Is Arctic Alumina conductive??

I thought it was some kind of epoxy with aluminum in it, which means it would conduct electricity, but see in some mod descriptions that it might not be that way.

I want to put an R2H Luxeon into a #222 screw-base incandescent bulb shell and direct drive it from 1x123. I'm trying to figure out what to use as a heat sink. The host light would be a Tekna Splash-Lite which is a lightweight plastic light, so it doesn't have much heat sinking capability of its own, though the reflector and retaining ring do hold a little heat.

Can I fill the bulb base with Arctic Alumina and not short the LED leads with it? Will that be enough heat sinking for the underdriven R2H? I've been running the light with a K222 600 mA krypton bulb which does get pretty warm in there.

never tried it on flashlights, but it's supposed to be non conductive. Might be a good idea to use it to attach the heatsink to the light on a mag mod, actually.

http://www.arcticsilver.com/arctic_alumina_thermal_adhesive.htm

You can pot electronic components with it, so I doubt it is very conductive at all. Not so with Arctic Silver though...

Jeez, that stuff is 7 dollars for 5 grams! It says you get 3 cc of adhesive. That's enough to pot about two screwbase or PR-base flashlight bulbs if I'm really lucky. Is this the right stuff to be using? Is it what they likely use in gizmos like the Everled? I guess it's not too expensive for a high class Luxeon but it messes up the economics of any less exotic bulb mods. Anyway, thanks!

Its pretty pricey stuff to use. /ubbthreads/images/graemlins/frown.gif As Mr B says, potting it on circuits is fine,

Yeah, I'm wondering if it's the best possible stuff for this, and also whether there's anything cheaper that might not be quite as good. I guess for real pricey stuff, there's the diamond bog that McGizmo used in one of his mods. I still haven't gotten over that.

you're going to use the epoxy as a heatsink?

Yes, that's the idea. What do they use in something like an Everled?

i'm afraid that would'nt work too well (read: /ubbthreads/images/graemlins/eek.gif boom!)

aa is a better thermal conducter than air (what you would get between the slug and heatsink if nothing was used) but not nearly as aluminum.

even with a very thin joint between the slug and the heatsink the resistance of aa is muuuuuuch greater than if there was no resitance.

basically, what i'm saying is that using aa as a heatsink would be barely better than not using one at all.

Hmm, what's the alternative really? Drilled copper slug with an insulated wire running through it to the bulb tip? Again I wonder how the Everled deals with this issue.

I'm expecting the R2H will run at 100 mA or so at 3 volts, so the heat dissipation won't be nearly as bad as running at full power, if that helps. The 600 mA K222 incandescent bulb gets the bulb and holder pretty warm with no apparent ill effects. It's giving off a lot of infrared but I think it's also dumping at least as much heat into the bulb base as the LED would.

As an alternative I might just use a yellow 5mm led, resistor limited to 30 mA or so. That should be an interesting light of a different sort. I gather I couldn't get decent brightness from a 5mm white led at that voltage.

paulr,

Alumina oxide is not electrically conductive. Anodize is alumina oxide I believe. You can buy alumina oxide powder bulk and it is sold as an electrical isolator. You are after a thermally conductive bog, welcome to the club! /ubbthreads/images/graemlins/grin.gif I think you would best served with some type of metal plug or slug that is thermally bonded to the LED heat sink. At 100 mA, like you have stated, the thermal output will be relatively low and manageable by less than ideal thermal paths.

You could do something like this:



This has an aluminum slug glued into the bulb base to draw some heat away from the Luxeon. If you don't have access to a lathe, the local hardware store may something that will fit. Just ignore the "you're crazy" looks as you sort through aluminum bar stock, cabinet handles, screws, nuts, bolts, etc. looking for something the right diameter.

Also note that per Lumileds, the bare emitter is limited to 100ma without heatsink by their specs.

Good luck!

Any use of these compounds as heat conductors should be with a very tight fitting device, because these compounds were merely designed to fill in microscopic crevices on very smooth surfaces (CPU and heatsink for computers) that are very tightly applied. Any globbing of the compound with loose fitting devices that leave gaps of compound where air would be will render the thermal conductivity essentially useless.

i have potted luxeons in pr and screw bases with jb weld and even ca.
good for 200ma and more if you have a bulb recepticle made of metal.it may run out of spec for temp but who cares when the luxeons were very cheap.ya do stuff like this when you get a baggie of rejects on ebay cheap.

Snakebite, what is "ca"? The bulb receptacle in this light is a flimsy piece of thin sheet metal the same diameter as a 123 cell, better than nothing but not by much. Also the application (direct drive from a 123) requires a good Luxeon with a low Vf bin. I might experiment first with a reject, of course. I should also put my led on a variable bench supply and measure the current at up to 3.2 volts or so (I think brand new 123's can go that high). Maybe I should even look for a J voltage bin diode instead of the H bin that I so greedily snagged /ubbthreads/images/graemlins/wink.gif.

If you put a metal slug in the bulb base, how do you attach the diode? Drill a hole through the slug and run a wire to the bulb's center terminal through the hole? The hole would have to be at a slant, entering the edge of the slug at one end (where the LED lead is) and coming out the center at the other end.

So how does this sound:

1) Cut off a piece of Al or copper rod stock just wide enough to fill the bulb base and stick out the top slightly (putting the LED at the same height as the old bulb's filament, to focus properly in the reflector)

2) Drill a slanted hole for the anode wire (I'd have to get someone to do that with a drill press, I guess).

3) Run insulated wire through the hole. Glue LED to the top of the slug with arctic alumina. Paint clear nail polish around the top of the slug to keep the LED leads from shorting against it. Solder one end of the wire to LED anode lead.

4) Hollow out a bulb base and drill out the center terminal. Glue the slug with LED into the base with AA or arctic silver, with anode wire running through the center hole. Solder anode wire to the hole and file it down leaving a solder blob.

5) solder another wire from LED cathode lead to the bulb base. (Hmm this could be tricky).

This is much more complicated than filling the shell with a thermally conductive, electrically insulating bog, but sounds like it should handle heat a lot better. Do I have it right? Thanks.

Something like: my torch mods scroll down to the copper slug mods. These are some of my first mods when I got a minilathe.

I still have a bunch of extra copper slugs from these projects. If any one wants any PM me and for packing/shipping cost I can send them to you. The focal position will vary since I made them from various torches and I just have a bunch sitting in a catch-all box in my workshop.

george.

paulr
i believe CA in this instance is superglue /ubbthreads/images/graemlins/smile.gif

ca= cyanoacrilate=krazyglue