What resistor should I use for Lux 3w??

[psab keel]

Hey Folks!

I searched all over the forums and I didn't wnat to create a whole new thread just for my question. Besides this pertains to this particular thread anyway.

This is my situation:

I am building an LED saber with a Star III Watt LED and I have it properly heatsinked with a two inch long multifacted sink. I'll be powering it on "direct drive" with a resistor.

4.8 (4 Qty. AA NiMH Rechargable Batteries) as my power source, and using a 1 Ohm (2 Watt) Resistor, from the shop here, to get an approximate rating of 900 mA.

I've never run any of my Star III Watts that bright before, and I wanted to know how much heat something like this might generate. My major concern is for the resistor. Will it heat up?

Any help or advice would be greatly appreciated.

Thanks.

[Do-Clo]

No offense but you found this thread and the very first post in it gives you a list of resisters required for different voltages all for the 3 watt star leds.

[xwingband]

Those of you that don't know, psab was one of the starters that really banged out luxeon sabers at ASAP. He got the idea for the fishing line blades that is now supplanted by Corbin's film. He just hasn't kept up. :P

Now on to the question... Your heatsink should be fine. About 9 square inches is recommended by luxeon. If that's a two inch cylinder then that wouldn't work. If it's a finned one then that's way overboard. A 1" radial with 1/16" fins will more than handle a 3W.

Follow the chart in the first post and you won't have to worry about the resistor heating either. You figure out wattage for the resistor by multiplying the amperage you are running it at (in amps not milliamps) times the voltage across the LED. So .9 x .9... less than a watt. No worries.

[psab keel]

I figured that the resistor would be fine, but after investing the amount of money that I have into this hobby, it's best to ask questions than to have to buy more parts. (Well, at least I have a one stop shop to get nearly everything I need. )

For a heatsink I have one from Lumileds. It's approx. 1 Inch square and 1 inch tall, with fins pointing out of the bottom. I have this stacked on top of another heatsink of the same dimensions. I figured that should be plenty to pull the heat from the bottom of the LED.

Looks sort of like this:

---1-1----- LED
! ! ! ! ! ! ! !
! ! ! ! ! ! ! ! 1 Inch tall heatsink
! ! ! ! ! ! ! !
------------
! ! ! ! ! ! ! !
! ! ! ! ! ! ! ! 1 Inch tall heatsink
! ! ! ! ! ! ! !


(Forgive the crude diagram, I'm not the most computer savvy.

Thanks for the advice. If you have any other information or tips, please feel free to let me know.


Psab

[james3]

Wow dude! Heck yeah you are go for launch with that bad boy. That should give you fine heat disapation.

Good luck and post some pics if ya can.

[psab keel]

Thanks for all the help!

It is much appreciated!

I'll try and post pics when I have a chance.