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

What grit of silicon carbide powder do you guys use?

I use one that is a mix of like 220 and 4xx. I have some 1500, but I don't use it because it goes airborne easily and I don't want to inhale it.

I noticed reading up on Arctic silver 5 that they actually use different grits in their mix. I’ll be ordering more silicon carbide soon in various grits. Makes sense to mix the smaller particles with some larger depending on what you are using it for.

Then there is this……http://www.pflexpro.com/ At the top of his page Flashlight 101, then to the left the list “Potting”

http://www.pflexpro.com/

Crazy question…would sensor safe RTV or silicon and the above silicon carbide make a softer easier to remove potting for say drivers in case you needed to “peel it off”

That is cool and they are right on about the potting. I also like the copper ring they use for the outside of the drop in. That is exactly what I do and it works. I can’t remember who it was on here that suggested that instead of the aluminum foil trick but they were sure right. Easy to take on and off and works perfectly. I have thought about going the extra yard and even filling that in more with potting compound but then it would no longer be a drop in at all. Still it would have some advantages depending on how hard you want to push it. I built a couple 502B’s with 5 amp dimming drivers and was tempted to pot the drop ins so they would bet even better thermal transfer. But like I said, they would no longer be drop in’s then. I did of course pot the drivers anyway.

I didn’t know silicon carbide, a mineral, was such a good thermal transfer material.

any material other than air is much better at moving/absorbing heat, especially stagnant air inside a pill that isn’t moving…air does “ok” if it is moving, but if it is just sitting there it really does no good at moving heat away from an object

http://www.ioffe.ru/SVA/NSM/Semicond/SiC/thermal.html

with mixing epoxy and silicon carbide, it still averages out much better than stagnant air

I actually put a blob of silicon over the chip on my TP4056 charger module…what I noticed was that instead of the chip getting so hot you can’t touch it at 1A draw, the entire board is now quite warm but not crazy “burn your fingertip hot” when air was the only medium to move the heat from the chip (sure if they had it soldered to a surface mount vias or whatever it would be better but the IC in that package pretty much just sits above the board and doesn’t transfer heat very efficiently), sure there is the issue of it maybe keeping the heat in, but when it diffuses the heat over a larger area, and allows the heat to soak away into the board it lowered the temperature (I’m sure there is a laundry list of calculations and maths involved…but it breaks my brain)…all fine and dandy until you put the daggum battery in backwards (no reverse polarity protection = kaput IC…dangit)
That is pretty much my real world experience with conformal coating/potting/heatsinking…

It’s actually really interesting stuff. It’s man made now and it’s considered a ceramic. It has very high thermal conductivity. On the chart I was looking at it was the best of the ceramics by quite a bit. I can’t find the chart right now but this site is pretty good shows it’s properties. Really neat stuff.

It probably would, Also I know that you can coat the emitter first with wax so that it will peal off. Comfychair does that I think. I would do that if I had an application where I was going to be messing with the driver later. But for me, I’m done once I finish. Some people of course want to be able to flash the driver later to change modes and stuff like that.

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.

Wow, this is really helpful - 18sizfifity, thanx! I really should buy some silicone carbide and whip up a batch. This just may solve some problems - I'm thinking the hot J18's I got with the beast drivers, most of which out there seemed to have died, but I use my J18's very sparingly...

Thanks Tom and I never got to try it on that driver because mine died. It’s one of the first things I thought of when I started using this. Dang wish I had used in on that driver. Especially when I killed one driving 3x MT-G2. The light was sweet while it lasted and if I had potted it well it might have lived.

You’re welcome and I bet it would work.

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?

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 :slight_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.

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.

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.