# Ceramic cement for potting ?



## videoman (Jul 22, 2010)

I need a much lower priced alternative to AA cement that I can use to mount leds and drivers to make lamp fixtures. Leds and driver will be mounted on aluminum heat sink. I came across this one and I need some advice on it, it must not conduct electricity as the underside of the driver has the exposed circuits.Any other ones out there that can be used? 

http://www.cotronics.com/vo/cotr/pdf/920 DS NP.pdf


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## 65535 (Jul 22, 2010)

I doubt it's half as conductive as Arctic ALumina, but I really don't feel like running the numbers, you can check for yourself.

At 3000F conductive is a relative term, at that temp, just about anything conducts heat well, at 150F it may not transfer enough heat from the LED die to keep it from burning up.


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## bshanahan14rulz (Jul 22, 2010)

If it's just one project, just get a little tube of AA, it'll be enough for mounting those stars to a heatsink.

Potting is where you fill a void space with material. It can provide mechanical stability (or just shear your components off of your circuit boards if you choose the wrong expansion coefficient), it can help transfer heat better than stagnant air, but you should probably just use thermal epoxy if you're just mounting stars and drivers to a heatsink.


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## jeffosborne (Jul 22, 2010)

Hey videoman, is this stuff that much less expensive? I would be interested in giving it a try myself, if you care to share your source. I know the AA comes in very small tubes, and is not cheap. 

How many lights are you making? Can we have a peek at one?

Cheers,
Jeff


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## 65535 (Jul 22, 2010)

I'd stick with AA it's not that bad if you only need a tube.


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## videoman (Jul 22, 2010)

Each fixture may require an entire AA kit as there are between 8 and 12 leds to cement on aluminum heat sink as well as the driver.I have already tried JB weld and it works fine with me, no heat or electrical issues. cheap when you consider the quantity and takes more time to set. I haven't got a price for Cotronics as I would like to know if that stuff will work better than JB weld.JB claims that it is non conductor of electricity even though some say that it has metal powder in it. If only AA would be available by the ounce and at a much lower price. I will give Cotronics a try soon and post with results soon.


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## thepaan (Jul 22, 2010)

Isn't the thermal resistance related to the thickness of the substance too? It might not matter if your heatsink is oversized and your adhesive application is obscenely thin.

Still, I think you may be overestimating the quantity required. I used a single Arctic Alumina for my last project (which had 5 LEDs and 3 drivers) and barely made a dent in the tube. I wasn't using stars though - just mounting the LEDs straight to the heatsink, but I did mess up the driver mounting and had to redo them.

What are your drivers? If they are luxdrive like I used then they don't need a heatsink. You could try using JBweld on the drivers and save the AA for the LEDs....

Anyway, good luck with your project.


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## videoman (Jul 22, 2010)

Other than the price, the main reason I am looking for an alternative to AA is to gain more "set time" I am positioning 8 to 12 leds in a confined space that also will have optics with holders on them. I am really within 1mm at best between spacing them. By using a cement that will take time to set, will allow me to precicely place them so that when the optics holder are attached, they just barely touch each other.AA sets way too fast and by the time I have the 8th one in place, the first ones are already dry, and cannot be re-positioned.Here's my sequence of production:I apply the adhesive on the leds, I roughly position the leds on the heat sink within about 2mm from where I really want them, I attach the optic holder to them without the optics, I slide them around untill they are in place, wait for the adhesive to dry, take out the holders, solder them, cement the holders on the leds, put the optics in. Any improvement to my method is appreciated. Thanks


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## MikeAusC (Jul 23, 2010)

Place all the items to be glued and the adhesive in the refrigerator overnight - it will take a lot longer to start setting.


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## Paul Baldwin (Jul 23, 2010)

I've been using the DX Fujik silicon thermal glue for ages now. One 50ml tube goes so far! Ive used it for fixing stars to sinks, fixing sinks to frames, fixing drivers to sinks etc. Its been ok for an mc-e running at 3.1 amps for extended periods and even stood up to the temperature of my log burners flue on a thermo-electric fan I made without burning up so for less than $8 I'd give it a go. Setting time hasn't been an issue either.


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## videoman (Jul 23, 2010)

Hi and thanks for all the suggestions. My only concern about DX Fujik is that I understand that it never really hardens and remains soft and by being so I am afraid that the optics may lose alignment and won't aim straight. Even a small shift in aim may throw the beam off. I will give it a try. My lights will be used in a rough environment that get tossed, banged around in a studio and on-camera ENG video environment, and used by many.


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## Paul Baldwin (Jul 23, 2010)

Can't you use standard two pack epoxy resin for the optics then? I've also used fibreglass resin and hardener to pot a worklight I made for a mechanic friend of mine. It's had a very hard life and is still working 18 months on. I just made a very rough mould around the top of a small heatsink with the led, lense holder and driver held in place with the fujik glue. I then filled it to the brim with resin, let it set and removed the mould afterwards. The "body" of the light is just the outside of the resin potting. Very rough and ready but I did it for him at cost price for the bits and knew it would be abused. It proved the fibreglass resin as a potting compound tho


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## Der Wichtel (Jul 23, 2010)

the cotronics compound should be very similar to arctic alumina as both are based on aluminiumoxide.

I'm mixing aluminiumoxide with epoxy myself with good results.


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## 65535 (Jul 23, 2010)

You could use Arctic Silver or similar thermal paste, then pot the entire LED and optic with 2 part epoxy.


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## Axkiker (Jul 23, 2010)

Der Wichtel said:


> the cotronics compound should be very similar to arctic alumina as both are based on aluminiumoxide.
> 
> I'm mixing aluminiumoxide with epoxy myself with good results.


 

I have thought about doing that as well since I have a big container of alum-oxide laying around.... how has it done for you ??


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## thepaan (Jul 23, 2010)

videoman said:


> Other than the price, the main reason I am looking for an alternative to AA is to gain more "set time"


 
Set time would be irrelevant if you didn't have to reposition anything. Are the optics just close or are they touching? If they are touching, you could glue them to each other then glue them over the emitters which would be attached at pre-marked locations. If they are close you could try some kind of spacer to make them touching at the correct spacing.


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