Mod a Mag with a Rebel.

Hi I decided to put some of my new 100 Lumen per Watt Luxeon Rebels to good use in a flashlight mod. I had an old mag 3D cell with a Hotlips heatsink and a 3watt Luxeon in it so I decided to remove the Lux3 and put in the Rebel. I came across a problem with these newer Rebels which are manufactured using the new TFFC technique. They are very susceptible to thermal damage and I managed to destroy the first 3 I played with as I hand soldered them to a copper sheet. I plan on starting a new thread to discuss this problem in more detail. I wound up having success using a very small PCB I laid out which has many small vias under the thermal pad of the Rebel and goes to a ground plane which covers the entire bottom of the board for the purpose of heat dissipation. I then used solder paste and a toaster oven as a reflow oven to bake the LED onto the PCB. The PCB was then epoxied to the Hotlips heatsink using Acrylic Aluminum. The results are defiantly better than the old 3W TV1J? That was in it. I think it could be much better with a deeper reflector as the rebel throws more light out the front as spill which could be better put to use in a tightly focused beam.
An interesting observation was made when I put my finger on the LED lens to see if it was getting hot and wound up almost burning my finger. I thought I had a thermal transfer issue and puled out a small K type thermocouple to try and measure a few things. I found that the side of the ceramic part of the LED was only like 35C and when I placed the probe about 5mm in front of the LED lens it read 60C. I had always assumed that sense LED's don't radiate any IR there was really no heat in the light coming from them, but I guess if you get enough of any light source there will be heat in in it.




The picture shows the Rebel on the PCB which is epoxied to the hotlips heatsink. To the right you can see 2 of the small boards I made for mounting the rebel (one showing each side) and on the left you can see a board I made for mounting 3 to be used as and experiment for a home lighting project.

I like your board design.

Does heat actually transfer well through a PCB board like that (vs. copper, aluminum, silver compound, etc)?

Edit - I re-read and now notice the several holes that pass through on it. I still am curious how that works compared to a solid contact to the heatsink/thermal compound using something like a copper base. But if it works, it works.

It doesn't through the PCB it's self but it does a decent job through the vias. Not as good as pure coper or aluminum but Lumaledes actually recommends a similar process for heat sink the Rebel. Their solution is to use a thicker copper trace on the top and and than place lots of vias all around the part to wick heat to the bottom of the board. They probably didn't recommend placing vias directly under neath the thermal pad for fear of the vias wicking away all of the solder and not providing a good connection between the Rebel and the board. I pretined the vias by hand to mostly fill them in with solder and then applied solder paste on top of the board and baked the LED on to the board.

Here is a link to the thread I started concerning the failure problems I had with the my Rebels
https://www.candlepowerforums.com/threads/169915

Some may wonder how I made these boards and was able to get all those small vias in them.

I use www.expresspcb.com they have a free cad program that is very easy to use and learn and you can order 3 identical boards of your own design that are 3.8" X 2.5". It is called the MiniBoard service and they are $61 and usually arrive within 3-4 buisnes days after you order the board. These boards are very high quality double sided boards with plated through holes.

Excelent job! I am impacient to see some beamshots of your new mod.

I was wondering if it woud be possible to design some kind of spring and pressure based mechanism to place the led.

I am thinking on something similar to the clips used with the sim cards on mobile phones. Having such a kind of mechanism, it would be very easy to replace leds, and the soldering problems would be history.

Brlux said:

Here is a link to the thread I started concerning the failure problems I had with the my Rebels
https://www.candlepowerforums.com/threads/169915

Some may wonder how I made these boards and was able to get all those small vias in them.

I use www.expresspcb.com they have a free cad program that is very easy to use and learn and you can order 3 identical boards of your own design that are 3.8" X 2.5". It is called the MiniBoard service and they are $61 and usually arrive within 3-4 buisnes days after you order the board. These boards are very high quality double sided boards with plated through holes.

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Watch these quick proto services. They are fast and the quality is good, but often they only use 1/2 ounce copper and you really need 1 and preferably 2 ounce or better copper for an LED.

