DIY Ultra Bright LED rear Foglamps

       We don't usually get thick fog in our area so I don't really need a rear foglamp but there are a lot of motorists that think driving with their high beams on in a well lit city is a good idea, then they usually like to tailgate me so something had to be done.

       I was originally planning on using DRLs (Daytime Running Lights) mounted at the back but I can't find an inconspicuous place to put them so I decided, why not the OEM rear foglamps? It already has a factory switch and wiring, a nice place in the bumper and I don't really use it.

       I started with three Luminus Phlatlight PT54 red LEDs with optics from harvested projectors and worked from there. Each LED is rated at 425 Lumens at 8.1A drive current. The three are wired in series and I used a buck regulator originally designed for an MPPT solar controller (my design) and modified it to run constant current output but only used 7A max drive current. According to the datasheet, it will do about 400lumens at 7A so we have 1200lumens shining at the back.

       The LEDs produce a LOT of heat! My heatsinking was limited by the maximum size I could fit inside the bumper and fans are a no-no because of moisture so I also modified the power supply to have automatic power control by utilizing the onboard thermistors in the LEDs themselves. All three thermistors are wired in series so that the controller can roughly sense all three LEDs. The power supply is set to reduce current to under 1A once the LED temps reach 57degC. With the LED on the bench and no airflow to the heatsink, the power stabilizes at about 1.8A when it heats up and temp equalizes after a couple of minutes. Since this will only be turned on only when there are tailgaters, the low duty cycle limit won't be a problem and it still runs at low power if I need to keep it on for a long time.

       The acrylic housing for the LEDs took a bit of work to fit the bumper contours well but I won't try to describe it any further. Here are the pictures of the build instead.


Machined heat spreader/base plate mounted to heatsink.


Phlatlight PT54 LEDs and optics housing milled to reduce size.


LED assembly mounted to heatsink.


Bench supply pushing 7.5A into the three LEDs in series.


All three LEDs are wired in series and powered with bench supply.


Getting a feel of the amount of light the LEDs put out.


Stock rear foglamp.


Stock rear foglamp at the bumper (me holding it since it isn't screwed in for the quick pic).


Acrylic housing to protect the LEDs from the elements.
It will be buffed and painted after the testing phase.


LED and powersupply ready to be installed.


Ghetto power supply mount.
It won't be an issue since this is still in testing phase and it's still summer.
Going to have to make a case before rainy season starts.


LEDs installed in the bumper.


Tailgate me now! 1200lumens total output for the tailgaters.


Wall about 30feet from the back of my car.

       27 Apr 2013:

       After a week of driving at night (had to do overtime at work) I wasn't able to try it on a tailgater! Murphy's law strikes again. I was able to try it on two friends and it is very effective. Either way, I decided to buff and paint the acrylic cover for the rear foglamp. Here are the pictures


Painted the inside of acrylic housing.


Outside buffed and cleaned using a headlight lens cleaning kit.


Foam added to where the acrylic housing contacts the bumper.


Front plate of the LED holder painted red - an attempt to make it look inconspicuous.


Wiring to the LEDs.


Finished and mounted.





Look from a bit farther.


Light'er up!


This is what it looked like when I tested it in the woods.

Page created and copyright R.Quan © 21 Apr 2013.