Calling knowledgeable modders for help with Cree XR-E headlamp project

I have been gathering parts to put together a headlamp. I got the idea from the instructable that was done recently. It can be seen here:

http://www.instructables.com/id/E2K9BN5EDKEUBYRD9V/?ALLSTEPS

I want my headlamp to have white output, though. I was going to use Luxeon I LEDs, but thought using 4 Cree XR-E stars might be a better option. I have some questions on making this setup:

1. Will the lens and lens holders (OP-015 and OH-ES1-CL) need to be replaced or are they compatible with the Cree XR-Es?
2. I want to harness the power of the LEDs, maybe using a 2000ma driver instead of 1000ma for a total of 500ma per LED. I did not see any 2000ma Buckpucks, though. What would be a good driver for this?
3. I still want 4 brightness levels, what resistors would I use?
4. Are there any differences between using Luxeons vs Cree that I need to deal with?

I have most of the parts I need, I think if I could get this done correctly it would be great, thanks.

Re: Calling knowledgeable modders for help with headlamp project

ok here goes, I am still trying to grasp some of these concepts myself so by no means take this as the 100% truth as YMMV.
1st- Cree makes an optic for the XR-E and so does someone else (L2 i think) but i am having trouble remembering who and am too lazy to google it right not. But i would try to get a Cree specific optic so that you would not have to modify anything.

2nd-I do not believe that anyone makes a 2000mA driver. One thing that you could do would be use 2 buck pucks and wire the LED's 2 in series per driver. But my loose understanding of electric principles tells me that if you run the LED's in series, like homeboy did on his turq headlamp, each light gets roughly the 1000mA, but you wind up adding the voltages together. So that would be roughly a 12v system plus with the Buckpuck, i think that you have to add 2v per LED for the driver to function right. I could be wrong, again too lazy to get the data sheet for the buckpuck, just going off memory which aint so accurate sometimes.

3rd- Resistors? Thats why i have an electical/computer engineer for a father-in-law, i let him tell me what to do there.

4th- Dunno of any other differences off hand other than geometry, and the crees can put out some light with less power thats about it.

One thing you might consider is using a 5k pot with the dimmable buckpuck instead of a bunch of resistors and multiple switches. Although you would have to come up with some sort of housing for it. I think you can get a pot with a built in switch, so it could be really clean. You could probably just get some PVC pipe with ends, drill a hole, and get some o-rings and a knurled nob for an electric guitar. And bam you have a couple problems solved. Just gotta go and get creative. Thankfully i have an ace hardware store like 2 blocks from my house, so i just ride my bike over there and walk the aisles till inspiration hits. I was in there 2x a day when i was trying to finish up my ghetto tac light.
WTYM

dave

So, using 2 1000ma Buckpucks would result in 1000ma per LED, not 500ma per LED?

What is a 5k pot?

Sorry, I am inexperienced with this.

If you wire them up the same as him in series/parallel, then 2 1000mA buckpucks would result in 1000mA per LED. However I really wouldn't recommend running XR-Es in parallel at all as the variation in Vf means you will end up overdriving some and underdriving others. You're best off wiring them all in series and running them off a single regulator - either use a single 700mA buckpuck (if you've got a high enough voltage battery), or if you want to use a lower voltage battery, a boost regulator like a Taskled Fatman.

In fact the design there isn't that great in several other ways - eg it would be better to use thermal epoxy to stick the LEDs to the heatsink rather than relying on the other glue on the top keeping them compressed well enough.

5k pot = is a potentiometer with 5k of resistance (not sure what the unit of measure is called other than Ohms or whatever, again not a well versed electrical guy). It basically varies the resistance so it would be used in place of the resistors. Its what the knob on your stereo is attached to so that you can turn up the volume and what not. Go to your local radio shack and go look for a Potentiometer. The will be back with all the little toggle switches and stuff. Or just google it. Google has a ton of info right there for ya.

as for the mA's, it all depends on how its wired as to how much each LED is gonna get. In the set up that the guy did in his article, they were all wired in series. Which means that the + from the power source goes to the #1 LED's + terminal. Then the wire from the - terminal on LED#1 goes to the Positive Terminal on LED#2 and so on with the rest of the leds. Then the the Wire from the - terminal on the #4 LED goes back to the power source. This is running them in "series". when you wire them like this, the full amount of mA's goes to each LED, but as the power goes from LED to LED, the LED's eat up a bit of voltage (lets say 3v per LED). So to get this system to power up you need to multiply the Vf or voltage forward for the LED's by the # of LEDs. which would give you 12v. So you will need a power source with slightly more than 12v to get the LED's to power up, as the Buck Puck regulator reduces the voltage out put slightly so that it can regulate the Current (mA). So in this example each LED recieves the full 1000mA but you need to have quite a bit of voltage.

