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Discussion Starter · #1 ·
Today I made my first ride with my own build helmetlight "Dinottestyle" Using two cree XRE leds combined with a 4 and 9 degree lens and driven by a 700mAh powerpuck (because I'm still waiting for my buckpuck) The batterypack is also selfmade with 8 4000Mah NiMh babycells, all glued in a shrinktube. My first impression is :eek: This thing really kicks ass, in fact I think the rabbits will need some:cool: glasses
Here are a few pictures of the end product;

the very beginning, building a housing for 1 cree XRE led and Ledil Lens


the light placed on a helmet.

Full blast

Beamshot in my garden, the tree is 10 meters away, the fence 15 meter, I also have a DIY 12v 20 watts halogen lamp and compared with that I think the output is about the same.
Next week........more pictures to come:D
 

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nice

Very professional looking.

I have a question on thermal control. How are you dissipating the heat from the MCPCB (junction) to the outer case?

I'm building a dual head XR-E body but I haven't settled on a thermal dissiaption method as yet.

Has anyone ever taken the Dinotte apart to see how they are doing it?

Bob
 

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Very nice work Gilbo, it must be handy having access to a lathe and milling machine like that. I can tell you've put some serious planning into this baby! :thumbsup:

You're going to get some sweet run times with nice light output too judging by your setup. Do you think you will try making a cut out / rubber pad DiNotte style so that you can mount them on your bars?

Do you have a shot from the rear to show how you have things mounted? It looks like you have a removable heat sink to mount the Cree to, and I assume the battery will be external and there will be enough room left in the rear to mount your smaller Buck Puck. Have you decided on a switch for it yet?

More photos to come hey… they'd better be posted sooner then next week! :p :D

Keep up the good work! :thumbsup:

Bob, just to clarify a few things, the "junction" you may read about in various datasheets is actually internal to the emitter and is on the bottom of the LED die, which sits between the clear lens and the ceramic substrate. The rectangular substrate is then reflow soldered on to the Star MCPCB.

For a good thermal connection between the Star MCPCB and your heat sink you will need some form of thermal compound (thermal grease), as used for computer CPU heat sinks. Personally I use Arctic Silver thermal compound, but if you need to glue your Star, then Arctic Alumina will work wonders. ;)

Most of us who build LED based systems use the whole housing as a heat sink. You need to have a read of the Cree XR-E datasheet to ascertain the exact thermal requirements, but the Cree based projects posted here on MTBR so far should be a good indication to what size you will need. Just remember physical mass isn't as important as surface area and the heat sinks ability to dissipate heat.

I hope that helps.

Dave.
 

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low_rider

I understand.

The heat is max at the junction and must be transported away if the temp is to remain within spec and allow the LED to operate without degradation. I'm going to use a rectangular aluminum tube (2"x1.25" with a wall thickness of .125") for the housing. This is a stock shape (no machining) and almost perfectly fits 2 LEDs with optics.

My current concern is moving the heat from the back of the MCPCP to the outer case. The two surfaces are at 90 degrees to each other. I see dropping a right angle piece of aluminum down from the inside of the case housing and bolting it to the back of the MCPCB. My calculation shows at least 1 square inch in contact with the MCPCB and then a square inch contacting the inside surface of the housing. With a .125 thick housing I can mill some heat dissipating channels as well on the outside. The .125" thick housing wall also allow screw holes to be installed which will greatly simplify the end cap design.

Thanks for letting me bounce this off you. Any input is appreciated.

Maybe a thread on housing design would be worth while.

Bob
 

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Discussion Starter · #5 ·
Low_Rider said:
Very nice work Gilbo, Do you think you will try making a cut out / rubber pad DiNotte style so that you can mount them on your bars?
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Thx for the reply, I already have made a groove in the bottom of the light to fit on a handlebar
I'll try to make some more pictures today, but since whe have organised a MTB trialride this sunday I have lots off work at the moment.
 

