OT: Marchal LED Conversion for 356, An LED Headlight Project Options

[Spoke]

A Porsche 356 owner contacted me about converting a set of Marchal fog running lights to LEDs. We talked about it and he asked if I could do it in 6 weeks. My response was I've never done a high power LED headlamp so it's more of a project than a product.

The Marchal running light is shown on this file-folder picture of a 356. That's not me nor the owner. (IMG:style_emoticons/default/smile.gif)



The idea was to design an LED-only board attached to a large heat sink and use a step-up dc-dc converter on a separate board to provide 0.275Amp to the LEDs.

The LEDs are Cree XP-G3 surface mount LEDs. These have a maximum current of 2 amps. The LEDs require a lens to focus the light pattern. The XP-G3 have a wide output light pattern and can't be used 'naked'. The lens per LED are Carclo's 10049 lens with a light pattern shown below.



The LED board uses 19 LEDs with lenses and holders. The board will be backed by a very large heat sink. The main killer of LEDs is heat. 2 amps through an LED with 3.5V is 7W in less than 1/4" square area. Massive power dissipation/heat in a very small area.

The PCB really should be an aluminum PCB but they are really expensive so the PCB is FR4 and is thin at 0.8mm to minimize thermal impedance of FR4. Vias from top to bottom are liberally applied to provide as much metal top-to-bottom for heat transfer. The clear area of the bottom of the board will allow maximum heat flow to the heat sink.

[Spoke]

This was the first light-up of the full 19 LED lamp. Here I'm running 0.35 amps through each LED.



This is the light pattern on the ceiling 6 feet from the LEDs. Pretty much the same as the lens manufacturer stated. Unlike headlights these days, the lenses don't offer a sharp cutoff in the vertical direction. These lamps will likely need to be pointed downward a bit to not blind oncoming traffic.



The LED board needed to be trimmed down a little to fit inside the bezel. The heatsink is a bit over 1 inch deep but still fits easily inside the case.



Getting the LED lenses and holders to fit under the glass was a chore. I had to place the LEDs so close to each other such that the holders overlapped each other by about 20 mil. Each holder had to be filed where they interfered with their neighbors. In the end it worked out ok.



The LEDs look really cool when not lit. They are so bright when lit that you can't look directly into them.



Here's the LED stack running 0.33 amps at 53V for a little over 17W dissipation. The step-up converter driving the LEDs is about 90% efficient so this lamp will burn about 20W and is a bit brighter than the low beams on my road car.