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Discussion Starter · #1 · (Edited)
I've nearly finished this dual Cree MC-E light. It's been fun following other threads on the MC-E as we all tried to figure out what was the best way to drive them, what optics to use, and how we would keep them cool enough. I was actually quite happy riding along with my Triple SSC light. But temptation set in, and be as it may, I succumbed to the pressure of jumping on the mult-die bandwagon.

Here is a photo of the light... I've since cleaned it up a little (removed the excess AAA) and added plexiglass to the front.
Specs: 3023 Buckpuck, 1A
2x MC-E (M-bin) wired in series (rated at 430 lumen each @ 350mA)
The two MC-Es are in parallel @ 500mA each.
Reflectors: Ledil Boomerang 1xSS and 1xMedium (?? should have used 2x SS)
Power: 14.8v, 4A Li-Ion pack.
Total Weight: 125g



For comparison purposes, I took some beam shots and compared it to my Triple SSC light.The top photo is the Triple SSC and the bottom is the Dual MC-E. The distance is about 50 feet to the fence. I really like how much better the ground between me and the bush next to the fence is lighted. The trails I ride are so twisty, there's rarely any distance greater than 50 ft. to look ahead.


Ride test next week!
Enjoy. I'll post some build pics soon!

NOTE: Just added an outgrowth of this light to the thread: a hybrid MC-E/SSC P4 as shown below. Discussion of this variation starts at post #29
 

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Discussion Starter · #5 ·
Thanks guys. It was fun to build. I don't think you can have too much cooling with the MC-E. Higher power? Hmmm... :D

Here is an interesting sequence of shots of how the body slides together. I was in a dilemma for a while about how to have the heat sink fins cover the entire top and still be able to pull the light apart and change reflectors, etc. Then I decided to cut them where the light halves join together.

 

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Discussion Starter · #7 ·
ocean breathes salty said:
You are simply put... the master of square tubing.

I had one go at an "achesalot" style light and realised precision wasn't my strong point :) (and promptly posted it in the fuglies :D )

Your seams look so good that they might almost be watertight.. congrats
Why thanks Ocean! My son certainly thinks that I'm the master at being square :)
 

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Wow, the hand shot shows how really small it is!

Is there a big temp difference on the bench between the front and back. Doesn't look to be a lot of surface area connecting the two.
 

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Very very nice build! So you reckon the Vfs of the 4S wired MC-Es are close enough to each other? That would sure simplify the wiring, but I'm not sure if running 2 2S2P wired MC-Es in series might be a bit better matched or not... I guess it would depend on whether CREE Vf matches the dies on each MC-E or not. Being able to run at 700mA over each die would be nice, but I think you've made the best compromise at 500mA... lose a few hundred lumens perhaps, but still getting 1000+ easy, and it makes the driver dilemma easy as pie. :) Good stuff!
 

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Discussion Starter · #11 ·
Troutie: Thanks. Yes, I will first try it as a standalone helmet light. I'm ordering another SS to replace the medium Boom. I always enjoy your threads Troutie... lot's of good fun!

Znomit: Yes. It is small. I was originally going to make it larger just for heat dissipation. The back part heats up first, of course, due to it having more contact area. I tried to make the front fit as tightly as possible along the sides of the 1/8" aluminum behind the stars. I also used threaded aluminum risers for connecting the front to the body. Since they are AAA'd behind the stars, they sort of act like heat pipes to get heat out to the sides. I use non-adhesive thermal compound on all the contact areas to help transfer between the two parts. After about 5 minutes of static testing, all of the fins, including the side ones and front ones are heated up, and the bottom of the light below the stars is cooler than the fins... I think that's a good thing. The feet even act as heatsinks. The worst part of this design (heatwise) is heat trapped in the body... we'll see how it does on the ride test with cool night air flowing over it!



Hack: Thanks! I went back-and-forth on wiring (you might be right on the 2S2P as way to go). The MC-Es were pretty close on Vf (I don't remember the exact numbers but only differed by less than 1/10 volt; 0.02 diff if I recall). I don't think I could keep it cool driving it with any more current and I don't want to draw any more from my battery. I think you'd really have to be aggressive on the heat management when driving them harder.

Consider Cree's Relative Flux versus Junction Temperature chart below:



It's real easy to get into the 10-15% and higher luminous flux loss if you're not careful. So at some point you are just sucking more juice from your battery and causing the LEDs to output less light (not to mention shorten their useful life).
 

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Discussion Starter · #13 ·
wkumtrider said:
Nice light achesalot. On the MC-Es, can you wire them so only one die works? I'm not sure I understand the dies and how they work. Is it like 4 leds in one package?

Thanks. I'm a dummy.
Yes. It is like 4 LEDs in one package. I'm not sure how that would affect the beam to just run some of them... I thought about trying that, but never did it. BTW, Thanks.
 

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Discussion Starter · #16 · (Edited)
Thanks Tex and Msxtr.

Here's another photo after the MC-Es were wired. It's always a good idea to check for shorts after doing this much soldering. It turns out I had one place where a small piece of solder had wrapped around (and shorted) to the metal part of the star and might have caused damage to the driver and/or LED chip had I powered it up like that. I always take my meter's continuity tester and check for shorts against the star body and the other connections before the smoke test.



Below is how the feet of the Boomerang reflectors had to be cutoff and a few other hacks made to accomodate my solder and wires on top of the star. Sorry I didn't take a before shot of the feet. I also had to trim just a bit off of the front edges (at two points) to get the reflector to fit inside the 1" square tubing (which is 1-7/8" ID).

 

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Once again, a masterful light achesalot. What are you using for a front cover?
 

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achesalot said:
It's real easy to get into the 10-15% and higher luminous flux loss if you're not careful. So at some point you are just sucking more juice from your battery and causing the LEDs to output less light (not to mention shorten their useful life).
That is a wise statement. It is very easy to get caught up in pursuing more and more lumens and not even realize you are making negative gains.
 
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