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Discussion Starter · #1 ·
Hi!
This is my first post here.
I am in a process of building my first LED bike light with the 3x XR-E R2 mounted on a CPU heatsink and powered by 4NiMH batteries.
I ordered DX 1920 optics but now I am worried that they are too narrow for handlebar light. Can anyone recommend a more floody optics from DX?
I was sure I saw a very nice beamshot of DX 4626 optics but now I can't find it. Does anyone have any experience with this optics? How hard is it to mount them over a Cree star?
I know that there are nice optics available on other sites but for me they are too expensive.

This is what the light will look like:

 

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Lets RIDE!
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The 4626 optic is not made to fit the Cree leds (it fits the Luxeon III well, and probably the Seoul P4...). But with a little modification and ingenuity it should be possible to make it work.....maybe just cut off the part that fits around the Luxeon emitter and let it stand on the Cree star on it's 4 legs. It won't snap tightly onto the emitter like the 1920 does, so you'd have to center it accurately, then work out a way of holding it where you want it. I have some that I've messed around with (just balancing the bare optic on the cree emitter, without the holder) and it produces a pretty smooth 20° - 30° flood....just a hint of a dark spot in the center. I think it would be a good combo with the 1920 optic, maybe two 1920s and one 4626.

Are you running that cooling fan on your light?

JZ
 

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Discussion Starter · #3 ·
That's exactly what I was thinking - two 1920 spots and one flood. I have two switches. One will control the flood and the other the two spots. I would really like to point the flood lens lower than the spots but don't know how to do that with only one flat surface. Can the 4626 lens be angled slightly relative to the star? As you said, it's not like it 'clicks' tightly around the emitter.
According to my calculations my 50x50x25mm heatsink can't dissipate enough heat from 3 leds driven at 900mA. For one led it should be enough even in a completely still air. The fan will activate when I turn on more than one led, hopefully providing enough additional cooling. The main 'box' holding batteries and current regulators (DX 3256) is made of plastic so no help there.
Or should I simply build two completely independent lights, each with two Cree R2 leds, so I can point them independently? With only two leds maybe I wouldn't need the fan? What do the people here think? Can I cool 2 leds with only one 50x50x25mm heatsink?
 

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IMHO the heatsink will be a bit of overkill. I have no experience with the actual thermal numbers but I've ran P4's with 3256 and 4.8-6 volts within a copper pipe fitting housing without a problem.
 

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Discussion Starter · #5 ·
VaughnA said:
IMHO the heatsink will be a bit of overkill. I have no experience with the actual thermal numbers but I've ran P4's with 3256 and 4.8-6 volts within a copper pipe fitting housing without a problem.
Well, it should be enough. According to my calculations, for two leds the heatsink should have thermal resistance better than 10C/W. According to the data I found on one site it's possible to determine the heatsinks approximate thermal resistance from it's volume (for the finned heatsinks in the still air). For 10C/W you need a heatsink of about 25cm^3. Mine is 60cm^3 so, in theory, it should be enough. For the 3 leds you need 50cm^3 and that's dangerously close to 60cm^3 to risk it.
 

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I agree with VaughnA...that's plenty of heatsink for 3 R2s without the fan. If you hunt around on this forum you'll find plenty of lights running higher powered leds with less elaborate heatsinking.

As for aiming the flood optic down, if the optic is not aimed perpendicular to the emitter it will distort the beam and transmit less of the light. You'd have to experiment with how far you can tilt it and still have a usable beam. But the floodiness of this optic will probably throw enough light that you won't need to angle it.

JZ
 

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The thing you need to realize is that the fact that it's a bike light implies that you will have a significant airflow running over the light most of the time which will help with cooling. Yours is the first bike light I have ever seen that has a fan. The reason is a fan is not needed and will only consume power without any light output.

It's debatable how how much area is needed per Watt of power. More cooling implies bigger and heavier. Less cooling implies the light may run hot which reduces the LED light output and LED life. More area is nice when you are stopped so the light doesn't heat up as much, on the other hand if you stop for a significant amount of time you can either turn off or dim your light.