If you run the LEDs in Parallel, you are basically hooking up each LED's Pos to the Pos on the power source and like wise with the neg side. With this, the voltage does not get added up, as each light only needs 3v to operate and they are not dependate on the one in front of it to pass along the current. So you would just need a 3v power source. But with this set up you will have to divide the current amongst the lights because each LED is trying to get their own piece of the pie so to speak instead of passing it on. So on 1000mA it would only be roughly 250mA (I might be off base and a little generalized with this, but this is my rudimentary understanding of this. Someone please correct me if i am wrong). But as chis_m said, Running them in Parallel off of a single regulator is not such a good Idea. For simplicty, i would just strait up copy with the guy did with his headlamp, but use a thermal epoxy like Arctic Alumina to hold everything down on the heat sink. And having 2 of the buck pucks and all the switches and what not would become a little bulky IMO. I would just run 1 buckpuck, 4 LED's in series (like the guy did), get a 700mA driver for the Crees, or a 1000mA for some LuxIII's. Just do what i did and research the crap out of it. And just give it a try, it really doesnt cost that much if you screw up (I think ive fried 3-4 LuxIII leds and a couple LuxV when i was just messing around).
Peace

Dave

Thanks for the input. I wouldn't mind the extra bulkiness of the extra Buckpuck and switch, but if it makes it a lot easier than I think I will run off one driver. Why is it that you recommend a 700ma driver for the Crees instead of a 1000ma driver like the Luxeons? I already have a 1000ma Buckpuck and the 4 Luxeon LEDs, should I just stick with that? How much brighter would 4 Cree LEDs be vs 4 Luxeon I LEDs if they are both running at the same 1000ma?

Just to correct a slight point - he isn't running the LEDs in series in that guide, but in series/parallel (two strings of two LEDs in series, with the two strings running in parallel with each other). As I said before, not something I'd recommend, so don't follow that design too closely.

It appears the design as mentioned is a series /parallel spilt which simply means for the 1000mA puck is paralleled to provide two 500mA sources of current and these are then used in series to provide a source for each led. It would be simply to use a 700ma in series for 3 watt leds,, as meyioned you will need to ensure sufficient battery power9(ie forward voltage). If your using LUX1 Cree will be probably 4x as bright however without the specifics of your bin it is difficult to be specific. At 700mA a P3 Cree bin will deliver 140 Lumens

Cheers
WL

Oh, I guess I missed what was being said... so running 700ma in series will mean each LED is receiving 700ma? By the way, I am using 8 AA nimh (9.6V)

iamerror

Do you have luxeon 1 or Luxeon111 LEDs
The max current for a luxeon 1 is 350ma

ie with your battery pack you could have a 700ma driver running two strings of 2 led - each with 350ma

Nick

Doh!Nut said:

Do you have luxeon 1 or Luxeon111 LEDs

Click to expand...

Read the thread title!

With an 8 cell NiMH pack, your voltage will vary from 11.2V down to 8V over the useful discharge of the pack. Since an XR-E is nominally ~3.5V when run at 700mA (mine have now dropped to ~3.3V average after some burning in), you'll only be able to run 2 in series with a buck regulator. So either you'd need two 700mA regs, or if you want to ignore the advice about parallel running, a single 1400mA reg (eg Konlux). However one other possibility is to use a boost convertor (eg TaskLED Fatman), which will work just fine with that battery and 4 LEDs in series.

Chris
I was refering to this bit (my bold)

iamerror said:

Thanks for the input. I wouldn't mind the extra bulkiness of the extra Buckpuck and switch, but if it makes it a lot easier than I think I will run off one driver. Why is it that you recommend a 700ma driver for the Crees instead of a 1000ma driver like the Luxeons? I already have a 1000ma Buckpuck and the 4 Luxeon LEDs, should I just stick with that? How much brighter would 4 Cree LEDs be vs 4 Luxeon I LEDs if they are both running at the same 1000ma?

Click to expand...

I would hate for him to try to put an amp through a Lux1 :thumbsdow

Nick

Ah, I missed that bit!

Looks like he has Lux 1s. Of course the original build referred to is also Lux 1s, but being run at 500mA (which does seem to be OK given adequate cooling, even if it is outside the spec.)