I have some in the mail (gotta pick them up from the P.O. this afternoon) unfortunately, the LED’s and drivers came in one shipment and the lenses and heat sinks came in another… which isn’t here yet… damnit.
I just couldn't see spending $300+ for LED lighting so I ordered some 1000LM Cree XM-L (xmlawt) and some drivers with 3 settings (low-med-high) so I don't burn the LEDs out.
My plan was to install them IN one of my roof rack cross bars. I haven't seen this done before.
I think I will make individual housings for each LED and then just drill a big enough hole for the housings to be inserted into the cross bar.
The one thing I worry about though is heat. These emitters are 10V and the warning label says that they should be treated as you would a laser because they will cause retina damage if you are too close to them. (at max power). So that leaves me with adding some sort of heat sink. Ideally, I would attach the heat sink as close to the star pcb as possible using thermal epoxy… but that leaves me with heat sinks on the INSIDE of the hollow aluminum cross bar and there won’t be any moving air in there? Back to the drawing board…
Another idea would be to use RC helicopter heat sinks on the housings. I am told that a 280 motor is about the size of the housings I want to build. Unfortunately, there aren’t many RC places up here in the high desert (that I know of) so test fitting stuff before I buy a bunch of stuff isn’t going to be easy. If I used that kind of heat sink, then I would have to have the LED housings sticking out of the cross bar a little more than I wanted. It’s not really all that far… I believe they are around 20mm deep? So that makes my cross bar look something like a comb? Well whatever, I will take pics and do a write up as I go.
(sorry for the rambling, I am mentally designing as I type)
OK, I like the idea, except for what you want the light to DO.
The XML is going to throw a flood of light...and at your roof brow area, that's going to glare on your windshield and hood, reducing your ability to see out past the ball of light you'll be in.
You'll need an optic/reflector to mount with the LED...I saw "Lens"? - To get enough throw to have the angle miss the hood at least. What kind of beam coverage were you trying to get?
As for cooling, yes...that's a lot of heat to dissipate, but a hollow AL tube is actually not a bad start...maybe run a copper bar inside the tube to mount it all to/act as a large sink, and then taking advantage of the fact that you have 12 v current, leave one end of the tube as an intake and the other as an exhaust, and use a fan to ventilate/drive off heat inside the tube.
If you put (Arctic Silver, etc) the LEDS right on the copper, and the back of the Cu is exposed to the airflow through the tube, that should cool well.
I'd set the fan blowing IN to put the tube under positive pressure/reduce weather leakage.
I'd also machine some fins/fluting, etc, into the back of the CU bar to maximize surface area for heat exchange.
LOL - If you wanted to go crazy, you could run a small duct from the AC, up the pillar to the cross bar to act as the make-up air source/positive pressure source...so if its especially hot, your AC is on too.
Essentially, by being able to leave the light engine assembly inside the cross bar...you avoid the "Comb" issue you worried about, as well as reducing exposure to damage.
By ventilating the inside of the cross bar, you carry the heat in the bar, out.
By using a copper (good heat conductor) - especially with flutes/fins, etc...it will absorb the heat from the LED if its in good thermal contact with it at one end, and radiate it out into the tube's airflow on the other end.
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