Help Selecting HS for Project (3 watt Star)

Well, I ordered some different size HSs for my Project. The project was to use Luxeon Stars on my ATV for a tail light and for underlighting.

In the Picture below the HS that is second most to the left is the one the company I ordered from recomended to me for the 3 watt blue star. It appears a bit big and bulky, and im doubting the cooling capabilities of it since all the fins are only along the boarder. They told me that the leftmost might be too small for a 3 watt, but I was going to use it rather than the bulkey one. From my experience it is a MUCH better design, and appears to itself be overkill for a 3 watt? (Im new to 3 watt LEDs though).

Just need some of your opinions.


(left to right)
HS = the one I would like to use for the 3 watt Blue Star resting on it
HS = recomended for 3 watt blue star resting on it.
top = 2 1 Watt Red Batwing's for taillight mounted is AS Silver
mid 2 more red batwings
lower 2 1 watt Cyan Batwings (30 lumens each for another project)
Far right = My new circuit to run the stars (2 1 watt's and 2 3 watts) off fluctuating 14.4V AC power.

Is the HS on the far left large enough to handle a 3 watt star driven at 1 amp?

The HS is probobably enough to handle it, just make sure not to use the thermal pad and use the AS Silver, but remember to be careful =p you probably already know that its slightly capacitative. How is the heatsink getting mounted? what going to house the luxeon/heatsink?

it will probably get somewhat toasty with the heatsinks depending on how its mounted

edit: btw the heatsinks they recommended dont look much better then the smaller ones when it comes to thermal dissapation.

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ufokillerz said:
The HS is probobably enough to handle it, just make sure not to use the thermal pad and use the AS Silver, but remember to be careful =p you probably already know that its slightly capacitative. How is the heatsink getting mounted? what going to house the luxeon/heatsink?

it will probably get somewhat toasty with the heatsinks depending on how its mounted

edit: btw the heatsinks they recommended dont look much better then the smaller ones when it comes to thermal dissapation.

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I hear you about the AS epoxy, I looked at 3 stores to find Artic Alumina Epoxy and all 3 were out. I coulden't think of any other stores that would sell it localy. But Since I figured im just using it to mount HS's it would probably be fine since I would not rely on AS Alumina to not conduct when the HS is pressed againstd the LED anyways. What would happen should the HS ground out?

Since the entire 3 watt LEDs will not be visable (1 mounted under fuel tank and front plastics and one mounted under rear plastics on my ATV) I figured I would just rig up some cheesey bracket with some aluminum stock and a dremel...I'm hoping to insulate the LED from the bracket using some thin rubber lining, but may end up just siliconing it with clear RTV silicon into place. Basicaly it will just be a metal plate with a hole drilled into it that the LED can poke through.

I'm having a much cooler looking (although not professional $$ wise) bracket made to hold the tail lights.

NOTE: Both lights should recieve some airflow, since they will only be fully powered when the engine is reved (no battery on the ATV just a stator and flywheel), (unless at idle and reving up) the ATV will be moving (Very fast I might add) so that should provide some aflow over the HS, which will be open to the air.

carefull with silicone on the actual led. It might off-gas while curing and cloud up the led lens...

Thanks for the heads up, I'll see what I can do to work around it, but at worst I don't think it would matter too much, since im just using it for a flood to light the ground under the ATV, and the engine etc.

Would it be better to make the mount attach to the Heatsik Vs Gluing/Siliconing the mount to the LED?

Ok I have the mounts designed, and I have tested my Circuit. It WORKS!

2 Problems though, which may or may not be minor. Please give me some feedback though! I appreciate the help!

The circuit is using LM317T and an LM317HTV to regulate current to the light. The Power souce is variable AC(don't worry I convert it). When I rev the bike up it puts out more juice, at idle it barley puts out anything. There is no battery on my bike.

1) Due to the above, the 3 watt LED's (for underlighting)light up before the 1 Watters Im using for the taillight. Since in using an LM317 your using a resistor to regulate current, the smaller of 2 resistors produces the larger current for the 3 watt leds, so more current flows to them first because it has less resistance to the LEDs (even if the 3 watt LED's have more resistance, first the current regulator is first so it decides)
THIS MEANS THE UNDERLIGHTING ON THE BIKE LIGHTS UP BEFORE THE TAILLIGHT. Im not too pleased but it will do for now.

2)The other problem is my HS selection. Although the HS for the 1 watt LEDs are smaller, I just now noticed they are heavier and made of more mass. The base plate the fins protrude from is much thicker than the ones im using for the 3 watters. So I actually epoxied the wrong HS's to the lights (I should have swapped the 1 watters and the 3 watters HSs). The thought of using the 1 watters (top mid in the pic) never even crossed my mind since those are what I have always used in the past.

The base of the 3 watt HS is MUCH thinner... Do you guys still think it will disipate enough heat??????????? Most of the time there will be some airflow over the HS, since the vehicle is moving, when the vehicle is stopped teh lights will be far from fully powered.

Thanks in advance!

As far as the heatsinking goes, you should use AA epoxy. You can get it from the Sandwiche Shoppe.

Just use a metal enclosure for the luxeon and mount the luxeon directly to the metal enclosure. Then mechanically mount the enclosure to the frame of the bike (Metal to metal fastener). Instant hugh as heat sink and more than enough surface area to dissipate heat.

Now as far as your electronics problem goes, I'm no electronics guru, but what are the Vf of the luxeons that you are using? Maybe there is a way to do this without using a circuit at all.

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Chop said:
As far as the heatsinking goes, you should use AA epoxy. You can get it from the Sandwiche Shoppe.

Just use a metal enclosure for the luxeon and mount the luxeon directly to the metal enclosure. Then mechanically mount the enclosure to the frame of the bike (Metal to metal fastener). Instant hugh as heat sink and more than enough surface area to dissipate heat.

Now as far as your electronics problem goes, I'm no electronics guru, but what are the Vf of the luxeons that you are using? Maybe there is a way to do this without using a circuit at all.

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I know I need a circuit because the power from the bike ranges from 1-14 volts and constantly fluctuates at lower speeds. The power is also AC and not DC. If I used resistors etc, they would only light up at full throttle. Sometimes I have sceen the bike peak over 14.4 volts the voltage regulator is supposed to regulate. The power is so unclean it definately needs some type of circuit, but that is already built and working, It was cool to see the 3 watt blues light up so bright last night /ubbthreads/images/graemlins/smile.gif Too bad they aer only 30 lumens, but they are much brighter than the 1 watt blues I fried a while back.

Im using AS epoxy, because I didn't want to wait for AA to ship. Im hoping to have this compleated for the ride this weekend.

What do you mean a metal exclosure? I was thinking of smearing some artic ceramique on the HSs for the 3 watters, then mounting a the HS's to a flat piece of aluminum which would extend the HSs some, then attach this piece of aluminum to the ATV's frame? Is that what your talking about?

All I'm talking about is giving the luxeon's heat a thermal path to follow and the best thing to do this with is metal.