# DIY Cree Bike Headlight



## Dan K (Oct 28, 2008)

Hi,

I'm very impressed with my Task Force Cree, and am considering a homebrew version for the other side of my handlebars on the mountain bike that's more focused on flood than spot. I see cree bulbs all over DX for just a few dollars. Could anyone recommend one in particular, and if you're feeling particularly generous link me to what else I'd need? I figure I can make a housing out of aluminum. I will probably need a reflector, maybe a lens (don't know how the bare cree would handle the elements) and whatever sort of controller is used to regulate power to the cree. I'd like to run it off 2 AA batteries located remotely, maybe in the handlebars. I've heard of people hacking up the TF to accomplish this, but it seems to be I should be able to do it for less from DX, plus my area is sold out of the TF lights.

Thanks,

Dan


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## Calina (Oct 28, 2008)

Here's a link to the highest bin (R2), Cree has to offer at the moment: http://www.dealextreme.com/details.dx/sku.15943

It's a start...


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## Dan K (Oct 28, 2008)

Thanks. Forgive the newbie Q, but is bin the brightness?


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## LukeA (Oct 28, 2008)

Dan K said:


> Thanks. Forgive the newbie Q, but is bin the brightness?



Yep. R2 is 114 to 121 lumens at 350mA.


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## Dan K (Oct 28, 2008)

Cool, thanks. So @ 114-121 lumens, I’m looking @ a bit more than 2/3 what the TF puts out? That should work, although being in the 150+ range of the TF would be nice. Then again, the TF is probably overrated, though I have no idea how to tell if this is similarly overrated.

I assume I would need a circuit board to regulate voltage to the light? Does it need to be specific to this light? 

Then, of course, I’ll need a suitable battery to power the whole deal. Something with a holder that I could solder wires to for connecting to the light (or driver/board) and to my chargers would be ideal. Unfortunately I don’t know where to start here. Is there a beginners guide someone could point me to if all the Q’s I’m asking have been beaten to death here already?

I know exactly what I want: A powerful cree emitter that I can put in a small housing (will likely be mounted to handlebars of mountain bike) with plenty of flood, and a separate power source that I can plug into the light as well as a charger. Maybe I could even use Deans Ultra connectors off the battery, to connect to both my charger and the light setup? I’ve got plenty of experience soldering and doing RC stuff, so I should be able to do the actually doing/assembly part of this, I just need some serious guidance on what to buy and what to do.

Thanks,

Dan


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## qwertyydude (Oct 28, 2008)

You're going to need more than 2 AA batteries if you're homebrewing a light. It's not as easy to get a decent boost circuit for high powered use. If you want to keep it simple I'd suggest direct driving the lights as this is the most efficient and simple way to power the lights.

Direct driving using nimh means 3 batteries in series, if you want a very good way to power them try using a 6 cell sub c pack available at hobby stores, these can have up to 5000 mah, you can run one light for a long time by wiring the pack in 3s2p mode or 2 lights by just keeping it stock.

One problem I did encounter is that direct driving higher bin led's while bright will burn them up reducing output unless you do some serious heatsinking, even going so far as to dismantle the star and mount it onto a solid copper heatsink. So if you're going the direct drive route it may be best to get a lower binned led like a P4, no problems so far on mine which has over 50 hours of use.

The easiest way to get an led with regulation, is to buy a P60 module, it may have too much throw but my solution to make it a flood is simple, sand the reflector with 320 grit sandpaper (make sure you remove all the orange enamel under the reflective material), then repolish it with metal polish I like mother's billet polish. By varying how much you repolish you can go from smooth flood to throwy spotlight or anywhere in between. You can then input almost any voltage above 3.7v up to 18v.

http://www.dealextreme.com/details.dx/sku.11836
here are the modules, plenty cheap and each one is run at about .6 amps, about 2 watts so you get about 200 lumens from each. Keep it that low and you won't need tons of heat sinking. Contact with the aluminum chassis of your light is enough.

http://www.dealextreme.com/details.dx/sku.14413
This is a P7 module, pretty large but naturally floody and if it drives the led at 2.8 amps as specified you've got close to 700 lumens, just keep in mind that this will definitely need good heatsinking.


