Don't use that HD heat sink compound. It's messy and leaves a very hard to remove residue. You don't see the residue, but it really interferes with soldering. I only use that stuff when I absolutely have to. When I do, I use as little as possible.
Sorry, please disregard. That’s exactly what I did and exactly why! Geesh! Getting old…
Garry, I haven’t used any of the Permatex RTV products for flashlights but I have used just about all of them over the years on motorcycles, automobiles, and tractors. The blue is my least favorite, it still smells like vinegar and doesn’t seem to ever dry 100%. I see that the box now says “new low odor formulation” so maybe they’ve changed things since I’ve used it last. My favorites are the Ultra-Grey, Red High-temp, and Ultra-Copper. The Ultra-Copper is supposed to be the highest temperature rated; if I remember correctly it doesn’t really contain copper and is non-conductive.
I don’t know how well it conducts heat, but for general use the GE Silicone II All-weather rated is awesome stuff. It dries smooth, sticks well, and stays pliable year after year in –10 F to 110 F weather. I can’t remember if it has the acetic acid/vinegar smell or not.
Thanks for the info RMM!
-Garry
This stuff should work okay. It's used for sealing ducts and electrical.
It's sticky, moldable, doesn't dry out, non-toxic, less than $3 a pound. It's also really good for catching pellets from an air gun.
If you try to find it, it's not in the hvac section, it's in the electrical section where the wire connectors are.
Hmm, does it work for pulling heat away?
-Garry
It should. It doesn't seem to have air in it.
Air is a great way to remove heat, just make sure it is moving. Thermal conductivity of compounds and all is great, but after the sink is full, it has to be “drained” Automobiles, motorcycles, computers use moving air. So far, flashlights have not utilized moving air.
BTW, here is an article comparing thermal compounds. Almost anything will work, some better than others of course. The MOST important thing is that something is used rather than nothing. Check out this chart carefully, I think it is rather humorous and sobering as to how well crazy compounds like mustard, creamcheese and toothpaste work. Heck, mustard works as well as Thermaltake TG-1
http://www.hardwaresecrets.com/article/Thermal-Compound-Roundup-January-2012/1468/5
The local bars here seem to do an excellent job of getting drivers potted… :party:
Thanks dchomak. I'll check out that chart. I studied quite a few before creating this thread. That and electrical conductivity charts.
Yeah, the potting compound's purpose in my case is to get the heat to the body of the flashlight so that the flashlight can get the heat to the air. I'm hoping this recipe of two cheap, readily available components, does the job. If it works good, I owe Texaspyro a big thank you.
Yes!, and then the heat comes along and throws em in the cooler! :bigsmile:
Leaftye, in post 84 suggested this stuff. I initially discounted it as I have had bad experiences with clay and heat. In my experience, clay tends to "melt" and run even at moderate temperatures, let alone at a couple hundred degrees Fahrenheit.
Well, it's been a long winter and I have not really had any opportunities to use the potting recipe I decided on above. The Silicone needs a decent temperature to cure at and I don't want that odor in the house. So, I decided to check the stuff out and do some very unscientific torture tests.
It seems to do pretty good. Before I talk about heat, I need to say that this stuff is amazing to work with. It's like clay, pliable, yet holds shape. It would be very easy to form over a driver components and into a pill, but yet be easy to remove.
First, I subjected to heat up to about 450 degrees for about 5 minutes, but took plenty of time getting it up to that temp. Probably about 15 to 20 minutes. Surprisingly, it didn't get runny. It did deform, but not anything like I expected.
Early in test, a few hundred degrees in to the test, and after test (flipped over). You can see the place it sat on the parchment paper during the test. It was just as pliable after the test. Didn't feel any different.
I decide to do another test to see if it would heat and cool faster with silicon carbide mixed in. I made 2 patties. One, pure duct seal. The other, I mixed in as much silicon carbide as I could before the stuff seemed to be getting to a point it would not hold together. I then subjected to heat again, but this time I threw it on a pre-heated hot plate (around 400 degrees). I tried to test to see which one heated up faster and which one cooled off faster. Sometimes the pure duct seal changed faster. Sometimes, the silicon carbide mix changed faster. No pattern emerged. Maybe this stuff has a lot of fine sand in it and conducts heat well on its own. The patties were too small for an effective test. The big news is that the silicone carbide mix did not appear to change shape at all.
Silcon Carbide mix on the right. Both were the same shape before the test started.
Looks promising. Way easier that potting silicone and waiting for it to cure in a pill. I need to test to see if it move heat well, but I may just go ahead and start using the stuff for now. Thanks Leaftye. 
Very cool!
-Garry
If by 'that odor' you mean the vinegar (acetic acid) odor, you have the wrong silicone. The acid in that one will attack electrical components. You would want the odorless silicone made for electronics.
http://www.americansealantsinc.com/388-electronic-grade-silicone/
http://www.amazon.com/Clear-Electronic-Grade-Silicone-Squeeze/dp/B0063U2RT8
Thanks for the info Gj. I never opened the silicone to find out what odor it has. I just didn't want anything curing in the house with my family breathing what ever it may be off gassing. I was in a hurry (as usual) and used "odor" as a shortcut. As documented above, I researched and identified an electrical component safe silicone that you can purchase off the shelf.
Are you going to test using the duct seal by itself versus duct seal with added silicon carbide?
-Garry
Sorry, I didn't re-read the earlier posts. Forum overload. 
No reason to apologize Gj. I do that all the time too. There just isn't enough time to memorize or read (or reread) everything in every thread.
Garry,
Not sure when I will do more testing. I don't see using the duct seal by itself as viable. It's a little sticky and I don't like that it may ooze around with heat and time. Adding the silicon carbide makes it not sticky at all and hold it's shape. I'm sure it will deform some over time, but I don't think it will be problematic. Here are the tests I want to run:
- Check for electrical conductivity. Not sure how well I can do that with just normal DMM's.
- Check for thermal conductivity. I'm sure it won't compete with the high end products, but I'm hoping it's a big improvement for a fraction of the cost. Plus it's easily reversible.
What grit size SiC do you use/think is best?
I don't have much of an opinion on that right now.
400 to 600 grit sounds good to me. I purchased a half pound of 120/220 and 1500. The 1500 looks way too fine. I'm hesitant to use the 1500 because I have a beard and can't get a good seal with a mask. I used the 120/220 mix in the above test. Seem like it is good enough, but finer would probably make a smoother product (and more surface contact). Supposedly, a mixture of fine and medium will give a tighter matrix.
A half pound seems like it could pot a lot of drivers.