problems with my tripple cree bike light-Beamshots added

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vinsanity286

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After seeing the new dinotte 500l tripple cree bike light, and just purchasing 3 cree p4's I decided to make my own bike light.
Instead of making a body, I used an aluminum 3aaa light that had enought room in the head for the 3 emitters. I used the lenses out of a few dorcy aaa lights which work excellent with the cree.
The problem is that driven either off of 3aaa's or 3aa's(both nimh, leds in parrallel) it just doesn't seem that it is kicking out the light that is should. I mean it definately puts out a good amount of light but no where near as much as the following lights..

These images are from the gear review 2007 led test, all bike lights.
The cat eye tripple shot pro 3 x 3 watt luxeons http://www.gearreview.com/images/led2007/beam/CatEye%20TSPro.jpg


And the new dinotte 500L (tripple cree light with claimed 500 lumens)
http://www.gearreview.com/images/led2007/beam/Dinotte%20Big%20Light.jpg

Are three crees just sagging the three cells too much? I know they should be all run in series but I don't have the batteries to do that right now. Sorry for the long post and thanks in advance for any help. I am going on a night ride soon and I want to get this thing up and running.
 
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Re: problems with my tripple cree bike light

You would have a much better light if you got a constant current supply in that setup.
Also if you ran the LED in series not paralell you could be sure that the same current passed through each LED

Have a look at the Sandwich Shoppe or Task Led, you would need a boost converter.
Nick
 
Re: problems with my tripple cree bike light

Thanks Nick, I know that they should be in series but even with each led possibly getting different current it should still be brighter.
 
Re: problems with my tripple cree bike light

So... are the Crees running direct on the 3 cells? If so, they are likely pulling way too much current for direct drive off of AAs... even NiMHs. 3 C or 3D cells would likely do the trick but it would probably be better to have some sort of regulator. Even running them each at 350mA would provide a LOT of light... around 300 Lumens or so. Also, in that small of a head without a proper heatsink, I'd expect heat would be an issue even if the cells would supply enough current to keep them going.

It might even be better just to have a single Lux III on a couple C or D cells because at least then, the light would be pretty linear.

Just to be sure, you have three Crees on a single AAA-sized light with no 'real' heatsink and running direct on the three AA or AAA cells?
 
Re: problems with my tripple cree bike light

Yes the crees are running direct drive. The light holds 3 aaa cells in a carrier. They are mounted on a 1/4 inch piece of aluminum plate that kept pressed against the body. The negative sides of the led are soldered to the aluminum. Heat sinking is not a problem, especially at the drive level they are at now. And like I said, they put out a bunch of light but not compared to the lights above or even the homemade cree lights on this forum.
I measured voltage under load with the aaa's to be 3.8 on fresh cells and 4 volts unloaded. 3.8 volts under load sounds impossible to me, but i checked it with 2 multimeters. Confused...On my crappy multimeter it pegs the 250ma scale but on my better multimeter(only goes up to 500ma) it reads under 200ma with greatly diminished brightness.

Hmm... I was just looking at the 2006 led comparison and there seems to be a large difference in all the beamshots. here is the double shot from 2007 http://www.gearreview.com/images/led2007/beam/CatEye%20DS%20-%20A.jpg

and here is the double shot from 2006 http://www.gearreview.com/images/led_lights/road_Cateye-Double-Shot-dual-3W.jpg

Huge difference. Maybe the 2007 pictures are greatly overexposed? Or visa versa?
 
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Re: problems with my tripple cree bike light

Well, at 250 or 200 mA, they shoul'd be pretty effecient, but possibly not putting out the kind of light you are wishing for.

I think the cheapest way to get more light would be to take a 4D frame pack, solder a spacer across one of the D cell areas, pop in three D cells and wire it into your light. But... if they supply the current the Crees want to pull, I really think heat will be an issue. Less of an issue if you use ample thermal coupound and less of an issue if the light is only on while you are acutally riding.

For perspective, my Tri Lux I light (three R**H Lux I stars) pull 1.2A off of three D cells.

I'd say to get in the ballpark of the light output you are expecting, each Cree will need 350-ish mA. That would get you in the range of 300 Lumens. The next issue might be getting a more proper reflector than the Dorcy lenses. Those must be holding back quite a few lumens and I'd imagine are reducing throw. Three IMS20s would be my starting point, but I've never used them with Crees.

Still, I think you have a great project. I'll have a couple SSC Stars on the way and was thinking of adding an emitter to put in a MiniMiniMag and running on a 14500 and a resistor.

I can't imagine having three Crees in a Minimag-sized light.
 
Re: problems with my tripple cree bike light

You are trying to direct drive 3 Crees off of 3 AAA batteries? 3 AAAs can barely run a single 3watt. You are maxing out the drain current from the AAA batteries. You should try something bigger like C or D cells.

If you were to run them direct drive in series you could try running them off of 4 123 batteries.
 
Re: problems with my tripple cree bike light

Thanks for your help cratz. The dorcy lenses produce a large even blob of light with no hotspot, just like with the 5mm led in the stock dorcy. I have one lense focused for flood and the other focused for medium range. The third cree is a stange one. I accidently knocked off the dome while handling it. I pulled out all the white glue and superglued the dome back on. The tint is not faintly green and the viewing angle is half of what an unmolested cree is. I must have put the dome back out of focus but it actually worked out well, and the green tint seems to have better color rendition outside.
 
Re: problems with my tripple cree bike light

Actually, another option might be one of the funky 3xAAA sized LiIon cells that AW sells. 18450 or something like that. That would likely supply enough current to run them, but I still think there will be issues with the heat. And runtime with any cells that are likely to fit in that small of a flashlight.

