That sinking Feeling.....

[Swallow]

Hello All, been away a long time since I finished making my mtb lights with all your help. Anyhow, now I'm onto a different project and need a little advice as to heatsinking. What I am making is a replacement "bulb" for the headlight of my vintage vespa. This will use three Cree Q5 Leds driven at 1A for low beam and then the same again (ie two sets of 3 q5s at 1A) when on high beam.

The picture shows the mount/heatsink I have made to put the leds on (awaiting delivery at the moment from dx) incompleted. When finished it will have copper "flats" as seen in the middle repeated either side and the same again on the opposite side of the assembly. Three leds on 14mm round boards mounted on top and three underneath (on opposite side, not visible in the photo). The copper sections are 14mmx20mm to give an idea of scale. The fins are 2mm thick, as are the copper flats which are joined to the aluminium using arctic silver.

This will all slip into the 5 inch diameter headlamp assembly, but what I really want to know is..... do you experts reckon the heatsinking is sufficient. I used seoul p4 leds in my mtb headlights:
http://www.candlepowerforums.com/vb/showthread.php?t=166203 these get warm but not too hot. As it is there will be little ventilation inside the headlamp unit. I have no experience with Cree Q5 leds and their heating issues!!!

All the best, Tom

 

[DaFABRICATA]

Look in the McGizmo furum....He upgrades the Light on his "Scooter" with LED's

Hope ya find the thread, he did some cool work and it was definately brighter!


Here it is: http://dmcleish.com/CPF/Vespa/index.html

 

[Swallow]

Thanks for that! I have already changed the rear lights for solid state, have a look at this

 

[Black Rose]

The forum limit on picture sizes is 800x600 I believe.

Might want to resize them or change them to links, before the mods do it for ya

 

[LukeA]

What are you doing about beam pattern? Something like McGizmo's is dangerous and illegal.

 

[Swallow]

What are you doing about beam pattern? Something like McGizmo's is dangerous and illegal.

by having three leds facing upwards (so at the top half of the reflector) that will aim most of the light out at horizontal or below for low beam. the other three leds will come on for high beam (making all 6 lit up) and being facing down straight at the lower half of the reflector , I am hoping that they will push their light out at horizontal or above. This is simply following what happens when using a dual filament incandescent bulb in the original setup. i can see howMcGizmo's setup just pumps out light forwards in all directions. I'm not looking for huge output, just something stable that wont dim under low revs - my scooter is a 1964 model and has no battery & anything would be better than the original.

Anyhow anyone got any ideas as to how effective a heatsink I have made for the crees Oh and sorry for large images, will try to resize.

 

[LukeA]

by having three leds facing upwards (so at the top half of the reflector) that will aim most of the light out at horizontal or below for low beam. the other three leds will come on for high beam (making all 6 lit up) and being facing down straight at the lower half of the reflector , I am hoping that they will push their light out at horizontal or above. This is simply following what happens when using a dual filament incandescent bulb in the original setup. i can see howMcGizmo's setup just pumps out light forwards in all directions. I'm not looking for huge output, just something stable that wont dim under low revs - my scooter is a 1964 model and has no battery & anything would be better than the original.

Anyhow anyone got any ideas as to how effective a heatsink I have made for the crees Oh and sorry for large images, will try to resize.

I think the LEDs need to be emitting downward into half-reflectors to have a cutoff. Otherwise, I'd say it looks good.

I have heard that fins spaced less than 6mm or so apart aren't effective, but that's for passive heat transfer. I would imagine that those concerns are largely alleviated by forced air, which this device will see most of the time.

 

[znomit]

Nice tail light. Looking to do something similar to my LX150 to tidy up the back end. Go Vespa.

Any reason not to put a fan in behind headlight leds to cool the heatsink?

 

[LukeA]

Nice tail light. Looking to do something similar to my LX150 to tidy up the back end. Go Vespa.

Any reason not to put a fan in behind headlight leds to cool the heatsink?

The fan uses power, and the scooter moving forward will put more air past the headlight than any suitable fan.

 

[Swallow]

The fan uses power, and the scooter moving forward will put more air past the headlight than any suitable fan.

It will be encased in glass though so even though the glass gets a rush of our cold british air, there wont really be any air movement over the led array - not really any room to put a fan although there is a 10mm hole drilled through the length of the assembly I could use a computerfan to suck air out of the lamp if I could find one small enough. I'll put up some photos tomorrow if I can 9hard to explain without seeing it all)...

 

[LukeA]

It will be encased in glass though so even though the glass gets a rush of our cold british air, there wont really be any air movement over the led array - not really any room to put a fan although there is a 10mm hole drilled through the length of the assembly I could use a computerfan to suck air out of the lamp if I could find one small enough. I'll put up some photos tomorrow if I can 9hard to explain without seeing it all)...