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## degarb (Oct 28, 2008)

qwertyydude said:


> One problem I did encounter is that direct driving higher bin led's while bright will burn them up reducing output unless you do some serious heatsinking, even going so far as to dismantle the star and mount it onto a solid copper heatsink. So if you're going the direct drive route it may be best to get a lower binned led like a P4, no problems so far on mine which has over 50 hours of use.




Whoo, I don't get this at all. 1. Wouldn't higher bin leds be less hot since more power is turned into light? 2. Would driving at 350 to 400 milliamps hurt since these are 3 watt leds? (What drive levels are dangerous? I don't find the 300 to 400 milliamp range to heat up like the >500 milliamp range.) 3. What is example of poorly heat sinked versus properly? (Like, I assume any plastic only head is bad. But can a head with metal in it be also as bad?)


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## qwertyydude (Oct 28, 2008)

They are more efficient but they also tend to have lower vF's. On a regulator .6 amps came at only 3.4 volts at the emitter, compare this to my P4 where .6 amps came at about 3.7 volts the direct drive means constant voltage. And at a little over 4 volts on a fresh battery pack or li-ion you'll get 2.1 amps into the R2, my P4 only runs at 1.6. Even if it's more efficient by about 10% you're still pushing an extra 2+ watts into the light period, this equates to about a 20% increase in total heat generation. Without a perfect heatsink this can lead to a drastic rise in die temperature and hence the risk of damage when running in a constant voltage mode (direct drive) vs a constant current circuit (regulated).


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## LukeA (Oct 28, 2008)

Dan K said:


> Cool, thanks. So @ 114-121 lumens, I’m looking @ a bit more than 2/3 what the TF puts out? That should work, although being in the 150+ range of the TF would be nice. Then again, the TF is probably overrated, though I have no idea how to tell if this is similarly overrated.
> 
> I assume I would need a circuit board to regulate voltage to the light? Does it need to be specific to this light?
> 
> ...



That's lumens at 350mA. You will probably want to run the LED at 2 or 3 times that current (for nearly two or three times as much light respectively)


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## dnlwthrn (Oct 29, 2008)

I'd go down to the bicycle section in the Transportation lighting part of the board and look around. There's a LOT of info down there on bike-specific DIY lights.

As LukeA said, the lumen rating is at 350mA. Most of us with DIY bike lights are running them in the 700-1000mA range... 

Easiest solution is to pick up a driver like the bFlex from TaskLED and use RC car batteries for your power source. That gives you a 7.2 or 8.4V source with anywhere from 1500mAh to 5000mAh. If you're running only one LED, you need a buck driver to give you the constant current and to drop the voltage down to the Vf of the LED (3.5-3.7V).

There are lots of good ideas for quick/cheap housings available too...

http://www.candlepowerforums.com/vb/forumdisplay.php?f=86


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## jrbruin (Oct 30, 2008)

Just thought I'd throw this out there.. I built my bike light based on this website:

http://bikeled.org/

The "copperhead" is the one I went with, looks and works like a charm.


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## jrbruin (Oct 30, 2008)

BTW, one LED (unless it's a P7) isn't going to do the job for a bike light unless you're riding in an already well lit area or you're not riding very fast (ie. < 10mph)

The 3 LED solution I have it pretty good, but I wouldn't mind more light - it's still possible to outrun my light when I get going really fast.


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## Dan K (Nov 2, 2008)

Thanks for all the replied guys. I'm already running one Task Force 3W Cree, which does pretty well for illuminating down the road. What I need is something more floody for when I'm off-roading. While I'm tempted to just buy the bulb and module suggested above and see what I can come up with, this seems like one of those times where some research now can save some frustration and money later. That said, I'm off to do some searching and reading in the bike light forum, thanks for the links and all the help everyone.


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