I have a Xenon knockoff that has the 4xD frame pack and I might try to mod it with a single Cree or SSC when it starts getting a bit warmer. But I'd probably only run it at 350mA or less. I think 200mA would be plenty bright for my needs.
 
Re: problems with my tripple cree bike light

Stoven, yes they are direct drive off of 3 nimh aaa's and i tried 3 nimh aa's. Wouldn't the aa's be able to handle the drain of 3 crees? The discharge would only be around 1C.

Eventually i might go with an 18650 or larger lithium cell but for now i am stuck with the aa's.
 
Re: problems with my tripple cree bike light

No. A properly driven single Cree is about the most an NiMH AA would be able to keep up with. Certainly not three.

Things rarely work out in the real world as they look on paper. I'd say a properly driven Cree would have at the very minimum 350mA. Three of them would be 1050mA. So assuming no internal resistance of the cell, driver or path, it still wouldn't even quite get there. And the 350mA per LED is on the lower end. Lots of lights will have them running at 750mA. But again, heat becomes an issue.

Think about it, if three crees could be adequately driven off of AAA or AA cells, why isn't the market flooded with multiple LED Cree lights? Truth is, a single NiMH cell can just about adequately drive a single Lux I LED at ~300 mA.

I say that for three Crees, you'll either need C or D cells, or LiIon cells. And even LiIon cells aren't 100%. R123s seem to be able to drive drivers better than 14500 cells and 18650s seem to be able to drive them much better than a single R123.
 
Re: problems with my tripple cree bike light

So if I ran 3 alkaline c cells or d cells would that work, or would i need a resistor to knock down the voltage. I can deal with the heat, the light will be on the bike so the air will cool it sufficiently. again, thanks for your help.
 
Re: problems with my tripple cree bike light

I'm not 100% sure, but I think three C or D cells direct would be fine. I haven't done such a mod so I'm purely guessing, but I'd expect three Crees to pull somewhere between 1.2 and 2.0 amps from three D cells... probably closer to 1.2. And even if they pulled the full 2.0 amps, the voltage and amperage shouldn't hurt the LEDs, it would be heat buildup.

But... if you are using one of the frame hang down battery packs, you could either use a convertor or wire in whatever resistors in place of the missing cell.

Really... if they are properly heats-sinked and have an adequate power supply, even if each only saw 350 mA, it would be extremely and impressively bright. Between the extra runtime (from having an extra cell) and the constant output (from having a constant current board), I think the way to go would be a basic regulator.

Be sure to keep us posted. Also, if you happen to lose this post somehow, it might get moved over to the modded lights forum.
 
Re: problems with my tripple cree bike light

I would think that they would pull at least 3 amps from 3 d cells and no resistor. The new deal extreme u2 cree light drives a single xre at 1.2 amps. I will try DD off of 3 D cells when I get back from class, I hope i dont fry them.
 
Re: problems with my tripple cree bike light

I don't understand the reason you're not making a better light by using a regulator. That way your light doesn't gradually die as the battery runs down. Seems a no-brainer to me if you're going to the trouble of making a homemade high-power light.
 
Re: problems with my tripple cree bike light

chris_m said:
I don't understand the reason you're not making a better light by using a regulator. That way your light doesn't gradually die as the battery runs down. Seems a no-brainer to me if you're going to the trouble of making a homemade high-power light.
Click to expand...

Well, I agree that a regulator would be better overall, but not always. For one thing, with a regulator, usually your light just dies with no gradual decrease in brightness. And of course, some effeciency is lost. This is especially true of, say, a 3D Lux I or Lux III Mag mod. A simple resistor, I think is the way to go.

But in this particular instance (not 100% sure what the OP is planning), but when I do my mod, I'll be using the 4D cell frame battery pack. Without a regulator, I'd have to wire one of the cell spaces for voltage reasons, but I'd be shorting myself an entire D cell battery. With a regulator, you get to keep all 4 cells. For my needs, this greatly outweighs the lost effeciency.
 
Re: problems with my tripple cree bike light

Thanks for the link. I will probably pick up some more aa's and run them in that way, direct drive off of 8 cells.
Last night I mounted my light to my bars and went for a ride on the road running them off of 3 aaa cells. They deffinately kick out alot of light and I was confortable even at fairly high speeds. There is snow on the ground here so I couldn't try them on a trail.
I only road for maybe 5 minutes(tooo cold) but after going inside and leaving the light on for another 5 minutes the leds were cool to the touch. It is definately underdriven.
I remeasured and with freshly charged aaa's it only pulls 300ma, so only 100ma per led. When a single cree is hooked up to the same batteries it pulls 150ma.
The reason I wanted to keep the leds in parrallel was so I could still use it as a flashlight with the 3 aaa carrier. It makes an excellent flood light. I will try to get some beamshots tonight.
 
Re: problems with my tripple cree bike light

Ok I just ran the 3 crees in parrallel direct off of 4 nimh aa's. I measured them to be 135 degrees ferenheit after about 2 minutes. What is the practical thermal limit of these leds? The heatsink was the same temperature as the crees so its definately working. But I must have a problem with my multimeter because all three emitters only drew 350ma running off of the 4 cells. Maybe I need a scale higher than 500ma to be more accurate.
 
Re: problems with my tripple cree bike light

maybe you cause a measurement mistake with the internal resistor of the multimerer (also with the wires inclusive contact resistance), so when you don´t put the multimeter in the cirquit, the cells run more current through the LES´s.

possible?
 
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