Here is a web site that you may find useful from one of the contributors on this forum. http://bikeled.org/ Good luck with your build.

dsvilko said:
Well, it should be enough. According to my calculations, for two leds the heatsink should have thermal resistance better than 10C/W. According to the data I found on one site it's possible to determine the heatsinks approximate thermal resistance from it's volume (for the finned heatsinks in the still air). For 10C/W you need a heatsink of about 25cm^3. Mine is 60cm^3 so, in theory, it should be enough. For the 3 leds you need 50cm^3 and that's dangerously close to 60cm^3 to risk it.
 

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Cool light, the heatsink should be more than enough cooling for 3 R2's, heck I would put 4 on there if they would fit (though you would need a bigger battery pack) :-D And I agree with Tex, you should ditch the fan unless you plan on using it off the bike - may make a good stand alone work light if it had a handle (dual purpose?).

How is the battery pack held in there? Are you planning a bezel to protect the optics and maybe weather seal it?
 

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Discussion Starter · #10 ·
HuffyPuffy said:
Cool light, the heatsink should be more than enough cooling for 3 R2's, heck I would put 4 on there if they would fit (though you would need a bigger battery pack) :-D And I agree with Tex, you should ditch the fan unless you plan on using it off the bike - may make a good stand alone work light if it had a handle (dual purpose?).

How is the battery pack held in there? Are you planning a bezel to protect the optics and maybe weather seal it?
My design goals are:
- can be used both on bike and as a regular flashlight (it's actually surprisingly comfortable to hold as it is!)
- small
- powered by AA batteries (preferably integrated)
- easy to mount and remove (as I often leave my bike in a not completely secure locations and so like to strip it of easily steal-able items)
- 45min runtime on the maximum output is enough
- would be really nice to be able to independently aim the spot and the flood beam

I think I'll build two almost identical 2xR2 lights. One with the 8-degree optics and the other with the 30-degree flood. There are a few advantages over the original one 3-led design:
- more lumens (I guess 800lm is not out of the question as each R2 should produce about 250lm @900mA)
- longer runtime (over an hour @800lm, 5 hours @200lm - with Eneloops)
- heatsink should be enough for two leds even without the air movement
- can lend one to my girlfriend when we go biking together (even 400lm from two emitters should be enough)
- independent aim (I am guessing that I should get much more light on the road as opposed to the sky if I aim the 30-deg beam a few meters from my bike and the 8-deg spot 20-50 meters ahead)

Not counting the batteries (allready have those), the light will cost me about $50 which, if I am not mistaken, is a really good price for a 800lm light.
Ok, now that I have talked myself into building not one but two lights I have to figure out how to do it. :) I've got a pretty good idea but we'll see... I think it will even be waterproof, apart from the batteries sticking out :)

To answer your question... the battery holder will have a 9V connector at one end:

and the matching connector will be glued inside the box so I will connect the batteries simply by sliding them inside. The batteries are held firmy by friction as they fit tightly. They'll stick out even when fully inserted so it will be really simple to remove them for the recharge.

If you or anyone else have any more advice/suggestions, I would be very grateful!
 

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Check this source of optics out. Lots of choices, reasonable shipping, faster than DX....I bought a bunch of optics from him and it took about 2 weeks to the US. He has leds too (no R2s but Q5s are very close) and an interesting handlebar mount that I wish I noticed when I placed my order :rolleyes:

JZ
 

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Discussion Starter · #12 · (Edited)
JimZinVT said:
Check this source of optics out. Lots of choices, reasonable shipping, faster than DX....I bought a bunch of optics from him and it took about 2 weeks to the US.
Thanks. The prices are not too high (as I would only need two lenses) but it's still much higher than DX. Also, is seems that all the 'wide' ledil optics are a combination of a standard narrow optics and different kinds of diffusers. The light loss due to diffuser should be larger than from a 'clear' optics designed for a wide spill (such as the sku.4626 seem to be). Of course, I could be completely mistaken.
If I go with the ledil optics, which one would you recommend? I need optics that, pointed about 2m from my bike would give me good, smooth illumination of a road from about 1m to about 8m from my bike.
 
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