Molding in LEDs with epoxy

Hi. Im making an underwater light for my masters thesis (ROV design). The light will have to withstand 100m depth, so stuff has to be completely waterproof.
Im thinking of using heat sink paste and screwing the LED board onto a aluminium U-profile, and then fill the profile with clear epoxy. The goal is to have approximately 5mm epoxy covering everything, and the aluminium profile conducting the heat out through the back. The led board is fitted with 18x2 LEDs, giving an output of 7200 lumens at 0,7A /54 V. The board is apprx. 25x200mm
As far as i have understood it, most of the heat is transferred out the back of the LEDs, so adding epoxy will not insulate too much.
My main concern is that the LED plastic is not compatible with epoxy, creating a reaction before the epoxy has cured. I believe there has been some issues with these LEDs in contact with silicone oil, where the LEDs turned black.

Do you guys have any experience with molding in the LEDs?

Thanks

This thread should answer most of your questions:

http://www.candlepowerforums.com/vb...ed-LED-Underwater-Transom-Mount-Fishing-Light

7200 lumens from 0.7amps at 54 volts? thats only 37.8 watts. that means you getting 190 lumens per watt. or maybe you ment each side was going to be fed 700mA?

yazovyet said:

7200 lumens from 0.7amps at 54 volts? thats only 37.8 watts. that means you getting 190 lumens per watt. or maybe you ment each side was going to be fed 700mA?

Click to expand...

Hi. Yes you are correct, each side will be fed 700mA giving the whole board 1400mA.

magnusrm said:

Hi. Im making an underwater light for my masters thesis (ROV design). The light will have to withstand 100m depth, so stuff has to be completely waterproof.
Im thinking of using heat sink paste and screwing the LED board onto a aluminium U-profile, and then fill the profile with clear epoxy. The goal is to have approximately 5mm epoxy covering everything, and the aluminium profile conducting the heat out through the back. The led board is fitted with 18x2 LEDs, giving an output of 7200 lumens at 0,7A /54 V. The board is apprx. 25x200mm
As far as i have understood it, most of the heat is transferred out the back of the LEDs, so adding epoxy will not insulate too much.
My main concern is that the LED plastic is not compatible with epoxy, creating a reaction before the epoxy has cured. I believe there has been some issues with these LEDs in contact with silicone oil, where the LEDs turned black.

Do you guys have any experience with molding in the LEDs?

Thanks

Click to expand...

Cree's Chemical Compatibility paper on LEDs. I suggest isolating the LEDs from the Epoxy. This will mechanically isolate the fragile dome, bond wire, and chip substrate from the mechanical stresses on the shell.

I could put a plain flashlight inside a strong polycarbonate (Or lexan, or steel, or...) container and drop it to any depth the shell will withstand. To simplify surprises (VOC contamination blackening the LED) or disasters (Mysterious blackout when pressure slightly bends the shell and cracks open your PCB traces, giving a short), I suggest building your light inside a container.

Thanks for that link, it was very useful!
The ROV will have a maximum operating depth of 100m, but the main concern is thermal strains, right? I am adding a picture of the profile im thinking of using.

I could of cource mill out a slot in a thicker aluminum plate and either glue or glue and bolt a 5mm polycarbonate sheet onto it. Renderings both show bolted sheet and inmolded design.

And thank you for the link, DIWdiver


Im thinking of using MAX 1618 crystal clear epoxy http://www.ebay.com/itm/EPOXY-RESIN...700?pt=LH_DefaultDomain_0&hash=item4843191d5c

Ive created another design after I have spoken to an experienced machinist and aqurium builder.
He told me that even though PC(lexan) has a higher fracture toughness, PMMA(plexiglas) is a better choice because of the optical properties. Would this be a smart idea?
The new design is aluminium housing with a 3x Cree XML2 1000lm LEDs with 20mm copper board and a 21mm collimator. Would a reflector be a better choice (why)? I have seen the XML LED mounted on copper boards as small as 14mm, and that would fit me great if I could find a suitable reflector / collimator to match the diameter. Any tips on 15mm ish mm collimators with a spread of 60 degrees ish? Adding pics of new design.

magnusrm said:

Hi. Im making an underwater light for my masters thesis (ROV design). The light will have to withstand 100m depth, so stuff has to be completely waterproof.
Im thinking of using heat sink paste and screwing the LED board onto a aluminium U-profile, and then fill the profile with clear epoxy. The goal is to have approximately 5mm epoxy covering everything, and the aluminium profile conducting the heat out through the back. The led board is fitted with 18x2 LEDs, giving an output of 7200 lumens at 0,7A /54 V. The board is apprx. 25x200mm
As far as i have understood it, most of the heat is transferred out the back of the LEDs, so adding epoxy will not insulate too much.
My main concern is that the LED plastic is not compatible with epoxy, creating a reaction before the epoxy has cured. I believe there has been some issues with these LEDs in contact with silicone oil, where the LEDs turned black.

Do you guys have any experience with molding in the LEDs?

Thanks

Click to expand...

I have a lot of molding and casting experience. I have used both Smooth-Cast 326 and crystal clear 202 to encase LEDS. I would recommend Crystal Clear 202 by Smooth On. It is often used to make lenses because it is UV stable and rock hard once cured. It will withstand a lot of abuse and will be 100% water proof. You can even sand it to diffuse the light if needed. With 800 or 1200 grit. I have encased entire PCBS with LEDS and a li-ion pack in it and used a wireless phone charger to charge it. I have a Smooth-on distributor 5 min from my house so I have tried a lot of their items.