Heat efficient LED mounting in Cateye ABS housing

OK then, I need to pick the collective CPF's brain on something.

I've built up my first light and learnt a lot. Now I want to improve on the design and make it more efficient. The main way this could be done is improving the way heat is moved away from the led's and conducted to the case for disaption.

Here's the housing that will be used:


Its cast aluminium, dead strong, pretty lightweight and has enough space inside for the driver and wiring.

Here are the dimensions including the cutter kit


The problem I've had with the cutter kit I used on the first builds was mounting the MCPCB that the LED's come on as the board is not quite a big enough diameter. I think if I made something that the led's could actually be mounted on that fitted exactly into the space available it could all fit together very nicely indeed.

I've been playing with google sketch and this is what I'm thinking of:

This is the side the led's would be mounted on


This is the back that would fit inbetween the fins seen in the picture of the housing (nb the 32mm dimension is wrong, I'd want it 33mm)


So with this led mounting I'd be aiming to get a snug fit so that the mount would be clamped by the bezel against the fins. There would be contact on the front of the mount (estimate 1mm all round), at the edge of the mount against the housing (2mm all round) and on the back of the mount 5mm up against the fins on the housing.

So now some questions:

How do I go about 'sticking' LED's down?
Its likely to be aluminium I use. Are there different options, maybe something that isn't completely permenant to allow upgrading of led's.

Is there a 'soft' material that I could use on the back of the mount to improve heat conductivity to the fins?
I'll obviously use heat transfer compound on all the connecting surfaces its just there is a lot of surface area there that could be maximised with something like heat transfer plasticine :duh2:

How thick would you make the mount?
Here I'm trying to balance weight against function. With the drawing I've made at the moment I'd have 7mm of aluminium behind the led's. More or less required?

Is it possible to lift the LED's off the MCPCB board provided by Cutter without trashing them?

Is there a source of LED's and optics in the uk. The service was great from Cutter its just it seems a long way to be buying things from.

Thanks folks

Ian

iggs said:

Is it possible to lift the LED's off the MCPCB board provided by Cutter without trashing them?

Click to expand...

You could buy bare emitters, dremel off the via's and just stick them on the heatsink directly with artic silver adhesive or another thermal epoxy.

About the topic title: 'ABS' suggests it's a plastic housing, not very similar to cast aluminium.

Brum said:

You could buy bare emitters, dremel off the via's and just stick them on the heatsink directly with artic silver adhesive or another thermal epoxy.

About the topic title: 'ABS' suggests it's a plastic housing, not very similar to cast aluminium.

Click to expand...

ABS is the model of lights. The ABS25, ABS30 and the ABS35 are all alloy housings

http://www.zyro.co.uk/product_detail.asp?pid=306

Sorry if it caused any confusion

You may have to drop the module back a bit farther. I see you have about 12-14mm from the inside of the bezel to the "seat area". That's a little tight to fit a front lens, reflector/optic, the LED and the heatsink. You may need a "sunken" heatsink.

I would not expect a good thermal contact for a heatsink butting against the internal ribbing. They are almost certainly not all perfectly on the same plane, so you will have some high/low spots.

It would be handy to mill the top of the fins to get a flat surface and thermal epoxy a flat disk to them to get a large surface for thermal transfer.

To answer your other question about removing the CREEs from their heatsinks:
1. Clamp the emitter/heatsink vertically in a metal vise.
2. Have something below to catch the emitter (it will be hot) or use some tweezers on it.
3. Heat the backside of the heatsink with a torch. The emitter will slide off as soon as the solder melts or tug gently on it with tweezers (be careful not to hit the dome).

Good luck!

Paul

hhmmmm, I like the idea of milling down the fins a couple of mill and epoxying a disk onto them to provide a flat surface for the led mount to sit onto. Using thermal epoxy to fill in the gaps at the sides and also a bit around the fins would maximise the surface contact there. If the mount tollerances were nice and tight too it could provide a nice wide path for heat transfer to the case

Thanks for the info on removing the CREE's from the board too

Ian