DIY, Budget, Reversible Potting Recipes (Sorry for big pics)

[ImA4Wheelr]

Sorry guys. I can't seem to get the pictures to shrink.

Here are 2 DIY potting recipes. They have not been tested for safety or effectiveness, but they should be quite effective. The first one seems to be doing its job in a couple high power flashlights I have built. One driving an MT-G2 at 11 amps with 3S KK ICR cells. They were created in search of a low cost way to reversibly pot my drivers. I have not tried the second recipe yest because the first one is so easy and fast with no curing time.

Very easy, clean, low cost, no wait recipe:

Ground Silicon Carbide (I think 400 Grit would work good)
Duct Seal

The Duct Seal has a flash point of 450F, but I figure if the temp in my light or laser gets anywhere near that high, I'm already having bigger problems.

Silicone Recipe (Haven't tried yet):

Ground Silicon Carbide
GE's Silicone II Caulk

GE Silicone II's are neutral cure silicone rubber compounds. Don't uses GE's Silicone I's as they are acid cure and bad for electronics.

Mix to desired consistency. For duct seal recipe, I like to mix as much silicon carbide in as I feel the it can take and still stick together. If I want it more pliable, I use less silicon carbide. For removal of the first recipe, pull off what you can by hand and then use an alcohol soaked Q-tip (cotton swab) to clean off the residue and potting stuck in hard to reach places.

Here are some very unscientific and some what inconclusive torture tests of the first recipe. Here is a product package picture of the binding ingredient.

It seems like clay. In my experience, clay tends to "melt" and run even at moderate temperatures, let alone at a couple hundred degrees Fahrenheit. Before I talk about heat, I need to say that this stuff is amazing to work with. Like clay, it's pliable yet holds shape. It's very easy to form over a driver components and into a pill.

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.

If anyone has their own recipe, please feel to share here.

 

[COMMANDR]

Sounds good for a reversible potting compound. I like the fact that at a future
date you can get back into the build and troubleshoot or upgrade when needed.
Have you measured the electrical conductivity of the potting???
How well does it set up or harden, will it stay in place like a glue?

I like Arctic Alumina™ Thermal Adhesive but it is permanent and irreversible.
------------------------------------------------------------------------------------------------------------
Characteristics:
Arctic Alumina Adhesive uses a layered
composite of aluminum oxide and boron nitride.


Temperature range:
- 40C to >150C (Bond strength is slightly weakened at temperatures below 0C due to crystallization.)

Pure Electrical Insulator:
Arctic Alumina Adhesive is a pure electrical
insulator, neither electrically conductive nor capacitive.

Compliancy: RoHS Compliant.

Precaution:
Arctic Alumina Thermal Adhesive is a permanent adhesive.
Components you attach with Arctic Alumina Thermal Adhesive will stay attached forever.
------------------------------------------------------------------------------------------------------------

I have heard that is you mix it with less harder that it is somewhat reversible.
I haven't tried it though, mileage may very. :>)

 

[ImA4Wheelr]

I've tried to measure electrical conductivity, but I get no reading. Just like holding the probes in open air. I just have several different average DMM's though. Nothing extra sensitive.

It's supposed to never harden and stay flexible "forever". I've have some oil base clays for decades and they are still pliable today. This stuff seems similar in characteristics, except oil base clays will liquify when they get hot.

It's sticky, but reduces in stickiness as you cut in Silicon Carbide. Takes a whole heaping lot of SC to make it not sticky though.

Silicon Carbide is supposed to have a thermal conductivity of 200 W/m.K, Aluminum Oxide is supposed to be 30W/m.K. I don't know the thermal conductivity of Duct Seal or of boron nitride.

What I do know is that this stuff is cheap and easy and has to be multitudes better than just air.

 

[rhd]

What I would love, is to find a cheap two-part, quick set, thermal epoxy, like arctic alumina or arctic silver, but perhaps not necessarily as fantastic on the thermal transmission end. Basically, a cheap two-part epoxy that stands up to heat better than the $1 dollar store stuff, and dries a clean color.

I find that I end up using arctic alumina as an epoxy even for tasks that might not really warrant the expense. In fact, I use it fairly frequently just because it's non smelly, dries white, can handle getting hot, and has a nice texture. It's just so bloody expensive.