Triple XM-L Driver?

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leesnuts
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Triple XM-L Driver?

I'm new here and have always wanted to try to build my own LED light. What I was thinking of is building a triple Cree XM-L light. I plan on running either with 1 to 4 18650 batteries. Can someone recommend a driver? Do I really need one or can i get away with just running the circuit with some resistors?

Don
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The simplest way would be some resistors. These will need to be able to handle up to around 30-40W which means large wirewound resistors (The 10W wirewound resistors available around here are 50x10x9mm). It would probably be simplest to mount the resistors in parallel and use 3-4 18650 also in parallel which would lead to a short, fat light. At full power with decent heatsinking you could draw up to 12A.

For a rough estimate of a resistor to start with, you want to limit the current to, say, 12A at around 3.6V. V=IR so 3.6=12x around a quarter to a third of an ohm. 3-4x1ohm 10 watt resistors in parallel is the sort of place to start looking unless someone knows better as lots of people here do.

Heat is going to be a problem, so make sure the LEDs are mounted on a heavy slug of metal (Preferably copper or aluminium (or, even better, silver)) to help with heat sinking. And the resistors are going to get warm too.

 

The numbers from my light tests are always to be found here.

https://spreadsheets.google.com/ccc?key=0ApkFM37n_QnRdDU5MDNzOURjYllmZHI...

Budgeteer
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Triple 18650 in parralel might do it too and add up some compactness. The runtime wil be short (40min-55min depending on cells, and current draw) but that's not really an issue since max brigness sessions would also be short unless you come with a excellent heatsinking designed host. I would reccomend you to get respectable cells for this setup.

You might want to DIY an host for triple X-ML dropin. Not the best approach but if youre building one from scratch it might save you dealing with drivers if you wish to not bother with them.

The resistor trick is okayish but i would not be impressed with since as voltage from the cells drop so does the output. No regulation at all (and resistors are basicly a heating waste of nergy in this kind of application, cheap tho... i admit).

Do you require a setup that can be lit at full brightness for lets say 30min in one session or just for a min or so at a time?

On a side note. If you have 3 XM-L dropins strap three flashlights together and see if you like that.

kragmutt wrote:

They're gonna send you a green redcat with a black LED.

leesnuts
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Can 3-4 batteries in parallel draw or provide 12A?

Do I have to run each resistor to or from each LED? Can I just bundle all 3 resistors in parallel with each other then run 3 separately lines to each LED?

 

 

Budgeteer
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4x Hi-max 18650 2600mAh is doable, unsure for XTAR 18700 2400 a bit tight perhaps. One thing to worry would be the possibility of uneven draw. Can't be a good thing. I would suggest the change of cell setup and choosing fewer (2 giant D size lithium class) but with greater capacity. Finding good ones is another story. Charging may be tricky though. Single or per led resistors may not have a significant difference. Fitting a large one may be difficult.

Out of couriosity... what kind of use you wish out of that monster light? Maybe if we picture it better we can perhaps provide new ideas.

If i were you i would power and drive individually each XM-L with 1 good 18650 cell. Would wire the switch for all three in one. Finding a 12A switch might prove difficult too.

 

kragmutt wrote:

They're gonna send you a green redcat with a black LED.

sixty545
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Budgeteer wrote:

Single or per led resistors may not have a significant difference. Fitting a large one may be difficult.

If i were you i would power and drive individually each XM-L with 1 good 18650 cell. Would wire the switch for all three in one. Finding a 12A switch might prove difficult too.

Parallelling 3 diodes would yield very different currents! It is imperative to use one resistor per diode.

[Edit]: If the LED's were connected in series, one resistor is sufficient.

Budgeteer
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Thanks for the heads up!

kragmutt wrote:

They're gonna send you a green redcat with a black LED.

leesnuts
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I'm really starting to like the 3 drop in idea running 3 18650 battries. With all of the modes, would it be difficult to keep them all running in the same setting? Just one switch would be nice.

You guys got me thinking, one housing with 3 drop in and 3 switches on the back. turn all 3 on for full brightness or 1 or 2 for lower amount of light.

What I am tring to build for fun is a light that I can hook up to my mountain bike. My friend just bought one which he paid a couple of hundred dollars for and I want to see if I could do better with less money. So I would like it to be small/light and insanely bright.

Mark Larson
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leesnuts wrote:

I'm really starting to like the 3 drop in idea running 3 18650 battries. With all of the modes, would it be difficult to keep them all running in the same setting? Just one switch would be nice.