Semiman

SemiMan said:

Watch these quick proto services. They are fast and the quality is good, but often they only use 1/2 ounce copper and you really need 1 and preferably 2 ounce or better copper for an LED.

Semiman

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It depends on the application. If you are relying on the copper trace for all heat transfer like Lumaleds describes in there Rebel application guide then yes it is needed but with the way I have laid the board out with the vias directly under the thermal pad it is not nearly as big of an issue, granted it would be better with heavier plating but what other options do you have for affordable getting high quality boards for prototyping.

I incorectly listed the board build price it went down a few months ago to $59 shipped UPS 2nd day.

It's too bad somebody doesn't make a Micro-MCPCB with a Rebel already mounted on it that's about the same size as a Luxeon...now that would make life easy for us to hand-solder and swap out existing emitters. Lets hope the new GenX K2 based off this technology comes out soon.

ace0001a said:

It's too bad somebody doesn't make a Micro-MCPCB with a Rebel already mounted on it that's about the same size as a Luxeon...now that would make life easy for us to hand-solder and swap out existing emitters. Lets hope the new GenX K2 based off this technology comes out soon.

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+1 thats a great idea it would sell alot of rebels to flashlight modders and lighting designers who dont like working with the tiny contacts on the rebel.

edit: looks like this would work http://theledguy.chainreactionweb.com/product_info.php?products_id=1001&osCsid=e8752e2778d99492a3558c208306b86b

ace0001a said:

It's too bad somebody doesn't make a Micro-MCPCB with a Rebel already mounted on it that's about the same size as a Luxeon...now that would make life easy for us to hand-solder and swap out existing emitters. Lets hope the new GenX K2 based off this technology comes out soon.

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Do you mean something like this?

josean said:

Do you mean something like this?

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Well yeah...but that's still a bit big. What I had in mind was a Micro-MCPCB literally the size of a standard Luxeon emitter. That board that DX sells looks like it's the size of the area that fits into Fenix-style clone flashlights. I suppose you could trim that one down to fit on a Mag O-Sink, but I'd rather have a Micro-MCPCB made to a smaller size. There's got to be someone out there who could do it...or we could simply wait until LumiLEDs comes out with their GenX K2 emitter--whenever that's going to be...

I have been wanting to do some beam shots but I don't have a good light to compare it to. It seems that almost every light I get becomes modified in some way making it no longer useful for a reference. But we did have a storm blow through last night and I could not help myself, All the dust and debre in the air made for some cool looking beam shots.
All the particles in the air makes the beam appear more intense than it really was, you should have seen my 80mw greeny!! It was like a light saber that seemed to stretched out to infinity. In the above photo you can see the width and intensity of the spill light.

Brlux said:

I then used solder paste and a toaster oven as a reflow oven to bake the LED onto the PCB

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That's such a freaking cool idea!

Is it possible to mod a Rebel into a MiniMab (AAA) and direct drive it with 10440ers ?

wischi

wischi said:

Is it possible to mod a Rebel into a MiniMab (AAA) and direct drive it with 10440ers ?

wischi

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the current draw would be too high for the 10440. it would work but would be a little harsh on the cell. the LF2 limits its current on 10440 to 600ma, and that seems to be fine.

I failed to mentone it but the current I am currently driving the Rebel in my Mag is 600ma with freshly NiMh cells. It is direct drive with a 1 ohm current limiting resistor. I may later push it to a higher current.

Brlux said:

I failed to mentone it but the current I am currently driving the Rebel in my Mag is 600ma with freshly NiMh cells. It is direct drive with a 1 ohm current limiting resistor. I may later push it to a higher current.

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I want to run an emitter at 1A (supply current is around 2.5A). What resistor value should I use?

LukeA said:

I want to run an emitter at 1A (supply current is around 2.5A). What resistor value should I use?

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The question is a bit confusing? What is your supply? I am guessing that 2.5A is likely the max current it can deliver. If it is a voltage regulated power supply what is the output voltage?

I dont see the advantage using the rebels
over better to handle, brighter, easier to install, better thermal placeable, ...
Crees / SSCs

is there any?