd have to test over time with typical batteries/

comfychair
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The critical point being overlooked is the amount of surface area vs. the amount of heat that has to be shifted. Why is the joint at the LED's thermal pad so critical? Because it's so small. But if you look at those wonderfully misleading 'thermal conductivity' charts, you see that solder in general has really awful thermal properties, and some is even worse than awful (lead free vs. the worse 63/37). But then... if these thermal conductivity numbers are so important, why then is there zero difference in light output between the thinnest possible layer of the best lead free solder, and an extra thick layer of the very worst 63/37 solder (like the extreme example of a non-direct thermal copper board with the dielectric layer gouged out)? 

Because once you pass a certain level there are no gains to be found no matter what material you use. It's not that solder is good, it's that the dielectric layer inside the MCPCB is so bad. Even bad solder is enough to carry the heat, but even the best dielectric layer isn't (even the fancy boards with the DLC dielectric aren't as good as a layer of bad solder). Same goes for thermal pastes, and aluminum vs. copper vs. brass. In potting drivers that are trying to set themselves on fire, any decent material (so, a real epoxy and not Fujik Bathroom Caulk) has enough surface contact to carry that heat load.

 

This belief in adding exotic stuff where it's not needed because finding out if it does anything is too much work is like saying "I always cross my fingers and look both ways before crossing the street and I've never been hit by a car, therefore crossing your fingers makes you immune to being run over."

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I had a light that the lumen output would drop to zero when the negative lead would desolder itself.  Added some very common, non-exotic silicon carbide in the mix because what the hey.  Why not put in the best cheap stuff I know of while I'm going through the trouble of potting.  Sure expoxy or silicone may have been good enough.  That's the great thing about a hobby.  No one to answer to but myself.

scottyhazzard
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ImA4Wheelr wrote:

I had a light that the lumen output would drop to zero when the negative lead would desolder itself.  Added some very common, non-exotic silicon carbide in the mix because what the hey.  Why not put in the best cheap stuff I know of while I’m going through the trouble of potting.  Sure expoxy or silicone may have been good enough.  That’s the great thing about a hobby.  No one to answer to but myself.

+1 on the hobby sentiment.

Also, never discount the immeasurable value of cool 8) I think multiple grit sizes of lapidary diamond and JB Weld would work better than just JB Weld for thermal potting. I don’t think it would be equal to copper but it would fill in the negative space well. And it would be cool.

I have not played with it yet as I have too many unfinished projects in the works. I am entertaining the idea of making a lantern for camping out of Portland cement and lapidary diamond. Useful and quirky at the same time.

"Those who hammer their guns into plows will plow for those who do not."

scottyhazzard
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Is there a way to mold JB Weld?

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ImA4Wheelr
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Mold JB Weld?  Here (In Post 8 ) is a pretty cool example of that.

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> mold JB Weld?
Yep, multiple hits in google on ways to do that

> Jefferson
Many have tried to cite that quote. Must’ve been someone else.

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