You guys got me thinking, one housing with 3 drop in and 3 switches on the back. turn all 3 on for full brightness or 1 or 2 for lower amount of light.

What I am tring to build for fun is a light that I can hook up to my mountain bike. My friend just bought one which he paid a couple of hundred dollars for and I want to see if I could do better with less money. So I would like it to be small/light and insanely bright.

There are a couple of 4-6 XM-L builds on CPF. One is rectangular like a cuboid, one is round like a coffee can.

If you're doing a bike light, you can luckily forget all the traditional constraints of a flashlight body and think in terms of a bike light (hint: external LiPo battery packs), and worry more about cutoffs and putting the light where you want it instead of having a bright hotspot with some spill. Smile

Flashaholic since 2003, loving this new forum!

uncajesse
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Mark Larson wrote:
There are a couple of 4-6 XM-L builds on CPF. One is rectangular like a cuboid, one is round like a coffee can.

Hah wow.  Yeah man, even one XM-L @ 3 amps probably owns your friend's bike light.  3 would be siiiick...  maybe a Manafont smooth in the middle (generally more throwy too), with two KD SMOs (larger hotspot) on your two slightly-to-the-side spots...  the overall spill might be as bright as your friend's hotspot, and your hotspot well...

Let's just say any oncoming traffic will be pissed off. Wink

leesnuts
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sixty545 wrote:

Budgeteer wrote:

Single or per led resistors may not have a significant difference. Fitting a large one may be difficult.

If i were you i would power and drive individually each XM-L with 1 good 18650 cell. Would wire the switch for all three in one. Finding a 12A switch might prove difficult too.

Parallelling 3 diodes would yield very different currents! It is imperative to use one resistor per diode.

[Edit]: If the LED's were connected in series, one resistor is sufficient.

In series, would i have to up the voltage? and if so would I need just one 1 Ohm resistor at 30Watts?

 

ledoman
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leesnuts wrote:
What I am tring to build for fun is a light that I can hook up to my mountain bike. My friend just bought one which he paid a couple of hundred dollars for and I want to see if I could do better with less money. So I would like it to be small/light and insanely bright.

You don't have to complicate that much. A bunch of people here we are runing MagicShine headlamps which also fits on bicycle bar. Take a look at:

http://www.dealextreme.com/details.dx/sku.44459 and similar. I've driving car @100km/h on motorway with it - just to check if doable.

Feel free to ask any question about those lights as I own one and seen many. And I'm imaging how would be with XM-L........... Should be better tnah P7.

Budgeteer
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If a bike light you want you might want to consider this:

http://cgi.ebay.com/5-x-Holder-for-18650-3-7V-Rechargeable-Lithium-Batte...

Make a nice battery pack the way and form you like. Put it in a bag.

Make a custom reflector with three XM-L. Get something like this: http://www.dealextreme.com/details.dx/sku.46683

And something like this:

http://www.manhattan-products.com/en-US/products/9111-socket-lga-1156-cp... - best got for a beer from a computer technician.

Drill it through and use the fins as heatsink on the body. You can manage this thing to look somehow decent if youre skilled enough. Since you are supposed to ride when illuminating, heatsinking can be a bit consservative but don't skimp on it.

Find a good driver(s) and run your XM-L's in parallel or serial. Due to recent events i would go for 2,5A for each XM-L. Doing it this way you need 3 emitters on star and not whole dropins. Put the switch between the batteries and the light. Maybe on the cable running to the battery pack.

And lastly, why 3 XM-L? Since youre not doing a flashlight you can go with just 2 XM-L. with 4 18650 2x 2 in series you also get some decent runtime out of it.

I like good aesthetics but for MTB downhills i would not bother how the bike light looks like. I rather have it reliable and keep all my teeth.

kragmutt wrote:

They're gonna send you a green redcat with a black LED.

leesnuts
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Decided to try 3 because of this reflector:

http://www.dealextreme.com/details.dx/sku.1912

with this: http://www.dealextreme.com/details.dx/sku.51989

I don't know if it would even work but this should give me a 2 inch diameter tube with 3 batteries. I really want just one driver broard but i don't know of just one board that could power all 3 xm-l.

On top of it being a bike light, I would like to have an all around super bringt light.

 

 

 

ledoman
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Not budget driver but you might get an idea what can be done: http://www.taskled.com/h6flex.html

Take a look on other Taskled drivers, too.

Also, see the other forum topic: http://www.candlepowerforums.com/vb/showthread.php?t=188227