Then I think that you should duct air in past the fins. There's no way a small case fan will move anywhere near that amount of air, especially not through a 10mm hole. And a fan certainly won't do it for free, electrical power-wise.

 

[McGizmo]

What are you doing about beam pattern? Something like McGizmo's is dangerous and illegal.

I agree that the high beam I have is dangerous and I would not use it with any oncoming traffic. As for the low or normal beam, I am not clear where the danger is. I have now ridden the scooter a fair amount at night and from what I can tell, my beam concentration is not encroaching into the lane of on comming traffic to any detrimental effect. It certainly provides me with better vision than the stock lamp did. :shrug: In terms of legality, I would imagine that anything not DOT approved would fall short of legal regardless of whether it was better or worse than an approved device.

Swallow,

Cool scooter! I believe your handle bars are cast aluminum?!? If yes, perhaps some copper strap from your sink to the handlebars can spread the heat and link you to a surface which is enjoying some airflow. Putting ducts into the headlamp or proximity will certainly introduce air if there is escape below or aft and it will also introduce rain and dust to areas which were not designed to be exposed to such a blast.

If you are using the original reflector or one similar to a typical scooter headlamp, I would test the beam pattern before committing to it if I were you. I may not be following what you have in mind but it seems that you will have your LED's well away from any single focal point of a reflector?!? :shrug:

 

[znomit]

LED headlights on the Rezistor electric vespa. Funny looking thing.

Beamwise... if you can wait for MC-E with 20mm carlco optics. Built in high/low beam. :twothumbs

 

[Swallow]

Copper Strap...? More details please. I think from the words copper and strap, I grasp the idea but what kind of reach would this allow between the assembly and say the handlebars/headset, where can I get the best.....
Cheers, Tom

 

[McGizmo]

Tom,
You should be able to find various widths of copper strap in various gages. You might be better off with a sheet of copper that you cut to suit. Without seeing your assembly in the handlebar, I can't comment on how viable this might be. The idea is to maximize the contact surface of some copper with your AL heat sink and bridge the sink to the handlebars in the shortest distance and again with maximum surface contact with the handlebars themselves. Perhaps on the back side of your sink, you could have similar "flats" as you have done for the LED pads but instead of trimming the copper to follow the profile, leave it in longer strips that either are free hanging or better yet some how secured to the handlebars. Copper is a good thermal conduit and easy to bend and form.

I am driving three Cree's at 917 mA on my Vespa and this is certainly more light than the stock headlamp. I imagine I could have gone for a lower drive current and still had adequate light output with less heat generated.

It sounds like you will be placing your LED module within a reflector and this may limit your access and room behind the module.

 

[frenzee]

Tom, I did something very similar except slightly smaller and for a tail-light using 5 LuxIII's at 1A (about 10W). From what I can see, I'm afraid without forced cooling you don't have anywhere near enough cooling with your setup. Keep in mind at 1A you are trying to dissipate the better part of 21W. I suspect your headlamp assembly is sealed or mostly sealed so there is little or no air movement at all past those fins so they are useless. With my setup, it got past 100C in less than a minute and that was holding it in open air where there is convective air movement. Also my fins were thinner and there were more of them (which is what you want). I had some success adding a tiny fan to move the heat away, but sill not good enough for reliable day-to-day operation.

May I suggest a different approach? How about using forward-facing emitters with individual narrow-beam optics mounted on a flat sheet of copper or even aluminum, attached to a finned heat sink on the back of the unit that is exposed to the air? That way you will better control over where the output is aimed and your thermal concerns will be resolved. Kind of like what McGizmo did, although you may have to reconfigure your entire headlight assembly.

 

[Swallow]

Tom, I did something very similar except slightly smaller and for a tail-light using 5 LuxIII's at 1A (about 10W). From what I can see, I'm afraid without forced cooling you don't have anywhere near enough cooling with your setup. Keep in mind at 1A you are trying to dissipate the better part of 21W. I suspect your headlamp assembly is sealed or mostly sealed so there is little or no air movement at all past those fins so they are useless. With my setup, it got past 100C in less than a minute and that was holding it in open air where there is convective air movement. Also my fins were thinner and there were more of them (which is what you want). I had some success adding a tiny fan to move the heat away, but sill not good enough for reliable day-to-day operation.

May I suggest a different approach? How about using forward-facing emitters with individual narrow-beam optics mounted on a flat sheet of copper or even aluminum, attached to a finned heat sink on the back of the unit that is exposed to the air? That way you will better control over where the output is aimed and your thermal concerns will be resolved. Kind of like what McGizmo did, although you may have to reconfigure your entire headlight assembly.

now I have got that sinking feeling....!:mecry: