Since I'm painting my mustang blue for this summer I thought if carry the theme inside. It's a basic black interior. Since the car didn't have courtesy lamps under the dash I thought I'd add some
I found some blue 10w LEDs on eBay for $1.35 each with free shipping. I don't need 10 watts so I plan to run then at 1/4 output so they should last forever
Step 1: Heatsinking
These leds get pretty hot if you run them at full power. The ones I purchased run on 9-12Volts at 1.2Amps. An LM338 and a 1 ohm resistor make a nice fixed current source for 1.2A. You can also use an LM317 and a 2.5 ohm resistor to limit it to 1/2A
I didn't need a current regulator here because I only plan to run them on 250mA using a simple 20ohm resistor in series. I used some old intel 486SX heatsinks to mount the led and resistor. aluminum angle iron or bar stock would have worked too. A quick bench test at 1/2 power proved just how hot they get...
Step 2: Mounting the LED Chip
I mounted the led off center to make room for the resistor next to it. Just place the chip where you want it. try your best to line up the holes with the spaces between the fins. I used a red marker to mark each hole then drilled them out for #4 self tapping screws. A small drop of heatsink grease in the center will help. If the screws are too long just grind off the tips...
Step 3: Final Assembly
I used a little epoxy to hold the resistor in place. That heatsink grease gets everywhere so use a little nail polish remover to clean the surface before you glue the resistor down. I used an old id card as a little mixing board for the epoxy. I keep plenty of these on hand. I used a binder clip to hold the resistor in place as the epoxy dried. be careful the clamp you use doesn't crack the resistor body.
I also added a little heatshrink tubing to insulate the resistor leads. A little more heatshink tubing and some speaker wire completes the lights. Self tapping #10 screws will fit nicely in the end slots of the heatsink for mounting.
Step 4: Testing
I ended up using a 22 ohm resistors so they draw about 200mA each at 15Volts. They are still really bright. If you run them at higher power they would be great for underbody accents too.