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Question

Looking at the picture with the heatsink it appears to be about 30 - 35 mm in dia. Is it touching the housing inside wall anywhere?

How are you getting the heat from this assembly to the housing? Convection through the air?

Bob
 

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Discussion Starter · #9 ·
The heatsinck/ledholder has the diameter of the inside of the housing minus 0.10mm so the heattransfer is garanteed. the light does not warm up at all, last wednesday Took it out for a testride and the light does not warm up at all (outside temp was 7°c)
 

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Gilbo

Just so I'm clear on this. There is a gap - a small one - between the heat sink and the inside of the housing?

Even a small gap will act as a relative thermal insulator between the housing and the heatsink. I say relative because the heat sink and the housing, being metal, are far better conductors of heat than air. However, you may not need to actually make contact to the housing as long as the junction temp remains in spec. They only way to tell would be to run the light for more than 20-30 minutes and measure any intensity drop. If none is detectable you're good to go. Your heatsink does appear to be robust. The design I'm working on would place two XR-Es in the same housing so I'll probably have to design a means to conduct the heat to the case efficiently while keeping the weight low.

Bob
 

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Discussion Starter · #11 ·
Bob, I think when the heatsink gets hotter it also becomes larger in diameter so the very tiny gap will be as good as gone. If there should be a problem I can always put some thermal paste inside the housing, butt again, I don't think there will be a problem.
 

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Gilbo

I agree. I don't think you'll have a problem either. There is a lot of metal there. Also, I sent my last post before looking at all of your pics. The one which shows the entire interior design answers my question. Your heatsink is connected to the case via the two rods that screw to the rear cap. The rear cap is touching the case - with significant surface area. I doubt if there would be a problem. You have considerable metal inside.

What does a single head weigh?

Bob
 

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Discussion Starter · #13 ·
Bob

The two housings together weigh just 250 grams ( there is a difference between the two because one light holds the switch and connect cable for the other lamp) I did not use a very accurate scale so i'll measure the exact weight next week at my work.
 

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Discussion Starter · #16 ·
achesalot said:
Nice job man! Good to see the final product. :thumbsup:
The Crees are certainly ruling the LED scene.... huh!

Are you happy with your lens choices?
Thx Allen,
Yes the 4 and 9 degree lens works together very well, I supposed that I would have a good amount of lightoutput, but this amount I had not expected, I can only say :eek:

Now I'm planning to change the halogen bulb in my other light also in a tripple cree setup ( have to do some measuring before to see if my housing is big enough, otherwise i'll have to make a new one:lol:
It's a petty that there is such a big distance between the forummembers, otherwise we could have a forumnightride. then you could see two things from space, the chinese wall and the MTBR nightriders:yikes:
 

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Gilbo said:
Then you could see two things from space, the chinese wall and the MTBR nightriders
Given the number of astonshingly bright lights that have been demonstrated here lately I think you might be correct.

I think this is a great forum. I have enjoyed the inventiveness that posters show, and the enthusiasm that is demonstrated when talking about the latests project's potential to deliver something brighter, longer or cheaper is heart warming.

Thanks to all the posters.

Wombat
 

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Bob, I think it's already been covered pretty well by Gilbo, but there is plenty of material there considering the drive current and the fact there's only one emitter per housing. I can't see there being any issues. ;)

Bob said:
They only way to tell would be to run the light for more than 20-30 minutes and measure any intensity drop. If none is detectable you're good to go.
While definitely measurable with quality equipment, any intensity drop caused by temperature would be barely noticeable with your eyes (if noticeable at all) with most emitters, even with a relatively huge temperature shift. Most emitter manufacturers agree that Vf shift as an indication of temperature change is a much superior method.

For most DIY guys, the "touch" test will probably suffice if a little consideration has gone into the design to start with. There are a few other relatively easy methods for those a little sillier. :D

Keep up the great work all! :thumbsup:

Dave.
 
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