This project started when I went to purchase a replacement halogen bulb for my outdoor lights. When I discovered that they cost about 6-7 dollars each, I had an idea to replace them with something that wold last longer and be less expensive. LED seemed like the obvious choice, especially since the cost of white LEDs has dropped in recent years.
For this project you will need:
LEDs (whatever color you like, make sure they are bright. I replaced mine with white ones)
Mounting hardware (however you want to secure your leds in the light fixture)
current regulator (this will vary depending on your LED specs and power supply of your existing lights)
wire (and solder + soldering iron)
adhesive (preferably epoxy, both thermal and regular)
Step 1: Existing Installation
My outdoor lighting setup consists of 15 of these "bullet" style lights. Each one has a 20 watt halogen bulb inside. They all run off of a typical 12v AC exterior lighting power supply. The power supply is rated at 300 watts, so I'm cutting it pretty close. All of these lights have the original bulbs that came with the unit when I installed them. Since they were installed all at the same time, the fact that one or two of the bulbs have gone out could mean that they are all reaching the end of their expected lifespan.
Step 2: Components
Once I decided to get replace the halogen bulbs with LEDs, I started looking for the necessary components. I would need:
current controller for the LED
I would also need a heatsink and some type of mounting bracket to hold the LED in the housing. Since I was trying to keep the cost of the replacement setup under or at the cost of the halogen bulb, I made use of what I have lying around. The aluminum angle brackets I used are made of bent pieces of aluminum strip from another project. I also decided to go with a "warm" white LED to match as closely as possible the color of the existing lights.
Step 3: LED
This is the most important component. I went with a warm white Rebel LED sold by Sparkfun Electronics . They were fairly cheap, around $4.50 each (buying in bulk), and could run up to 1 amp. They are also sold with a breakout board , but I decided against that to minimize the cost. Also, since I would be attacking them to the mounting bracket which would double as the heatsink, I figured I could dispense with the board. I have included the Datasheet which contains dimensions and more technical information.
Step 4: Driver
This was probably the hardest part to find. The driver needed to work with the existing AC line, but needed to be small and inexpensive. I found these 650ma drivers from DealExtreme. 650ma is plenty for what I need and would also minimize the heat generated by the LED. They also incorporate an AC/DC converter. These drivers also have two pins soldered to the inputs which are meant to mate with the MR16 lamp sockets on the lights. $6 for a five pack kept the cost down as well.
Step 5: Construction
The build time on these was fairly short. I soldered leads to the LEDs positive and negative pads. The LED was then mounted on the aluminum bracket using thermal epoxy*. When doing this be sure that only the thermal pad comes into contact with the epoxy. Some thermal epoxies are slightly conductive which could cause problems with the driver. The entire assembly was then glued into the light housing. After the glue had set I soldered the leads to the driver.
*Thermal epoxy is not absolutely necessary. I used it because of the way my LEDs are built and the fact that they require a heatsink. You might be to get away without using the thermal epoxy if your LEDs are of lower power.
Step 6: Testing
These lights performed perfectly. As I expected, 650ma was more that sufficient and actually produces more light than the halogen bulbs. The color is slightly different, but it looks fine to me. I also checked the temperature of the driver and LED to see if they were overheating, but they were just barely warm to the touch after about an hour of continuous running.
Step 7: Final Remarks
Overall I am pleased with how the modification turned out. I haven't had any problems so far and the they look great. The drop in power usage is also noticeable. Before, the PS would get very warm while running, but now it doesn't even change temperature. I could probably replace it with one of lower wattage.
Now I need to find something to use all these halogen lamps for.